WHO VBC 87.941 Eng.Pdf

FOREWORD

Since 1970 the Vector Biology and Control Division of WHO has prepared, with the assistance of collaborators outside the Organization, a number of papers on vector control. The Expert Committee on Insecticides held in October

1974 (Technical Report Series No. 561) recommended that these documents general reviews of the ecology and control of individual vector groups - should be continued and reviewed from time to time to provide workers with up-to-date

practical information on the particular subject.

In 1985, with the greater demand for this material for use as training and

information guides by different categories of personneL, particularly in the developing vector-borne disease endemic countries, it was decided to develop two

separate series of these documents; an advanced series for students in medical

entomology as well as for reference use by professional staff , and a middle

level series for less specialized workers in the community.

This advanced series will cover the relevant subject in considerably more

detail and at a higher technical level. It is believed that this type of

information will assist vector control specialists to acquire the knowledge

required for their daily work.

In order to improve the value and usefulness of this guide, evaluation

forms are attached, and users are requested to send the completed forms to the

WHO Division of Vector Biology and Control in Geneva so that their comments may

be taken into consideration when the guide is revised. ~ \1-Lf-t.f WORLD HEALTH ORGANIZATION DISTR.: GENERAL(E) WHO/VBC/87.941 ORGANISATION MONDIALE DE LA SANTE

XIV. THE TRIATOMINE BUGS - BIOLOGY AND CONTROL

C. J. Schofieldl, D. M. Minterl, R. J. Tonn2

lnepartment of Entomology, London School of Hygiene and Tropical Medicine, Keppel Street, London, England.

2Division of Vector Biology and Control, World Health Organization, Geneva, Switzerland.

This document is not a formal publication of the World Ce document n'est pas une publication officielle de !'Orga Health Organization (WHO), and all rights are reserved nisation mondiale de Ia Sante (OMS) et taus les droits y by the Organization. The document may, however, afferents sont reserves par I'Org<>nisation. S'il peut etre be freely reviewed, abstracted, reproduced or translated, commente, resume ou cite sans aucune restriction, i I ne in part or in whole, but not for sale or use in conjunc saurait cependant etre reproduit ni traduit, partiellement tion with commercial purposes. ou en totalite, pour Ia vente ou a des fins commerciales.

The views expressed in documents by named authors Les opinions exprimees dans les documents par des auteurs are solely the responsibility of those authors. cites nommement n'engagenet que lesdits auteurs. WHO/VBC/87.941 page 2

CONTENTS

I Introduction 3

II Biology ...... · ...... · • · •. · • • • • • • • · · • • • • • • • • • • • 3

II.l Life history .....•...... · ..... • • • · • • • • • • · ... 3

II.2 Habitats and distribution 8

II. 3 Population dynamics . , .....•...... •...... 14

III Taxonomy and identification ...... 15

III.l Systematics ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 15

III.2 Reference centres 16

IV Public health importance ...... 17

IV.l Disease transmission ...... •...... 17

IV.2 Iron deficiency anaemia and psychological stress •••••••••••••••••••••••• 19

v Survey and surveillance ••••••••••••••••••••••••••••••••••••••••••••••••••••• 19

V.l Methods to detect infestation 19

v.2 Quantitative sampling methods 20

V.3 Epidemiological indices •••••••••••••••••••••••••••••••••••••••••••••••••• 21

v.4 Survey methods for silvatic Triatominae 22

VI Control 23

VI.l Methods of control ...... 23

VI.2 Health education 27

VI.3 Control campaigns and post-control vigilance •••••••••••••••••••••••••••• 28

VII Glossary of terms 30

VIII Bibliography •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• 34

IX Evaluation ...... 36

A. Questionnaire for self-evaluation 36

B. Questionnaire for return to the Division of Vector Biology and Control 39 WHO/VBC/87.941 page 3

I. INTRODUCTION

The order Hemiptera* consists mainly of plant-sucking bugs, but two families of the Hemiptera contain medically important insects: the Cimicidae or bed-bugs*, and the Reduviidae* or assassin bugs. Most Reduviidae are predators* of other insects, but one subfamily - the Triatominae - are adapted to suck the blood of vertebrates. The Triatominae are notorious as blood-sucking household pests throughout Latin America, and as the vectors of the trypanosome, Trypanosoma (Schizotrypanum) cruzi, which causes Chagas' disease (American trypanosomiasis) in human beings and infects many other mammals. Birds, however, are refractory to infection with T. cruzi. Some species of Triatominae also transmit another trypanosome, T. (Herpetosoma) rangeli, which is considered to be harmless to mammals but can be pathogenic to its insect vectors.

The disease and its vectors are distributed throughout the American continent and some Caribbean islands, roughly between latitudes 40oN and 46oS. Some potential triatomine vectors also occur in ·Africa, Asia and Australia, but the causative agent, T. cruzi, has not been reported from the Old World (Ryckman & Archbold, 1981). Of the 115 species of Triatominae now recognized (see pages 15-16 on systemics), over half have been naturally or experimentally infected with T. cruzi and, from their similar behaviour and physiology, all species must be regarded as potential vectors. Some other invertebrates, particularly cimicid bed bugs and ticks, have been experimentally infected, but probably have no natural role in transmission. Houseflies and cockroaches may act as carriers of infected bug faeces (dogs have been experimentally infected by this means) and thus represent a risk both in the home and in laboratories where experimental work and xenodiagnosis* is carried out. All stages (except the egg) and both sexes of triatomine bugs suck blood and can therefore become infected with T. cruzi if they feed from an infected host.

The parasite multiplies in the gut of the infected bugs and, when the bugs feed again, parasites are voided in the bug faeces. While they feed, many species of triatomi_ne bug defaecate on the skin of their vertebrate hosts. Parasites deposited on the skin in the bug faeces may then penetrate through abrasions* in the skin or pass directly through the mucosal membranes to initiate a new infection. T. cruzi (a Stercorarian* trypanosome) is never transmitted by the bite of the triatomine (Fig. 1), unlike T. rangeli (also a Stercorarian trypanosome) which is transmitted by the bite (Fig. 2).

II. BIOLOGY

II.l Life history

The Triatominae, like all other bugs, are hemimetabolous* (with no pupal stage) exopterygote* insects, in which metamorphosis* is simple and direct. The life-cycle proceeds from the operculate* eggs, through five nymphal stages, to male and female adults (Fig. 3). The eggs hatch and a first-instar nymph emerges, leaving behind the open egg-shell. The nymph then feeds and moults to successive stages, leaving behind an exuvium* (cast skin) after each successful transition. The five nymphal stages are similar in behaviour and appearance to·the adults, but they are smaller, sexually immature and lack wings. Fifth-instar nymphs are readily distinguishable from the younger stages by the presence of prominent wing-pads on either side of the thorax.

The life-cycle of the Triatominae is long ·compared to many other medically important insects. Even relatively small species such as Rhodnius prolixus take at least 3-4 months to complete their development from egg to adult under good laboratory conditions. Most Triatominae take 5-12 months to complete their development, but some may take as long as two years. In the laboratory, most species thrive at temperatures between 24-27oC; development is more rapid at higher temperatures, but there is a greater mortality. Most species fail to complete their development at temperatures below 160C and rapidly die at temperatures above 37°C. Temperatures of between 400C and 41°C are fatal to most species.

*Terms marked with an asterisk are defined in Section VII - Glossary. WHO/VBC/87.941 page 4

G) Blood-st~eam @ Trypomastigotes trypomast1gotes shed into blood stream ingested by triatomine @ First epimastigotes, then trypomastigotes as 'pseu~-ocyst'ruptures ~ ~~ develop '--.J )~ ll_' ~ ~)~~ ~ ~ ~

@ Blood-stream trypomastigotes begin to differentiate:\ (j);: .. ;., Most circulating epimastigotes and multiplication sphaeromastigotes )~of amastigotes tryomastigotes } ·,formation of continue the predominate ) ) • 'pseudocyst' intracellular cycle ~ @Massive~ multiplication ~ . in hind gut · \ Metacychcs penetrate 1~"'--~"--- mucous m~mbranes ,,~ __ , ')' "'. · ; abraded skm of host to enter _, . ~ _ ~ ~ ~ blood stream ·· ,. @ Trypomastigote @ Trypomastigote ~ ~-----...... '---- · . becomes an penetrates tissue ~@ ~ ,·"- immobile amastigote cell, often muscle 4 Infective me.tacyclics "'- 1 shed m faeces ~

Fig. 1 The Trypanosoma cruzi cycle in the vector and in the host's blood is complicated by the fact that the parasite undergoes morphological changes, each stage of which has been named specifically by parasitologists. The figure above indicates this cycle and is depicted solely for information and to observe that infection is through the taeces of the bug.

Eggs. Eggs are laid 10-20 days after copulat.ion*; unmated virgin females may lay a few eggs but these are infertile. Fertilized females generally lay a few eggs at a time, but normally continue to lay eggs throughout their adult lives which may last for six months or longer. The total number of eggs laid per female, and the frequency of oviposition*, depends mainly on the amount of blood ingested (see the section on population dynamics, page 14); typically, each female will lay 100-600 eggs during her adult life of 3-12 months. Triatomine species that normally occupy terrestrial* habitats* generally lay their eggs singly or in groups wherever the female happens to be, but species that normally occupy arboreal* habitats, such as most species of Rhodnius, lay their eggs in small groups cemented to the substrate*. The eggs are oval in shape, with an operculum or cap at one end through which the first-instar nymph will emerge at eclosion (act of emerging from the egg). Eggs are at first either pearly white or greyish, usually changing to pink or reddish as the embryo develops inside. Rhodnius eggs are usually already pink when they are laid.

Eggs hatch 10-30 days after they are laid, depending on temperature; newly-emerged nymphs are soft-bodied and pinkish but their cuticle soon hardens and darkens. Young nymphs are ready for their first bloodmeal 2-3 days after hatching, but they can survive for several weeks if no host is available.

Nymphs. Successive nymphal stages differ from each other in minor morphological* detail (Lent & Wygodzinsky, 1979), but they can be readily distinguished from each other by the size of the head capsule and leg thickness. These criteria can also distinguish the cast skins, or exuvia, of each stage which remains after each moult. Overall body size is not a good criterion to distinguish nymphal stages because of the great size difference between fed and unfed bugs of the same stage. The wing-pads are clearly visible in the fifth-stage nymphs, but can also be distinguished in the third and fourth-stage nymphs. Future males and females can also be distinguished by careful examination of the posterior sternites* on the underside of the posterior end of the abdomen. WHO/VBC/87.941 page 4

about 2-4 times their own weight. Fifth-stage nymphs usually take the largest quantity of blood; this is often in the range 400 - 1000 mg for species associated with man. The largest known species of Triatominae, Dipetalogaster maxima, from a remote rocky area of Baja in Mexico, takes huge blood meals: in one study, a single female took over 4 g of blood from a chicken. All nymphal stages and both sexes of D. maxima can survive long periods without food, up to eleven months in some cases. However, many smaller species of Triatominae have a similar capacity to survive for long periods without food.

IV NYMPHS

Note that all developmental EGGS ~ stages are similar, occupy a similar habitats, and have 77 /1?77 similar feeding habits

Fig. 3 Life cycle of a Triatomine bug

Sometimes, a single replete blood meal is sufficient to start the moult to the next stage. However, most species require 20-30 minutes to take a replete meal, and, because they are easily disturbed by movements of the host, they may have to feed several times before they can moult to the next stage (see also page 15). Most Triatominae are nocturnal and feed at night when their vertebrate hosts are resting, but species that feed on lizards or nocturnal animals often feed during the day.

During or soon after feeding, nymphal stages and adults begin to defaecate. The dejecta consist mainly of excess water from the recent blood meal, suspended spheres of uric acid (the nitrogenous waste product from blood digestion, equivalent to urine), and haem which represents the undigested part of the haemoglobin from the previous bloodmeal, and is equivalent to faeces (this is used as indirect evidence of infestation in a house - see page 20). The timing of defaecation in relation to the bug's contact with the host is of crucial importance in the transmission of T. cruzi, because if the bug is infected, the infective metacyclic forms of the parasite are shed in the faeces. Thus good vectors are those that defaecate on their host while feeding, whereas species such as the North American Triatoma protracta is a poor vector because it defaecates much later, after having completed feeding and left the host.

Freshly deposited bug faeces appear to contain a volatile pheromone* that attracts unfed nymphs. Under crowded laboratory conditions, nymphs of some species of Triatominae have been seen to occasionally imbibe (drink) freshly-deposited faeces from recently-fed bugs. Also, WHO/VBC/87.941 page 7

some nymphs have been seen to probe and feed directly from other bugs. However, neither coprophagy (dung-eating) or "cannibalism" is thought to be important under natural conditions.

Adults. Adult Triatominae differ from the nymphal stages by the presence of fully developed fore and hind wings, and they are sexually mature, with fully developed genitalia. However, adults of Triatoma spinolai, a species found only in Chile, show marked alary polymorphism* (different wing development); females are invariably wingless, while males may be wingless, or may have normal or extra long wings. This polymorphism appears to be under genetic* control. In other species, both sexes of adults have membranous hind wings, with the forewings basally hardened and pigmented, like other Hemiptera. At rest, the forewings overlie the hindwings which are folded over the abdomen. In flight, the membranous hind wings are firmly linked to the hemelytra* by a coupling mechanism (coaptor) of the "hook and scroll" type.

Both sexes have fully developed external genitalia. In females, the tip of the abdomen has a pointed or lobed appearance, whereas in males the tip of the abdomen has a smooth, rounded appearance when viewed from above. Females are often bigger than males, but this is not always so (Fig. 4).

anteclypeus

spongy fossul

pronotum

humerus

connexlvum

hemelytron (wing)

tarsus -----4

Fig. 4 External morphology (dorsal aspect) of an adult male Triatoma

Both nymphs and adults have a pair of compound eyes and antennae on the head. The position of insertion of the antennae is useful to distinguish important genera of Triatominae (see the section on systematics, pages 15-16, and Fig. 5). Adult Triatominae also have a pair of light-sensitive ocelli (eye spots) at the back of the head just behind the eyes. Nymphs do not have ocelli. WHO/VBC/87.941 page 8

Rhodnius Long head, with antennae inserted at the front, near the clypeus

Triatoma Intermediate length head, with antennae inserted midway between the eyes and the clypeus

Panstrongylus Short, robust head, with antennae inserted immediately in front of the eyes

Fig. 5 The heads of Rhodnius, Triatoma and Panstrongylus

Under the microscope, the cuticle of adults is clearly distinguishable from that of nymphs. Adults are often more colourful than nymphs; many species have bands or patches of red, brown, yellow, orange or pink along the lateral margin of the abdomen (the connexivum)*, and may also have similar markings on the legs and thorax. The background colour of Triatominae is usually black or brown, with similar coloured eyes, but white- and red-eyed forms have been recorded. Eye colour is genetically determined; red-eye is a recessive, autosomal character.

!!.2 Habitats and distribution

All species of Triatominae are silvatic* in origin, primarily associated with the nests of a wide variety of small mammals and birds, and occasionally, with lizards (Fig. 6). Most species retain close associations with their original silvatic habitats and hosts, and many have not been found outside a specific habitat, cr away from a specific type of host. Some species, however, have adapted to a greater or lesser degree to the domestic* and peridomestic* environments offered by human activity (Fig. 7). Thus, amongst the 115 species of Triatominae, some are found exclusively in silvatic habitats, some are occasional visitors to human homes (as flying adults which may be attracted to light), some form small colonies in houses and domestic animal shelters (Minter, 1978) in addition to their colonies in silvatic habitats, while a few species have become highly adapted to human dwellings and form large colonies in houses (Schofield, 1979). These species, which form close associations with human WHO/VBC/87.941 page 9

beings, are the important vectors of T. cruzi to man. The most important of these is Triatoma infestans, which has a wide distribution in houses and animal-shelters throughout the southern and north eastern parts of South America, but primary silvatic colonies have been found only amongst rocks associated with wild guinea-pigs in the Cochabamba valley of Bolivia.

Fig. 6 Example of a silvatic habitat of triatomine bugs. Large numbers of Rhodnius neglectus were found in the crowns of these 'Buriti' palms in central Brazil.

Fig. 7 Example of a rural house infested with triatomine bugs. When this house in central Brazil was demolished by a research team from the University of Brasilia, over 1000 Triatoma infestans were collected from cracked mud walls. WHO/VBC/S7.941 page 10

The most important vector species are as follows. Their distribution is shown in Figures SA - E.

Triatoma infestans (Fig. SA): widely distributed throughout Argentina, Chile, southern Peru, Paraguay, Uruguay and Brazil. In Argentina, T. infestans is found as far south as 460S and in the Andean region it has been found in houses up to 3600m altitude. In Chile this species is found from just south of Santiago (Rancagua) up to the northern frontier and across into southern Peru. In Brazil, T. infestans occurs throughout the south and east-central part of the country, where it has replaced Panstrongylus megistus as the most important domestic vector in many areas.

------~-.• ' Triatoma infestans

I'J

Fig. SA Distribution of Triatoma infestans WHO/VBC/87.941 page 11

The distribution of T. infestans appears to be spreading northwards, and it has recently been found in the northern Brazilian states of Piauf, Maranhao, Pernambuco and Paraiba. Its recent spread is well documented, and seems to be mainly 'due to human population movements, as agricultural and other developments have drawn large numbers of migrant workers northwards into the Sao Francisco river valley from the endemic areas of southern and central Brazil. Inadvertently, these migrants have undoubtedly imported eggs and small nymphs of T. infestans amongst their baggage and furniture as they travelled north by bus and truck in search of employment. In Chile, T. infestans has been found breeding in long-distance passenger trains on the route to the north of the country, and this has no doubt contributed to the wide dispersal of the bugs in that country.

,. ------.• Panstrongylus megistus

?0 - --~---- -··

,,,

80 60 50 40

Fig. 8B Distribution of Panstrongylus megistus WHO/VBC/87.941 page 12

Panstrongylus megistus: a larger species than T. infestans, with a less extensive range (Fig.8B). P. megistus nas silvatic ecotopes (biotope) associated with tree-holes and ground nesting mammals. It used to be the most important domestic vector of T. cruzi in Brazil (and was the first species to be implicated in transmission by Carlos Chagas in 1907), but has been replaced as a domestic vector in many areas by T. infestans. P. megistus retains silvatic ecotopes throughout its original range however, and may reinvade houses after T. infestans has been eliminated by control interventions. In humid areas of coastal Brazil, especially in Bahia, P. megistus is still the most important domestic vector of T. cruzi, and is found mainly in houses.

Triatoma brasiliensis: similar in appearance to T. infestans, but readily distinguishable by.its paler colour. T. brasiliensis is the main vector ofT. cruzi in the arid caatinga

Triatoma brasiliensis

;::c1

80 60 50 40 Fig. 8C Distribution of Triatoma brasiliensis WHO/VBC/87.941 page 13

(open low forest area) of north eastern Brazil (Fig. 8C). Its silva tic habitats include rodent nests in rocky areas and in the crowns of cultivated wax-palms.

Rhodnius prolixus: like most Rhodnius species, R. prolixus is a relatively small bug primarily associated with mammals and birds nesting in the crowns of palm trees. Household infestations are encouraged by the use of palm leaves for roofing material, because Rhodnius eggs are often cemented to the surface of the leaves. Hence, replacement of palm roofs with tiles or corrugated metal sheets discourages infestation with this species.

R. prolixus is the most important domestic vector of T. cruzi in Venezuela (Telford & Tonn, 1982), Colombia and parts of Central America (Fig. 8Dy:-1n Panama, R. prolixus is rare and R. pallescens is the most important vector. R. prolixus is more common further north in Central America, from Honduras up to the south of Mexico. The discontinuous distribution of R. prolixus is thought to relate to the finding of eggs and young nymphs amongst the feathers of birds (particularly storks) which migrate seasonally between Venezuela and Colombia and the northern parts of Central America.

A closely related and morphologically similar species, R. neglectus occurs in Brazil south of the Amazon, where it also occupies palm tree crowns and may occasionally colonize houses, although it ls not an important domiclliary vector. Reports of R. prolixus in central and southern parts of Brazil may be due to confuslon between these closely related species.

Triatoma dimidiata: this is a fairly large species wlth very distinctive colouration. It is an important vector in Central Amerlca (Fig. 8E), where lts geographical distribution often overlaps with that of R. prolixus, although when the two occur together, as in El Salvador, R. prollxus seems to be more common at lower altitudes, while T. dimidiata ls found in houses at altitudes above 300m (Cedillas, 1975). T. dimidlata has been found jn a variety of silvatic habitats, particularly in hollow trees and caves occupied by bats. It ls an .important domestic vector in humid areas of northern Peru, Ecuador and Colombia. T. dimidiata is often found in urban-, areas in towns along the coast of Ecuador.

•.:

Rhodnius prolixus

120 105 90 75 60 45 Fig. 8D Dlstribution of Rhodnius prolixus WHO/VBC/87.941 page 14

;3o I

\ I I I

•.! ~ .. 15

Triatoma dimidiata

120 105 90 75 60 45 Fig. BE Distribution of Triatoma dimidiata

O~her species of local importance include T. maculata in Venezuela, and the Caribbean (Petana, 1978), Panstrongylus herreri which is quite widely distributed in Peru, T. barberi and T. phyllosoma in Mexico, and T. sordida which is widely distributed in central Brazil, Paraguay and northern Argentina, where it is mainly a peridomestic species particularly associated with chicken-houses but frequently forms small colonies in human dwellings.

In the United States of America, where only three human cases of T. cruzi infection have been reported, T. protracta (and less common species such as T. gerstaeckeri, T. rub ida and T. sanguisuga) have occasionally been found in human dwellings.

There are no important domestic vectors of T. cruzi in the area of the Amazon basin. Nonetheless, there are many silvatic species present, and T. cruzi is a common parasite of these bugs and of the many wild animals with which they are associated. In forest settlements of Brazil, French Guyana, Guyana, Suriname, and Venezuela silvatic species of the bugs such as R. robustus, R. pictipes and Panstrongylus geniculatus often fly into houses and may bite human beings and form small colonies there.

II.3 Population dynamics

Triatomine bugs have a much longer 1 i fe cycle and lower rate of reproduction than most medically important insects, such as mosquitos. They are often described by ecologists as "K strategists"*, adapted to living in the relatively stable environment offered by a mammal nest or human home (this is in contrast to "r-strategists"* such as mosquitos which are better adapted to unstable, changing environments, in which their populations go through irregular cycles of high and low densities). Domestic species of Triatominae, such as T. infestans, reach high population densities in houses, maintaining population numbers that are stable from year to year, although there are seasonal changes in actual numbers and in the population age structure.

Typically, there are two generations per year, with peak adult emergence in the summer (December-January in the southern hemisphere), and a smaller peak during the autumn. In fact, there is considerable overlap between successive generations, and most developmental stages of WHO/VBC/87.941 page 15

domestic species are usually present throughout the year. The peak adult numbers in summer coincide closely with the seasonal peak of acute cases of Chagas' disease.

The density of Triatomine bug populations seems to be regulated by a density-dependent* interaction with their vertebrate hosts. As bug numbers increase, each host is attacked by a greater number of bugs and appears to become progressively more disturbed by the bites. As a result, the bugs are more likely to be interrupted while feeding, and tend to break off feeding before they are fully engorged. The resulting reduction in nutritional status of individual bugs has three main consequences: (1) the rate of nymphal development becomes slower, so their development time increases and slows the rate of recruitment to successive stages. Thus females emerge at a slower rate, and, (2) because the females also take in less blood, they lay fewer eggs. Also, (3) both male and female adults that experience low nutritional intakes become increasingly more likely to disperse by active flight. These three factors, acting together, tend to reduce the population density relative to a fixed number of hosts (Rabinovich, 1972). Conversely, if the bug population declines then each bug attains a superior nutritional status and the above three processes are reversed, allowing the population to increase at a more rapid rate.

This system of density regulation provides a well-defined mechanism. Any intervention, such as insecticide application, which reduces the density of bugs in houses, allows the survivors to reproduce at their maximum rate and, if unchecked, to return to their original population density. However, with the detailed understanding of bug populations now available, predictive models are being developed that can facilitate the design of large-scale control programmes.

III. TAXONOMY AND IDENTIFICATION

III.l Systematics

The 115 species of Triatominae form a uniform subfamily of the Reduviidae (Zeledon & Rabinovich, 1981). The Reduviidae can be distinguished from most other Hemiptera by the presence of a three-segmented proboscis* which, at rest, is folded under the head to just reach the prosternal stridulatory groove* between the first pair of legs. In plant-sucking Hemiptera, the proboscis is four-segmented and, at rest, usually extends well beyond the first pair of legs, often to beyond the junction between thorax and abdomen.

In predatory subfamilies of the Reduviidae, the proboscis is stout, rigid, and often curved, adapted to pierce the hard integument (body covering) of other arthropods. In the Triatominae, however, the proboscis is always straight and slender, adapted to pierce the softer integument of vertebrates.

The subfamily Triatominae, established by Jeannel in 1919, is divided into five tribes and 14 genera as follows:

ALBERPROSENIINI: Alberprosenia (1 sp.)

BOLBODERINI: Belminus (4 spp.) Bolbodera (1 sp.) Parabelminus (2 spp.) Microtriatoma (2 spp.)

CAVERNICOLINI: Cavernicola (2 sp.)

RHODNIINI. Psammolestes (3 spp.) Rhodnius (12 spp.)

TRIATOMINI. Dipetalogaster (1 sp.) Eratyrus (2 spp.) Linshcosteus (5 spp.) Panstrongylus (13 spp.) Paratriatoma (1 sp.) Triatoma (66 spp.) WHO/VBC/87.941 page 16

The single species genus Alb.erprosenia contains the smallest triatomine species known, with adults only 5 mm in length, whereas the genus Dipetalogaster contains the largest species, with adults up to 42 mm long. The important genera Rhodnius, Panstrongylus and Triatoma can be distinguished by the shape of the head and the relative distance between the eyes and the insertion of the antennae (Fig. 5). In Rhodnius, the antennae are inserted far from the eyes at the front of the long head; in Panstrongylus, the head is shorter and the antennae are inserted just in front of the eyes; in Triatoma the antennae are inserted midway between the eyes and the front of the head.

Lent & Wygodzinsky (1979) list 112 species of the Triatominae, providing keys in English, Portuguese and Spanish to the adults, and to the first and fifth ins tar nymphs. The first instar key will normally distinguish second-instar nymphs, while the fi fth-instar key will normally also distinguish third and fourth-instar nymphs. To this list have been added Triatoma brailovski from Mexico, T. bruneri from Cuba and Cavernicola lenti from Brazil.

Useful checklists for the Triatominae of the Old World have been compiled by Ryckman & Archbold (1981), and for the Triatominae of North and Central America and the Caribbean by Ryckman & Blankenship (1984 b).

III.2 Reference Centres

Although identification of the Triatominae to species is not normally difficult, especially if adults have been reared out from any nymphs, it is always advisable to submit material for expert confirmation. Reference collections should ideally include both sexes and all nymphal stages, and each specimen must be accurately labelled with the place and date of collection. Specimens should be pinned, or mounted on card points, and shipped in stout wooden boxes that have been treated with a chemical repellant such as naphthalene or paradichlorobenzcne to protect the specimens from damage by insect pests.

Some reference centres are listed below:

Argentina: Dr D.E. Gorla Facultad de Ciencias Exactas, F{sicas y Naturales Universidad de Cordoba Velez Sarsfield 299 Cordoba, sooo Argentina

Brazil: Professor H. Lent Academia Brasileira de Ciencias Rua Anfilofio de Carvalho 29/3a andar Caixa Postal 229 Rio de Janeiro, RJ 20000 Brazil

Professor O.P. Forattlni Faculdade de Saude Publica Avda Dr Arnaldo 715 Sao Paulo, SP Brazil

Costa Rica: Professor R. Zeledon Ministro de Ciencia y Tecnologia y Presidente del Consejo Nacional de Investigaciones sobre Ciencia y Tecnologia Apartado 10318 San Jose Costa Rica WHO/VBC/87.941 page 17

Mexico: Centro de Investigaciones Ecologicas del Sureste San Cristobal de las Casas Chiapas Mexico

United Dr C.J. Schofield Kingdom Department of Entomology London School of Hygiene and Tropical Medicine Keppel Street London WCl E7HT England

United States Professor R.E. Ryckman of America Department of Microbiology School of Medicine Lorna Linda University California 92350 USA

Dr P. Wygodzinsky Department of Entomology American Museum of Natural History New York, NY 10024 USA

IV. PUBLIC HEALTH IMPORTANCE

IV.l Disease transmission

Chagas' disease is among the six priority diseases of the WHO/UNDP/World Bank Programme for Research and Training in Tropical Diseases. After malaria, it is the most serious and widespread parasitic disease of human beings in the Americas.

Trypanosomes. Triatomine bugs are important as vectors of T. cruzi. The most recent data available to WHO indicate over 24 million persons are infected, or at least serologically positive for T. cruzi (Petana, 1980), with about 65 million people at risk in the endemic areas. This represents an average prevalence of about 7% of the total population of Latin America, although in some areas, the local prevalence may exceed 75%. Crude estimates of incidence, based on serological studies and published demographic data, suggest there may be up to 850 000 new infections per year.

No vaccine is available, and except in the very early stage of the infection, there is no effective chemotherapy. About 10% of those infected wi 11 die during the acute phase of the disease, during the first 3-8 weeks following infection. Of those who survive, about 40% will progress to the chronic, indeterminate phase of the disease and may later develop symptoms· of irreversible, 1 i fe-threatening damage to the heart and other internal organs. The remainder appear to remain as asymptomatic carriers of the disease, with a poorly understood prognosis.

T. cruzi occurs in many areas in a zoonotic cycle of transmission between silvatic species of Triatominae and small mammal hosts such as opossums, rodents and armadillos. In the course of human settlement in Latin America, the parasites, together with certain species of triatomine vector and some species of small mammals, have become associated with human dwellings and begun domestic cycles of transmission, including transmission to man.

There is growing evidence that Chagas' disease and its vectors were known to prehispanic American cultures, especially those in the Andean mountain valleys. However, the main expansion of the disease seems to have occurred since the 17th century as pioneers migrated to the interior of the continent and settled into subsistence agricultural activities. The simple rural houses of subsistence farmers often offer a good habitat for domestic triatomine species, while the farmers themselves, together with their domestic animals, offer an abundant WHO/VBC/87.941 page 18

source of blood for the bugs. In these situations, domestic populations of bugs can build up to hundreds or thousands of insects which can transmit T. cruzi between the people and their animals.

In the big cities, the parasite is sometimes transmitted by transfusion of blood from infected donors; the donors are often drawn from the rural poor who migrate to the cities in search of employment. Often, employment is refused to migrants with positive serology for Chagas' disease, because of their poor prognosis for future health and because of irrational fears of possible transmission to other citizens.

Transplacental transmission of T. cruzi is also known to occur, and the parasite may occasionally be transmitted in the mother's milk.

T. rangeli is transmitted by triatomine bugs mainly in the northern part of South America, especially Colombia and Venezuela. It is generally considered harmless to humans, although it may be pathogenic to the bug vectors.

Even in the acute stage of infection with T. cruzi, direct detection of parasites in the blood stream is difficult. Several serological methods are available to detect circulating antibodies, but the most widely used method of direct parasitological diagnosis is that of xenodiagnosis (Cedillos, et al., 1982). Uninfected triatomine bugs, bred in the laboratory, are held in a secure, gauze-covered container, and allowed to feed on the patient. The bugs are maintained alive for about 30 days and then their rectal contents are dissected into a drop of saline on a microscope slide and examined for parasites. This diagnostic method relies on the fact that any parasites in the blood of the patient will multiply in the gut of the bug, and therefore be easier to detect. Xenodiagnosis is also used to detect infected domestic and wild animals for research and survey purposes.

Several species of Triatominae have been used for xenodiagnosis. Ideally the species should be cheap and easy to breed in the laboratory, tolerant of travel to field areas, ready to fecJ on chickens in the laboratory and on humans in the field, and should be highly susceptible to infection with T. cruzi.

The Mexican species, Dipetalogaster maxima, fulfils these criteria very well, and has the added advantage that it can be shipped to field areas as eggs, which are more tolerant of storage and travel; they are then allowed to hatch and applied to the patients as first-instar nymphs. Because D. maxima is the largest species of Triatominae, first-instar nymphs take as much blood in a single meal as third or fourth-instars of many other species.

It is recommended, however, that xenodiagnosis should preferably be carried out using a local species, to avoid the risk of accidental escape and introduction of an alien species into new areas. If R. prolixus or T. infestans are used, 10-20 fifth-instar nymphs are applied to each patient, in boxes of five nymphs each. The boxes are usually applied to the forearms or legs of the patients.

Patients may become allergic to the bites of the bugs used in xenodiagnosis; in some individuals the reactions are severe. Partly for this reason, and because it may be less objectionable to some people, a form of "artificial xenodiagnosis" has been developed, in which bugs are fed through a suitable membrane (such as part of a rubber condom) on venous blood drawn by syringe from the patient. Such methods are said to be as sensitive as conventional xenodiagnosis but can be more difficult to carry out under field conditions.

In northern areas of South America, and in Central America, some patients may be infected with the harmless T. rangeli. Some of these patients may have both T. rangeli and T. cruzi circulating in their blood, and both species can infect the bugs used in xenodiagnosis. In areas where T. rangeli occurs, it must be carefully distinguished from T. cruzi: the forms of T. rangeli in the gut of triatomine bugs are longer than those of T. cruzi, and do not show the large distinctive kinetoplast* at the posterior end. For practical purposes, epimastigotes of T. rangeli can often be found by cutting off a leg of an infected bug and examining a drop of haemolymph expressed from the cut onto a microscope slide. T. cruzi is never found in the haemolymph. WHO/VBC/87.941 page 19

Viruses and bacteria. Like bedbugs, triatomine bugs have been implicated in the transmission of viral hepatitis. However, the virus appears not to multiply in the bug, and viral antigen is detectable in the bug faeces for only about 14 days after an infected blood meal. Similar results have been obtained with the viruses that cause equine encephalites; T. sanguisuga, which is sometimes found in horse stables in the USA, has been implicated in the transmission of Western Equine Encephalitis virus. Multiplication of paratyphoid bacteria (Salmonella paratyphi) in T. infestans has also been reported.

IV.2 Iron deficiency anaemia and psychological stress

Because of their high demand for vertebrate blood, domestic Triatominae, like cimicid bedbugs, probably contribute to chronic iron deficiency anaemia. In one Brazilian house heavily infested with T. infestans, the average daily blood-loss from each person was estimated at 17 ml, although this was undoubtedly an extreme case. Studies of domestic infestations with R. prolixus in Venezuela, and T. infestans in central Brazil, give estimates of about 2.5 ml blood-loss per person per day as a more likely average. Nonetheless, regular blood-loss of this magnitude could be serious for children and for persons on an inadequate diet, especially when combined with other parasitic infections such as hookworm.

Various studies have revealed a wide variation in the level of perception of domestic triatomine bugs by people living in infested homes. Many people seem to view the bugs as normal phenomena or "acts of God" - annoying, but perhaps not as bad as, say, bedbugs or fleas. There is no doubt, however, that for some families, a heavy domestic infestation with bugs that is beyond their abilities to control can result in severe psychological stress, sometimes leading to the break-up of the family unit.

V. SURVEY AND SURVEILLANCE

V.l Methods to detect infestations

Domestic infestations of triatomine bugs may be revealed by the finding of bugs themselves, or indirect evidence of infestation in the form of egg-shells, exuviae, or streaks of faeces. The usual sequence of examination of a house in an endemic area is (1) to_question the householders to see if they have encountered bugs or been bitten within the house; (2) to examine the walls, especially the upper parts, and any artifacts such as pictures or calendars on the walls, for indirect evidence of infestation such as streaks of bug faeces; and (3) to search the house and outbuildings systematically for the bugs themselves.

Householders reports

A well-trained inspector will show prepared specimens of the bugs to the householders, and will refer to the bugs by their local names (Table 1). Sometimes the householders may not recogniz_e nymphs and adults of Triatominae as a s.ingle ent.ity, unaware of the relat.ionsh.ip between the stages. Moreover, although most householders in endemic regions will differentiate between triatomine bugs and c.imicid bedbugs, they may confuse predatory reduviid bugs (and some plant-sucking bugs) with the Triatominae.

Table 1. Some local names for triatom.ine bugs

Argentina Vinchuca Bel.ize Bush chinch Bolivia Vinchuca Brazil Barbeiro, Bicudo, Chupao Chile V.inchuca Colomb.ia Chipo, Pito Ecuador Chinchorro Mexico Pi to Paraguay Vinchuca Peru Ch.irimacho Uruguay Vinchuca USA Cone-nose bug, K.iss.ing bug Venezuela Chipo, Pito, Iquipito, Chupon WHO/VBC/87.941 page 20

If the house is heavily infested, the householders will generally be well aware of the bugs, although if the level of infestation is low they may not. Generally, the inhabitants of infested houses will readily admit to the infestation, especially if they believe that some control measures will result. Occasionally, people will affirm that their house is infested, even though it is not, in the hope that treatment will eliminate other household pests such as cockroaches and fleas. More rarely, householders may deny an infestation because of embarrassment, or because they are reluctant to be disturbed by the inspectors.

Indirect evidence of infestation. Streaks of bug faeces on walls and on artifacts, such as pictures or calendars hung on the walls, provide indirect evidence that a house is, or h!iS been, infested. Faeces of triatomine bugs have a distinctive streaked appearance, likened by some to a "dripping candle-wax effect", and usually present a mixture of black or very dark brown streaks (due to the undigested haem from the bug's bloodmeal) and creamy-wh.ite streaks (due to uric acid). The finding of bug faeces should be recorded as firm evidence of past, but not always of present, infestation. If faecal streaks are found on a recent and datable feature, such as a calendar, this is a more reliable indicator of an existing infestation.

A useful survey method is to tack coloured, dated papers on to the walls of houses to collect streaks of bug faeces; because each paper is dated, any streaks of faeces demonstrate the recent presence of bugs. Schofield et al. (1986) give a key to distinguish the faeces of different domestic arthropods that may be detected by this method.

Direct evidence of infestation. The only direct evidence of a current infestation is to find live bugs in the house. Typically, an inspector will examine the inside of a house for 15-30 minutes, using a torch to see into dimly l.it crevices and behind clothes and pictures hung on the walls. He will probe into crevices with long, blunt-ended forceps, and attempt to capture any live bugs that he finds. (Live bugs can often be induced to leave their crevices by spraying the walls with an irritant miyture of a dilute pyrethroid insecticide in water).

The finding of dead bugs, exuviae, or egg-shells, is a clear indication that the house has been i,tfested, but, as with faecal traces, does not necessarily indicate a current infestation. On the other hand, if only one or two live adults are captured, in the absence of other evidence of infestation, this may indicate only casual immigrant bugs, rather than an established infestation. However, the finding of live nymphs in the house is the clearest proof of an existing infestation.

Any live bugs that are captured should be counted and kept alive in a suitable secure container, labelled with the date and place of capture, until they are subsequently examined for the presence of trypanosomes.

When surveying an area prior to a control campaign, it is sufficient to note the position of houses on the sketch-map of the area, marking those houses in which live bugs were captured, and those where other indirect evidence of infestation was recorded. During the attack phase* of a control campaign with insecticides, all the houses in the area will be sprayed, whether or not they were infested. However, in the post-treatment follow-up, it is necessary to determine which houses remain infested, in order to assess the effectiveness of the control measures and the necessity for selective res pray of persisting infestations (see page 28). Evidence of previous infestation, such as streaks of faeces on the wall, is then unreliable because the inspector cannot know if the faeces were deposited before or after the control intervention. Moreover, even if infestation ~ersists, it will probably be at a low level and live bugs may not be detected in a routine 15-30 minute search of the house.

V.2 Quantitative sampling methods

Samples based on the numbers of bugs captured in a house during a timed search are usually expressed as the "number of bugs per man/hour". Unfortunately, th.is index may be derived from, say, two men catching bugs during 30 minutes each, or one man catching for 15 minutes with the result multiplied by 4, or any s.imilar combination. If the same routine is followed, with the same collectors and the same technique for each house, then the index of "number of bugs per man/hour" provides a crude relative estimate of abundance of bugs in each house, which can be suitable for routine control evaluation. WHO/VBC/87.941 page 21

However, because of different techniques, and because different inspectors will catch different numbers of bugs, the relative indices of abundance est•_mated in this way are not strictly comparable with results from other studies. Moreover, the number of bugs caught "per man/hour" is not necessarily related to the actual number of bugs present, and gives a very biased indication of the population age-structure because larger nymphs and adult bugs are seen and captured more easily than the smaller nymphs which are more difficult to catch. To overcome these difficulties, several quantitative sampling techniques have been used, mainly for research purposes, and three methods are described below.

(i) Removal sampling. Removal sampling assumes that by capturing a sample of bugs from the house, the number remaining will then be reduced. If a subsequent sample is taken, then the remaining population will be reduced further. In theory, therefore, if suffici.ent samples are taken until no more bugs can be captured, then the sum of the samples represents the total bug population.

In practice, two or more successive samples are taken from a house, usually by collecting bugs for 15 minutes on each occasion. Each sample is counted and the count is then plotted on a graph, against the number of bugs already captured. Thus, the first sample will be plotted (on the verticle y-axis) against 0 (on the horizontal x-axis) because no bu~s have already been caught, and the second sample will be plotted (on the y-axis) against the first (on the x axis) which represents the number of bugs already caught. Any subsequent samples are then plotted against the sum of the previous samples.

Extrapolation of the graph to where it intersects the x-axis then gives the estimate of the bug population size. Formal calculation of the estimated population and its variance may be followed from standard texts (e.g. Seber, 1973; Southwood, 1978).

(ii) Mark, release and recapture. The simplest version of a mark-recapture method is the Li.ncoln Index. A sample of bugs (A) is either reared in the laboratory or taken from the house. These bugs are marked and then released into the house. After 24 hours, a second sample of bugs (N) is taken from the house, which will include a number (R) of the previously marked bugs. The total bug population (T) can then be estimated as:

T = (A x N)/M and the standard error of the estimate is given by: SE = Square root (A2 x N x (N - R))/R3

Other, more complex methods of mark-recapture estimates are given in standard texts (e.g. Seber, 1973; Southwood, 1978).

(iii) House demolition. Experimental field work shows that none of the available sampling methods are very accurate for determining the numbers of triatomine bugs in a house, and their population age-structure. This is due to the uneven distribution of bugs in a house, the difficulty of capturing large samples, and the inherent bias in manual capture, because the larger numphs and adults are much easier to find than smaller nymphs. For an ecological study, the only satisfactory approach has been to purchase and demolish selected houses ·and collect a very large sample of the bugs by carefully examining the whole house, piece by piece, as it is demolished. Efficiency of capture during house demolition can be estimated using a Lincoln Index as above.

V.3 Epidemiological indices

For survey purposes, the proportion of houses infested is usually expressed as the percentage of houses infested out of those examined. If bugs are dissected individually to see if they are infected with T. cruzi, then it is often useful to express the result as the average percentage of bugs infected out of those examined. Other epidemiological indices include measures of the percentage of people in the area with a positive serology for T. cruzi, and the percentage of people in both seropositive and seronegative classes, who have significant indications of heart damage attributable to Chagas' disease.

Other information of value to epidemiologists is the rate of construction of new houses in the area, and the rate at which old houses are abandoned, because this data can help in WHO/VBC/87.941 page 22

predictions of changes in infestation rates. Similarly, information on the human birth and death rates in the area is important.

V.4 Survey methods for silvatic triatominae

Habitat dissection. Silvatic Triatominae can occur wherever there is access to a silvatic blood source. In general, they are associated with the nests or resting places of small mammals and birds. Thus, as a first approach to study of the silvatic Triatominae in a specified area, it is often fruitful to dissect silvatic habitats where vertebrates may have made their nests. Examples include piles of rocks, where small rodents or lizards may be present: these could also contain rupicoline* species of Triatominae such as T. costalimai in central Brazil. Stone walls dividing fields provide similar habitats for species such as T. spinolai in Chile or T. arthurneivai in Brazil.

Bromeliad epiphytes* often provide lodges for opossums, and in Bahia are often infested with T. tibiamaculata. The crowns of palm trees harbour a variety of animals, and 3re frequently infested with species of Rhodnius; adhesive tree-bands have been used to sample arboreal bugs in Venezuela. Psammolestes species are often associated with the "hanging basket" nests of birds such as Phacelodomus.

Several species of Triatominae are commonly associated with bats in caves and hollow trees; examples include Cavernicola pilosa which is exclusively associated with bats, T. dimidiata in bat-caves in Belize, and T. cavernicola recently described from caves in Malaysia. In the southern USA, T. protracta and related species are frequently found in the nests of woodrats (Neotoma spp.).

Examination of silvatic habitats depends on the type of habitat. Bat-caves, for example, are examined using a torch and long forceps in much the same way as in the examination of a house. For most silva tic habitats, the components of the bird or mammal nests should be located, placed on a white sheet and carefully dismantled to allow each part to be meticulously examinrd.

Bugs will not be found in the very wet parts of a habitat, such as between the leaves of a bromeliad where water is retained, but only in the dry parts of the habitat being examined.

In general, each silvatic bug population will be very small, such that only one or a few bugs may be recovered from examination of several likely habitats. However, palm tree crowns often yield large numbers of bugs.

Mammal tracking. In some areas, particularly in forests, locating mammal nests may be particularly difficult. An alternative approach is to track the mammals back to their nests. Mammals are first trapped in cage traps. They can then be subject to xenodiagnosis (see page 18), and a sample of tail blood taken for serological study to determine a possible infection with T. cruz!. The animals are then fitted with a spool of thread in a plastic holder which is securely taped around the abdomen of the animal. One end of the thread is tied to a convenient piece of vegetation and the mammal is then released to go its own way, and eventually return to its nest. As it goes, the thread is paid out behind to mark where the animal has travelled. Using different sizes of spools for different species of mammal, it is possible to locate the nests of many forest mammals, from which various species of Triatominae have been collected.

This type of study has both zoological and epidemiological importance. Not only does it contribute directly to our understanding of the biology and host associations of poorly-known species of Triatominae, but it also allows the biochemical characterization of trypanosome isolates from the host mammals, and from the bugs in their nests. By comparing the characteristics of these trtpanosomes with those isolated from domestic cycles of transmission (using, for example, isoenzyme* characterization), it can be shown whether or not there is any significant overlap between domestic and silvatic cycles of T. cruzi transmission.

By the use of mark-release-recapture methods in Venezuela, it was shown that opossums moved between silvatic and peridomestic habitats over periods of one year or more. A study of WHO/VBC/87.941 page 23

young opossums in the pouches of their mothers also showed that about 1% became infected with trypanosomes (in this case T. rangeli) at this stage of their lives. Recent studies in Brazil have shown that opossums infected with T. cruzi produce metacyclic trypanosomes in their anal scent glands and that these parasites can be discharged in their faeces.

Artificial habitats. Artificial habitats, usually in the form of small chicken houses, have been used to study both domestic and silvatic species of Triatominae. The habitats are normally constructed of local materials, and provided with chickens as resident hosts; chickens are relatively inexpensive and are not susceptible to infection with T. cruzi. For domestic Triatominae, artificial refuges are particularly useful to study the long-term development of bug populations, following the introduction of laboratory-reared insects or those recently collected from the field. The chicken houses can be dismantled and are built at intervals in order to study the development of the bug populations.

Studies in Venezuela also showed immigration and emigration of adult bugs, and entry into the chicken houses of bug predators and wild animals (detected by identification of blood-meals in the gut of the triatomine bugs).

In•. the study of silvatic Triatominae, experimental chicken houses are also useful to monitor the influx of flying adults. The chicken houses are erected at different sites, stocked with chickens, and then regularly checked for any recently-arrived bugs. In this sense, the artificial habitats give a direct measure of the colonizing ability of different bug species. They can be used to assess both the presence of silvatic species in the area, and the possible risk that some silvatic bugs may invade homes following, for example, deforestation or major changes in agricultural practice, or after a control campaign directed against the domestic bug species.

VI. CONTROL

Although there is no effective chemotherapy or immunoprophylaxis, interruption of vector borne transmission of T. cruzi is entirely feasible. Moreover, even if new drugs or vaccines are developed, control of the vectors and elimination of household infestations will remain a priority in endemic regions of Latin America.

Given the determination and expertise of control authorities in Latin America, and the successes already achieved in many areas, the wisest strategy may be to place less emphasis on the possibilities of immunoprophylaxis and concentrate resources on the immediate and tangible benefits which would accrue from vector control. There is no doubt that throughout Latin America, the only serious limitation to the interruption of vector-borne transmission of T. cruzi is a lack of appropriate financial resources for the various control agencies. Even the simplest theoretical comparisons unequivocally demonstrate that Chagas' disease should be one of the easiest of all vector-borne diseases to control, given adequate resources and good management.

VI.l Methods of control

Many possible approaches to the control of domestic triatomine bugs have been tested and evaluated (Schofield, 1985). But of the methods listed below, only residual insecticides, housing improvements, and public health education, are of major importance (especially when used in combination).

Insecticides. Compounds from almost every class of organic insecticide have been tested against triatomine bugs in the laboratory, and many have been field-tested. These are summarized in Table 2. WHO/VBC/87.941 page 24

Table 2. Insecticides that have been field-tested against triatomine bugs

Organochlorines

Dieldrin, HCH and lindane

Organophosphates

Malathion Fenitrothion Fenthion (not recommended due to high toxicity) Chlorpyriphos Iodofenphos Pirimiphos-methyl

Carbamates

Bendiocarh Propoxur

Pyrethroids

Permethrin Deltamethrin

DDT, although one of the least expensive insecticides, is relatively ineffective against triatomine bugs. HCH, or lindane, have been used extensively in the field against Triatominae since early trials in Brazil by Pellegrino in 1947. HCH is normally applied as an aqueous suspension of wettable powder* (containing not less than 30% of the active gamma isomer). Target delivery is O.S-2.0 g active ingredient per m2 sprayed over all internal and external walls, roofs and outbuildings of infested houses. Dieldrin, although more expensive and more toxic than HCH, has been widely userl in Venezuela against R. prolixus, with good results; dieldrin resistance has been found in a few areas of Venezuela, but rloes not appear to be widespread and can be dealt with, replacing it with organophosphates or carbamates.

In general, neither organophosphates nor carbamates offer significant advantages, although they are more expensive than HCH or dieldrin. Their use seems to have been largely the result of difficulties in obtaining supplies of organochlorines, since many companies have ceased manufacturing them due to widespread concern about possible environmental contamination. However, some synthetic pyrethroids, particularly permethrin (Pinchin, et al., 1982) and deltamethrin, are highly effective against triatomine bugs and have much greater residual activity on mud walls compared to other classes of insecticirles. Thus, although pyrethroids tend to be considerably more expensive than organochlorines (at least ten times the price of HCH per kg), they can achieve very satisfactory levels of control at lower doses and with less frequent applications.

Insect growth regulators. Many natural and synthetic compounds affect the growth and development of trlatomine bugs. Of experimental interest are the juvenile hormone analogues, and the anti-juvenile hormones or precocenes*. Juvenile hormones act on 5th-stage nymphs in such a way that the subsequent moult, which normally gives rise to an adult, gives rise to a supernumerary nymph, or at lower doses, to a sterile adultoid* (pseudoadult) with morphological characteristics intermediate between those of adults and nymphs. Precocenes act in the opposite way. When applied to 1st, 2nd, 3rd or 4th-stage nymphs, the sub~e'1nent moult gives rise to a precocious sterile adultoid. Precocenes also have some ovicidal activity.

Insect growth regulators do not act on all stages of the insects and although slow-release formulations of juvenile hormone-analogues have been tested in the field, they have little practical significance for the control of triatomine hugs. Juvenile hormone-analogues are generally very specific to particular insect species, and are harmless to mammals. Althougl1 WHO/VBC/87.941 page 25

this implies that they would be very safe to use, their specificity means that the potential market for them is limited, and none has been developed for commercial use against Triatominae.

Insect pathogens. Despite wide interest in the use of pathogens to control other insects of medical importance, there are few reports that consider this type of control against triatomine bugs. A useful checklist and bibliography of parasites, predators and symbionts of Triatominae is given by Ryckman & Blankenship (1984 a).

Without exception, those pathogens that have been seriously proposed for the control of domestic triatomine bugs, such as the fungus Metarrhizium anisopliae, and entomogenous nematodes, have been ineffective in small-scale field trials. The pathogens seem to be severely limited by low humidities and high temperatures.

Insect predators and parasitoids. Many species of predatory arthropods are known to feed on triatomine bugs either in nature or experimentally (Ryckman & Blankenship 1984 a). Mites (particularly Pimeliaphilus spp.) and certain protozoa (particularly Blastocrithidia triatomae) also parasitlze triatomine bugs and can cause serious mortality in laboratory colonies. However, only microhymenopterous parasitoids of triatomine eggs, such as certain scelionid and encyrtid wasps, have been seriously considerd as potential biological control agents against domestic Triatominae.

However, consideration of the population dynamics of triatomine bugs, simulation models, and experimental field trials all show that these egg parasitoids would fail to produce adequate or cost-effective control of domestic Triatominae. Inundative release of laboratory reared wasps would be expensive, and if the wasps destroy all, or most of the bug eggs in a house, then the wasp population would become extinct due to a lack of unparasitized host eggs, allowing any remaining or immigrant female bugs to lay more eggs and return the bug population balance to normal. Release of smaller numbers of wasps would not affect the numbers of nymphs and adult bugs in a population unless over 90% of the eggs were parasitized; yet average levels of egg parasitism in nature are only about 14%.

Genetic control. Chemosterilants have received little attention for triatomine control, largely due to the potential hazard of introducing them into the domestic environment. Me tepa, a powerful chemosterilant, is also attractive to R. prolixus; it has been suggested that the danger inherent in the use of chemosterilants in the domestic environment could be reduced by incorporating metepa as the bait in an enclosed trap. However, traps for domestic triatomine bugs have met with little success (see below), and the use of chemosterilants should be discouraged for safety reasons.

Genetic manipulation of laboratory populations, followed by the release of the altered insects (such as sterile males), has obvious advantages over chemosterilants or other pesticides in not polluting the environment. This approach has met with encouraging success for the control of some insects, and may be useful in the control of mosquitos, where altered males can be released with safety because they do not suck blood, nor transmit human diseases. However, in the case of triatomine bugs, where males are also blood-suckers and can transmit Chagas' disease, release of sterile males would be unethical. Moreover, the chromosomes of triatomine bugs are of a type that makes it almost impossible to induce lasting sterility.

Traps. No efficient attractant has been developed for use in traps for domestic triatomine bugs. Small chemical lights, although effective as attractants in laboratory tests, were ineffective in the field. Traps baited with small mammals caught few bugs in Venezuelan houses, presumably because they only attract unfed bugs and must compete with the much larger biomass of man and other animals in the house; also, animal-baited traps are expensive to maintain because the animals must be adequately looked after. Sex pheromones are not known from triatomine bugs, and the aggregation pheromone from freshly-deposited bug faeces seems too volatile for use as a trap bait.

Passive "traps", such as the Gomez-Nunez box or the Cohen box, are useful as sampling techniques, especially after control interventions (see section VI.3, pages 28-29), but are unlikely to contribute directly to bug control because very few bugs are collected in them. The boxes act as artificial refuges for the bugs; their efficiency can be marginally improved WHO/VBC/87.941 page 26

by coating their internal surfaces with a non-drying adhesive to trap the bugs, or with residual insecticides to kill them, but they are relatively expensive to make and install, and are inefficient to control bug numbers. Often, the boxes are removed by children or adults and use.d for other purposes.

Housing improvements. The improvement of rural housing has been well recognized as a desirable long-term social objective, but has received less attention as a means to control domestic triatomine bugs because of the anticipated expense of large-scale rehousing schemes (D1as & Dfas, 1982).

The idea of house improvement is simple: bugs live predominantly in the cracks and crevices of poor-quality rural houses, so if there are no cracks then there is no extensive habitat for bugs to colonize. For the bugs, the domestic environment offers protection from climatic extremes, protection from predators, and an adequate supply of food from the blood of man and domestic animals. Removal of domestic animals to appropriate outbuildings would limit the size of the household bug populations by reducing the number of available hosts (see Population dynamics, page 15) and experimental work in many endemic areas has shown that simple improvements to rural houses, such as replacement of palm-thatch with roofs of corrugated metal sheets, and plastering over the cracked mud walls can render a house unsuitable for domestic bug infestations (Schofield & White, 1984). In Costa Rica, improvement of the cracked mud floors of rural houses led to a decline in the number of houses infested with T. dimidiata.

Conceptually, it is important to distinguish between the replacement of rural houses, which would necessarily be expensive, and the improvement of existing houses using skills, materials and techniques appropriate to the local people. Rural houses in Latin America, although modest, have many desirable features that should be retained. In general, they have been designed and constructed in accordance with the skills and preferences of their inhabitants and they offer comfortable protection from extremes of climate.

The use of cement or fired bricks for rural houses is expensive in terms of imported materials, energy, and distribution costs, and may not retain the climatic characteristics of the original houses. More importantly perhaps, these materials require special skills which the local people may lack, and may impose design constraints which they find unacceptable.

Techniques to be emphasized therefore include the replacement of palm thatch with roofs of locally-made ceramic tiles or cheap corrugated metal or plastic sheets, and the smooth rendering of existing mud and adobe walls using a wall-plaster of local materials. In Brazil, good quality wall-plaster that resists cracking and powdering can be prepared by mixing sand, cow-dung, earth and lime (Schofield & Marsden, 1982). The lime can usually be prepared locally by heating small limestone rocks overnight in a wood-fired kiln and then pulverising the white residue.

Where the structure of a house is too poor to upgrade, it may be more appropriate to build a new house using inexpensive methods. In areas where the local clays are rich in kaolin, adobe blocks made from these clays are strong and relatively resistant to erosion and cracking. More often, however, locally-made adobe blocks readily crack on drying and rapidly erode during the rainy season. If the adobe is fired in a klln to make fired bricks, considerable energy must be expended, both in the firing and in subsequent distribution costs. The quality of such bricks rarely merits this expenditure.

The earth used in traditional rural housing can be stabilized against erosion, shrinkage and cracking, by the addltion of bitumen or asphalt (to make asfadobe), cement (to make soil cement), or lime. Stabilized earth can be further improved by compaction in a mechanical ram. Alternatively, earth can be compressed in situ, by ramming it firmly between wooden formers. This is the basis of the Venezuelan "taplale" and Brazilian "talpa pilao" construction, or the French "pise de terre" which is still widely used in parts of francophone Africa.

Several types of hand-operated rams have been developed for the manufacture of compressed, stablized buildlng blocks. One of the best known is the CINVA ram, developed in Colombia, which applies a pressure of about 2 meganewtons/square metre (MN/m2) (about 8 tonnes) to produce blocks similar to traditional adobe. A hydraulically-assisted manual press has been developed by the UK Building Research Establishment, which applies a pressure of about 10 MN/m2 WHO/VBC/87.941 page 27

(about 40 tonnes) to produce blocks that are equal or superior to fired bricks in terms of load-bearing strength.

The superior performance of compressed soil blocks, and their ease of manufacture by local people, could bring about considerable improvements in the quality of rural housing at relatively low cost. Such machines can be adapted to make floor and roof tiles, and for the liners of sanitary pipes and pit latrines. The non-porous compressed blocks also offer a better surface for the action of residual insecticides, compared to adobe blocks made from the same material.

VI.2 Health education

From the preceding sections it will be apparent that public awareness of bug infestations, and the health hazard that they represent, has a vital supportive role in any form of control. The aims of health education, in relation to primary health care and community involvement in control and surveillance activities, should be broadly as follows:

(i) To create public awareness of Chagas' disease and the role of the vectors.

(ii) To create public demand and accP.ptance of suitable control measures, provided always that the demand created can be promptly and effectively met by the organization responsible.

(iii) To encourage local communities to cooperate, and where appropriate participate, in control measures directed at the vectors.

(iv) To encourage evaluation by householders of the effectiveness of control activities in each house, and to inform the spray-team leaders of any apparent failures.

(v) To encourage the public to improve the structure of their own homes to reduce infestation levels, by appropriate individual or community measures to reduce the cracks and crevices available to the bugs.

(vi) To encourage community members themselves to eliminate peridomestic and other potential sources of household infestations wherever possible, by appropriate recommended actions.

(vii) Where appropriate, to encourage the community to play an active part in control, evaluation and surveillance activities, together with or under the supervision of the responsible authorities.

Increased public acceptance of insecticidal measures, if not soon followed by control actlvities, may lead to indiscriminate private purchase and use of proprietary insecticides. If such attempts fail, as they frequently do, this may lead to public rejection of insecticidal control. In this context, it is important that irresponsible advertizing of proprietary products is discouraged by the health authorities.

Ideally, public health education in the field of Chagas' disease vector control should proceed concurrently with the chosen control intervention and, where promises are met, health education is a powerful adjunct to vector control campaigns. The use of posters, radio and television broadcasts, and particularly the involvement of primary school teachers and their pupils in rural zones has, in general, been both useful and productive.

Even in the absence of other measures, careful and appropriate health education can lead to domestic improvements by encouraging affected people to maintain better standards of hygiene, removing domestic animals to appropriate outhouses (see II.3), carrying out simple modifications to their houses, such as applying wall-plaster, and removing stored produce and other material that provides a refuge to bugs and other vermin.

The necessity for this type of health education is seen from the few surveys available. For example, a small survey in an endemic area of Brazil revealed that over 40% of rural people were unaware of any connection between triatomine bugs and Chagas' disease. A larger survey, of about 24 000 parents, teachers and schoolchildren in Argentina, revealed that, although over 90% of school teachers were aware of the relationship between triatomine bugs and Chagas' WHO/VBC/87.941 page 28

disease, fewer than 60% of parents and children were similarly aware. In parts of Nayarit in Mexico, elderly men believe that triatomine bugs have aphrodisiac powers if eaten, while children believe that rubbing the bugs on the skin cures warts and verrucas. In parts of northern Chile, children sometimes play a game to see who can squash a recently-fed bug on their hand to make the biggest stain.

One of the main contributions of public health education during a control campaign lies in the participation of the community in post-treatment vigilance schemes, whereby any bugs found in their houses are reported to a central post for confirmation, followed by selective respraying of the houses involved. This now forms an essential component of most large-scale control campaigns with insecticides (see below).

VI.3 Control campaigns and post-control vigilance

Although housing improvements will probably become increasingly important in Chagas' disease vector control campaigns, in the short-term, reliance will continue to be placed on the repeated application of insecticides to houses and outhouses. Gamma-HCH remains the insecticide of first choice in most regions, due to its low cost and familiarity with its use. However, many control authorities are beginning to try other insecticides as HCH has become increasingly scarce on the world market. Propoxur and fenitrothion are now frequently used instead of HCH, and many authorities are considering the use of synthetic pyrethroids such as permethrin or deltamethrin as compounds of first choice. Studies with deltamethrin in Brazil have shown that the extended time of apparently effective control, which reduces the required frequency of respraying, can make pyrethroids more cost-effective than organochlorines (see section VI.l).

Insecticide campaigns typically proceed in three phases: (1) preparatory*, (2) attack, and (3) vigilance*. After financial support is assured, personnel are recruited and trained; the areas to be treated are sketch-mapped and each house is examined for signs of infestation. During this preparatory phase, evidence of infestation may be the finding of live or dead bugs, bug faeces or other indirect evidence, or reports from the householders (see section V.l).

During the attack phase, all houses are treated in communities where infested houses have been located (not just the houses in which bugs were found). In Brazil, each spray team, usually of two spraymen, driver and supervisor, can spray about 16 houses per day depending on the weather and distribution of the houses; in other countries, the team organization and rate of attack may be different. In areas where the population is very dispersed, the treatment rate may be reduced due to the long distances and poor roads. With 30% HCH wettable powder, target delivery is 0.5-2.0 g active ingredient/m2 over all internal and external walls, roof and outbuildings. After spraying, householders are warned not to wash off the insecticide deposits and to wait as long as possible before returning their furniture, food and domestic animals to the house.

The staff training programmes necessary before triatomine control is begun are organized and administered in much the same way as in malaria control programmes, and are often developed from them. Current trends in vector control are leading away from vertical programmes towards decentralization, with growing emphasis on an active role for primary health care workers, and for the whole community. This trend is a result of the realization at government levels that vector control is an open-ended, long-term and expensive activity. The downward transfer of active responsibility and participation allows health ministries to devote the scarce skilled manpower and other available resources to other priority projects. Although community-based control can have serious disadvantages in practice, every effort must be made to make it more effective, efficient and feasible on a large-scale basis.

During the vigilance phase which follows a successful attack phase, it is vital to detect houses where bug populations remain, or which have been recolonized. Inspectors should visit the houses to examine them for continuing bug presence, especially if the householders report seeing bugs in their houses.

Three simple vigilance methods may be used. Gomez-Nunez or Cohen boxes can be placed in the houses (see pages 25-26); these act as artificial refuges where bugs may hide (Cohen boxes also contain an insecticide designed to kill any bugs that enter, but this may have a repellent WHO/VBC/87.941 page 29

effect on the bugs, reducing the efficiency of the boxes as a vigilance method). If bugs visit the boxes, then examination after 3-4 weeks may reveal bugs or their exuviae inside the boxes, or more frequently, streaks of bug faeces on the pape~s inside the boxes.

Alternatively, sheets of coloured papers can be tacked to the walls of a house to pick up recent deposits of bug faeces (see page 20). It has been suggested that a complete vigilance should be installed in houses following a control campaign; this could consist of an educational poster mounted on a Gomez-Nunez box, to which is attached a self-sealing plastic bag (or a matchbox) in which the householder can put any bugs that he collects (Marsdon & Penna, 1982). Participation of the community is essential in order to discover quickly any houses in which bugs reappear. During the vigilance phase, any house in which live bugs are detected is resprayed in order to maintain satisfactory levels of control within the community.

Assessment of a control campaign is normally recorded as a reduction in the number of houses infested, and by reductions in the numbers of bugs caught in infested houses, based on timed collections of bugs. Final evaluation can only be done several years later, by comparing the seropositivity of children born after the campaign, with that of children in the same age group before the campaign began.

Chemical control must be a continuous activity to ensure success. Retreatment on a regular basis is an integral element in chemical control, and requires careful planning of staff time, finance, equipment and vehicle maintainance, and safe storage and handling of insecticides. The role of community participation in control and surveillance activities should also be stressed (see Section VI.2). WHO/VBC/87.941 page 30

VII GLOSSARY

ABRASION Damaged area of skin.

ADULTOID See PRECOCENE.

ARBOREAL Living in trees.

ATTACK PHASE (Of a control programme) the phase in which all houses are treated, regardless of whether or not the house was infested.

BEDBUGS A term for small blood-sucking Hemiptera of the family Cimicidae, genus Cimex. These bugs are related to the Triatominae in the sense of being in the same order, the Hemiptera, but are not involved in natural transmission of Trypanosoma cruzi.

CONNEXIVUM The prominent lateral margin of the abdomen of Hemiptera. In adult triatomine bugs, the connexivum is often marked with distinctive coloured patches (usually yellow, red or brown) which can be useful in identification. In some species, such as Rhodnius prolixus, the connexivum contains a folded membrane that can be expanded as the bug engorges with blood.

COPULATION Physical union of the male and female Triatominae.

DENSITY-DEPENDENT A term used to describe factors that vary according to the population density, and provide a form of "negative feedback" to stabilize population numbers. All living populations must be limited by density-dependent factors operating on either their birth-rate or death-rate (or both), otherwise their populations would increase forever. In some cases, however, populations can be limited by density-independent factors, before density-dependent factors come into operation.

DOMESTIC Associated with houses.

EPIPHYTE A plant living on the surface of another plant such as a tree, rather than on the ground.

EXOPTERYGOTE Adjective from Exopterygota - a division of insects including the Hemiptera and several other orders, in which metamorphosis, or development through the life-cycle, proceeds from eggs through nymphs to adults. This form of life-cycle is sometimes referred to as hemimetabolous or incomplete metamorphosis (because there is no pupal stage), in contrast to Endopterygote or holometabolous insects (such as mosquitos and other Diptera) in which the life-cycle proceeds from eggs through larval and pupal stages to the adults. In exopterygote insects, the immature stages (nymphs) usually occupy the same habitat, and have similar behaviour and feeding requirements to the adults (thus, in the case of trlatomine bugs, the nymphs, as well as the adults, suck blood and can transmit Chagas' disease). In endopterygote insects, the immature stages are usually quite different to the adults, with different diet, habitat, and behaviour.

EXUVIUM The cast outer skin which is shed when an insect moults to its next developmental stage.

GENETIC A hereditary factor controlled by genes of the previous generation.

HABITAT The natural home of the Triatominae.

HEMELYTRON (Plural hemelytra) - the forewings of Hemiptera, which are divided into a thickened basal part and a membranous distal part. (The hind wings of Hemiptera are completely membranous). WHO/VBC/87.941 page 31

HEMIMETABOLOUS see EXOPTERYGOTE.

HEMIPTERA One of the 29 orders of insects, which contains the "true bugs". Hemiptera have characteristic forewings (see HEMELYTRON) and have piercing and sucking mouthparts (see PROBOSCIS).

ISOENZYME One of several molecular forms of enzyme, sometimes in the same cell, having an individual form and specific function. Characterization is carried out by electrophoresis to show specific isoenzyme bands.

KINETOPLAST A unique organelle (a specialized protoplasmic part) containing DNA generally situated posterior to the flagellum and anterior to the nucleus occurring in the order Kinetoplastida of which the Trypanosoma forms part.

K-STRATEGIST Organisms whose life history is adapted for existence in a stable environment. The term K is used by mathematical biologists to denote the "carrying capacity" of a particular environment, i.e. the maximum number of individuals of a particular species that the environment can support. Species are said to be K-selected or to show a K-strategy if they are adapted to exploit stable environments over long periods of time. This contrasts with r-strategists which are opportunistic species adapted to reproduce rapidly when conditions permit (r denotes the intrinsic rate of natural increase of a species). Thus K-strategists tend to reproduce slowly and to show only minor fluctuations in numbers provided their environment remains stable. They respond poorly to changes in their environment; whereas r-strategists tend to reproduce quickly and are adapted to exploit sudden changes in their environment.

The term r- and K-strategist are convenient descriptive terms, but they really refer to two extremes of what is really a continuous spectrum of adaptations. It is more correct to describe a particular species as more r-selected (or more K-selected) than another.

METACYCLIC The infective trypomastigote forms of trypanosomes (sometimes called metatrypanosomes). Metacyclic stages of Trypanosoma cruzi (and T. rangeli), can be recognized in the rectum and faeces of Triatominae by their characteristic size, shape and movement. They are the final stage of the trypanosome life-cycle which occurs in the insect vector, and do not normally reproduce at this stage.

METAMORPHOSIS See EXOPTERYGOTE.

MORPHOLOGY The physical form of the insect.

OPERCULATE Used to describe eggs that have a distinct cap (or operculum) through which the hatching nymph or larva will emerge.

OVIPOSITION The laying of eggs.

PERI DOMESTIC Associated with outhouses, storage houses, chicken houses or other animal enclosures, etc., near the house.

PHEROMONE A substance secreted by an insect which influences the behaviour of other insects.

POLYMORPHISM Presenting distinct forms, that are not related to stages in the life-cycle. For example, adult males of Triatoma spinolai may be winged or wingless, and they therefore present alary polymorphism; similarly, different isolates of Trypanosoma cruzi may present different forms of a particular enzyme, and they are therefore said to show enzyme polymorphism. WHO/VBC/87.941 page 32

PRECOCENE A type of insect growth regulator which acts on the corpora allata to inhibit the secretion of juvenile hormone. In the absence of juvenile hormone, nymphal stages 1 to 4 of triatomine bugs moult to precocious adults (known as adultoids) which are small and usually sterile; however, nymphal stage 5 will moult to an adult in the normal way.

PREDATOR An insect that naturally preys on others.

PREPARATORY PHASE (Of a control programme). The planning phase, when areas are mapped and surveyed for infestations, prior to the attack phase.

PROBOSCIS The mouthparts of Hemiptera, which form a tube folded under the head. This tube contains the stylets which penetrate the host tissues in order to suck up the host fluids.

R-STRATEGISTS See K-STRATEGISTS.

REDUVIIDAE A family of the order Hemiptera; most subfamilies of the reduviidae consist of predatory bugs (sometimes known as assassin bugs) that feed on the juices of other invertebrates. Only the subfamily Triatominae contains blood sucking bugs, that feed on the blood of vertebrates, although some predatory reduviids may occasionally bite vertebrates, usually as a defence mechanism (if they bite man, the bite is usually very painful).

RUPICOLINE Adjective to describe animals or plants which are particularly associated with rocky or stony places. The similar word rupicolous is sometimes used but has the same meaning. Both words derive from the Latin rupes meaning a rock.

SILVATIC Not associated with domestic or peridomestic environments. (Literally: associated with the forest).

STERCORARIAN A grouping of trypanosomes that describes their development in the gut of the insect vector. In contrast, Salivarian trypanosomes (such as those responsible for African sleeping sickness) develop in the salivary glands of their insect vectors. Trypanosoma cruzi is a stercorarian trypanosome, and develops only in the gut of its vectors; T. rangeli Is also a stercorarian trypanosome that develops in the gut of its vectors and then migrates to the vector's salivary glands.

STERNITES Hard chitinous plates.

STRIDULATORY A transversely-ridged groove on the underside of the prothorax (just GROOVE between the two anterior legs) of adults and nymphs of the Reduviidae and some closely related families of the Hemiptera. In the Triatominae, and other Reduviidae, adults and nymphs occasionally rub the tip of their proboscis along the groove to produce a vibration that may contain audible and ultrasonic components. Stridulation means the production of sound by rubbing together two parts of the body, and is a common phenomenon in insects.

SUBSTRATE The solid underlying material to which the bug attaches itself.

TERRESTRIAL Living on the ground.

VIGILANCE (Of a control programme). The surveillance phase, following an attack PHASE phase, when houses are checked and resprayed if evidence of a new infestation is discovered. WHO/VBC/87.941 page 33

WETTABLE A water dispersable, but insoluble, formulation of an insecticide, in which POWDER the active ingredient is bound to an inert insoluble carrier material such as talcuum powder. Wettable powder formulations are mixed with water to be sprayed, and usually have greater residual activity than liquid formulations of the same insecticide.

XENODIAGNOSIS A method of parasitological diagnosis of Chagas' disease, by allowing non infected triatomine bugs to feed on a patient, and then examining the rectal contents of the bugs 30 days later for any parasites which would have multiplied in the gut of the bugs. WHO/VBC/87.941 page 34

VIII BIBLIOGRAPHY

1. Lent, H. & Wygodzinsky, P. Revision of the Triatominae (Hemiptera, Reduviidae), and their significance as vectors of Chagas' disease. Bulletin of the American Museum of Natural History, 163: 125-520 (1979).

2. Marsden, P,D. & Penna, R. A vigilance unit for households subject to triatomine control. Transactions of the Royal Society of Tropical Medicine and Hygiene, 76: 790-792, (1982).

3. Rabinovich, J.E. Vital statistics of Triatominae (Hemiptera: Reduviidae) under laboratory conditions. I. Triatoma infestans. Journal of Medical Entomology, 9: 351- 370 (1972).

4. Ryckman, R.E. & Archbold, E.F. The Triatominae and Triatominae-borne trypanosomes of Asia, Africa, Australia and the East Indies. Bulletin of the Society of Vector Ecologists, ~: 143-146 (1981).

5. Ryckman, R.E. & Blankenship, C.M. The parasites, predators and symbionts of the Triatominae (Hemiptera: Reduviidae: Triatominae). Bulletin of the Society of Vector Ecologists, != 84-111 (1984a).

6. Ryckman, R.E. & Blankenship, C.M. The Triatominae and Triatominae-borne trypanosomes of North and Central America and the West Indies: a bibliography with index. Bulletin of the Society of Vector Ecologists, != 112-130 (1984b).

7. Schofield, C.J. The behaviour of Triatominae (Hemiptera: Reduviidae): a review. Bulletin of Entomological Research, 69: 363-379 (1979).

8. Schofield, C.J. The control of Chagas' disease vectors. British Medical Bulletin, 41: 187-194 (1985).

9. Schofield, C.J. & White, G. B. House design and domestic vectors of disease. Transactions of the Royal Society of Tropical Medicine and Hygiene, 78: 285-292 (1984).

10. Schofield, C.J. et al., A key for identifying faecal smears to detect domestic infestations of triatomine bugs. Revista da Sociedade Brasiliera de Medicina Tropical, ..!.2_: 5-8 (1986).

11. Seber, G.A.F. The Estimation of Animal Abundance and Related Parameters. Griffin, London, 1973, 506 PP•

12. Southwood, T.R.E. Ecological Methods. 2nd edn. Chapman & Hall, London, 1978, 524 pp.

13. Zeledon, R. & Rabinovich, J. E. Chagas' disease: an ecological appraisa 1 with special emphasis on its insect vectors. Annual Review of Entomology, 26: 101-133 (1981).

Bibliographies to earlier literature are given by:

1. Dvorak, J.A., Gibson, c.c., Maekelt, A. A bibliography on Chagas' disease (1968-1984). National Institutes of Health, Washington DC, 1985, 397 pp.

2. Miles, M.A. & Rouse, J. Chagas's disease. (South American trypanosomiasis). A bibliography compiled from the Sleeping Sickness Bureau Bulletin, 1908-1912 and Tropical Disease Bulletin, 1912-1970. Bureau of Hygiene and Tropical Diseases, London, 1970, 209 PP• 3. Olivier, M.C., Olivier, L.J., Segal, D.B. A bibliography on Chagas' disease (1909-1969). Index-catalogue of medical and veterinary zoology. Special publication No. 2. US Department of Agriculture, US Government Printing Office, Washington DC, 1972, 633 PP• WHO/VBC/87.941 page 35

4. Prata, A. & Sant'Anna, E.P. de. Bibliografia brasileira sohre doenca de Chagas (1909- 1979). Conselho Nacional de Desenvolvimento Cientifico e Tecnologico, Brasilia, 1983.

5. Ryckman & Blankenship (l984a and h) (cited above) include extensive bibliographies which give many more recent references.

WHO/PAHO supports the BIREME library, the PAHO Regional Library of Medicine, in Sao Paulo, Brazil, which has an excellent coverage of the literature on Triatominae and Chagas' disease, and who can usually supply photocopies of the literature and WHO and PAHO publications (see below). Their address is: BIREME, CP 20381, Vila Clementino 04023, Sao Paulo, SP, Brazil.

Some WHO/PAHO publications are available through WHO and PAHO programme coordinators or country representatives; a number of these publications are cited below:

1. Cedillas, R.A. Chagas' disease in El Salvador. Bulletin of the Panamerican Health Organization, 9: 135-141 (1975).

2. Cedillas, R.A., et al. Comparacion de los metodos de laboratorio para examenes xenodiagnosticos. (Comparison of two laboratory methods in xenodiagnosis). (In Spanish). Boletfn de la Oficina Sanitaria Panamericana, 92: 49-56 (1982); also published in English: Bulletin of the Panamerican Health Organization, 16: 255-260 (1982).

3. D!as, J.C.P. & Dfas, R.B. Housing and the control of vectors of human Chagas' disease in the state of Minas Gerais, Brasil. Bulletin of the Panamerican Health Organization, 16: 117-129 (1982).

4. Minter, D.M. Efectos de la presencia de animales domesticos en viviendas infestadas sobre la transmision de la enfermedad de Chagas al hombre. (Effects on transmission of Chagas' disease to man of the presence of domestic animals in infested households). (In Spanish). Boletin de la Oficina Sanitaria Panamericana, 84: 332-343 (1978).

5. Pan American Health Organization. New approaches in American trypanosomiasis research. Proceedings of an international symposi.um, Belo Horizonte, Minas Gerais, Brazil, March 1975. Scientific Publication No. 318, PAHO, Washington DC, 1976, 410 PP•

6. Petana, w.B. American trypanosomiasis (Chagas I disease) in the Caribbean. Bulletin of the.Panamerican Health Organization,~: 45-50 (1978).

7. Petana, W.B. La importancia de los efectos cl'fnicos, psicologicos y sociales experimentados por pacientes con tripanosomiasis americana (enfermedad de Chagas). (The importance of psychological, and social effects experienced by patients with American trypanosomiasis (Chagas' disease)). (In Spanish). Boletin de la Oficina Sanitaria Panamericana, ~: 214-217 (1980).

8. Pinchin, R., Oliveira Filho, A.M. de, Gilbert, B. Un ensayo de permetrina en el terreno para el control de Triatoma infestans. (Field trial with permethrin for the control of Triatoma infestans). (In Spanish). Boletfn de la Oficina Sanitaria Panamericana, 92: 238-247 (1982).

9. Schofield, C.J. & Marsden, P.D. Efecto del revoque de las paredes sobre una poblacion domestica de Triatoma infestans. (The effect of wall plaster on a domestic population of Triatoma infestans). (In Spanish). Boletfn de la Oficina Sanitaria Panamericana, 93: 3-9 (1982): (also published in English): Bulletin of the Panamerican Health Organization, _!i: 356-360 (1982).

10. Telford, Jr., S.R. & Tonn, R.J. Dinamica de Trypanosoma cruzi en poblaciones de un reservorio primario, Didelphis marsupialis, en los llanos altos de Venezuela. (Dynamics of Trypanosoma cruzi in populations of a primary reservoir Didelphis matsupialis, in the upper llanos of Venezuela). (In Spanish). Bolettn de la Oficina Sanitaria Panamericana 93: 341-364 (1982). WHO/VBC/87.941 page 36

IX. EVALUATION

A. Questionnaire for self-evaluation

Complete the following questions with the correct answers.

1. State three reasons why Triatominae are important in public health (pages 17-19):

(a) ...... (b) (c) ......

2. State three characteristics that differentiate good vectors of Trypanosoma cruzi from less good vectors (pages 6, 8/9):

(a) (b) (c)

3. Name the 7 stages in the life-cycle of a triatomine bug; put an asterisk next to those stages that can transmit trypanosomes (pages 3-7):

(a) ...... (b) (c) (d) (e) (f) (g) ......

4. Name three phases of Chagas' disease, stating a typical symptom of each (page 17):

(a) ...... (b) ...... (c) ......

5. Apart from transmission by the insect vector, name three other ways in which Trypanosoma cruzi can be transmitted (page 18).

(a) ...... (b) (c) ......

6. State the most important vector of Trypanosoma cruzi in each of the following countries (pages 10-14):

Brazil ...... Argentina ...... Chile ...... Colombia ...... Uruguay .•.•••.••.• • • •• • • •. • • • · • • • • • • • • · • • • • • • • • • • · • • • • · • • • • • · • • • • • • • • • • • · • • • • • • • • · · • • • • • Paraguay •••••••••••••••••••••••••.••••.•••.•• • • • • • • • • • • • • • • • • • • • • · • • • • • • • • • • • · • • • • • • • • • • Venezuela ••...... •.•...... •....••...... • •...... · • • • • . • · . Costa Rica ...... Panama ...•• • • . • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • · • • • • • · • • • • • • • • • • • • • · • Bo 1 i via ••••••••••••••••••••• • •.•• • • • • • • • • • • • • • • • • • • • • • • • • • • • · • • • • • • • • • • • • • • • • • • • • • • • • • • • WHO/VBC/87.941 page 37

7. On examining a triatomine hng from Venezuela, you find that it is infected with trypanosomes. State three criteria by which you would ;udge if it was Trypanosoma cruzi or T. rangeli (page 18):

(a) ...... (b) (c) ......

8. Give three examples of silvatic habitats of Triatomine hugs (pages 8, 9, 22):

(a) ...... (b) (c)

9. Name three common silvatic reservoirs of Trypanosoma cruzi (pages 8, 9, 22):

(a) (b) (c)

10. Name one species of bird commonly infected with Trypanosoma cruzi (page 22):

(a) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • ••• • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • •

11. Where in a house are triatomine bugs likely to be encountered (page 20):

(a) (b) ...... (c)

12. What information should be collected in a survey of households for the presence of triatomine bugs (page 19):

(a) (b) (c) ......

13. List three indices used in the preliminary phase of Chagas' disease surveillance (pages 20-22):

(a) (b) (c) ......

14. Name three insecticides of choice for the control of domestic infestations of triatomine bugs (page 24):

(a) ...... (b) ...... (c) ......

15. State two other important components of Chagas' disease control (pages 26-28):

(a) ...... (b) ......

16. Name the three phases of a typical Chagas' disease control programme, statin~ what each phase consists of (page 28): (a)...... • .• .• .• .• . ••. .• .• . • . • .• .• . • . • . • . • . • . • . • . • .• .• .• .• .• . • .• .• .••• .. . • .• .• . • .• . • . • . • . • .• .• . • .• .• .• .• .• . • . • . • .• .• . • . • .• . • . • .• .• .• .• .• .•• . . • .• .• .• . • .• .• .• .• . • .• . • . • . • . • . • . • .• .• WHO/VBC/87.941 page 38

(b) ••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• (c)...... 17. Why should it be more easy to control Chagas' disease vectors than other insect vectors of disease such as mosquitos:

......

18. What are the most frequent problems encountered during each of the three phases of Chagas' disease vector control (pages 28-29):

(a) • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • • (b).. . . .••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••• ...... (c) •••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••••

19. Name the most important vector of Trypanosoma cruzi in the USA. Why is Chagas' disease not an important public health problem in the USA, compared to Latin America (pages 6, 14): WHO/VBC/87.941 page 39

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