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Courtney Terry, DVM Courtney Terry is a 24 year
old graduate of Mississippi State University's College of Veterinary
Medicine. Courtney competed in both the 2002 Miss Rodeo America Pageant and the 2002 Miss Rodeo USA Pageant.
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by
Courtney Terry, DVM Related Article:
West Nile Update West Nile virus (WNV) is one of the fastest-growing threats to horses nationwide. First documented in cities along the coast of the eastern US, the virus has rapidly spread westward. Leading equine industry experts predict that WNV will soon have a coast-to-coast presence. This dangerous disease is carried by infected birds, which spread it as they migrate across the country. Mosquitoes become infected after they take a blood meal from an infected bird. The infected mosquitoes then transmit the virus to other birds and mammals, including people and horses. Answers to some commonly asked questions: How
is West Nile virus transmitted? The
typical transmission cycle goes from bird to mosquito;however, mosquitoes
can infect birds and vice versa. Mosquitoes become infected when they bite
birds that are carrying WNV. The virus can be carried by many different
species of birds, including migratory birds such as ducks and geese,
enabling the virus to be spread over a very large area rapidly. People
and mammals are “dead-end” hosts. This means that the virus level in a
mammal’s blood generally is not sufficient to transmit the virus back to
a mosquito, thereby ending the cycle. Horses and people bitten by infected
mosquitoes may test positive for WNV, even though they may not become ill. How
does the virus affect horses? West
Nile virus causes fatal encephalitis in about 40% of equine cases. What
are the clinical signs/symptoms in an infected horse? Clinical signs of
WNV include fever, stumbling/tripping, muscle weakness/twitching, partial
paralysis, head pressing, inability to rise, convulsions, and coma. It is
important to realize that there are SEVERAL diseases that can cause
similar signs in horses; therefore, it is very important that you consult
your veterinarian to obtain a definitive diagnosis of WNV. Can
the virus be spread from one horse to another via shared stalls, tack,
feed buckets, etc? No. West Nile
virus is transmitted by a bite from an infected mosquito. How
is West Nile virus diagnosed? WNV is diagnosed via a blood sample submitted by a veterinarian to a laboratory for testing.
Will
horses that have been vaccinated test positive for WNV? It IS possible for a horse
that has been “exposed” to the virus, by vaccination to test positive
for WNV on certain tests. (This phenomenon is called cross-reaction and
depends on whether an ELISA or IgM laboratory test is used.)
A trained laboratory technician can usually tell the difference
between a test indicating that an animal that has merely been exposed and
one that is truly infected.
Can
West Nile virus be prevented? There is a
vaccine now available for West Nile virus. Healthy horses should receive
two doses three weeks apart initially, followed by annual revaccination.
This vaccine is available to and should be administered ONLY by licensed,
practicing veterinarians. (It is important that the vaccine be
administered by a veterinarian so that there is a record of which horses
have been vaccinated. This becomes important when differentiating a
positive test from a “vaccine positive” in a horse that is showing
signs of illness.) At
what age should foals be vaccinated? Foals should be
vaccinated for West Nile virus beginning at 3-4 months of age. Can
humans be infected by contact with an infected horse? No. West Nile
virus is transmitted to people only through the bite of an infected
mosquito. Do
all infected horses die? No.
However, up to 40% of horses that have been diagnosed with WNV have died
or been euthanized. Horses that are very young, old, or have an impaired
immune system are most susceptible to the virus.
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