Development of an Indirect ELISA to Detect Equine Antibodies to <i>Theileria haneyi</i>

Abstract

The apicomplexan parasite <i>Theileria haneyi</i> is one of two known causative agents of equine theileriosis. It causes milder clinical disease than its more virulent counterpart, <i>Theileria equi</i>, in experimentally infected horses, and can superinfect <i>T. equi</i>-positive horses. The current equi merozoite antigen 1 (EMA1)-based competitive enzyme-linked immunosorbent assay (ELISA)used in the U.S. to detect equine theileriosis detects <i>T. equi</i> but not <i>T. haneyi</i>, and the complexity of molecular assays precludes widespread use for epidemiologic studies. In order to facilitate urgently needed studies on the prevalence of <i>T. haneyi</i>, the goal of this study was to develop a sensitive and specific serologic assay for the diagnosis of <i>T. haneyi</i> based on the equi merozoite antigen 11 (<i>Th</i>EMA11). To achieve this objective, <i>Th</i>EMA11 was recombinantly expressed in eukaryotic cells and its antigenicity assessed using sera from <i>T. haneyi</i>-experimentally infected horses. Confirmation of sera reactivity enabled design and optimization of an indirect ELISA. Specificity of the ELISA for <i>T. haneyi</i> was assessed using a cohort of sera from horses experimentally infected and confirmed PCR-positive for either <i>T. equi</i> or <i>T. haneyi</i>. Data from field samples further demonstrate that the <i>Th</i>EMA11 ELISA is capable of identifying <i>T. haneyi</i> antibodies in horses from multiple continents around the world.