Researchers at the University of Kentucky Livestock Disease Diagnostic Center (LDDC) have uncovered one more piece in the puzzle that is known as mare reproductive loss syndrome (MRLS). Whatever caused early fetal losses and late-term abortions in 2001 and 2002 also has been related to a few cases of uveitis (eye) and pericarditis (heart). An abstract from a researcher at LDDC has added encephalitis (inflammation of the brain) to the health problems that occurred during the first MRLS outbreak in 2001.

The September Veterinary Pathology journal contained abstracts for the American College of Veterinary Pathologists’ annual meeting this December. Among the abstracts was one from Manu Sebastian, DVM, MS, a graduate student doing work at the LDDC. He discovered that three adult female horses tested positive for Actinobacillus species, the same bacteria that was isolated from many MRLS-associated late-term aborted fetuses. The synopsis also noted that Actinobacillus species have not previously been reported to produce encephalitis in adult horses, and these cases occurred within the four weeks of the MRLS outbreak of 2001.

Two of the mares had acute neurologic disease, and one mare had cardiac disease involving the valves, as well as having pneumonia. The brains of all three mares had observed changes by light microscopy consistent with clinical symptoms.

While the significance of this finding is not yet known, it could indicate that whatever caused MRLS was transported through the bloodstream in order to reach the brain, eyes, and heart, as well as the reproductive tract.