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West
Nile Virus and Horses
Q.
Has West Nile virus caused severe illness or death in horses?
A. Yes, while data suggest that most horses infected with
West Nile virus recover, results of investigations indicate that
West Nile virus has caused deaths in horses in the United States.
Q.
How do the horses become infected with West Nile virus?
A. The same way humans become infected—by the bite of infectious
mosquitoes. The virus is located in the mosquito's salivary glands.
When mosquitoes bite or "feed" on the horse, the
virus is injected into its blood system. The virus then multiplies
and may cause illness. The mosquitoes become infected when they
feed on infected birds or other animals.
Q.
How does the virus cause severe illness or death in horses?
A. Following transmission by an infected mosquito, West Nile
virus multiplies in the horse's blood system, crosses the blood
brain barrier, and infects the brain. The virus interferes with
normal central nervous system functioning and causes inflammation
of the brain.
Q.
Can I get infected with West Nile virus by caring for an infected
horse?
A. West Nile virus is transmitted by infectious mosquitoes.
There is no documented evidence of person-to-person or animal-to-person
transmission of West Nile virus. Normal veterinary infection control
precautions should be followed when caring for a horse suspected
to have this or any viral infection.
Q.
Can a horse infected with West Nile virus infect horses in neighboring
stalls?
A. No. There is no documented evidence that West Nile virus
is transmitted between horses. However, horses with suspected
West Nile virus should be isolated from mosquito bites, if at
all possible.
Q.
My horse is vaccinated against eastern equine encephalitis (EEE),
western equine encephalitis (WEE), and Venezuelan equine encephalitis
(VEE). Will these vaccines protect my horse against West Nile
virus infection?
A. No. EEE, WEE, and VEE belong to another family of viruses
for which there is no cross-protection.
Q.
Can I vaccinate my horse against West Nile virus infection?
A. A West Nile virus vaccine for horses is available through veterinarians. Horse owners throughout the US should consider vaccinating their equines. Consult your veterinarian for more details on timing of vaccination.
Q.
How long will a horse infected with West Nile virus be infectious?
A. We do not know if an infected horse can be infectious
(i.e., cause mosquitoes feeding on it to become infected). However,
previously published data suggest that the virus is detectable
in the blood for only a few days.
Q.
What is the treatment for a horse infected with West Nile virus?
Should it be destroyed?
A. There is no reason to destroy a horse just because it
has been infected with West Nile virus. Data suggest that most
horses recover from the infection. Treatment would be supportive
and consistent with standard veterinary practices for animals
infected with a viral agent.
Q.
Where can I get more information on horses and West Nile virus?
A. Visit the USDA Web site Animal
and Plant Health Inspection Service (APHIS).
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