EQUINE | International News
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to surgical intervention. CSM occurs primarily in
young horses (3 months to 1 year of age) where it
is a multifactorial disease. In older horses, CSM
is often secondary to osteoarthritis of vertebral
articular process joints.
The neurologic exam for suspect EPM horses
shows asymmetric ataxia, often with upper and
lower motor neuron signs and muscle atrophy.
Sarcocystis neurona is the most common cause of
EPM, but Neospora hughesi infection can also cause
similar clinical signs.Several studies of S. neurona
demonstrate that horses residing in states with
opossums have an exposure rate of 33% to 53%.
The exposure rate for N. hughesi appears to be
much lower, although less epidemiologic data is
available for this organism. Risk factors for S. neu-
rona infection include age (< 5 and >13 years), time
of year (summer and spring more than winter),
whether previous cases had been recognized on the
farm, presence of a wooded area, and presence of
opossums on the farm. Prevalence of the disease
was reduced on farms where wildlife had little or
no access to feed and if a creek or river was on the
premises. Diagnosis of EPM remains a challenge
and should begin with physical and neurological
examinations. This is followed by measurement of
antibodies against the causative organisms in blood
and CSF. Unfortunately, the only definitive test for
EPM is a postmortem examination.
The third common cause of spinal ataxia in
horses is equine degenerative myeloencephalopa-
thy (EDM). This condition has been recognized
in several breeds and has a familial predisposition.
EDM is caused by oxidative damage to propriocep-
tive relay tracts, thus measurement of vitamin E
has been used as a marker for this condition. More
recently a genetic marker has been associated with
the disease and genetic testing has proved valuable.
Equine herpesvirus 1 myeloencephalopathy
(EHM) is an infrequent but serious outcome of
equine herpesvirus 1 infection. Although the vi-
rus has been recognized for a long time, a link to
neurological disease was only made in the past fifty
years. More recently, a point mutation in the virus
has been identified that allows it to replicate rapidly
and results in a higher frequency of neurologic dis-
ease. Damage to the nervous system develops near
infected blood vessels, which results in “stroke-like”
episodes. The disease usually follows an initial
phase of viral replication in the respiratory tract
and peripheral blood mononuclear cells. Viral
replication also occurs in respiratory epithelium,
gonadal cells, and tissues of the gestating fetus.
Infection can result in fever, respiratory disease,
weak foals, abortion, and neurological disease.
Neurologic signs often include ascending paralysis
with urine dribbling, loss of anal tone and control,
poor tail tone, and pelvic limb weakness.Diagnosis
of EHM is easier to establish when several horses
on the same premises present with fever, followed
by ataxia and urine dribbling and in some cases
abortion. When spinal fluid is collected it often
appears xanthochromic as a result of the vascular
damage leading to increased protein but no in-
crease in cell count. Beyond this, diagnosis can
be established by recognition of clinical signs and
positive EHV-1 PCR results of a nasal swab and
buffy coat. Confirmation of the disease is by virus
isolation in cell culture.
Recognition of specific clinical signs, anatomic
localization of lesions, and utilization of diagnostic
tests can help differentiate the common neurologic
diseases.
CONTACT:
Stephen M . Reed, DVM, Dip ACVIM
sreed@roodandriddle .com
(859) 233-0371
Rood and Riddle Equine Hospital
Lexington, KY
Traceability of Equine Microchips
F
or years, equine owners have been implant-
ing microchips into horses for unique and
unalterable identification. While the safety and
practicality of this practice is well-established,
there is little information available about trace-
ability of microchips. Given the long lifespan of
horses, the ability to trace microchips over many
years is necessary.
Reasons to trace microchips are few, but vital
when encountered. Regulatory officials use the
microchip of a horse involved in a disease investi-
gation to trace back to additional exposed horses
or premises. First responders to natural disasters
have significant challenges in identifying owner-
ship of displaced horses. Individuals searching for
a lost or stolen horse have a critical reliance on the
• Volume 20 Issue 1 | April 2018 •
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