MARE REPRODUCTIVE LOSS SYNDROME, EQUINE - USA: (KENTUCKY)

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Date: 14 May 2010
Source: Horsetalk [edited]



Four dead late or full-term foetuses taken for examination at the
University of Kentucky's Livestock Disease Diagnostic Centre showed
signs consistent with mare reproductive loss syndrome (MRLS). The
syndrome is linked to the accidental ingestion of eastern tent caterpillars.

The university warned in mid-April 2010
() that
caterpillar numbers were up for the 3rd consecutive year and advised
horse owners to reduce the chances of pregnant mares ingesting the
caterpillars.

The disease centre said the fetuses and foals had lesions and
bacterial isolates consistent with the syndrome. "All were either
term-foals or late-gestation fetuses," it said. "The cases occurred
as single losses on different central Kentucky farms. The 1st case
was submitted on 1 May 2010, and these cases correspond temporally
with MRLS cases occurring in prior years."

During the 2009 foaling season, about 12 cases of MRLS foal losses
were diagnosed.

Kentucky horse owners have been advised to check wild cherry and
related trees for eastern tent caterpillar activity to determine
whether management is necessary.

--
Communicated by:
ProMED-mail

[Mare reproductive loss syndrome is a real syndrome which remains
somewhat elusive but which has come to be recognized as strongly
associated with the eastern tent caterpillar.

This syndrome includes early fetal loss, late fetal loss, uveitis,
pericarditis, and encephalitis, [from] tissue penetration by septic
barbed setal fragments (septic penetrating setae) from eastern tent
caterpillars (_Malacosoma americanum_). Once ingested, these barbed
setal fragments migrate through moving tissues, followed by rapid
hematogenous spread of bacteria, bacterial emboli, and/or septic
fragments of setae (septic penetrating setal emboli), collectively
referred to as septic materials.

Pathogenic bacteria, therefore, enter the horse as hitchhikers on or
in the caterpillar setal fragments, and MRLS is caused by 1) the
barbed setal fragments' ability to penetrate moving tissues,
including blood vessels, releasing septic materials which rapidly
distribute hematogenously; 2) the high sensitivity of the pregnant
mare to bacteria from such septic materials introduced into the
uterus, fetal membranes, or fetal fluids; 3) the unusually broad
spectrum of bacterial pathogens carried on or in the setal fragments;
and 4) the less effective antibacterial responses in certain
susceptible extracellular fluids (e.g., fetal, ocular, pericardial,
and cerebrospinal fluids).

These caterpillars are very small and easily consumed in the grass as
they drop off the trees surrounding the pastures. Some years are
worse for these caterpillars than other years. However, it takes 10
or less of these extremely tiny caterpillars to affect a 680 kg (1500
lbs) pregnant mare.

The eastern tent caterpillar occurs throughout the eastern United
States west to the Rocky Mountains and north into southern Canada. It
is native to the region, and references to it as a tree pest date
back to early colonial times from the mid-1600's. However, references
to it as a problem for horses seem to have begun about 2000-2001. A
photo of the caterpillars may be seen at:
.

The eastern tent caterpillar is largely resistant to many
insecticides. This creature is a pest to many, especially the equine industry.

Portions of this comment have been extracted from
and
.
- Mod.TG]
................................................tg/msp/dk

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