Comparison of parasitological, serological and molecular diagnostic tests for detection of subclinical Trypanosomosis in two organised dairy herds

Abstract

Trypanosomosis also known as ‘Surra’ caused by Trypanosoma evansi is of significant economic importance in livestock production. Diagnosis of subclinical infection and carrier state of disease is far difficult. Therefore, the present study was conducted to compare parasitological, serological and molecular diagnostic tests for detecting subclinical trypanosomosis in two dairy herds of Murrah buffalo (n=27) and crossbred cattle (n=22) in Hisar district of Haryana. Peripheral blood samples collected from all the animals were subjected to blood smear examination and DNA isolation for molecular detection by PCR, and like-wise serum samples were collected and subjected to latex agglutination test (TE-LAT) for T. evansi antigen detection. PCR products from positive samples were purified and sequenced for confirmation of T. evansi DNA. None of the animals in the two herds was found positive for T. evansi parasites by microscopic examination of thick blood smears. In buffalo farm, 29.62% samples each were found moderately and weak positive by TE-LAT, whereas PCR assay test yielded 40.74% samples positive for T. evansi DNA. In cattle farm, TE-LAT showed 18.18%, 31.89% and 9.09% samples to be strong, moderate and weak positive, whereas 50% samples were found PCR-positive for T. evansi DNA. Agreement among TE-LAT and PCR assay, as expressed by the kappa value, was found to be poor. To conclude, each test has its own merits and limitations. While TE-LAT is suitable for screening purpose, PCR assay confirms parasite in blood. For clinical diagnosis, results of laboratory diagnostic tests must, however, be correlated clinically before initiating the therapy.