Equine Piroplasmosis
Equine Piroplasmosis (EP) is classified as a foreign animal disease (FAD) not endemic in the U.S. Regulations requiring the testing of all horses entering the U.S. to determine their EP status have been in place for many years. EP occurs in Africa, Europe, Asia, South and Central America. The tick vectors that spread the disease exist in the United States.
EP is a protozoal infection of horses spread by ticks. The disease may be fatal in up to 20 percent of previously unexposed animals. After having the clinical disease, horses can be carriers for long periods of time. Currently, there is no vaccine for the disease and treatment options are not fail-proof. It appears that the major threat to the U.S. is the non-clinical seropositive lifetime carriers.
For many years the Complement Fixation Test (CFT) was used as the import test to determine the EP status of imported horses. However, research as far back as 1971 has shown that the CF test is not an appropriate test for EP because equine immunoglobulin IgG(T) does not fix complement. This yielded an unknown small percentage of “false negative” test results. Consequently, an unknown number of EP seropositive horses legally entered the U.S. In August 2005, the C-ELISA test was declared the official diagnostic test at import to replace the CFT.
Background
In October 2009, the Texas Animal Health Commission (TAHC) quarantined a ranch in Kleberg County, Texas after a 7-year-old Quarter Horse mare tested positive for Equine Piroplasmosis (EP). Immediately following the quarantine, the United States Department of Agriculture, Animal and Plant Health Inspection Service (USDA-APHIS) and the TAHC initiated an emergency response to this FAD.
Over 3,000 horses have been tested for EP as part of the traceback and epidemiological investigation with over 400 positive horses disclosed in connection with the outbreak. Recent enhanced surveillance and movement testing has led to the disclosure of over 130 EP-positive horses in the U.S. These findings are unrelated to the 2009 Texas ranch outbreak and were found in a total of 16 states. This traceback and epidemiological investigation remains on-going.
EP positive horses are found in U.S. fall within three distinct sub-populations: horses from the index premises in South Texas, Quarter Horse racehorses (primarily those involved in unsanctioned racing), and horses imported into the U.S. prior to August 2005, when the official U.S. import test was the CFT.
In response to disclosure of the EP-infected herd in Texas, many states and Canada have implemented movement restrictions and enhanced testing requirements for horses originating from Texas and other EP affected areas. In November 2009, New Mexico began requiring EP testing of Quarter Horse racehorses entering New Mexico racetracks. Racetracks in other states subsequently began requiring EP testing to enter sanctioned racetracks.
Because of the number of EP positive horses that may have legally entered the U.S. over many years when the CFT was in use, positive horses may be detected from time to time. Horses that are being exported with the intention of being returned to the U.S. will likely be tested for EP prior to export to help ensure their return. In such cases, the U.S. needs to have a plan of action on how any positive results will be handled. Some possible solutions being considered include lifetime quarantine or euthanasia. The current focuses are to maintain existing import restrictions, to develop cohesive state and federal policy, and to fund research for an effective treatment.
Status
In response to the evolving EP incident, the National Equine Piroplasmosis Working Group (NEPWG) consisting of state, federal, research, laboratory, and industry representatives was established in November 2009. The charge of the group was to provide perspectives and recommendations on Equine Piroplasmosis in the U.S. to USDA-APHIS-Veterinary Services (VS).
USDA-VS is currently reviewing the NEPWG long-term recommendations along with the AHC’s comments on those long-term recommendations.
AHC Position
The AHC supports many of the NEPWG’s long-term recommendations. The AHC supports additional funding to advance research in diagnosis, treatment, and transmission of EP to maintain an EP free status in the US.