IMPACT OF BIOLOGICAL FACTORS ON THE INTERPRETATION OF BOVINE TRYPANOSOMOSIS SEROLOGY

A total of 457 cattle from dairy farms in Mukono County, Uganda, were investigated for Trypanosoma antibodies by ELISA, The objective of the study was to identify explanatory covariate factors for seropositivit y among nine farm-specific and four animal-specific variables. We used logistic regression models for parasitological and serological outcom e variables and then compared the adjusted odds ratios for explanatory factors between the models. Age is positively correlated with seropos itivity but not with the detection of the parasite. Therefore, age gro up-specific cut-off values were established using mixture-distribution analysis. This procedure, as well as a mixture-distribution-derived c ut-off value for the total sample, resulted in a greater relative effi ciency of the ELISA as compared to conventional interpretation (cut-of f value defined using non-exposed negative controls). The relevance of age and other biological factors for the serological status is briefl y discussed. (C) 1997 Elsevier Science B.V. All rights reserved.