EQUINE BRUCELLOSIS
Equine brucellosis is caused by Brucellaabortus
and most commonly manifests as fistulous withers in horses,
which can be a source of exposure to humans. Clinically,
brucellosis may also be associated with poll evil, nonspecific
lameness due to joint infection or, rarely,
late abortions in mares. Infected horses may not show
signs of the disease for as long as two (2) years post-exposure.
Fistulous withers has been reported sporadically in the
United State
for over 70 years. The incidence of B.abortus infection
in fistulous withers has progressively declined over the
years. In the 1930s, 82% of the horses with fistulous
withers had positive titers for B. abortus(titer>
1:50.) In the
1940s, the prevalence rate dropped to 73%. In recent
review, the prevalence of sero-positive B.abortus
reactors declined to 37.5%. Much of the decline in equine
brucellosis is attributed to the Brucellosis Eradication
program for cattle. Today, the highest prevalence of
equine brucellosis is in Texas
that has Class B status for brucellosis, the incidence
is also higher in some Class A states, such as Florida,
Alabama,
and Louisiana,
as compared to the brucellosis-free states. Indiana
is a brucellosis-free state and has not had a reported
case of equine brucellosis in the past two years. However,
Brucellaabortus should be a differential
diagnosis for Indiana
horses with fistulous withers, especially if they have
been transported from Brucellosis positive regions.
Although no brucellosis eradication program exists specifically
for equine, standards for diagnosis and treating B.abortus
associated fistulous withers have been established as means
to monitor possible bovine brucellosis and to help protect
the public from exposure to this zoonotic pathogen. The
Animal and Plant Health Inspection Service has mandated that
a sample of the infected site be obtained for culture in all
cases of fistulous withers. Isolation should be done at
a federally accredited facility such as the ADDL. Because
B. abortus is difficult to isolate, horses with fistulous
withers should also be serologically tested for evidence
of antibodies to B. abortus. Whole blood or
serum may be submitted. Titers (plate agglutination) greater
than or equal to 1:50
has generally been considered positive. More recent investigators
propose that a plate agglutination titer of 1:100 or 1:160
or less to be negative for Brucella infection. In
the state of Indiana,
horses with confirmed B. abortus infection must be
reported to federal authorities.
REFERENCES AVAILABLE UPON
REQUEST
Gloria S.McFadden-Class of '94
Edited by W.G.VanAlstine
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