A comparison of the antigen detection ELISA and parasite detection for diagnosis of Trypanosoma evansi infections in camels.

Two herds of 60 camels each, living in Trypanosoma evansi endemic areas, were selected and studied for a period of 18 months. Animals in one herd were treated prophylactically with quinapyramine prosalt (May and Baker, Dagenham, UK), while those in the other herd were treated individually with quinapyramine dimethylsulphate (May and Baker, Dagenham, UK) when proven parasitaemic. The herd on prophylaxis was sampled for antigen and patent infection monthly. The other herd was sampled weekly for patent infection and fortnightly for antigen. The results obtained could be divided into four categories. The first category comprised cases (52 out of 61) in which the presence of trypanosome antigens could be correlated with parasitological diagnosis. In 80% of these animals the antigens disappeared from the circulation within a period of 30 days following chemotherapy. The second category comprised those animals with parasitologically proven infections but which did not have antigens in their sera. This was observed in nine camels, seven of which were from the herd that was being examined weekly for the presence of trypanosomes. These were considered to be animals in early infection, as the subsequent sera were also negative for anti-trypanosome antibodies and immune complexes. The third category comprised camels which were antigen-positive but aparasitaemic. Sera from these animals were also positive for anti-trypanosome antibodies, indicating that antigen-positivity was a true reflection of trypanosome infections in these animals. The last category comprised pre-weaned camel calves which appeared to have some form of protection against trypanosomiasis, as evidenced by the absence of trypanosomes, antigens and antibodies throughout the early period of their lives. Only occasional antigenaemia was found in a few calves. It is concluded that trypanosome antigen detection may give a more accurate idea of the prevalence of T. evansi infections than does whole parasite detection.