A comparative study of the parasitological buffy coat technique and an antigen enzyme immunoassay for trypanosome diagnosis in sequential Trypanosoma congolense infections in N'Dama, Gobra zebu and N'Dama x Gobra crossbred cattle.

The buffy coat/dark ground techniques (BCT) and an antigen enzyme immunoassay (Ag-ELISA) were compared for the diagnosis of trypanosome infection in N'Dama, Gobra zebu and N'Dama x Gobra (F1) crossbred cattle following two sequential experimental Trypanosoma congolense infections. Both first and second challenge were performed by intradermal needle inoculation of trypanosome bloodstream forms. During the course of the first challenge, the overall trypanosome percentage of positive cases detected by BCT in blood samples was higher (P < 0.001) in comparison with that obtained by Ag-ELISA in tested serum samples of the three cattle breeds. Conversely, in the second infection the overall number of infections detected by BCT was lower in N'Dama (P < 0.005) and F1 (P < 0.001) than that obtained using Ag-ELISA; nearly identical positive rates were detected by the two diagnostic techniques in Gobra zebus. Both in the first and second T. congolense challenge, positive rate obtained using BCT significantly decreased as the infection progressed. On the other hand, the positive rate given by Ag-ELISA and its sensitivity manifested a significant opposite trend during the course of the first infection. No relationship between progression of infection and Ag-ELISA positive rate as well as Ag-ELISA sensitivity was found in the second T. congolense challenge. The Ag-ELISA was less than 50% sensitive in detecting circulating antigens during the first 2 months of the primary infection. However, it showed a high and stable sensitivity throughout the second trypanosome infection. It was concluded that the Ag-ELISA was suitable for use in detecting chronic or repeated infections but needs to be combined with BCT to provide reliable results.