Comparative evaluation of the antibody-detection ELISA technique using microplates precoated with denatured crude antigens from Trypanosoma congolense or Trypanosoma vivax.

Abstract

Two FAO/IAEA indirect enzyme-linked immunosorbent assays (ELISA), which use microplates precoated with denatured crude Trypanosoma congolense or Trypanosoma vivax antigen for detecting anti-trypanosomal antibodies in bovine sera, were evaluated for their sensitivity, specificity and positive and negative predictive values, using 320 Ugandan field samples (known negative sera, n = 80; known positive sera, n = 80; cattle herds where control of tsetse and trypanosomosis was practiced, n = 80; and cattle herds where there was no such control, n = 80). Cut-off points of 30% and 25% positivity were determined for the T. congolense and T. vivax assays, respectively, using a modified ROC (receiver operating characteristic) analysis. The T. congolense assay had estimated diagnostic sensitivity and specificity of 63.7% and 57.5%, respectively, while the T. vivax assay had estimated diagnostic sensitivity and specificity of 81.3% and 81.3%, respectively. The two assays conducted in parallel had estimated diagnostic sensitivity and specificity of 82.5% and 88.7%, respectively. Using the sera from the cattle in the area with control (detected prevalence of trypanosomosis 0%), both the T. congolense and T. vivax assays had negative and positive predictive values of 100% and 0%, respectively. Using the sera from the cattle in the area without control (detected prevalence of trypanosomosis 15%), the T. congolense assay had negative and positive predictive values of 91% and 33%, respectively, and the T. vivax assay had negative and positive predictive values of 93% and 27%, respectively. The T. congolense assay was in fair agreement with the buffy coat technique (BCT) (kappa = 0.25), while the T. vivax assay was in substantial agreement with the BCT (kappa = 0.625), and both assays conducted in parallel were in substantial agreement with the BCT (kappa = 0.708). Both assays were found to be proficient and suitable for the diagnosis of bovine trypanosomosis, especially when used in parallel.