One Case of MRLS Confirmed in Florida; Tests Pending

One confirmed case and two suspect cases of mare reproductive loss syndrome have been diagnosed in Alachua County, Fla., according to Dr. Dana Zimmel of the University of Florida's College of Veterinary Medicine.

One mare produced a septic foal March 18 that was euthanatized after two days of intensive treatment. University of Florida pathologist Dr. John Roberts, who worked at the University of Kentucky Livestock Disease Diagnostic Center during the MRLS outbreaks in Kentucky in 2001-02, concluded the pathology on that foal was consistent with MRLS.

Samples from an earlier abortion on the same farm were re-examined and showed indications of MRLS; Roberts has termed that case suspect. The third case was a foal born March 26 that was treated in the neonatal intensive care unit at the University of Florida for 12 hours before being euthanized. Though complete histopathologic evaluation won't be completed until March 30, Roberts said the pathology was consistent with MRLS.

In the Kentucky outbreaks of 2001-02, there was a strong association between the presence of unusually large numbers of Eastern tent caterpillars and MRLS. Pregnant mares experimentally fed caterpillars typically aborted within several days. Eastern tent caterpillars were found on the Alachua County farms and have been collected for future study.

Research has been ongoing since the Kentucky outbreak began. The most recent information on the state of the research was published by The Horse in December 2005. In that article, Dr. Bruce Webb, a University of Kentucky entomologist who has been studying MRLS, said: "We can prevent mare reproductive loss syndrome as we experienced in 2001 and 2002 by keeping horses away from caterpillars."

MRLS -- which historically can cause late-term abortions, early-term fetal losses, pericarditis (heart problems), unilateral endophthalmitis (problem in only one eye), hyphema (blood in the eye) in foals, mouth ulcers, and laminitis -- was first seen in Kentucky and surrounding states (and as far north as Canada) in 2001, with a reduced incidence in 2002.

MRLS was first recognized as an outbreak of fetal deaths, foals born weak, and late-term abortions in Kentucky the first weekend in May of 2001, but the outbreak was traced back to April 23 of that year. All breeds were affected.

Because of the high number of pregnant Thoroughbred mares in the area and the records kept on those horses, statistics on that breed reflect what was going on in the general horse industry. In 2001, there were 516 late-term abortions and 2,998 early fetal losses in Kentucky's Thoroughbred industry alone. There also were about 60 cases of pericarditis and 50 cases of unilateral uveitis reported in Central Kentucky horses.

More than 30% of the anticipated 2002 Thoroughbred foal crop in Kentucky was lost due MRLS. The economic cost to the state from losses suffered by all horse breeds was estimated at nearly $336 million, according to a study commissioned by then Kentucky Gov. Paul Patton and conducted by the University of Louisville's Department of Equine Business.

The cause was never absolutely defined, but most experimental models showed a strong link of MRLS to the Eastern tent caterpillar. There was a huge hatch of caterpillars in 2001, with a large, but reduced number, that hatched in 2002.

Dr. Terry Fitzgerald, the "tent caterpillar guru" based at The State University of New York who helped Kentucky researchers during the 2001-02 outbreak, said March 28 that where there are apple and cherry trees, there will be Eastern tent caterpillars, though mid-Florida marks the far southern extreme of the caterpillar's distribution.

"They are common in North Florida and Georgia," he said.

It has been reported that the caterpillars have a 10-year cycle of high numbers then nearly disappear for a time before building back up to high numbers. However, Fitzgerald said there is really no basis for that report.

"They have an irregular cycle," he said. "In one area it was 30 years between, or it could be three or four years. The large number seen in Kentucky (in 2001-02) might never come back, especially since you cut down all the cherry trees (the Eastern tent caterpillar's favorite feeding and nesting site)."