Wildlife Disease and Zoonotics


Date of this Version



USDA. (2011). Equine piroplasmosis domestic pathways assessment 2011: pathways assessment for the spread of the causative agents of equine piroplasmosis from the movement of a horse from a quarantined premises within the contiguous United States. USDA:APHIS:VS:CEAH:National Center for Risk Analysis. Fort Collins, CO. March 2011. 62 pages.


This article is a U.S. government work, and is not subject to copyright in the United States.


Abstract: Equine piroplasmosis (EP) is a tick borne disease of equids. It is considered a foreign animal disease in the United States. However, from January 2009 through November 2010, 542 confirmed positive cases have been identified in 16 different States. This domestic pathways assessment evaluates the risk of releasing an EP pathogen (Theileria equi or Babesia caballi) from a quarantined premises through movement of horses. In addition, this assessment evaluates the risk of disease transmission by ticks, vertical transmission, or iatrogenic transmission. When an acaricide is applied correctly, the risk of EP transmission by ticks to a horse is low. In addition, infected reservoir hosts, environmental factors, and competent vectors must be present for the disease transmission cycle to occur. Vertical transmission of T. equi is considered a moderate risk pathway and the risk of vertical transmission of B. caballi is negligible. Iatrogenic transmission via whole blood transfusion, blood doping, commercial serum/blood plasma, and contaminated equipment poses the highest risk of disease transmission. Blood is an efficient vehicle of transmission for EP pathogens and even a small volume of blood can be infectious. Exposure of an uninfected horse to any of these pathways is likely to result in EP transmission. Iatrogenic exposure may be difficult to regulate. Management practices such as testing blood donors would help mitigate this risk but these practices vary throughout the equine industry. The overall risk of EP spread by the movement of a horse from a quarantined premises is moderate.