Comparison of antigens prepared from culture-forms and bloodstream-forms of Trypanosoma brucei for use in the ELISA test for the serodiagnosis of trypanosomiasis | A comparison of antigens prepared from culture-forms and bloodstream-forms of Trypanosoma brucei for use in the ELISA test for the serodiagnosis of trypanosomiasis

This thesis is concerned with an evaluation of antigens derived from culture forms and bloodstream-forms of Trypanosoma brucei for use in enzyme-linked immunosorbent assays (microELISA tests) for the diagnosis of trypanosome infections. MicroELISA determinations were carried out with serial sera from trypanosome- infected rabbits and cattle using two batches each of culture-form antigen (Cl, C2) and bloodstream-form antigen (Bl, B2) of the same strain of T. brucei. It was necessary to carry out preliminary tests to determine optimal antigen coating levels and dilutions of antisera and the enzyme-(Horseradish peroxidase)-labelled antiglobulin. Incubation times with C2 and B2 were reduced from 60 to 15 minutes and it was shown that fairly uniform results could be obtained on the same microELISA plate using the same antigen coating level and dilutions of the same serum and conjugate. However, variations occurred when assays of the same serum at the same dilutions using the same conjugate dilutions were carried out on different plates (even of the same make) and on different days. For this reason, each comparison of the two antigens had to be carried out on the same plate. Results thus obtained were then comparable and could be used in linear regression analyses. These analyses showed significant high positive correlation coefficients between results obtained with Cl and Bl as well as between those obtained with C2 and B2 for all determinations carried out, except for those with Cl and Bl using sera from rabbits infected with T. brucei from culture. It was concluded that antigens prepared from T. brucei grown in culture are as good as antigens obtained from bloodstream trypanosomes for use in ELISA tests. Slightly higher ELISA values were obtained with homologous antisera (against T. brucei) than against heterologous antisera (against T. congoiense and T. vivax), especially with samples taken early in infections .W ith either culture-form antigen or bloodstreamform antigen of T. brucei,fluctuating ELISA values were found with serial sera from trypanosome infected cattle throughout the course of infection even up to 450 days post-infection. Also high ELISA values were detected in trypanosome infected rabbits long after treatment and it could therefore be concluded that the diagnostic value of ELISA as used at present, in common with other serological tests is low in trypanosomiasis.