Immunosorbent assay for detection of Trypanosoma evansi infection in multiple host species using chimeric protein A/G conjugate.

Surra caused by an extracellular hemoflagellate, Trypanosoma evansi, leads to severe economic loss to livestock productivity in India. Among the various mammalian pathogenic trypanosomes, T. evansi has the widest host range.Usually, species specific conjugates are used in conventional indirect immunosorbent assay (ELISA) for diagnosis of T. evansi infection in different animal species. The aim of the study was to explore the use of non-species specific conjugates viz., protein A, G and chimeric protein A/G instead of species specific conjugates for development of indirect ELISAs. These assays were used for detection of antibodies against T. evansi infection in multiple animal species viz., equine, cattle, buffalo, dog, pig and camel. The functional affinities of serum immunoglobulins of six different animal species with different conjugates were determined by estimation of relative avidity index (RAI). The species specific conjugate based whole cell lysate- T. evansi antigen ELISA was considered as reference assay for comparison of sensitivity and specificity of non-species specific conjugates based ELISAs optimized in the present study. Data showed that serodiagnosis of T. evansi can be carried out by using chimeric protein A/G conjugate in multiple hosts viz., equine, buffalo, camel, pig and dog; protein G conjugate in equine and buffalo and protein A conjugate in camel, pig and dog. The relative diagnostic sensitivity and specificity for chimeric protein A/G conjugate varied from 60 to 100% and 79-100%, respectively for different livestock species. This approach might be helpful in monitoring and surveillance of T. evansi infection in multiple hosts in particular when host specific secondary antibody conjugates are not available. Investigations should be made in wild animals and other warm-blooded vertebrates to validate this hypothesis.