Characterization ofTrypanosoma congolenseserodemes in stocks isolated from Chipata District, Zambia

Abstract

Six stocks ofTrypanosoma congolensewere cloned from 17 stocks isolated from Eastern Zambia and used to initiate insect-formin vitrocultures producing metacyclic trypanosomes. Serological assays were then developed using thesein vitro-derived metacyclics as a reference collection of antigens. Monoclonal antibodies recognized 8 metacyclic variable antigen types (M-VATs) of one stock,T. congolenseTREU 1885, representing 70–80% of that stock's M-VAT repertoire, and in an indirect fluorescent antibody test (IFAT) there were no cross-reactions between them and the metacyclic trypanosomes of the other 5 stocks. Cross-protection assays between the 6 stocks in mice showed that the stocks culturedin vitrowere serologically distinct. In order to facilitate serological typing for serodeme characterization, an IFAT was developed using formalin-fixed metacyclic trypanosomes to identify VAT specific immune responses using 21 day post-infection antisera. The cultured stocks reacted only with their homologous antisera thus confirming the results obtained in the cross-protection assays. No cross-reactions were observed with the 6 cloned stocks and antisera against the 11 stocks ofT. congolenseisolated in the same area at the same time suggesting that these stocks were different from the reference collection of cultured metacyclics. Hence, at least 7 serodemes ofT. congolensehave been identified from the 17 stocks isolated.