Immunokinetics of Theileria equi specific antibodies: a comparison in serial and single dilution ELISA antibody end titres

Abstract

Theileria equi, a haemoprotozoan of equids, is responsible for endemic infection/latency in tropical/subtropical parts of the world. The present study investigated the immunokinetics of T. equi infection in experimental animals and the diagnostic applicability of single dilution ELISA vis-à-vis conventional serial dilution ELISA. Sequential serum samples were collected up to 90 days postinfection (PI) from 4 donkeys experimentally infected with T. equi. Immunokinetics of T. equi antibodies end titre were determined by serial and single dilution ELISA. A significant rise in initial ELISA antibody end titre (1:800 in serial dilution ELISA and from 1:600 to 1:650 in single dilution ELISA) was observed from day 9 PI in all 4 donkeys, which plateaued between days 66 and 73 PI (end antibody titre varied between 1:6400 to 1:25,600 and 1:6050 to 1:22,100). The efficacy of these ELISAs was also determined by testing 256 field serum samples at 1:200 dilution, collected from apparently healthy animals. Sample analysis revealed overall seroprevalence of 91.01% in the horse population. The frequency distribution of antibody titre of these field samples by single dilution ELISA exhibited that most of the positive horses had high levels of specific antibodies. This study has emphasised the usefulness of single dilution ELISA as a diagnostic assay in determining the end antibody titre by testing it at a single dilution of 1:200.