MRLS in Washington State?

While there has been speculation that several cases of mare reproductive loss syndrome (MRLS) happened in Washington state during the spring of 2003, the number of accessions to the state's diagnostic lab doesn't uphold that theory. Charles Leathers, DVM, PhD, professor of pathology at the Washington Animal Disease Diagnostic Laboratory, said, "From our perspective, we have not seen the numbers to make an association with MRLS. We're not minimizing any farm's losses, but we are not seeing an increase in the number of successions (animals/fetuses submitted for necropsy) to the lab."

Leathers said Kenneth Feigner, DVM, a Western Washington veterinarian who made the MRLS claims in an article that appeared both in the Washington Thoroughbred and DVM Magazine, has submitted only one fetus to the lab in the last three years. "No cause was found for that abortion, but we do know what we are looking for," said Leathers, who has worked with Lynn Harrison, DVM, head of the Kentucky Livestock Disease Diagnostic Lab on this theory of MRLS in Washington.

Leathers said samples of the caterpillars were sent to Harrison for testing. The first question was whether the caterpillars were Eastern or Western tent caterpillars, and whether there were any possible toxic fractions.

The MRLS seen in Kentucky and surrounding states in 2001-2002 is thought to be linked to Eastern tent caterpillars (ETC). The problem in Washington was suggested to be linked to Western tent caterpillars (WTC), a close relative.

It was noted in the Washington Thoroughbred article that in Kitsap and Pierce Counties, especially in 2003, there was an extreme population of caterpillars. Gary Wolbert of Wolbert's Olympic Horticultural Spray Services, told that publication that most area veterinarians believe the contamination of caterpillars to horses occurs from those floating at the surface of water troughs. He stated that 2003 was an exceptionally bad year for caterpillars.

Debra Sellon, DVM, PhD, associate professor of equine medicine at Washington State University, said she has heard the rumors, but hasn't seen anything confirmed. She said no one has called her regarding pregnancy loss, pericarditis (heart problems), or any of the other illnesses associated with MRLS in Kentucky.

Terry Fitzgerald, PhD, the "tent caterpillar guru" based at Suny University in New York who helped Kentucky researchers tremendously during the 2001-2002 MRLS outbreak, said he had had heard there was concern that Western tent caterpillars might be capable of causing abortions in mares in the Pacific northwest.

"The WTC is closely related to the ETC, so I would not be surprised if this occurred in areas experiencing outbreak populations of the caterpillars," said Fitzgerald. "We are currently experiencing a population explosion of forest tent caterpillars in New York state, and there is some concern for their potential affect on livestock.

"There have been no experimental studies with either New York or Washington state caterpillars of the sort needed to establish that caterpillars from these areas are capable of causing MRLS, but it is probably only a matter of time before such studies are conducted. The availability of funding is the main issue."

The current theory is that the setae (hairs) on the Eastern tent caterpillar (and possibly the WTC and other related species) lodge in the alimentary tract of the horse (from the mouth to the anus), causing inflammation and an entryway for bacteria normally found in the tract to enter the horse's bloodstream. That would allow infections to set up in other areas of the horse's body, including the placenta, eye, heart, etc.


About the Author

Kimberly S. Brown

Kimberly S. Brown was the Publisher/Editor of The Horse: Your Guide To Equine Health Care from June 2008 to March 2010, and she served in various positions at Blood-Horse Publications since 1980.

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