No Horsin' Around With These Tests

Imagine you are returning from an exciting European vacation only to be stopped at the airport by health officials because you had visited an area that had a contagious disease. Even though you feel fine, you're forced to spend weeks alone in the hospital while doctors poke, prod, and test your body for any hidden signs of the disease.

That's what horses often have to go through while being transported from country to country. But now there are tests to make this less of an ordeal for the animals.

The tests check for two tiny blood parasites that cause the horse disease, piroplasmosis (PEER-oh-plas-MO-sis). The scientific names of these parasites are Babesia equi (BUH-bess-eya EQ-wee) and Babesia caballi (BUH-bess-eyuh CUH-ballee). In some countries, horses often carry the parasites but don't get sick. American horses aren't always so lucky, because they're not used to the parasites. Ticks pass the piroplasmosis parasites from one horse to another by feeding on their blood.

Piroplasmosis isn't found in the United States. But when taken to other countries to run in races, the Olympics, or other competitions, American horses also run the risk of being bitten by parasite-carrying ticks. So, before foreign horses are allowed into a new country, or to return home, officials must check the animals to make sure they're healthy.

Until now, such officials didn't have a reliable way of detecting the two parasites. This sometimes meant having to run two tests because the first one didn't tell whether a horse had the disease. Or, if answers weren't clear-cut, the horse had to stay under quarantine for 10 days for retesting. The horse, meanwhile, couldn't go anywhere or do much of anything.

Another problem with earlier tests: They sometimes led officials to believe a horse was infected even though it didn't actually have the disease. These earlier tests also couldn't tell one piroplasmosis parasite from another. This complicated veterinarians' treatment strategies for one of the parasites.

At ARS' Animal Disease Research Unit in Pullman, Washington, scientists searched for easier, more accurate methods of checking for the two horse parasites.

Veterinary medical officer Donald P. Knowles and colleagues developed two tests--one for each parasite. First, they discovered specific proteins in B. equi and B. caballi that could be used to identify only those specific parasites. They then developed a monoclonal (mon-oh-CLONE-al) antibody for each parasite protein.

In the two tests--called CI-ELISA (for competitive-inhibition enzyme-linked immunosorbent assay)--a horse's blood sample is put on a special plastic plate. Scientists then add in the monoclonal antibodies.

Here's a play-by-play of what happens next when scientists check for the B. equi parasite: If the horse blood has natural antibodies already in it, these antibodies attach to B. equi proteins on the plate's surface. However, this prevents the monoclonal antibodies from attaching to those same proteins.This also prevents another part of the monoclonal antibody, called an enzyme, from causing a color change on the plate's surface. When the plate's color does not change, the test is said to be positive, meaning the horse IS infected by B. equi.

If the horse blood doesn't have natural antibodies, the B. equi proteins attach to the monoclonal antibodies instead. When this happens, the enzyme kicks-in and changes the color of the plate's surface. This means the test is negative, and that the horse IS NOT infected by B. equi. But it may be infected by B. caballi. So, the other test must be done as well.

Once regulatory approval is granted on the new test, a Pullman, WA, company called VMRD plans to produce it for commercial use.

-- By Kathryn Barry Stelljes, formerly Agricultural Research Service, Information Staff, along with Jan Suszkiw, ARS Info.