Equine piroplasmosis is a parasitic blood disease that affects horses in many regions of the world. The disease is also known as babesiosis and bilary fever. It is transmitted by species of ticks affecting horses that were introduced into the United States around 1958 with importation of horses from Cuba to Florida. Equine and is now considered endemic in some area of the Southeastern United States.
Tick-born disease in horses
Piroplasmosis in horses is similar to malaria in humans, with insects transmitting the infectious agent that attacks and destroys red blood cells.
Piroplasmosis in horses is similar to malaria in humans, with insects transmitting the infectious agent that attacks and destroys red blood cells.
So when Washington State University and U.S. Department of Agriculture veterinary scientist Don Knowles got word two years ago that a rare but deadly infection was discovered among a group of horses in south Texas, he felt a jolt of adrenaline. Not only were the horses infected with a parasitic disease similar to malaria in humans, but the epicenter of the outbreak was at no ordinary ranch.
It was the King Ranch, legendary for its world-class quarter horses, including former winners of the Triple Crown and Kentucky Derby. The 825,000 acre family-owned estate that stretches across four counties is one of the largest and most famous ranches in the world.
As leader of the USDA's Animal Disease Research Unit at WSU, Don Knowles had a Texas-sized riddle to solve.
Parasitic storm in horses
Equine piroplasmosis is so feared in the U.S. that the government bans horses that test positive from entering the country. Until the outbreak in Texas, only a few sporadic cases had ever been reported.
"We had regarded piroplasmosis as a foreign animal disease and suddenly here it was on U.S. soil, with not one or two cases but nearly 300 -- all concentrated at a ranch recognized for exemplary management practices," said Dudley Hoskins, an attorney with the American Horse Council in Washington, D.C., at that time. "To say we were concerned would be an understatement."
Piroplasmosis, also called equine tick fever, is transmitted to horses through the bite of a tick that carries either the Babesia caballi or Theileria equi parasites in its saliva. Similar to malarial parasites that infect humans, these pear-shaped creatures travel through the horse's circulatory system, multiplying, drilling through red blood cells and multiplying some more.
No treatment, painful options for horse owners
Many infected horses exhibit little more than cold-like symptoms, but in regions where piroplasmosis is uncommon -- such as the U.S. -- horses have no natural resistance to the disease. Unimpeded, the parasites proliferate and destroy blood cells, triggering fever, anorexia and anemia.
Before the outbreak in 2009, no standard treatment existed. If a horse tested positive for piroplasmosis, the owner had three government-mandated options to keep the disease from spreading: euthanize, quarantine or ship the horse out of country.
Armed with two decades of piroplasmosis research and a team of scientists from his USDA unit and WSU, Knowles not only contained the outbreak but he and colleague Glen Scoles also identified a new blood-sucking culprit that had spread it.
"Prior to that outbreak, we knew of two tick species capable of transmitting the disease. There, we discovered a third," said Knowles.
He and his team identified the cayenne tick as the predominant carrier, a finding so important that the group later published a paper about it in the journal Emerging Infectious Diseases.
It's likely a cayenne tick snagged a ride on an infected horse years before the outbreak, drawing parasites in through its blood meal then moving on, injecting and infecting other horses, said entomologist Scoles who, after the outbreak, proved that the cayenne species was involved.
The outbreak at King Ranch "could have coincided with climate factors which, in turn, caused an increase in tick numbers," said Scoles.
"They saved our horses"
All said and done, Knowles and his team did more than identify a new eight-legged transmitter of piroplasmosis and develop an internationally accepted test to diagnosis it.
"How about, 'They saved our horses?' " said Delaney of King Ranch.
With high doses of imidocarb dipropionate, a drug used to treat certain diseases in cattle, "The parasites appear to be eradicated. All of our horses are healthy," he said.
The outcome of administering the drug was so successful that, after subsequent trials, it is now being evaluated as a standard treatment protocol in the U.S.
This edited news story is taken from materials provided by Washington State University and reprinted in Science Daily. The original article was written by Linda Weiford