A new method for fixation and preservation of trypanosomal antigens for use in the indirect immunofluorescence antibody test for diagnosis of bovine trypanosomiasis.

A new method for fixation of trypanosomes for use in the indirect immunofluorescent antibody test (IFAT) is described. The method involves fixation of live trypanosomes, in suspension, using a mixture of 80% cold acetone and 0.25% formalin in saline. The fixed trypanosomes were stored in suspension at -60 degrees C, 4 degrees C or at room temperature for at least one year without loss of antigenicity. Using trypanosomes prepared this way as antigens in IFAT, species-specific antibodies were detected within 2 weeks of infection in sera of cattle infected with T. brucei or T. vivax. Thereafter, antibodies recognizing antigens common to the two species as well as T. congolense were detected. The antibody levels to common antigens of the three species declined 2-3 months post-infection, leaving only the species-specific antibodies. The sera obtained from T. congolense infected animals, did not react with T. vivax or T. brucei antigens. The non-specific fluorescence commonly associated with this assay was eliminated by prior absorption of the test sera with normal bovine lymphocyte lysate. This treatment of serum did not affect the specific antibodies to trypanosomal antigens. Analysis of bovine sera prepared from cattle in Kisiwani and Muhaka, along the Kenya coast, using the fixed trypanosomes revealed that some animals had antibodies to one trypanosome species only while others had antibodies to 2 or all 3 trypanosome species.