Eastern tent caterpillars implicated in swine abortions

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Eastern tent caterpillars can interfere with more than equine reproduction. Recent experiments show that these caterpillars can cause abortions in pigs, say University of Kentucky researchers.

Eastern tent caterpillars were first implicated in causing mare reproductive loss syndrome in 2001 and, since then, further research has supported this theory. Karen McDowell, PhD, an associate professor at the University of Kentucky's Department of Veterinary Science, says they conducted experiments in swine to study whether caterpillar exposure could cause fetal loss in other species. They chose pigs because of the similarities to horses in fetal development and placentation. It also offered an opportunity to study the disease in a litter-bearing species.

The researchers collected eastern tent caterpillars in central Kentucky and then mixed these caterpillars into swine feed. They chose 10 pigs in mid-gestation of their first pregnancy, and provided five with normal feed and the other five with feed that contained caterpillars. Two of the five pigs fed caterpillars aborted their entire litter, whereas the five control pigs had normal pregnancies.

Investigators euthanatized the pigs and, on further examination, isolated Streptococci from the fetuses of all pigs fed caterpillars, whether or not they were aborted, and from the fetuses of one control pig. The bacteria isolated from the control fetuses were less numerous and of a different strain than those isolated from the fetuses of ETC-treated gilts. In addition, only pigs that ate caterpillars had the larvae's setae, in their alimentary tracts. The researches do not know whether the setae or bacteria caused the abortions.

Dr. Tom Burkgren, executive director of the American Association of Swine Veterinarians, says that he doesn't know of any reports of eastern tent caterpillars causing problems in the swine industry. Dr. McDowell says that she also doesn't know of any instances, but wonders whether it could be a problem on small farms where pigs are housed outside. Does she think caterpillars could cause problems for other animals?

"I don't have a crystal ball, so I can't really answer this question," she muses. "I wouldn't be surprised if other animals could be affected, especially ones that don't have much transplacental transfer of antibodies." If a bacterium were indeed the culprit, fetuses without antibodies would have less chance of surviving.