Equine Piroplasmosis (EP) is a disease we have not spent much time thinking about. EP is a tick-borne protozoal disease affecting the equine species —- horses, donkeys, mules and zebras. In fact, wild zebras are considered to be an important reservoir for the disease in Africa. The protozoal agent carried by ticks is either Theiler equi or Babesia Caballi. Those organisms, once they enter the body of their equine host, set up residence in the animal’s red blood cells. The problem comes when the immune system begins to drop laser-guided bombs on the infected red blood cells. The collateral damage is not a pretty sight.
Although EP is endemic (meaning the disease normally occurs) in 90 percent of the world, the United States, Canada, Australia, Japan, England and Ireland are not considered to be endemically infected. It is more prevalent in the tropics and sub-tropical areas of the world…probably because ticks enjoy the climates in those regions and are more numerous there. The United States did experience an epidemic in Florida during the 1960s after the introduction of horses from Cuba. During that outbreak, about 20 percent of the horses on the Brighton Indian Reservation died. I don’t care who you are, that is a high mortality rate. After that there was an extensive tick elimination program in place and, in 1982, the United States was considered to be EP free. (Some of you may remember my article about tick fever in the November 2008 issue. I am still trying to figure one good thing ticks are responsible for.)
In general the United States does not allow horses that test positive for EP to come into this country. Please bear in mind, testing positive does not always mean the horse is infected. It means an exposure has caused the immune system to build antibodies against the PE organism. On the other hand, a negative test may not always mean the horse is negative. It may just mean antibodies were not circulating in the blood at detectable levels at the time the blood was drawn. Anyway, in the 1996 Olympics in Atlanta, some horses that tested positive for detectable PE antibodies were allowed to compete in the stadium events: jumping and dressage. Those horses were housed in isolated stalls with strict tick control in place. Additionally, no PE positive horses were allowed to compete in field events like cross-country races because of the potential for tick exposure. Similar measures were taken by Australia in 2000 when the Summer Olympics were held in Sydney.
Referring back to the title of this article, PE is out there on the radar screen. Those of you who visit some of the more popular horse websites like thehorse.com may be aware, in October 2009, a seven-year-old mare in Texas became ill and tested positive for EP. Follow-up testing on the ranch found over 30 horses to be positive. Afterward, traces to possible exposed horsed began. By November 30, over 1,200 horses had been tested with 342 horses testing positive. 289 of those horses are in Texas. One horse originating in Texas was traced to Alabama and has tested positive. Besides Texas and Alabama, at least 10 other states have positive horses. These animals and farms are under quarantine as we move through the process to deal with the disease.
Clinical signs of the disease mimic many other diseases. (How many times have you read that statement?) Horses infected with EP may exhibit loss of appetite, lack of energy and weight loss. Other signs include anemia, rapid breathing and rapid pulse, colic or diarrhea, kidney damage or even kidney failure, and swelling of the lower limb. Foals may become infected in the uterus and be born weak and anemic. And while some horses that become infected may spontaneously clear the organism over a period of several months, others become long-term or chronic carriers. When stressed, these carrier horses may show signs of the disease again and become more likely to spread the disease.
There is no vaccine for the disease. Strict tick control is absolutely vital to controlling the disease. Although most articles include the use of a single hypodermic needle on multiple horses for vaccines or treatment as a means of spread, I will just say, if you are doing that, you have larger problems than EP. In fact, if you are using a dirty needle on horses…well, we will save that for another article.
In the spring of 2010, Kentucky will host The Kentucky International Equine Summit, the likes of which the equine industry has never experienced. There will be horses from all over the world. You can bet that EP issue has my counterpart, Dr. Bob Stout, and his staff working overtime to make sure EP does not become an issue for them.
Be assured, we are working with USDA to make certain EP or any other new disease does not come into Alabama and establish residence. If you have questions about your horse’s health, we encourage you to contact your local veterinarian or feel free to call us on issues involving unusual disease signs.