The use of Immunodiagnostic Techniques in Sheep for the Epidemiological Surveillance of Cystic Echinococcosis

Abstract

Objective: Cystic echinococcosis (CE) is a parasitic zoonosis caused by Echinococcus granulosussensu lato. Immunodiagnostic techniques such as Western blot (WB) or enzyme-linkedimmunosorbent assay (ELISA), with different antigens, can be applied to the diagnosis ofsheep for epidemiological surveillance purposes in control programs. However, its use islimited by the existence of antigenic cross-reactivity between different species of taeniidaepresent in sheep. Therefore, the usefulness of establishing surveillance systems based on theidentification of infection present in a livestock establishment, known as the (Epidemiological)Implementation Unit (IU), needs to be evaluated.Materials and Methods: A new ELISA diagnostic technique has been recently developed andvalidated using the recombinant EgAgB8/2 antigen for the detection of antibodies against E.granulosus. To determine detection of infection at the IU level using information from thisdiagnostic technique, simulations were carried out to evaluate the sample size required toclassify IUs as likely infected, using outputs from a recently developed Bayesian latent classanalysis model.Results: Relatively small samples sizes (between 14-29) are sufficient to achieve a highprobability of detection (above 80%), across a range of prevalence, with the recentlyrecommended Optical Density cut-off value for this novel ELISA (0.496), which optimizesdiagnostic sensitivity and specificity.Conclusions: This diagnostic technique could be potentially used to identify the prevalence ofinfection in an area under control, measured as the percentage of IUs with the presence ofinfected sheep (infection present), or to individually identify the IU with ongoing transmission,given the presence of infected lambs, on which control measures should be intensified.