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 seropositivity among nine farm-specific and four animal-specific variables. We used logistic regression models for parasitological and serological outcome variables and then compared the adjusted odds ratios for explanatory factors between the models. Age is positively correlated with seropositivity but not with the detection of the parasite. Therefore, age group-specific cut-off values were established using mixture-distribution analysis. This procedure, as well as a mixture-distribution-derived cut-off value for the total sample, resulted in a greater relative efficiency of the ELISA as compared to conventional interpretation (cut-off value defined using non-exposed negative controls). The relevance of age and other biological factors for the serological status is briefly discussed.