There is new evidence that the setae (hair-like projections) on Eastern tent caterpillars (ETC) can become embedded in the submucosal lining of the alimentary tract (from the mouth to the colon) of animals and cause microgranulomas (small, localized areas of inflammation only visible under a microscope). These sores could possibly allow bacteria normally found in the alimentary tract access to the circulatory system. Two recent research projects pointed to this discovery and a potential link to mare reproductive loss syndrome (MRLS).

Early in MRLS in 2001, researchers at the University of Kentucky’s (UK) Livestock Disease Diagnostic Center (LDDC) noticed an unusual abundance of a couple of families of bacteria in aborted fetuses (Streptococcus and Actinobacillus). These bacteria are normally found throughout the alimentary tract of horses and naturally occur in the environment. However, there was never clear evidence how these bacteria were linked to MRLS.

In the first setae experiment headed by Karen McDowell, PhD, of UK’s Gluck Equine Research Center, pigs were fed ETC in an effort to cause abortions similar to MRLS in broodmares. Abortions did occur as a result of feeding ETC to the pregnant pigs, but more importantly, Neil Williams, DVM, PhD, of the LDDC, who performed the histological (tissue) examinations of the pigs used in the experiment, noticed multiple small, localized areas of inflammation in some of the pigs. He discovered that all five pigs which had been fed caterpillars had these microgranulomas and none of the pigs with a diet free of ETC had the lesions.

Further study showed that the microgranulomas contained hair-like fragments identical to ETC setae