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) (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. haneyi^EP were evaluated, including ability to superinfect in the presence of T. equi-Texas (T. equi^TX), the isolate responsible for the reemergence of T. equi in the U S. Experimental infection with T. equi^TX or T. haneyi^EP revealed minimal clinical disease however, T. equi^TX infection led to significantly greater neutropenia. Comparison of time to antibody detection following inoculation revealed significantly greater time to detectable anti-T. haneyi^EP antibody (26.67 days post-inoculation (DPI)) than T. equi^TX (11.67 DPI). Regardless of initial infection with either T. equi^TX or T. haneyi^EP, superinfection was established. Comparative analysis of antibody responses from a splenectomized horse infected with T. haneyi^EP to that of a spleen intact horse infected with T. equi^FL revealed a different antibody binding profile to T. haneyi^EP, T. equi^TX and T. equi^FL merozoite antigen and limited shared antigen/cross-reactive antibody(s). Affinity purified T. equi EMA-1 and EMA-2 from T. equi^FL were shown as targets for horse antibodies against T. haneyi. Data presented here show (1) T. haneyi^EP can superinfect in the presence of T. equi^TX infection and co-persists for minimally 25 months, (2) intravenous challenge with T. haneyi is subclinical, and (3) limited cross-reactive antibody between T. haneyi^EP and T. equi includes reactivity to EMA-1 and EMA-2.

Keywords: Apicomplexan; Equine theileriosis; Piroplasmosis; Superinfection; T. equi; T. haneyi.