Infection dynamics of Theileria equi and Theileria haneyi, a newly discovered apicomplexan of the horse.

Abstract

Theileria equi infection, exotic to the United States has reemerged through intravenous (iatrogenic) and tick-borne transmission. Surveillance at the US-Mexico border identified a new species, Theileria haneyi, (T. haneyi) (EP = Eagle Pass, Texas) which warranted additional investigation due to inability to detect by PCR targeting of T. equi ema-1 and EMA-1-cELISA validated for T. equi. Infection dynamics of T. haneyiwere evaluated, including ability to superinfect in the presence of T. equi-Texas (T. equi), the isolate responsible for the reemergence of T. equi in the U S. Experimental infection with T. equior T. haneyirevealed minimal clinical disease however, T. equiinfection led to significantly greater neutropenia. Comparison of time to antibody detection following inoculation revealed significantly greater time to detectable anti-T. haneyiantibody (26.67 days post-inoculation (DPI)) than T. equi(11.67 DPI). Regardless of initial infection with either T. equior T. haneyi, superinfection was established. Comparative analysis of antibody responses from a splenectomized horse infected with T. haneyito that of a spleen intact horse infected with T. equirevealed a different antibody binding profile to T. haneyi, T. equiand T. equimerozoite antigen and limited shared antigen/cross-reactive antibody(s). Affinity purified T. equi EMA-1 and EMA-2 from T. equiwere shown as targets for horse antibodies against T. haneyi. Data presented here show (1) T. haneyican superinfect in the presence of T. equiinfection and co-persists for minimally 25 months, (2) intravenous challenge with T. haneyi is subclinical, and (3) limited cross-reactive antibody between T. haneyiand T. equi includes reactivity to EMA-1 and EMA-2.