Comparison of monoclonal antibody based latex agglutination test with PCR for diagnosis of Trypanosoma evansi in domestic animals
Abstract
Trypanosoma evansi, a blood protozoan parasite causes a serious disease known as ‘surra’ in domestic and wild animals. It is an arthropod borne disease and Tabanus spp. has been implicated as the main vector. It is the most widely geographically distributed pathogenic trypanosome in Africa, South and Central America and Asia. In India, T. evansi infection is widely prevalent in different parts and is of significant economic importance in livestock production. Though trypanosomosis has been studied since many years, its definite diagnosis still suffers from low sensitivity and specificity. Therefore, the present investigation has been carried out with the aim of detecting T. evansi in cattle, buffaloes and equines in the state of Haryana by parasitological (WBF), antigen-detecting (MAb-LAT) and DNA-detecting (TE-PCR) tests and to compare these tests for their relative sensitivity and specificity.
A field isolate of T. evansi collected from an infected cattle was propagated in rats and PCR was standardized using DNA isolated from infected rat blood. The assay employed synthetic oligonulceotide primers (21 mer sense and 22 mer antisense) targeted to a repetitive nuclear DNA sequence of T. evansi. TE-PCR positive signal (227bp) was obtained with template DNA content of 12 trypanosomes extracted from whole blood sample.
Field serum samples were screened using monoclonal antibody based latex agglutination test (MAb-LAT) and blood samples by WBF and TE-PCR. Out of 205 blood and sera samples from cattle (n=88), buffaloes (n=46) and equines (n=71) examined, 1.95% were found positive for T. evansi infection by WBF while 59.51 and 60.49 per cent found positive by MAb-LAT and TE-PCR, respectively. D-SN and D-SP values of MAb-LAT using TE-PCR as reference test were 88.43% and 81.48% respectively. D-SN and D-SP values of TE-PCR were 87.70% and 82.50% respectively using MAb-LAT as reference test. Prevalence of T. evansi was 3.41%, 60.23% and 65.91% in cattle; 2.17%, 78.26%, and 76.09% in buffaloes and nil, 46.48% and 43.66% in equines, by WBF, MAb-LAT and TE-PCR, respectively.
A good correlation was found between MAb-LAT and TE-PCR. It was inferred that MAb-LAT, being simple to perform, rapid, convenient, cost-effective could be quite suitable for field-level diagnosis and screening of trypanosomosis. However, PCR on the other hand has its role in monitoring the efficacy of trypanocidal treatment.