King Ranch of South Texas watched helplessly as prize-winning quarter horses fell to a deadly illness called Equine Tick Fever (Piroplasmosis). The ranch reported a single positive case and by the time Department of Agriculture's veterinary scientist, Don Knowles, arrived there was a full-blown outbreak of 300 infected and dying.
The disease, principally considered an issue for countries outside the United States, would sporadically appear in Florida. The fact that the disease would randomly appear stateside caught Knowles attention; who believed a state of preparedness was prudent in the event of an outbreak. Initially, it was believed that there were two tick species responsible for transmitting the illness, the American dog tick (Dermacentor variabilis) and the cattle tick (Rhipicephalus microplus). However, Knowles' due diligence, along with a gifted research team, discovered the actual carrier of the disease as the cayenne tick (Amblyomma cajennense).
When a horse becomes infected with Equine Tick Fever, its immune system does not have the ability to fight off the parasites carried in the tick's saliva. As a result, the animal's red blood cells are systematically destroyed causing the horse to suffer from a high fever and anorexia. The infected ultimately die from extreme anemia.
One of the major factors considered for the aggressive appearance of cayenne ticks is the change in climate conditions. The prolonged warm weather and proximity of the ranch to water makes it an ideal breeding ground. The disease spreads so prolifically that the United States government mandates that infected horses are either put down or quarantined away from other horse populations.
The King Ranch became center stage for putting a lot of theoretical probability into action. Knowles deduced that using large amounts of a drug called Imizol (Imidocarb dipropionate) should counteract the parasitic infection and spare the horses. Imizol is primarily used as a remedy for tick fever in cattle (Bovine Babesiosis). Left untreated, cattle exposed to tick fever suffer a similar fate as horses and die from extreme anemia. Knowles research indicated that Imizol should be theoretically effective in horses but had not been tested prior to the King Ranch outbreak. The Imizol regimen worked and the horses at the ranch were spared.
Upon a successful outcome to Knowles hypothesis, Imizol is going through the United States Food and Drug Administration process to become a standard treatment protocol for horses. Dudley Hoskins, an attorney with the American Horse Council, stated, "If approved for use, the treatment would offer a way to clear horses of infection. This could be huge." The ranch was asked what they thought about the experiment. The reply was heartfelt and direct, "They saved our horses."