Re-emergence of the apicomplexan Theileria equi in the United States: elimination of persistent infection and transmission risk

PLoS One. 2012;7(9):e44713. doi: 10.1371/journal.pone.0044713. Epub 2012 Sep 6.

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.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antiprotozoal Agents / therapeutic use
  • Female
  • Horse Diseases / drug therapy
  • Horse Diseases / epidemiology*
  • Horse Diseases / parasitology
  • Horse Diseases / transmission
  • Horses
  • Imidocarb / analogs & derivatives
  • Imidocarb / therapeutic use
  • Polymerase Chain Reaction
  • Risk Factors
  • Theileria / isolation & purification*
  • Theileriasis / epidemiology*
  • Theileriasis / parasitology
  • Theileriasis / transmission
  • United States / epidemiology

Substances

  • Antiprotozoal Agents
  • Imidocarb
  • imidocarb dipropionate

Grant support

This work was supported by United States Department of Agriculture-Agricultural Research Service 5348-32000-034-00D. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.