Imidocarb Dipropionate Lacks Efficacy against Theileria haneyi and Fails to Consistently Clear Theileria equi in Horses Co-Infected with T. haneyi.

Kelly Sears,Marta Silva,Kelcey Dinkel,Lindsay Fry,Cynthia Onzere,Philip W Mshelia,Donald Knowles

doi:10.3390/pathogens9121035

Kelly Sears, Marta Silva + Show 5 more

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https://doi.org/10.3390/pathogens9121035

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Abstract

Control of Theileria equi, the primary cause of equine theileriosis, is largely reliant on acaracide use and chemosterilization with imidocarb dipropionate (ID). However, it is currently unknown if ID is effective against Theileria haneyi, the recently identified second causative agent of equine theileriosis, or if the drug maintains effectiveness against T. equi in the presence of T. haneyi co-infection. The purpose of this study was to address these questions using ID treatment of the following three groups of horses: (1) five T. haneyi infected horses; (2) three T. haneyi-T. equi infected horses; and (3) three T. equi-T. haneyi infected horses. Clearance was first evaluated using nPCR for each Theileria sp. on peripheral blood samples. ID failed to clear T. haneyi in all three groups of horses, and failed to clear T. equi in two of three horses in group two. For definitive confirmation of infection status, horses in groups two and three underwent splenectomy post-treatment. The T. equi-nPCR-positive horses in group two developed severe clinical signs and were euthanized. Remaining horses exhibited moderate signs consistent with T. haneyi. Our results demonstrate that ID therapy lacks efficacy against T. haneyi, and T. haneyi-T. equi co-infection may interfere with ID clearance of T. equi.

Highlights

The apicomplexan hemoparasite Theileria equi is the primary causative agent of equine theileriosis and is endemic in both tropical and subtropical regions of the world
T. haneyi in the U.S, the lack of information regarding its susceptibility to imidocarb dipropionate (ID), and the presence of horses super-infected with T. equi and T. haneyi at the U.S.-Mexico border, the goals of this study were: (1) to assess whether ID treatment is an effective chemosterilization agent for T. haneyi infected horses and
The data presented demonstrate that imidocarb dipropionate is not effective for chemosterilization of horses infected with T. haneyi

Summary

Introduction

The apicomplexan hemoparasite Theileria equi is the primary causative agent of equine theileriosis and is endemic in both tropical and subtropical regions of the world. The few remaining, non-endemic countries employ stringent importation testing and prohibit entry of positive equids, resulting in “ongoing economic and regulatory challenges regarding international horse transport” [1]. This testing barrier imposes a significant economic impact on the equine industry of endemic countries that are subsequently unable to export to non-endemic countries [3]. T. equi is invariably fatal in splenectomized equids, which develops

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