REVIEW paper: mare reproductive loss syndrome.

This research article examines an epidemic known as the mare reproductive loss syndrome (MRLS) which caused early and late fetal losses, fibrinous pericarditis, and unilateral uveitis in mares during 2001 and 2002, with associated economic losses. The study suggests that the syndrome might be linked to eastern tent caterpillars, and gives insights into potential hypotheses for how this interaction may occur.

Introduction to MRLS

• The article is centered around an epidemic that occurred during 2001 and 2002 that resulted in mare reproductive loss syndrome (MRLS), characterized by early fetal loss (EFL), late fetal loss (LFL), fibrinous pericarditis (inflammation and fluid in the cardiac sac), and unilateral uveitis (inflammation of the middle layer of the eye).
• Similar, but less intense, occurrences were reported from southern Ohio, West Virginia, and Tennessee during the same time frame.
• The estimated economic loss from the syndrome in 2001 and 2002 approximated $500 million.

Clinical and Pathological Findings

• The researchers discovered that both EFL and LFL were characterized by the absence of distinct clinical signs in aborting mares, complicating diagnosis.
• They identified nonhemolytic Streptococcus species and Actinobacillus species accounting for 65% of the organisms found in fetuses examined in postmortem during the MRLS outbreak in 2001 and 2002.
• In cases of LFL, pathologic findings included bronchopneumonia and funisitis (inflammation of the umbilical cord), while no remarkable findings were noted in EFL.

Link to Eastern Tent Caterpillars (ETC)

• Epidemiologic studies, conducted in 2001, revealed a correlation between the presence of eastern tent caterpillars (ETC) in pastures and MRLS incidents.
• Experimental exposure of pregnant mares to ETC, or administration via food or stomach tube, reproduced EFL and LFL, supporting the hypothesis of a causal link.
• The same experiments in mice, rats, and goats did not yield similar results, indicating species-specific susceptibility.

Hypotheses for MRLS

• The first hypothesis is that an ETC-related toxin results in MRLS, with subsequent opportunistic bacterial invasion of the fetus.
• The second hypothesis proposes a disruption of gastrointestinal mucosal integrity by ETC hairs, leading to a bacteremia (bacteria in the blood) and consequent MRLS.
• The supporting evidence for these hypotheses is based on outbreaks of similar abortion storms in Australia in 2004, where caterpillar exposure was identified as a risk factor, and in Florida and New Jersey in 2006.