Suratex: a simple latex agglutination antigen test for diagnosis of Trypanosoma evansi infections (surra).

A simple and rapid, field-oriented latex agglutination test for the detection of circulating invariant trypanosomal antigens in Trypanosoma evansi infections (surra) is described. In an initial evaluation, the test, Suratex, detected the antigens in 53 (88.3%) of 60 serial blood samples collected over a period of 11 weeks from 3 experimentally infected rabbits. By comparison, the buffy coat technique and wet blood film examination diagnosed the infection in 22 (36.7%) and 2 (3.3%) of the blood samples, respectively. In experimental infections in camels, Suratex diagnosed the infection in 10 of the 12 animals by day 7 post-infection, compared to 7 animals detected by the buffy coat techniques. The 5 animals misdiagnosed by the buffy coat technique remained parasite negative throughout the study period of 127 days, yet they had persistent antigenaemia. Analysis of field sera from two camel herds which were experiencing a T. evansi outbreak, confirmed the superior sensitivity of Suratex. Whereas only 5 (15.6%) animals in a herd of 32 were diagnosed by the buffy coat technique, 30 (94.0%) tested positive for antigens. This high prevalence of T. evansi infections in the herd was confirmed by the high antibody titres detected in sera from all the 32 animals. The second herd, consisting of 60 camels, was investigated using both mouse inoculation and Suratex. Twenty-eight (46.7%) of the animals were diagnosed to be infected with T. evansi by mouse inoculation, while Suratex showed all the 60 animals to be infected. Four of the 5 camels diagnosed using the BCT and all the 28 detected by mouse inoculation (32/33; 97.0%) were Suratex positive, thus showing a high degree of correlation between parasitological results and those obtained by Suratex. All the control sera from 30 camels from a T. evansi-free herd were negative.