Preliminary observations on the use of the latex agglutination test for detecting circulating trypanosomal antibodies in game animals in the Lambwe Valley

Bull. Org. mond. Sante 1972, 47, 781-783 Bull. Wid Hith Org. Preliminary observations on the use of the latex agglutination test for detecting circulating trypanosomal antibodies in game animals in the Lambwe Valley G. BINZ 1 & R. ALLSOPP 2 The first use of the latex agglutination test (LAT) for determining the frequency of circulating trypanosomal antibodies in a sample ofgame animals collected in the Lambwe Valley, Kenya, is described. The immunological examination of animals belonging to 9 species revealed an incidence of circulating antibody of 25.5 %, which was only slightly higher than, and therefore in close agreement with, the results of a concurrent parasito- logical survey. It is concluded that the LAT is very suitable for determining the overall incidence of trypanosomal infections in wildlife communities. The results of concurrent serological and parasito- logical examinations of human and cattle popula- tions strongly support the view that such a dual diagnostic approach is essential for the accurate appraisal of the incidence of trypanosomal infections (see, for example, Binz (1972). Since studies by Allsopp (1972) on the role of game animals in the zoonotic transmission of the trypanosomiases in the Lambwe Valley included the parasitological exami- nation of several species of wild animal to determine the incidence of trypanosome infections in natural hosts, it was considered of particular importance to conduct complementary investigations on trypano- somal antibodies in the animals examined. This communication describes the use of the latex agglutination test (Binz, 1972) for studying circula- ting trypanosomal antibodies in sera collected from game animals in the Lambwe Valley, an area of endemic and enzootic trypanosomiases. MATERIALS AND METHODS Altogether, 90 serum samples from 9 species of game animal were collected during studies conducted 1 Project Technical Officer (Immunology). Present address: 1711 Ependes/FR, Switzerland. ' Project Game Ecologist (FAO). Present address: 52 Peel St., Sutton-in-Ashfield, England. by Allsopp (1972) in the Lambwe Valley Game Reserve. A general description of the Lambwe area has been given by Allsopp & Baldry (1972), while Allsopp et al. (1972) have described the relation- ships between its game community and the tsetse Glossina pallidipes. Parasitological examination of the animals from which the sera were collected included the routine microscopic examination of stained blood films and animal inoculation tests. Immunological tests for detecting circulating try- panosomal antibodies were performed on sera by the latex agglutination test (LAT) as described by Binz (1972), using a Trypanosoma brucei antigen. RESULTS The frequencies of circulating trypanosomal anti- bodies detected by the LAT, in the various species of game animal examined are presented in Table 1 together with parasitological findings in the same animals. The overall frequency of antibodies in the whole sample of game animals was 25.5 % which is slightly higher than the parasitological infection rate of 20.0 %. The highest frequencies of circulating antibodies were in bushbuck (66.6%) and reedbuck (36.0 %); there was possibly also a high incidence in waterbuck but the number of sera examined was very small (only 3). 2965 -781- 782 G. BINZ & R. ALLSOPP Table 1. The frequency of circulating trypanosomal antibodies, detected by the latex agglutination test using T. brucei antigen, in game animals in the Lambwe Valley, in comparison to the results of parasitological findings in the same animals No. of animals parasitologically positive No. of for trypanosomes No. and percentage of Species animals positive LAT reactions examined Ptoei Non- TotalPathogenic pathogenic No. No. bushbuck 9 8a 0 7 77.7 7 66.6 bushpig 3 0 0 0 0.0 0 0.0 duiker 10 0 0 0 0.0 1 10.0 hyaena 4 2b 0 1 25.0 0 0.0 impala 6 0 0 0 0.0 0 0.0 oribi 17 0 2 2 11.7 2 11.8 reedbuck 36 3 4 7 19.4 13 36.0 topi 2 0 0 0 0.0 0 0.0 waterbuck 3 0 1 1 33.3 1 33.3 totals 90 13 7 18 20.0 24 25.5 a One bushbuck infected with T. congolense gave a negative LAT reaction. bi One hyaena infected with T. brucei gave a negative LAT reaction. Circulating antibodies were not detected in bush- pig, impala, or topi, nor were they found in hyaena despite the fact that one animal was infected with T. brucei. Similarly, a negative LAT reaction was obtained with the serum of one bushbuck infected with T. congolense. Positive LAT reactions were obtained with sera from the following animals: (1) 9 reedbuck, 1 oribi, 1 duiker, and 1 waterbuck in which trypanosomes could not be demonstrated; (2) 2 bushbuck and 1 reedbuck with T. brucei infections; (3) 1 reedbuck with a T. rhodesiensel infection; (4) 1 reedbuck and 1 bushbuck with T. congolense infections; (5) 2 bushbuck with T. vivax infections; (6) 1 bushbuck with a mixed T. bruceilT. congo- lense infection; (7) 1 reedbuck and 1 oribi with non-pathogenic T. theileri infections. 1 Identified by the blood incubation infectivity test of Rickman & Robson (1970). Negative LAT reactions were obtained with sera from the following animals: (1) 20 reedbuck, 14 oribi, 9 duiker, 6 impala, 3 bushpig, 3 hyaena, 2 bushbuck, 2 topi, and 1 water- buck in which trypanosomes could not be demon- strated; (2) 1 hyaena with a T. brucei infection; (3) 1 bushbuck with a T, congolense infection; (4) 3 reedbuck, 1 oribi, and 1 waterbuck with T. theileri infections. There is an obvious discrepancy between the para- sitological and immunological findings for one bush- buck infected with T. congolense and one hyaena infected with T. brucei. The negative LAT reaction obtained from the bushbuck might be explained in terms of the nonspeciflcity of the LAT antigen, which was prepared from T. brucei. However, it seems more likely that both the bushbuck and the hyaena were harbouring recent infections that were not sufficiently well established to stimulate a detec- table antibody response, particularly since this phe- nomenon is known to occur in domestic animals and man with new infections. LATEX AGGLUTINATION TEST FOR TRYPANOSOMAL ANTIBODIES 783 DISCUSSION It is evident from the results obtained in this study that serological tests combined with parasito- logical examinations ofgame animals indicate a higher frequency of trypanosome infections than either test alone. Alternatively, the results may indicate that some species of game animal, e.g., reedbuck, may display spontaneous cure of certain types of trypano- somal infection. Unfortunately, insufficient time was available for the collection of a larger number of samples. Had this been possible, a fairly accurate assessment of the distribution of trypanosome infections in game animals could have been made. However, the immu- nological findings reported here agree with the results of investigations by Allsopp et al. (1972) on the relationships between game animals and G. palli- dipes, in that the highest frequencies of circulating trypanosomal antibodies were detected in two spe- cies, reedbuck and bushbuck, the most available and the most preferred hosts, respectively, of G. pallidipes. It is concluded that the LAT is sufficiently simple, rapid, and specific to be of considerable use in evaluating the overall frequency of trypanosomal infections in communities of game animals. ACKNOWLEDGEMENTS The authors are grateful to the Director of Veterinary Services and the Chief Zoologist, Ministry of Agriculture, Kenya, for providing of facilities at the Lambwe Valley field station, and thank the Chief Game Warden, Kenya Game Department, for allowing specimens of game animals to be collected in the Lambwe Valley Game Reserve. RJ SUM t OBSERVATIONS PRELIMINAIRES SUR L'EMPLOI DE L'EPREUVE D'AGGLUTINATION AU LATEX POUR LA DETECTION DES ANTICORPS TRYPANOSOMIQUES CIRCULANTS CHEZ LES ANIMAUX SAUVAGES DANS LA VALLEE DE LA LAMBWE On a utilise 1'epreuve d'agglutination au latex avec comme antigene Trypanosoma brucei pour rechercher les anticorps trypanosomiques dans des echantillons de serum preleves chez 90 animaux sauvages appartenant A 9 especes. Des examens parasitologiques ont 6te effec- tues simultanement chez tous les animaux etudies. Les examens s6rologiques ont r6vele une prevalence globale d'anticorps circulants de 25,5 %, taux l6g6rement superieur au taux d'infection decel6 par les examens parasitologiques (20,0%). Les serums les plus fr6quem- ment positifs ont ete ceux de cephalophes (66,6 Y.), d'antilopes-chevreuils (36,0%) et peut-etre ceux de kobs dont 3 serums seulement ont ete examin6s. Des r6actions negatives ont ete enregistr6es avec un s6rum d'hyene infectee par T. brucei et un s6rum de cephalophe infecte par T. congolense, mais on estime que ces deux animaux etaient atteints d'une infection recente n'ayant pas encore suscite de reponse immunitaire d6celable. Etant donn6 1'6troite concordance des resultats fournis par les 6preuves serologiques et par les examens parasito- logiques, les auteurs concluent que le test d'agglutination au latex, d'execution facile et rapide, est extremement utile pour apprecier la prevalence globale des infections A trypanosomes dans les populations d'animaux sauvages. REFERENCES Allsopp, R. (1972) Bull. Wld Hlth Org., 47, 735 Allsopp, R. & Baldry, D. A. T. (1972) Bull. Wld Hlth Org., 47, 691 Allsopp, R. et al. (1972) Bull. Wld Hlth Org., 47, 795 Binz, G. (1972) Bull. Wld Hlth Org., 47, 775 Rickman, L. R. & Robson, J. (1970) Bull. Wld Hlth Org., 42, 650