Detection of Trypanosoma congolense antibodies with indirect ELISAs using antigen-precoated microtitre plates

The study reports the performance of four indirect enzyme-linked immunosorb ent assays (ELISAs) for antibody (AB) detection using microtitre plates whi ch were precoated with native or heat/detergent denatured antigens (AGs) fr om Trypanosoma congolense (T.c.) and T. vivax (T.v.), and stored for betwee n 1 to 206 days at +37 degrees C. Bovine serum samples were obtained by seq uential bleeding of 3-months old T.c.-infected bulls and their uninfected c ohorts, as well as by a single bleeding of uninfected adult cattle. The fir st day of AB detection, and observations on samples after this (defined as estimated ELISA sensitivity), depended on the cut-off value in the specific ELISAs. Cut-off values from pre- and early post-infection samples of indiv idual animals demonstrated a seroconversion in all ELISAs on average after 10-15 days post-infection (dpi). The AB detection was delayed in the T.c. n ative and denatured AG-based ELISAs using cut-off points from uninfected co hort cattle (16.5 dpi, 19.3 dpi) and the adult cattle population (22.1 dpi, 25.0 dpi). The T.v. AG-based ELISAs however lacked crossreactiviy to T.c. ABs. The estimated sensitivity of each T.c. AG-based ELISA was above 96% th roughout, but significantly lower for the T.c. native AG-based ELISA (91.1% ) when the adult cattle derived cut-off point was used (p<0.01). The sensit ivity of the phase contrast buffy coat technique was similar to the T.c. AG -based ELISAs, but significantly lower when the T.c. denatured AG-based ELI SA was used at the adult cattle derived cut-off point (p<0.05). The implica tions of the results and future research aspects on ELISAs to detect trypan osomal ABs and AGs are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.