SENSITIVITY AND SPECIFICITY OF ANTIGEN-CAPTURE ELISAS FOR DIAGNOSIS OF TRYPANOSOMA-CONGOLENSE AND TRYPANOSOMA-VIVAX INFECTIONS IN CATTLE

Sensitivity and specificity of the FAO/IAEA antigen-ELISA kits for dia gnosis of bovine trypanosomosis were investigated using sera from expe rimental cattle infected by tsetse challenge with cloned populations o f Trypanosoma congolense (three populations) or T. vivax tone populati on). The kits are based on monoclonal antibodies that recognise intern al antigens of tsetse-transmitted trypanosomes. Ten cattle were infect ed with each trypanosome population for at least 60 days, and in combi nation with uninfected cohorts (n=16) were used in a double-blind stud y design. Sensitivity and specificity of the tests depended on the cho ice of positive-negative thresholds expressed as percent positivity wi th respect to the median OD of four replicates of the strong positive reference serum provided with the kit. In general, while overall speci ficities were high, sensitivities of the antigen-ELISAs were poor. For example, at a cut-off of 5% positivity, the sensitivities of the anti gen-ELISAs were 11% for samples (n=1162) from T. congolense infected c attle (n=30), and 24% for samples (n=283) from T. vivax infected cattl e (n=10). The corresponding specificity values were 95% and 79%, respe ctively. At a cut-off of 2.5% positivity, sensitivity for T. congolens e was 25%, and for T. vivax 35%; corresponding specificity values were 85% and 63% respectively. There were no values of the positive-negati ve threshold at which both sensitivity and specificity were satisfacto ry. Restricting the analyses to samples taken more than 2 weeks after tsetse challenge did little to improve sensitivity estimates. Trypanos ome species specificities of the antigen-ELISAs were also poor. Sensit ivity and species specificity of the antigen-ELISA for Trypanosoma bru cei infections were not investigated. In contrast to the antigen-ELISA , the sensitivity of the buffy-coat technique when applied to the same experimental animals was fairly high at 67% for T. congolense infecti ons and 60% for T. vivax infections. For samples taken more than 2 wee ks after tsetse challenge, high sensitivity estimates of 96% for T. co ngolense and 76% for T. vivax infections were obtained. (C) 1998 Publi shed by Elsevier Science B.V. All rights reserved.