Skip to main content
ARS Home » Pacific West Area » Pullman, Washington » Animal Disease Research » Research » Publications at this Location » Publication #284671
Title: Re-emergence of the apicomplexan theileria equi in the United States: Elimination of persistent infection and transmission risk

Author
item Ueti, Massaro
item MEALEY, ROBERT - Washington State University
item Kappmeyer, Lowell
item White, Stephen
item KUMPULA-MCWHIRTER, NANCY - Washington State University
item PELZEL, ANGELA - Animal And Plant Health Inspection Service (APHIS)
item GRAUSE, JUANITA - Animal And Plant Health Inspection Service (APHIS)
item BUNN, THOMAS - Animal And Plant Health Inspection Service (APHIS)
item SCHWARTZ, ANDY - Texas Animal Health Commission
item TRAUB-DARGATZ, JOISE - Colorado State University

Submitted to: PLOS ONE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/7/2012
Publication Date: 9/6/2012
Citation: Ueti, M.W., Mealey, R.H., Kappmeyer, L.S., White, S.N., Kumpula-Mcwhirter, N., Pelzel, A.M., Grause, J.F., Bunn, T.O., Schwartz, A., Traub-Dargatz, J.L. 2012. Re-emergence of the apicomplexan theileria equi in the United States: Elimination of persistent infection and transmission risk. PloSONE 7(9):e44713.

Interpretive Summary: Restriction in the movement of infected horses with Theileria equi represents significant economic problem for the horse industry worldwide. In this study, we tested the usefulness of imidocab dipropionate in the elimination of T. equi in naturally infected horses from an outbreak within the United States. Imidocarb treatment was able to eliminate T. equi in 24 of 25 treated horses. Further investigation demonstrated that blood transfer from 24 treated horses failed to transmit to unexposed horses indicating that the original horses were no longer infected. These results support the use of imidocarb dipropionate to assist in the control and eradication of this tick-borne parasite. Successful imidocarb treatment of infected horses provides a tool to aid the global equine industry by removing risk associated with infection and facilitating international movement of horses between countries.

Technical Abstract: Arthropod-borne apicomplexan pathogens that cause asymptomatic persistent infections present a significant challenge due to their life-long transmission potential. Although anti-microbials have been used to ameliorate acute disease in animals and humans, chemotherapeutic efficacy for apicomplexan pathogen elimination from a persistently infected host and removal of transmission risk is largely unconfirmed. The recent re-emergence of the apicomplexan Theileria equi in U.S. horses prompted testing whether imidocarb dipropionate was able to eliminate T. equi from naturally infected horses and remove transmission risk. Following imidocarb treatment, levels of T. equi declined from a mean of 10 (4.9) organisms/ml of blood to undetectable by nested PCR in 24 of 25 naturally infected horses. Further, blood transfer from treated horses that became nested PCR negative failed to transmit to naïve splenectomized horses. Although these results were consistent with elimination of infection in 24 of 25 horses, T. equi-specific antibodies persisted in the majority of imidocarb treated horses. Imidocarb treatment was unsuccessful in one horse which remained infected as measured by nested PCR and retained the ability to infect a naïve recipient via intravenous blood transfer. However, a second round of treatment eliminated T. equi infection. These results support the utility of imidocarb chemotherapy for assistance in the control and eradication of this tick-borne pathogen. Successful imidocarb dipropionate treatment of persistently infected horses provides a tool to aid the global equine industry by removing transmission risk associated with infection and facilitating international movement of equids between endemic and non-endemic regions.