Equine Piroplasmosis

Background

Equine Piroplasmosis (EP) is classified as a foreign animal disease not endemic to 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.  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 (CF) test 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 CF test. 

Current Status

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 a foreign animal disease investigation.

As of February 2010, the National Veterinarian Services Laboratory (NVSL) confirmed EP in 370 horses directly linked to the affected premises in Kleberg County.  The positive linked horses are currently located in 13 States as follows: Texas, Alabama, California, Florida, Georgia, Indiana, Louisiana, Minnesota, North Carolina, New Jersey, Tennessee, Utah, and Wisconsin.

Authorities have tested over 1,700 horses as part of the investigation, and all known EP positive horses are currently under quarantine.  However, investigations and studies are continuing and testing of all linked horses is ongoing.  Several states and Canada have imposed movement restrictions on horses originating from Texas.

In December 2009, three horses tested positive for EP as a result of New Mexico’s race track screening program.  The positive horses did not show any clinical signs of the disease and a preliminary investigation found the transmission may have resulted from management practices (needle sharing).  The three horses screened in New Mexico are not linked to the other EP positive horses found under the investigation initiated in Texas.

Because of the number of EP positive horses that may have legally entered the U.S. over many years when the CF test 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.

AHC Position

The AHC supports the continued discussion and evaluation of how to address U.S. resident equines that test positive for Equine Piroplasmosis and supports the funding of research for an effective treatment.