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Are stable (Diptera: Stomoxyinae) vectors of vivax in the ? Frank d’Amico, Jp Gouteux, Florence Le Gall, D Cuisance

To cite this version:

Frank d’Amico, Jp Gouteux, Florence Le Gall, D Cuisance. Are stable flies (Diptera: Stomoxyinae) vectors of Trypanosoma vivax in the Central African Republic?. Veterinary Research, BioMed Central, 1996, 27 (2), pp.161-170. ￿hal-00902409￿

HAL Id: hal-00902409 https://hal.archives-ouvertes.fr/hal-00902409 Submitted on 1 Jan 1996

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Are stable flies (Diptera: Stomoxyinae) vectors of Trypanosoma vivax in the Central African Republic?

F D’Amico JP Gouteux F Le Gall D Cuisance

1 Laboratoire d’écologie moléculaire, I8EAS, université de Pau et des Pays de 1 Adour, 64000 Pau; 2 Laboratoire de mathématiques appliquées, lpra, Orstom, c% université de Pau et des Pays de l’Adour, avenue de l’Université, 64000 Pau, France; 3 World Bank, Agricultural Technology and Services Division, 1818 H Street, NW, Washington, DC 20433, USA; 4 Cirad-EMVT, c% Orstom, 911, avenue Agropolis, BP 5045, 34032 Montpellier cedex 1, France

(Received 7 April 1995; accepted 21 November 1995)

Summary ― The epidemiology of Trypanosoma vivax was studied at a riverside site in the Ouro-Djafoun area situated in the Central African Republic during the period between July 1991 and July 1992. This paper examines the possibility that stable flies (Diptera: Stomoxyinae) were also vectors of this trypanosome species in a non-cyclic way. Previous studies have revealed that the usual cyclic transmission by the tsetse Glossina fuscipes fuscipes was probably not the only trans- mission route. At the study site, at least five species or subspecies of stable flies were encountered: Sto- moxys nigra nigra (approximately 60% of the sample), S taeniata, S sitiens, S omega omega and Haematobia spp. The hypothesis that stable flies could be good vectors of T vivax in this country is sup- ported by three main observations: i) stable flies were very abundant at the resting site; ii) an esti- mation of the ’contact index’ between the cattle and stable flies demonstrated close interactions between cattle and stable flies at this site, particularly during the rainy season, and iii) there was a good correlation (P < 0.05) between the apparent stable fly densities at the resting site and the frequency of T vivax in the cattle. The relevance of this phenomenon in terms of epidemiology and combatting T vivax-caused nagana is discussed.

Trypanosoma vivax / stable fly (Diptera: Stomoxyinae) / non-cyclical transmission / nagana epidemiology / Central African Republic

* Correspondence and reprints: Maison du Parc, Gabas, 64440 Laruns, France Résumé ― Les stomoxes (Diptera : Stomoxyinae) sont-ils vecteurs de Trypanosoma vivax en République centrafricaine ? L’épidémiologie des trypanosomoses à T vivax a été étudiée le long d’une galerie forestière dans la zone d’élevage d’Ouro-Djafoun (République centrafricaine) entre juillet 19911 et juillet 1992. Des recherches antérieures indiquent que la transmission cyclique de ce trypanosome par la glossine Glossina fuscipes fuscipes n’est probablement pas la seule voie. Ainsi, le présent tra- vail traite de la possibilité pour les stomoxes (Diptera ; Stomoxyinae) d’être des vecteurs de T vivax par voie mécanique. Sur les sites étudiés, au moins cinq espèces ou sous-espèces de stomoxes ont été recensées : nigra nigra (approximativement 60 % de l’échantillon), S taeniata, S sitiens, S omega omega et Haematobia spp. L’hypothèse selon laquelle les stomoxes pourraient être de bons vecteurs de T vivax dans cette région est supportée par trois faits majeurs : i) les stomoxes étaient très abondants au niveau de l’aire de repos du bétail, ii) l’utilisation d’un <·index de contact» entre le bétail et les stomoxes a permis d’établir l’existence d’interactions étroites entre ces animaux à l’aire de repos, en particulier en saison des pluies, iii) il existait une bonne correlation (p < 0,05) entre les densités apparentes des stomoxes à l’aire de repos du bétail et les fréquences de T vivax chez les zébus. Les auteurs discutent finalement de l’importance de ce phénomène en termes d’épidémiologie et de lutte contre les trypanosomoses à T vivax.

Trypanosoma vivax / stomoxe (Diptera: Stomoxyinae) / transmission non-cyclique / épidé- miologie du nagana / République centrafricaine

INTRODUCTION Claxton et al, 1989), trypanosome infec- tions and challenges at three study sites (D’Amico, 1993). Moreover, a recent sur- The Central African Republic (CAR) is a vey on the feeding behavior of this that does not have a tra- country breeding demonstrated that the number of dition for cattle. Mbororo cattle arrived there species bloodmeals from cattle was rather low (12% around the 1920s (Boutrais, 1988). By on average) (Gouteux et al, 1994). Thus, 1928, the cattle number was estimated at we postulated that others vectors might 3 500 (Bertucat, 1965; Crouail, 1969). At play an important role in the transmission of present, there are two million head of cattle trypanosomosis to the cattle, in particular (99% of which are trypano-susceptible Trypanosoma vivax. Mbororo zebu). Due to the presence of tsetse flies and ticks, the humid savannahs The purpose of the present paper was of the CAR remain somewhat unsuitable to investigate stable flies as potential vectors for livestock production. As Mbororo zebu of these trypanosomes. cannot be kept without chemoprophylaxis, trypanosomosis is a major threat to pro- ductivity. We therefore undertook studies MATERIALS AND METHODS of the epidemiology of bovine trypanoso- mosis in the CAR. Previous studies have emphasized the role of Glossina fusca con- Area of study golensis (Yvor6 et al, 1965a, b) and G fuscipes fuscipes (Finelle, 1957; Cuisance The investigation was carried out in the centre et al, 1992). In the centre of the CAR, where of the CAR, in the Ouro-Djafoun breeding zone of G f fuscipes is dominant, we found that this the Ouaka district. A total of 19 Mbororo zebu cattle herds were studied Gall et al, species appeared to be a poor of (Le 1995). One of these, because of its epidemiological inter- Trypanosoma species in cattle as no rela- est and numerous other facilities, was specifi- was observed between the Berenil tionship cally chosen for this study. The study area lay 60 index (for definition, see Rogers, 1985, and km east of the village of Bambari on the South bank of the Mbonou river. In this zone, as else- Cattle surveys where in the country, the climate is characterized by a short dry season from December to March The movements of the cattle were monitored in and a longer rainy season from April to November order to establish how their range related to (Franquin et al, 1988). The average rainfall grazing the distribution of the stable flies. This was achieved recorded at Bambari from 1950 to 1981 was 1 500 by observing the daily activity patterns for 5-7 days mm per year. The landscape consists of wet in the dry season (February), interseason (May) savannahs with a large gallery forest network. and season 1992). The times of The main tree are rainy (August species africana, for the and site and the lanceolata and Daniella olivieri. The departure grazing drinking Lophira times of return from the savannah were noted. grasslands are characterized by the development The of in the blood of of Andropogon gayanus, Hyparrhenia welwitschii presence trypanosomes and H familiaris (Boulvert, 1986). the cattle was determined by parasitological and serological techniques. Blood samples were col- lected from the cattle in October 1991 and Febru- ary, June and August 1992. The parasitological of stable flies Survey techniques used were haematocrit centrifugation and examination of the buffy coat or direct micro- The apparent densities of stable flies were deter- scopic examination of the thin and thick blood films mined from catches in bipyramidal traps (Gou- stained with Giemsa (Molyneux, 1975; Murray et al, teux, 1991) and were expressed as the number of 1977). The serological technique used was antigen flies caught per trap per day. Specific identification detection using monoclonal antibodies (ELISA), of the flies was made according to Zumpt (1973). as described by Nantulya and Lindqvist (1989) Their distribution was monitored along a 500 m and Nantulya et al (1992). Each that was transect using 11 traps set at regular intervals. found to be positive by buffy coat examination was The transect followed the usual path used by the immediately treated with Berenil’A, at a dose of 3.5 herd daily to reach the drinking site and savannah mg/kg body weight. The frequency was assessed grazing areas (fig 1 The flies were sampled for from parasitological and serological data and was 9-12 days per month from July 1991 to July 1992, calculated as the number of tested positive with the exception of January 1992. in the herd at one time. Data analysis encountered. Four species belonged to the genus Stomoxys: Stomoxys nigra nigra The data were analysed: i) in order to estimate the Macquart, 1851, S taeniata Bigot, 1888, intensity of contact (K) between stable flies and S sitiens Rondani, 1873 and S omega cattle at the two of points presumed interaction, ie, omega Newstead, 1907. The individuals the drinking site and the resting and milking site; that to the genus Haematobia Kwas determined from the product of the appar- belonged ent density of flies and the time (h) spent daily have yet not been accurately identified. The by one zebu at these two sites (fig 1) divided by most widespread species was S nigra nigra the number of zebu in each group (n); and ii) to (approximately 60% of the whole sample) examine the between stable den- relationship fly followed Haematobia In the follow- sities and trypanosome frequency. The latter rela- by sp. all these are tionship was measured after pooling monthly data ing discussion, species grouped for stable fly densities at the resting site; these under the name ’stable flies’. Their distri- values were then compared with the next month’s bution and abundance, along the transect, trypanosome frequency in the cattle. Statistical are shown in figure 2. The stable flies were analysis was performed using regression analy- sis (Foucher, 1992). caught anywhere along the main cattle paths between the resting site and the drinking site as well as the grazing site further away. RESULTS However, the maximum density was observed at the resting and milking site where it reached up to ten flies per day at Stable and relative densities fly species trap 10, in June 1992. During the dry sea- son, the number of flies caught greatly At the study site, at least five species decreased, to less than 0.1 fly per trap per belonging to two genera of Diptera were day. Daily activity pattern of cattle can assume that only rare interactions occur between the cattle and the stable flies at the drinking site. In contrast, such interac- Our field work showed that time spent at tions are frequent particularly during the the resting site, as well as at pasture, varied rainy season (August) at the resting and according to the season. During the dry sea- milking place and they are higher for calves son, it was shorter than in the season. rainy than for adults. The time spent at the drinking site was extremely short, averaging 5 to 10 min per day (see table I). Trypanosome frequency in cattle

Contact index between stable flies Table II shows the four monthly estimates of and cattle trypanosome frequency detected in Mbororo cattle using either parasitological techniques or a serological immunodiagnostic technique A simple index of contact (K) between one The ELISA revealed a zebu and stable flies was calculated for (ELISA). technique of the domi- calves and adults at two sites: high frequency T congolense, particular nant T vivax from the cattle and site; and species. frequency ranged i) resting milking 0 to 14.5% methods the cattle site. K estimates for using parasitological ii) drinking and from 8.2 to 19.4% ELISA. the months of February (dry season), May using (interseason) and August (rainy season) are shown in table I. This index is extremely Relationship between stable flies low or even zero at the site. It drinking densities and between 0.02 and 2.94 at the rest- trypanosome ranges frequency in cattle ing and milking place. K is always higher for calves than it is for adults. Thus, if K actually reflects the interactions existing No relationship was found between the four between the cattle and the stable flies, we monthly estimates of trypanosome fre- quency of T congolense and T brucei using DISCUSSION either parasitological techniques or the immunodiagnostic technique. Significant The possibility of haematophagous arthro- regressions occurred between the four pods transferring trypanosomes between monthly estimates of T vivax frequency in hosts without any biological development cattle and the stable fly densities at the rest- of the agent has been under study for a long ing site. This relationship was highly signif- time (Bouet and Roubaud, 1912; Buxton, icant (P < 0.05) with a correlation coefficient 1955). Many species of trypanosomatids (r) of 0.968 for parasitological techniques are known to be transmitted through a and of 0.997 for the ELISA technique. The mechanical mechanism (Wells, 1972; Foil, equations obtained for the regression anal- 1989). T evansi, the first pathogenic try- yses shown are y = 0.207x - 0.062 if the panosome shown to cause disease in parasitological frequency was considered domestic livestock, is usually mechanically and y= 0.149x+ 0.046 if ELISA data were transmitted by tabanids and stable flies used (fig 3). (Luckins, 1992). In South and Central Amer- ica, T vivax is thought to be transmitted sim- the CAR, our preliminary investigations ilarly (Gardiner, 1989). In these areas, reveal the occurrence of at least five devoid of tsetse, 5 calcitrans and flies species. Further studies, together with a such as Cryptotylus unicolor (Foil, 1989), systematic revision of the stable fly group, Tabanus importunus (Raymond, 1990) and will probably lead to an increase in this num- T nebulosus (Otte and Abuabara, 1991) are ber. Independent of the abundance and efficient transmission vectors. In tropical ecology of each species, our work sug- , where tsetse flies, tabanids and sta- gested that these were good ble flies coexist, the problem of determin- candidates as vectors of T vivax try- ing the contribution of mechanical trans- panosomosis in this country. This hypoth- mission is especially acute. The persistence esis, initially proposed to explain the appar- of trypanosomosis due to T vivax in endemic ent seasonal and uncertain aspects of cyclic foci in tsetse-free areas emphasizes the role trypanosome transmission due to of other such as tabanids and stable G f fuscipes (D’Amico, 1993), was supported flies (Bauer et al, 1988; Nawathe et al, 1988; by the data presented above. The first Chollet, 1992; Van der Merwe, 1992). In observation was the abundance of stable (Buxton, 1955) and (Boyt flies at the cattle resting site. The second et al, 1970), the existence of mechanical was the high value for the contact index transmission for T congolense has been between cattle and Stomoxys spp at this suspected. It has been experimentally resting site. The concept of contact index, demonstrated with the tabanid Tabanus tho- although imperfect and simply calculated, racinus (Foil, 1989). It has now been exper- is of interest and deserves a more refined imentally proven that T brucei can be trans- mathematical approach. The third correlation ferred through non-cyclic propagation by was the one existing between the apparent tabanids (Foil, 1989), the stable fly 5 calci- densities of the Stomoxys spp at the resting trans (Straif et al, 1990) and by G morsi- site and the T vivax frequency in cattle. tans morsitans (Roberts et al, 1989). Although it was based on a small sample, Recently, Mihok et al (1995a) demonstrated limited in space and time, and the ELISA that six taxa of African stomoxyinae biting immunodiagnostic technique needs further flies (S niger, 5 niger bilineatus, S confirmation, the general association varipes, 5 taeniatus, 5 pallidus and Haema- seemed valid. Moreover, this hypothesis tobosca squalida) were capable of trans- was also supported by the fact that a control mitting T brucei, T vivax and T evansi strategy using bipyramidal traps set at cat- mechanically to mice in laboratory. How- tle drinking points had no effect upon the ever, until now, little data was available to Tvivaxfrequency in cattle (D’Amico, 1993). address the question of the relative impor- This observation suggested that this parasite tance of non-cyclic transmission of try- species was probably not transmitted at this panosomes under natural conditions when site by only the tsetse fly G f fuscipes, as the major route of transmission of these par- populations of this tsetse species are seri- asites is due to tsetse flies (Wells, 1972; ously affected by this mode of control (Gou- D’Amico, 1993; D’Amico et al, 1992). teux and Le Gall, 1992; Le Gall et al, 1995). Since the beginning of studies of nagana However, to confirm the proposed in Africa, the group of Stomoxyinae flies has hypothesis that stable flies were efficient been the least studied among all proven or vectors of T vivax we must initially extend suspected vectors. Nevertheless, it is a well- our observations to larger epidemiological distributed group in several countries and foci in the CAR and secondly we need to the recent study of Mihok (1993) in acquire direct evidence. The presence of demonstrated 11 species and subspecies. In trypanosomes in stable fly proboscids should be conclusively proven by PCR tech- privileged site of transmission. In future, it niques (Masiga et al, 1992; Bromidge et al, must be considered that modes of try- 1993). However, the detection of the para- panosomosis transmission are more com- site does not unequivocally prove its trans- plex than previously thought. mission to cattle. Similarly, the existence of G f fuscipes is the main vector of T con- the pathology in the cattle is not proof of golense, T vivax and T brucei, because it transmission. This neverthe- knowledge is, transmits these parasites cyclically and per- less, essential as it the estimation of permits haps mechanically and also because it con- the of stable flies proportion bearing try- stitutes an important reservoir for these try- in natural and is of panosomes populations panosomes (D’Amico et al, 1992). Although particular value for quantifying the impor- intervention by stable flies is highly probable, tance of mechanical transmission under nat- the possible role of other haematophagous ural conditions. The actual demonstration diptera such as horse flies and G fusca must of the mechanical transmission of T vivax be kept in mind (Finelle, 1957; Finelle et al, in situ by Stomoxys spp requires experi- 1963). Finally, it is very likely that this epi- mental transmission trials. the Eventually, demiological system is based on a mixed information obtained from control campaigns transmission, combining mechanical and against haematophagous insects using cat- cyclical methods, and involving at least two tle will be ’pour-on’ important groups of vectors. According to this theory, in the existence of mechan- demonstrating cattle resting and milking sites are at risk ical transmission. At the we are moment, from trypanosome challenge as well as testing the effects of pour-on impregnations drinking points. The epidemiological impli- and Flumethrin (Deltamethrin Spot-on* cations of movement patterns of cattle are Bayticol°) on natural populations of stable detailed elsewhere (D’Amico et al, 1995). flies and tsetse flies in the Ouro-Djafoun These facts are important for nagana livestock area of the CAR. control. At present, the campaign against In conclusion, in tsetse-infested areas, this pest in CAR is based on a combina- the possible occurrence of mechanical trans- tion of chemoprophylaxis and trapping mission of T vivax to cattle by against G f fuscipes using bipyramidal traps haematophagous insects continues to be (Gouteux, 1991) set at drinking points (Cui- an unresolved problem. Although mechan- sance et al, 1992; Gouteux and Le Gall, ical transmission by stable flies and partic- 1992). Strategies should now include tech- ularly by horse flies has already been exper- niques for reducing the number of stable imentally proven, the epidemiological flies which are, in any case, serious live- importance of this phenomenon in the field stock pests, causing irritation to the cattle is still poorly understood. In the CAR, our which results in weight loss and reduction in initial investigations suggest that mechani- milk yield. Following the strategy chosen cal transmission does take place and we in this country, we advocate the use of have presented evidence that stable flies bipyramidal traps at both the drinking points were significant vectors of T vivax and per- and the resting sites. The traps designed haps T congolense or T brucei. This study for collecting tsetse flies have also proved provides new data concerning the modes effective against Stomoxys (Rugg, 1982; of transmission of bovine trypanosomosis Mihok et al, 1995b). There is also scope in the CAR. Until now, in most epidemio- for improving the traps and controlling sta- logical foci, the transmission of nagana was ble flies populations by using colour blue chiefly ascribed to G f fuscipes and the cat- (Holloway and Phelps, 1991 ). In the future, tle drinking point was considered to be the there is a need for studies to assess the efficacy of bipyramidal traps in catching sta- Boyt WP, McKenzie PKI, Ross C (1970) An attempt to demonstrate the natural transmission of bovine ble flies in the CAR. We also look forward to try- panosomiasis by agents other than Glossina in the the results of the programme presently Sabi valley of Rhodesia. Rhod Vet J 1, 7-166 being initiated in the same areas to attempt Bromidge T, Gibson W, Hudson K, Dukes P (1993) Iden- to control the populations of tsetse flies and tification of gambiense by PCR stable flies using ’pour-on’ and amplification of variant surface glycoprotein genes. ’spot-on’ Acta 107-119g formulations of insecticides placed directly Trop 53, Buxton PA (1955) The Natural History of Tsetse Flies. on the cattle. London School of Hygiene and Tropical Medicine, Report No 10, Lewis, London Chollet JY (1992) Epidemiologie de la trypanosomose ACKNOWLEDGMENTS bovine dans le Nord-Cameroun. In: First Interna- tional Seminar on Non-Tsetse Transmitted Animal Trypanosomoses, 14-16 October 1992, Annecy, This study received financial support from the Fondation M6rieux, Veyrier-du-Lac, 170 Government of the CAR, the World Bank, the Claxton JR, Leperre P, Rawlings P, Snow WF, Dwinger European Development Fund and the govern- RH (1989) challenge estimation ment of France (Fonds d’aide et de cooperation). in using the Berenil Index: comparison F D’Amico was financially sponsored by the gov- between Zebu and N’Dama. In: Proc 20th Meeting ernment of France (Ministere de la Recherche et ISCTRC, Mombasa, Kenya, Fondation M6rieux, de I’Espace). We thank the director of CIRAD- Veyrier-du-Lac EMVT (France), the director of the D6partement Crouail JC (1969) Une btape vers la sbdentarisation de Sant6 of ORSTOM (France), the director and the l’blevage Mbororo en Republique centrafricaine : le bain d6tiqueur adapte a I’elevage bovin. Veterinary staff of the nationale pour le d6veloppe- Agence doctoral thesis, Toulouse, France, 83 p ment de [’61evage (CAR), VM Nantulya and PAO Majiwa of ILRAD (Kenya), JL Frezil and C Bel- Cuisance D, Gouteux JP, Cailton P et al (1992) Probl6- d’une lutte contre les la lec of ORSTOM (France), C Mouches of Univer- matique glossines pour pro- tection de 1’61evage zebu en Republique cen- site de Pau et des de I’Adour M Pays (France), trafricaine. 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