Equine Piroplasmosis Table Topic (AAEP 2011)
Josie Traub-Dargatz, DVM, MS, Dipl. ACVIM, is a professor of equine medicine and epidemiology for Colorado State University’s veterinary school in Fort Collins, Colo., and Angela Pelzel, DVM, a Western region epidemiologist with the USDA Animal and Plant Health Inspection Service, facilitated a table topic on equine piroplasmosis (EP) during the 2011 American Association of Equine Practitioners Annual Meeting, held Nov. 18-22 in San Antonio, Texas. Among the attendees the topics requested for discussion included a brief background on EP from a historical and recent findings perspective, the need to have uniformity across racetracks in various states regarding EP testing requirements, a review of the laboratory testing options for detecting infected horses, and an update on success of treating infected horses as part of the USDA Agricultural Research Services (ARS) research project. A comprehensive literature review on EP is available online.
Several veterinarians involved in decision-making regarding requirements for horses’ entry to racetracks in various states discussed the lack of consistency in tracks’ requirements in different states and the need for further discussion to determine if the epidemiologic data available could lead to decisions that would provide more consistency. There was clarification that the official tests for EP for domestic horses in the United States are conducted at the National Veterinary Services Laboratories (NVSL) or approved laboratories within the National Animal Health Laboratory Network (NAHLN ), while all import testing is conducted at NVSL. A listing of approved laboratories is available on the NVSL website.
Pelzel indicated that there have been more than 147,000 horses in the United States tested for EP from Nov. 1, 2009, through Nov. 1, 2011, through movement and enhanced surveillance testing. There have been 178 EP-positive horses identified during this time period that are unrelated to the 2009 EP outbreak on a ranch in Texas. These positive horses are confined primarily to two specific segments of the U.S. horse population: horses imported prior to 2005 when the import testing method was updated and horses involved in Quarter Horse racing. Equine piroplasmosis has been detected in a small number of Thoroughbred racehorses, but most of these had a link with a trainer or an owner also involved in Quarter Horse racing.
Lastly, Pelzel shared some encouraging results from treating Babesia equi (a causative agent)-infected horses enrolled in the ARS treatment research program. Researchers have developed a protocol for determining clearance of infection, and multiple horses primarily from a ranch in south Texas have been enrolled in the research program. While the majority of treated horses have been shown to be free of B. equi after treatment, caution is warranted as not all treated horses were cleared of the infection on the initial treatment attempt. Work to try to determine the reason for initial treatment failure in these horses is ongoing. This breakthrough offers hope for future management of EP in the United
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