i

Jean-Marci Duplantier and Daniel Rakotondravony

Abstract

In Madagascar the rodent problem is linked to one species, the black rat (Rattus rattus). This chapter will describe its population dynamics in agro-ecosystemsand its impact in agricultural crops, in stored grain, on human health and on the endemic rodent community. The black rat has spread absolutely everywhere: from sea level to more than 2,000 m-in houses, fields and also in the forests. It represents more than 95% of rodent catches in the fields and inside houses. Reproduction of rats living in fields stops during the cold season when their maximum annual abundance is observed. Irrigated rice crops suffer the greatest damage with losses estimated at 2.5% of the harvest. Rodent damage is also important for pluvial riceand to a lesser 'fi-- degree for cassava, sweet potatoes and tomatoes. Damage to cacao and sugar I cane are important only in the small, poorly-maintainedpersonal plantations. Plague ,I is undeniably the most important disease linked with rodents in Madagascar. It is endemic to the centre of the island in rural areas located above 800 m and its 5: prevalence is increasing. Rodent control in Madagascar is extremely complex because of the economic difficulties facing the country and because the black rat has displayed such successful colonisation in absolutely all habitats.

Keywords

Black rat, conservation biology, Madagascar, plague, rice fields, rodent control, rodent damage

!

In : <( Ecologically-based rodent management $h. - Eds : Grant Singleton, Lyn Hinds, Herwig Leirs and Zhibin Zhang ACIAR editions, septembre 1999

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o 1O026038 Ecologically-based Rodent Management

INTRODUCTION years ago. Significant immigration occurred only 1,000 years ago. The human settlers are of both Asiatic (Indonesian) and African N MADAGASCAR,the rodent origin. A mountain range, 2,800 m high, problem is clearly linked to one divides the island into two from north to I species, the black rat (Rattus raffus), south (Figure 1).The east side of the country and concerns both agriculture and public is more abrupt than the west. The effect of health, as well as conservationbiology. the monsoon and the trade winds on this Eruptions of rat populations were reported relief determines the different climates and in 1916,1932 and 1965 (Rakotomanana 1965; different types of vegetation within the Ravoavy 1966; in Zehrer 1999). After the last island. Human activities have significantly eruption, black rats were declared a public changed the vegetation and now the calamityby the Malagasy state, and different climatic regions can be agricultural pest management of rodents characterised by their agricultural became state-controlled. With respect to landscapes. public health, the major disease problem is The east coast of Madagascar has no dry undeniably the plague (caused by the season and rainfall ranges from 2,000 to bacillus Yersìnia pestis). It spread from the 3,000 mm per year. The original type of seaports of Madagascar at the end of the last vegetation is rainforest. This type of forest is century and during the past 70 years in rapid regression, due mostly to 'slash- permanent rural foci have existed in the and-bum' agriculture. The centre of the-

Ir central part of the island, above 800 m. island, called the highlands, has a high Another major issue is that Madagascar's altitude, tropical climate characterised by a endemic rodents are threatened with cold and dry season from May to October extinction as a result of competitionwith the and a hot, rainy season from November to black rat in addition to habitat loss. This April. Before human settlement, it was a chapter will examine how this situation mosaic of forests-savannah. Today, the arose, and describe the impact of the black landscape is totally modified by people, rat in agricultural fields, in stored grain, on dominated by rice-growingin the valleys human health and on the endemic rodent and by dry farming-on the slopes (mainly community in Madagascar. corn and cassava). The primary forests are Madagascar is the fourth largest island in extremely rare, but there are plantations of the world (after Greenland, New Guinea and pin$and eucalyptus. The drier, west coast is Borneo), with a surface area of 587,000 less populated, and is a mixture of square km.It is 1,600 km long from north to cult&vationand pasture. The south is semi- south and 580 km at its widest point. It has aridkith a 10 month dry season, dominated been separated from the African continent by spiny bush. It is a cattle-rearing region for 160 million years. The minimum distance with some small patches of cultivated land. to Africa is now 300 km. The first human settlements occurred approximately2,000

442 Rodent Problems in Madagascar

Y

NU t

plague areas

<200m

200-500m

1 500-1 OOOm >1 OOOm

120km

Figure 1. Map of Madagascar: relief, localisation of plague foci, main towns and study sites.

443 Ecologically-based Rodent Management

COMMUNITY THE RODENT IN the catches in the capital, Antananarivo MADAGASCAR (Rakotondravony1992), which is situated in the centre of the island, and today it has At least 23 species of rodents exist today in reached nearly 95% (Duplantier et al., Madagascar (Rakotondravonyand unpublished data). Recently, we trapped Randrianjafy 1998).Like all animal and plant some individuals in rice fields on the east groups on the island, this order is .coast, several km from the cities. characterised by a high rate of endemism. The house mouse is commonly found in All the endemic rodents belong to the same houses but is less numerous than the black sub-family, Nesomyinae, which is divided rat. It is also found in rice fields, savannas into 8 genera and 20 species. They live and swamp edges, but in low numbers. The almost exclusively in the forest and their date and method of its settlement of current distribution is limited to the Madagascar is not known. remaining primary forests. Brachyiiromys raniirohitra and Nesomys ..lfus are captured The black rat could have come to on farmland but only where this is close to a Madagascar with the first immigrants forest (Rakotondravonyand Randrianjafy approximately2,000 years ago, however its 1998).The destruction of primary forests in presence is confirmed only from the 11th Madagascar, well illustrated by Green and century from excavations of an Islamic Sussman (WO), threatens the extinction of a archaeological site in the north of great number of animal species. It is Madagascar (Rakotozafy 1996; Radimilahy particularly the case for endemic rodents of 1997).The shrew Stincus murinus, native to the Nesomyinae sub-family: not only do all Southeast Asia, must have settled in a of them live in the forests and will therefore similar way. Today, the shrew is found all suffer from habitat loss, but the over the island, but it is less abundant than fragmentation of these forests makes it easier the black rat. The black rat has spread for the highly competitiveblack rat to everywhere.It can be found from sea level to penetrate into the forest. Today, it is more than 2,000 m-in Kouses, fields and common to encounter this species in the also in the forests. In the highlands and in primary forests (Goodman 1995). the middle-west, R. rattus represents more In Madagascar, populated areas are the than 98% of rodent catches both inside and exclusivi domain of three introduced outside buildings (Duplantier et al., species, &e black rat (R. raftus),the Norway unpublished data). Rats$nanosika (1995) rat (Rat& norvegicus) and the house mouse quoted the same figure Gom the east coast (Mus musculus). R. noruegicus has the most coconut plantations. In the fields of the restricted distribution-it is only found in coastal regions of Tulear (south-west) and the seaports and the big cities. It has been Tamatave (east), Rafanomezana (1998a) located in the seaports since the 1930s, but found 97% of rodents to be R. rattus. In the the date of its spread to the highland cities is natural forest of Andranomay, in the unknown (Brygoo 1966). At the beginning of highlands, R. ratfusrepresented two thirds the 1980s, it represented more than 80% of of captures from 1981 to 1982 and the

444 Rodent Problems in Madagascar

endemic genus Eliurus only one third Reproduction of the black rat (Rakotondravony1992). At the edge of the forests and within fields at Important studies have been undertaken Andranomay, Rakotondravony (1992) recently on the endemic rodents which are monitored the reproduction in the black rat the most threatened order of mammals in over two years (1981-1982) (Figure 2). Madagascar (Goodman1995). However, due Reproductionbegins before the rainy season to their restricted distribution and scarcity, (Novemberto April) with the maximum they are of minor importance to agriculture number of pregnant females occurring in the and probably also to human health. middle of this period. These data have been confirmed recently: in 1996-1997 there was an interruption to reproduction in the fields POPULATION OF THE BIOLOGY from May to August, with maximum BUCK RAT reproduction in January (Rafanomezana It is a paradox that the black rat is the 1999). number one problem of agriculture and In Mandoto, reproduction of rats living in public health but little research has been houses does not seem to be linked with conducted on this species. Different survey season (Figure 3; Rahelinirina and programs have been conducted by the Duplantier 1999). However, among the rats Department of Plant Protection (Ministry of trapped outside, no reproduction occurs Agriculture), but most of the results are still between July and December-thereafter unpublished except for some data on breeding increases until May and ceases reproduction (Rafanomezana 1999).In fact, abruptly in June. In this region, reproduction only three studies provide accurate data seems to be linked with the harvest of crops through at least one annual cycle: first, the rather than rainfall. The first rice harvest in study conducted at Andranomay (Figure 1) the valleys takes place in in the 1980s by D. Rakotondravony (1981, December-January, then, from February till 1992) which was mostly carried out in the May-June, there follows one after another forest but also in slash-and-burn agriculture the harvest of corn, cassava, peanuts and pluvial rice on the hills. A second rice areas. This was followed up by a monthly survey in the fields of this locality which was harvest can take place in the valleys in May, conducted in 1996-97 (Rafanomezana 1999). at the beginning of the dry and cold season Secondly, a month$ survey of less than a (Handschumacheret al. 1999). i year was conducted in the Lake Alaotra In Andranomay, as in Mando tt, these region (Figure l),&ich is one of the most data are confirmed by the age structure of important rice growing regions of the the rat populations: there are no young less country (Salvioni 1989).Finally, Duplantier than 50 g from May to September in et al. (unpublished data) conducted a Andranomay, whereas in Mandoto they monthly two-year survey in the villages and are least abundant from September to fields of the middle-west region around the March. . city of Mandoto (Figure 1).

445 Ecologically-basedRodent Management

NO DO JO FU MO AO MO JO.JO AO SO O0 JO FO MO AO MO JO JO AO SO O0 NO DO 19810 19820

Figure 2. Percentage of pregnant female black rats among adult females trapped monthly in Andranomay forest in 1981-1982 (Rakotondravony 1992).

-#i#-Inside -+- Outside

f

JuIU Aug Sep Oct Nov DecO Jan0 Feb Mar Apr May Jun Julo 1996 1997 Figure 3. Percentage of pregnant female black rats among adult females trapped monthly Inside and outside houses In vlllages of the middle-west region around Mandoto (Rahellnirina and Duplantler 1999).

446 Rodent Problems in Madagascar

In the Lake Alaotra fields, reproduction is refuge and in addition, they are situated concentrated between March and June and near-or even sometimes against-houses seems to be linked with the availability of where supplies of food are available. food in the fields (Salvioni 1989). However, Conversely, their abundance is lowest in the in the presence of a permanent source of dry farming areas because these provide food and a shelter, the rats can breed food for rodents only for a short period and throughout the year. the fields are often burned by fire once a Differences between these localities are year. probably linked with the different In Andranomay, trap success is higher in landscapes and crop types. In the less fields than in the forest (Figure 4; modified landscape of Andranomay (small Rakotondravony1992). Data collected slash-and-burn agriculture areas around Lake Alaotra confirm that surrounded by forests), rainfall seems to be environmentswith abundant vegetation and the most important factor influencing the near farms host a high density of rats season of reproduction. By contrast, where (Salvioni 1989). irrigated fields are predominant (Mandoto and Lake Alaotra), the seasonality of Seasonal variation in abundance harvests seems more important. In the fields of Mandoto, we observed a well- The aforementioned sites are in the marked, seasonal variation in the abundance highlands. In coastal regions, specifically of rodents with a maximum in July-August Fénérive-Est on the East coast (Figure l),the in the irrigated fields as well as in the dry minimum number of pregnant females is farming areas on the hills (Figure 5; observed from July to October and the Duplantier et al., unpublished data). This maximum from December to March. In the was also noted by Salvioni around Lake Tulear region (Figure l), on the south-west Alaotra (Salvioni 1989). On the other hand, coast, the maximum rate of pregnancy the fluctuations in population abundance occurs approximately over the same period observed in the villages, inside houses and (January to March) while the minimum in the sisal fences do not show any marked occurs earlier, from May to August seasonal variation. In the Andranomay (Rafanomezana 1999). forest, populations peak earlier between February and April (Figure 4; i Variations in abundance with habitat Rakotondravony 1992). Rafanomezana In the Mandoto region, we compared fogr (1999) observed a similar pattern in fields in different habitats: houses; sisal fences i the same locality. around cattle pens; dry farming on the hills; Thus, the annual maximum abundance of and the irrigated fields in the valleys rat populations occurs in the middle of the (Duplantier et al., unpublished data). The cold and dry season on the borders of the black rats were most abundant in the sisal highlands (Mandoto and Lake Alaotra), and fences. The permanent and spiny canopy of earlier, at the end of the rainy season, in the the fences provides a good, permanent centre of the highlands (Andranomay).

4.47 Ecologically-basedRodent Management

J FMAMJ JASOND

Figure 4. Monthly variations of black rat abundance in Andranomay in forest and field habitats (Rakotondravony 1992).

Dry ~~~ + farming -iI- Irrigated rice fields

60U

i

19960 19970 199817

Figure 5. Monthly variations of black rat abundance (trap success perl00 trap nights) in villages of the middlewest region around Mandoto from 1996-1998 associated with (I) dry farming and (il) irrigated rice fields (Dupiantler et al., unpublished data).

448 Rodent Problems in Madagascar

?

inter-annual variation DAMAGEIN THE FIELDS Only one long-term study has been undertaken: from 1980 to 1986, in A survey conducted throughout the country Andranomay (Figure 6; Rakotondravony showed that 86% of the farmers considered 1992). Inter-annual variation in the that they had suffered important damage populations of black rats in the forest is low, from rats during the previous year. Rodent but there is high variation in the fields, with control was used by 82% of farmers, mostly in the rice fields (29%)and in the granaries the maximum abundance about eight times 41% higher than the minimum. In these slash- (27%); used rodenticides and 27% used and-burn fields, harvest differs greatly from traps (Rafanomezana 199813). one year to another, being especially reliant According to Zehrer (1998), it is the on the distribution and the total rainfall. irrigated rice that suffers the greatest However, it is important to note that at the damage. From surveys conducted in the same time, Rakotondravony(1992) observed different rice-producingregions of the similar inter-annual variations among urban country, rodent damage affects around 2.2% populations of black rats. During the 1980s, of cut stalks, which is equivalent to a loss of their abundance in the capital 2.5% of the harvest (Raobsoamanitrand- (Antananarivo)was double that of normal rasana 1998).For all the country, the overall densities in each of 1981,1985 and 1989. annual losses caused by rats are estimated at 62,500 t of rice paddy or 40,000 t of marketable rice.

i

19800 1981 1982 1983 1984 1985 1986

Figure 6. Annual variations of black rat abundance In Andranomay from 1980-1986 in forest and fleid habitats (Rakotondravony 1992).

449 Ecologically-based Rodent Management

Rodent damage is also important on to that caused by insects (37.5% versus pluvial rice cultivated on the hills or on 36.1%). It is only in the south (Tulear region) slash-and-burn areas (Zehrer 1998) Other that the damage caused by rodents is low cereals (wheat, barley and oats) seem to be compared to insect damage (24% versus less affected. With respect to tubers, little 58%) (Andriantsileferintsoa 1998).Most damage is observed in potato crops, whereas harvested crops are stored in heaps, except rodents damage cassava and sweet potatoes. rice which is generally held in sacks. In the In market garden farms, the more important centre, the north and +e west of the country, damage is to tomatoes and, to a lesser approximately 74% of the rural respondents degree, to green beans, peas, cabbages and assert that rodent attacks are continuous. In cucumbers. the south only 21% of farmers feel this to be Among the fruits, the most damage the case. cuased by rodents is to pineapples. Damage With respect to health, the abandonment to jackfruit and papaya has also been of traditional granaries by the farmers is a observed, but only rarely to bananas. problem. Traditionally, different types of Damage to cacao is important in the small, independent granaries, set apart from poorly-maintained personal plantations, but human houses exisied according to the low in industrial plantations-a similar regions (huts built on stilts, cavities dug in situation applies to sugar cane plantations. the earth etc.) (Rasamoel 1998). Nowadays According to Rasolozaka (1998), damage -for security reasons and for fear of caused by rodents is estimated at 19% of the robberies -a great number of farmers prefer production in the coffee plantations of the to store their cereals in their houses and even east coast. According to Zehrer (1998), in their bedrooms. This increases the although the farmers complain a lot about possibility of man-rodent contact and thus rat depredation and large quantities of the risk of disease transmission. This could rodenticides are used, the damage is difficult be one of the causes for the increase in cases to evaluate. Indeed the majority of imported of human plague in recent years. rodent poisons in the 1980s were used in these coffee plantations. Finally, in the industrial coconut plantations of the east . Intermediary stores coast, the losses caused by rodent damage are estimated at 2.2% of production These are stores ,used by the collectors (Rakimanosika 1998). who gather the haGest of the farmers before selling it to retailere or big mills. These DAhAGE TO STORED FOODS structures are rareli rat-proof and the hygiene is rudimeniary (Andriantsile- Village stores ferintsoa 1998). However, the duration of storage is limited, and this reduces the In rural areas, according to surveys importance of damage despite the lack of conducted in four of the six provinces of the protection. country, the damage caused by rodents is considered by rural respondents as similar

450 Rodent Problems in Madagascar

Industrial stores during the third pandemic. During the 1920s it reached the highlands, but disappeared In Madagascar, only the national silo from the coastal regions. Thus, the plague (where seeds are stored) and the warehouses became endemic to the centre of the island in of big commercial companies are rat-proof. rural areas located above 800 and is now According to Andriantsileferintsoa (1998), m on the increase (Chanteau et al. 1998b),From these companies do not have any serious 1925 until the Second World War, more than problems caused by rodents. Their one thousand human cases occurred warehouses are new and well-kept, and they annually. A maximum of more than 3,000 regularly use the services of rodent/insect cases was reached in 1935. Mass vaccination control companies that exist in the capital. campaigns, insect control and the arrival of antibiotics caused an important regression in RODENTSAND HEALTH morbidity and mortality; for more than Buck and Courdurier (1962), as well as Ribot thirty years, an average of only about fifty and Coulanges (1982), established the first cases were reported annually. However, in lists of the main zoonoses in Madagascar. A 1978, the plague reappeared the capital synthesis of rödent-bome zoonoses was after a 28-year absence. Since-the end of the completed recently (Duplantier 1999).The 1980s, in the country as a whole, the number most well known disease linked with of human cases increased to more than 100 rodents is the plague, but rodents are also per year, reached 200 in 1994, and 459 in involved in the transmission of viruses, 1997. In 1991, the human plague reappeared including hitaviruses. The importance of in the seaport of Mahajanga after an absence rodents in the transmission of other diseases of 63 years (Chanteau et al. 1998a;b). These in Madagascar is either poorly known (e.g. official figures include only the cases intestinal bilharziasis), or less important (e.g. confirmed by a bacteriological test. rabies). Due to the isolation of the island and Serological tests indicate the number of cases its particular community of rodents (a single to be two to three times higher (Chanteau et endemic sub-family with a very restricted al. 1998a). distribution), a number of diseases linked The real situation is difficult to estimate. with rodents and important elsewherein the On the one hand, important regions are out world are unknown on the island (Brygoo of reach of health services, and on the other, 1972). Howevir, the invasion of all the information campaigns of thejnational habitats by the black rat allows for rapid program of plague control seeup since 1991 propagation o€ any rodent-borne epidemics clearly increased the number df declarations. throughout Mbdagascar. Despite a low number of official cases compared with other diseases, the economic Plague cost of plague is very high for the Malagasy Plague is undeniably the most important govemment, which must cover all the disease linked with rodents in Madagascar medical expenses in the treatment of this (Brygoo 1966).It reached the largest seaports disease. Due to the slowness of the of Madagascar between 1898 and 1907, bacteriological diagnostics (several days are

451 t Ecologically-based Rodent Management

necessary), all cases suspected from clinical A program set up in 1996 by the MinistTy examinationmust be immediately treated. of Health (DLMT), the Institut Pasteur de In addition, all persons in contact with those Madagascar (IPM) and the Institut de suspicious cases must also undergo an Recherche pour le Développement (IRD, ex antibiotic treatment. The houses inhabited ORSTOM-the French Scientific Research by people with suspected cases, as well as all Institute for Development through the neighbouring houses, must be treated Cooperation) has made it possible to better with insecticides by the health services. understand the mechanism of the Malagasy Therefore, several thousands of people are foci. The beginning of the human plague treated every year. season in the highlands (November) The plague is transmitted from one rodent coincides with the minimum abundance of to another, and from rodents to humans rats outside houses and the annual maximum through haematophagous flea vectors. In abundance of fleas. We have shown that most of the plague foci in the world, the particular habitats seem to be important for reservoirs are wild rodents resistant or less transmission; i.e. the sisal fences around the sensitive to the plague bacillus (Yersinin cattle pens, situated inside or on the edge of pestis). They generally belong to the Sciuridae villages. These are where the rodents and the family (marmots, prairie dogs) and to the fleas are most abundant, and it is also where Gerbillinae sub-family (gerbils, Meriones etc.). the highest antibody seroprevalence against The black rat is sensitive to plague and thus Y. pestis was noted among rats. The rural cannot be, in principle, the reservoir. It is a plague occurs only above 800 m, yet the black t commensal rodent which is the link between rat is widespread throughout the island from the wild rodents and humans and hence sea level to more than 2,000 m, and it is the provokes urban epidemics. The distinctive same chromosomal form (2n = 38) regardless feature of the Malagasy foci lies in the absence of the altitude. Inside houses X. clzeopis is also of a wild reservoir; the black rat is involved in present independent of the altitude. all kinds of foci, urban as well as rural However, below 800 m, outside the houses, as (Brygoo 1966).It must also be noted that well as on the rodent fur and in their burrows, different fleas are involved depending on the we found almost no fleas, while an average of different habitats: Xenopsylla cheopis OCCLI?~ two fleas per rodent was observed during the inside houses and SynopsyZZtlsfonquwniei, an same season above this altitude endemicspecies, occurs $utside. Thus, it (IRD/IPM/DLMT, unpublished data). $us, seems that in Madagasc4 the black rat is at it seems that the distribution of the plagGe in the same time the reservQirand the main Madagascar is limited by the factors thati victim of plague. This pdadoxical and influence the geographical distribution o$ the unique situation is the result of a balance endemic vector, S.fonqtierniei, which between the mortality due to plague and the parasitises exclusively rats living outside. It re-colonisation abilities of the black rat, which will be important for plague control to is spread all over the island, while the plague monitor the evolution of its distribution for a occurs only in very localised outbreaks. possible extension of plague foci below the present limit.

452 Rodent Problems in Madagascar

Other diseases linhed to rodents in 1982; Ribot and Coulanges 1982). Yet, Madagascar recently a Schistosoma tnansoni adult worm was found in one of ten black rats trapped in Murine typhus is relatively important in the Antananarivo suburbs (E. Sellin, pers. Madagascar because Mayoux and CO".). Larger surveys and more sensitive Coulanges (1970) found positive serologies techniques of detection (work in progress: in 20% of the rats tested in Antananarivo. Ministry of Health/ Institut Pasteur/IRD- Borreliosis (or relapsing fever) is a ORSTOM) will determine if the black rat is a disease transmitted by ticks living in the wild reservoir, as is the case in the West rodent burrows. It has been well known in Indies and South America (Rey 1993). the west of the country since the 18th century, but there have been no human cases The only known reservoir of rabies in described since the 1950s (Brygoo 1972). Madagascar is the domesticated dog. No rodent has been found. to be a rabies carrier Leishmaniasis is unknown in (Ribot and Coulanges 1982). Madagascar, although infested dogs have been imported (Brygoo 1972) and despite Until now, no human case of R. raftusbeing a known reservoir in Italy, haemorrhagic fever with renal syndrome, and R. rattus and R. norvegictis being due to hantaviruses, has been reported in suspected reservoirs in many other countries Madagascar. Since 1985, however, (WHO 1990). According to Brygoo (1972), it antibodies of hantavirus have been reported was the absence of vectors that has in rodents (H. Zeller, pers. CO".). More prevented the occurrence of this disease in extensive studies are under way (Institut Madagascar. However in 1982, Ribot and Pasteur/IRD-ORSTOM) to determine the Coulanges reported the discovery of a importance of these viruses in black rat potential vector, an anthropological populations trapped in different phlebotome. Nevertheless, no human cases environments. have been reported. The absence of leptospirosis in RODENTCONTROL IN MADAGASCAR Madagascar is undoubtedly a paradox, as it Organisation of rodent control is a disease which is characteristically associated with rice fields, sugar cane Big cities, and the administrative centres of plantations and pig rearing (majorffarming the provinces (with more than 100,000 activities in Madagascar),and A. rdtttis and inhabitants) have a Health Municipal Office, f R. norvegictis, as well as S. mtiriniis ka very dependent on the mayor. This department is i widespread shrew in Madagascar$ are well responsible for keeping the town clean, known reservoirs (Faine 1987). In addition, monitoring epidemics and controlling this disease occurs in the neighbouring insects and rodents. In the largest cities of island of Reunion. the highlands, it is this department that is in Intestinal bilharziasis is widespread in charge of plague control. The Health humans, especially in the highlands, but has Municipal Office is also in charge of control not been reported in rodents (Breuil et al. (by trapping) of plague among rodent

453 Ecologically-based Rodent Management

populations in the capital, Antananarivo, In collaboration with GTZ (Deusche and since 1998, in the seaport of Mahajanga. Gesellschaftfür Technische Zusammen- In small towns and villages, the arbeit -the German Technical Department of CommunicableDiseases Cooperation), the Division of Rodent (Ministry of Health) intervenes as soon as Control carries out three types of actions: human plague cases are reported and b a survey of the population dynamics in organises the control of fleas and rodents in experimentalstations situated in the collaboration with the basic health care different agricultural regions of the units. country; In rural areas, it is the Department of Plant Protection (Ministry of Agriculture) b the promotion of snap-trap use by which leads the farmers in rodent control in demonstrationin experimental stations the fields and in and around food stores. and through selling at a low price; and b training and communication on health Activities of the Department of matters, cleanliness and promotion of rat- Plant Protection proofing methods. After the 1965 outbreak of the plague, 1 Activities of the Division of r rodents were declared a public calamity by the Malagasy state, which meant that the Communicable Diseases state covered all the expenditure incurred in This division is responsible for the national rodent control. Then in 1976, a division program of plague control and hence rodent inside the Department was created and control. The agency supports the local health dedicated to rodent control. Until the 1980s, structures during epidemics and usually this division provided free rodenticides to provides some training and information. the farmers, who in turn provided the baits. In collaboration with the municipal Zinc phosphide was first used in the health office, a survey of the prevalence of seventies and progressively replaced by plague in rat populations has been set up in anticoagulants, mainly chlorophacinoneand the two most important urban foci: coumatetralyl. Plant protection technicians Antananarivo and Mahajanga.This division determined the abundance of rodents by . has distributed two thousand live-traps to trapping in different regions and crop types i the health centres located in the plague and then, according to the trap success in i, endemic zones. These traps are for use in eachparticular situation, decided whether to i epidemics, and thus promote this type of use rodenticides. However, this practice was i rodent control. abandoned due to the deterioration of the The aim of these training and information economic situation. Nowadays, the farmers campaigns is to improve the hygiene within are in charge of rodent control with only habitations. Information posters written in supervision provided by technicians of the Malagasy on the plague-also highlighting Department of Plant Protection. rodent control methods in plague foci-are posted in all health centres within the plague

454 Rodent Problems in Madagascar

areas. A technical guide, which is regularly Improving rodent control updated and includes rodent control methods, is given to all the doctors working As described above, until recently, few in the plague endemic zones (Division de la studies of black rats had been performed. peste 1990). Rodent control in Madagascar took place when damage was significant but rarely took into account knowledge of the biology The particularities of rodent control in of the black rat. Since the beginning of the plague foci 199Os, with the creation of a national program of plague control by the Ministry of The control of rodent populations in plague Health and the project “Promoting foci must follow certain rules. One must integrated protection of crops and stored always remember that the main problem is foods” by GTZ and the Department of Plant not the rodent itself but the fleas. To avoid Protection, new studies have begun with the proliferation of the disease, it is imperative aim of improving rodent control. to kill the flea before killing the rodent. During the plague season, rat poisoning Since 1993, twelve monitoring stations must not be done without prior insect have been established throughout the control. Live-traps are better than snap- national territory by the Department of Plant traps, because the latter encourages the Protection. For various reasons, only eight dispersion of the fleas immediately after the stations have operated correctly to provide rodent’s death. For the same reason, in the reproductive data and two have monitored case of chemical control, one must not use abundance. As soon as this program acute rodenticides but anticoagulants that becomes fully efficient, it will provide useful work only after a few days, thus giving time data which will enable an adequate control for an insecticide to kill the fleas before the schedule for each region to be established. rodent dies. Until now, anticoagulants have Two long-term studies of the black rat are been little used in Madagascar, so no being undertaken on the east and north-west resistance problems have been reported. coasts and these will provide important However, resistance to insecticides is additions to our knowledge of population multifaceted and very widespread in fleas dynamics, which tdday, is restricted to the (Ratovonjato et al. 1998).The annual use of cenpal part of the island. preventive insect controls in some cities is concerning plague control in the mainly responsible for this situation and has hig&ands, the monthly survey carried out had to be abandoned. In rural areas, the ovei the past two years already allows us to problem is also encountered due to propose that rodent control should be resistance to the insecticide DDT, which has focused on a particular area and season. We been used extensively for malaria control. have demonstrated that sisal fences are the All these factors indicate the need for a most important refuge area for rodents, fleas regular survey of the efficiency of the and plague. According to the maximum different insecticides and for a rotation in the annual abundance of rats and fleas and use of these products. taking into account the agricultural

455 Ecologically-based Rodent Management +

activities, we consider that the best time to areas, better coordination of the activities of practice rodent control is in May-June. the health services and the plant protection Human Sero-positive results against Y, pestis services is necessary. are more numerous in houses located at the edges of the villages, where sisal fences are ACKNOWLEDGMENTS more abundant and in houses where food is stored in bedrooms. This clearly shows that We would like to thank the Department of it is necessary to break the close rodent-man Plant Protection for providing copies of contact and this could be achieved by manuscripts still 'in press' and L. Wilme for developing rat-proof buildings. the English translation.

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