Changing trends in diagnostics of trypanosomosis in animals

Abstract

Animal trypanosomosis presents special problems with regard to diagnosis since the clinical signs are not pathognomonic and standard parasitological techniques are not sufficiently sensitive. Formol-gel and mercuric chloride tests using serum of infected animals were adopted as a routine diagnostic tool for trypanosomosis, however, these chemical tests suffer from inherent problem of non specificity. To overcome this problem, alternative methods of diagnosis were developed, which detected antibody responses to antigens of infecting trypanosomes. Indirect immunofluorescent antibody test, enzyme immunoassay (ELISA) and the card agglutination test for trypanosomosis (CATT) were found to be useful tests for the diagnosis of Trypanosoma evansi infections in view of their sensitivity and specificity. However, antibody detection tests failed to distinguish between current and past infections because of persistent antibody titres. Recently, development of assays for the detection of circulating trypanosomal antigens in infected animals has circumvented this problem since antigen-positivity indicates existing infection. Latex agglutination test, being simple to perform, rapid, convenient, cost-effective could be quite suitable for field-level diagnosis and screening of trypanosomosis. Presently molecular diagnostic techniques like polymerase chain reaction (PCR) and DNA probes for detection of parasitic DNA have been used more efficiently as these indicate a sure sign of an active infection. These techniques eliminate the possibilities of cross-reaction and offer high specificity and sensitivity for detection of trypanosomosis in animals.