The analysis of the cross- reactions occuring in antibody-ELISA for the detection of trypanosomes can improve identifiaction of the parasite species involved

In Africa, the main pathogenic trypanosomes of livestock are Trypanosoma vivax, T. congolense and T. brucei. The geographical distributions and hosts of these three species are very similar. As they differ markedly in pathogenicity and epidemiology, however, a species-specific serological test for infection would be very useful for epidemiological studies. The antibody-ELISA (Ab-ELISA) that have been developed for detecting the Trypanosoma spp. most commonly infecting livestock give satisfactory sensitivity and genus specificity. Unfortunately, they are not species-specific because of strong cross-reactions between the pathogenic Trypanosoma spp. In the present study, carried out in Burkina Faso, the results of standardized Ab-ELISA for T. vivax, T. brucei or T. congolense were compared using 1288 plasma samples from sheep experimentally infected with T. vivax, T. evansi and/or T. congolense. If the results were interpreted, as usual, only using a positivity threshold (PT), the strong cross-reactions observed led to a mean species-specificity of <30%. However, analysis of the reactions observed in the three types of Ab-ELISA revealed that the homologous reactions were stronger than the heterologous for almost all of the single and mixed infections (98.3% and 99.0%, respectively). In monospecific infections exceeding the PT study of the positivity score produced in each of the three types of Ab-ELISA increased species-specificity to >96%. It therefore appears that comparison of the strengths of the reactions seen in Ab-ELISA could greatly improve sero-epidemiological surveys of trypanosome infections in domestic ruminants, although the technique remains to be evaluated in experimentally infected cattle. (Résumé d'auteur