Piroplasmosis in Texas ~ By Pauline Singleton ~ December, 2009
We have a new problem. This time, its name is equine piroplasmosis (EP for short). EP is a blood-borne disease generally spread by certain kinds of ticks. More than 300 head of horses have contracted EP in Texas. So far, all live on a ranch in Kleberg County OR once lived on that ranch. Is your horse at risk for contracting this disease? Not at this time—especially if you live in an urban or suburban setting where there are no ticks. And even if you live in a rural setting, your horse is probably not in any immediate danger. There is no need to panic, but it is time to become informed about EP.

Just because your horse or my horse is not in immediate danger of becoming ill, doesn’t mean we don’t have a problem. Just ask Darolyn Butler. She is a world-class competitor in endurance races. This month (December, 2009) she hauled ten head of horses to Florida for a race, and all had to be tested for EP before they could enter the state of Florida. The test cost $35 per horse, so the bill was $350 (and trust me, some veterinarians charge more). Florida will honor the test for 30 days. In other words, if Darolyn brings those horses back to Texas, and takes them back to Florida two months later, she will incur that expense again. A number of states, and Canada, will not allow Texas horses in without a CURRENT test for EP. How “current” is defined varies from state to state and situation to situation. The state of Oklahoma requires the test within 10 days of entry.

Darolyn hopes to compete in the 2010 World Equestrian Games, which will be held in Lexington, Kentucky. If she does, her horses will have to be tested for EP before they leave Texas, and AGAIN when they arrive in Lexington. (Yes, any venue may have their own testing requirements, which may be stricter than what states require.)

It should now be clear to you that anyone who hauls a horse out of Texas for showing, racing, breeding or any other reason, is going to incur some new expenses.

Why all the fuss? Consider Florida’s experience. In 1960, there was an outbreak of EP in south Florida. The origin is thought to be imported horses. Twenty-six per cent of infected horses died of the disease, according to the USDA. It took Florida more than a quarter of a century, and millions of dollars, to eradicate EP. Who can blame them if they don’t want a repeat of that experience? At the least, EP is a drain on the horse industry wherever it occurs, both through morbidity and mortality of infected horses, and resources spent trying to treat/control/contain/eradicate the disease.

There is good news. Several veterinarians have told me they believe that the south Texas outbreak will be contained to the ranch where it was found. As of December 8, no infected horses have been found on adjoining ranches (and yes, such horses are being tested). If you’ve received your January 2010 issue of The Horse, you perhaps have seen a map showing EP-infected horses in 12 other states, from California to Florida, and as far north as Michigan.

All of the infected horses in these other states were purchased from the Kleberg County ranch. So far, no other horses have contracted the

disease from these horses. More worrisome is the fact that there are EP-infected horses on other Texas premises (horses purchased from the Kleberg County ranch).

There is some more not-so-good news, too.  I obtained the APHIS factsheet on EP and found something interesting. That factsheet states: “EP is not endemic to the United States; native tick species do not currently carry the parasites that cause the disease.” The first question that popped into my head was “COULD our native tick species serve to spread EP if conditions are right?” A few paragraphs later, the factsheet states: “The only known vector of EP in the United States is the tropical horse tick, Dermacentor nitens, found in the southern United States. Babesia caballi and B. equi (the causative agents of EP) have been experimentally transmitted by three other U. S. tick species: D. albipictus, the winter tick; D. variabilis, the American dog tick; and Boophilus microplus, the southern or tropical cattle tick.”

So that’s four species of ticks known to be capable of spreading EP.

As one would expect, field workers have been collecting ticks from infected horses on the ranch in question. These ticks are being sent to a USDA research facility in Pullman, Washington for study. So far, there has been one surprise. Of the ticks collected and studied so far, the one tick that has been confirmed as able to transmit EP is not on that list of 4 ticks mentioned in the last paragraph. The culprit is the Cayenne tick, Amblyomma cajennense.

So our list of potential vectors, turned out not to be a complete list.  Is it complete now? Time will tell. Studies are ongoing, and the results should be interesting.

Do we know the range of the ticks capable of spreading EP? Are they limited to south Texas? Do any of us know enough about ticks?

Another troubling detail about the current outbreak is that its source is unknown at this time.

State and Federal agencies continue to investigate the outbreak, trace horses, study ticks, and no doubt are making plans for how to best respond to the situation in the months to come.

We’ll try to keep you posted.

Click on Piroplasmosis for more information. We shall try to add to it as we acquire more information. Last updated January 2, 2010.