Alarm Over New Equine Piroplasmosis Outbreak

The third case of Equine piroplasmosis in the last 12 months has raised concerns that the disease may become endemic in the United States.

On October 19th, National Veterinary Services Laboratories (NVSL) confirmed equine piroplasmosis in 32 working Quarter Horses located on a ranch in Kleberg County, Texas. The USDA Animal and Plant Inspection Service (APHIS) and the Texas Animal Health Commission (TAHC) are conducting a comprehensive epidemiological investigation of the event. Since confirmation that more horses at the premises were infected, a further 96 horses are being tested, and as yet results have not yet been presented.

A report filed by John Clifford, DVM, deputy administrator of the USDA’s Animal and Plant Health Inspection Service, to the World Organization for Animal Health has revealed further details of the outbreak. On October 2nd, a 7-year-old mare was presented to a local veterinary hospital where a blood-borne pathogen was subsequently suspected, and quarantine was not placed on the premises or it’s horses until 13th October. Measures imposed on the ranch include disinfection of the premises, but also prohibit any horses from being vaccinated or treated by veterinarians.

Equine piroplasmosis is an infectious disease spread by ticks which transmit the protozoan parasites Theileria equi and Babesia caballi. Equine piroplasmosis affects all horse species including horses, donkeys and zebras and only a few countries are not considered endemically infected, including Canada, the United States, the United Kingdom and Ireland. An outbreak of piroplasmosis from imported horses resulted in 20% of horses on the Brighton Indian Reservation dying. The case fatality rate for piroplasmosis-infected horses can approach 50%, and the only treatment is a very stringent chemotherapy which can have serious side effects.

The United States has again been considered free of the disease since 1982, following an aggressive eradication program, but a case was reported in Florida in October 2008, leading to the quarantine of 20 premises and the euthanizing of 20 horses. And in June 2009, 5 more horses in Missouri were euthanized after testing positive for piroplasmosis, but 3 horses that tested positive and were removed from quarantine have been missing ever since.

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