WHO VBC 87.941 Eng.Pdf
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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 by 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.