Equine Piroplasmosis
Josie L. Traub-Dargatz, DVM, MS, Diplomate ACVIM; Michael A. Short, DVM;
Angela M. Pelzel, DVM; Tracy E. Norman, VMD, Diplomate ACVIM; and
Donald P. Knowles, DVM, PhD, Diplomate ACVP
Equine piroplasmosis (EP) is the disease caused by protozoan hemoparasitesBabesia caballiand/or
B. (Theileria) equi. The natural transmission of these parasites is through competent tick vec-
tors. These blood parasites can also be transmitted by transfer of blood from infected to naïve horses
through iatrogenic means. American Association of Equine Practitioners members played a key role
in the identication of clinical cases of EP in the United States in 2008 and 2009. Through
regulatory response and epidemiologic investigation, all known infected horses in the United States
are under quarantine as of the spring of 2010. Interim guidance on management of positive and
exposed horses has been developed. These guidelines are available through State Animal Health
Ofcials and Federal Area Veterinarians in Charge in each state. Long-term guidelines for man-
agement of infected and exposed horses are under development. Equine practitioners can play a role
in the identication and work-up of suspect cases and the education of their clients about EP. Au-
thors’ addresses: Department of Clinical Sciences, Colorado State University, College of Veterinary
Medicine and Biomedical Sciences, Fort Collins, Colorado 80523 (Traub-Dargatz); Equine Program
Manager, Division of Animal Industry, Florida Department of Agriculture and Consumer Services,
407 South Calhoun Street, Mayo Building Room 329B, Tallahassee, Florida 32399 (Short); United
States Department of Agriculture:Animal and Plant Health Inspection Services Veterinary Services
Western Region, 2150 Centre Avenue, Fort Collins, Colorado 80526 (Pelzel); Large Animal Clinical
Sciences, College of Veterinary Medicine and Biomedical Sciences, Texas A&M University, College
Station, Texas 77843-4475 (Norman); and United States Department of Agriculture Animal Disease
Research Unit, Agricultural Research Services and Department of Veterinary Microbiology and
Pathology, Washington State University, Pullman, Washington 99164 (Knowles); e-mail: Josie.Traub-
Dargatz@colostate.edu. © 2010 AAEP.
1. Introduction
The goal of this article is to provide background on
the causative agents, methods of transmission, clin-
ical signs of disease, diagnostic testing, manage-
ment of infected horses in the United States,
treatment challenges, and history of equine piro-
plasmosis (EP) in the United States. In addition,
short updates on recent outbreaks in the United
States and research is provided.
2. Background on EP
Causative Agents
EP is a tick-borne disease that affects horses, don-
keys, mules, and zebras. There are two distinctive
EP causative agents,Babesia caballiandB. (Thei-
leria) equi. It has been proposed thatB. equibe
given a taxonomic classication ofT. equi,
1whereas
other researchers have suggested that a more accu-
AAEP PROCEEDINGS
Vol. 56
2010 1
IN-DEPTH: EQUINE PIROPLASMOSIS
NOTES