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EQUINE MATTERS
West Nile
Virus
Andrea Kilduff-Taylor VetMB BA MRCVS,
608 Farm and Equine
A number of outbreaks of West Nile Virus
in southern France in 2015 have caused
concern, but should we really be worried
?
West Nile Virus is a virus mainly affecting
birds, humans and horses that is transmitted by
mosquitoes (especially Culex species). A bird
with the virus cannot pass the disease directly
onto another bird. Instead, a bird with the
disease is bitten by a mosquito; the mosquito
then bites another bird, passing on the
disease.
Horses and humans are ‘dead-end hosts’,
meaning that they do not develop high levels
of the virus in their bloodstream once
infected. This means that a mosquito biting
an infected horse or human cannot become
infected and pass it onto another animal.
So why worry about the disease at all
?
Well,
in horses, the disease can be deadly. About
10 to 39% of infected horses will develop
clinical signs, and once signs have
developed, around 30% of these horses will
die or require euthanasia. Signs can range
from flu-like symptoms (lethargy, fever, lack of
appetite) to severe neurological signs. These
can include incoordination, muzzle twitching,
vision impairment, circling, head pressing,
paralysis, convulsions and death. Treatment is
basically supportive, including pain relief,
fluids and padding around the stable to
prevent injury.
Where is this disease located and do we
need to worry about it in the UK
?
West Nile
Virus occurs in quite a lot of places:
●
Africa
●
Europe
●
Middle East
●
North America
●
Central and South America
●
West Asia
The most likely route of entry into the UK would
be via migrating birds. We definitely have the
correct mosquito species in the UK to transmit
the disease, so therefore it is probably only a
matter of time before the disease is detected in
the UK. The transport of horses into the UK
presents zero risk if we remember the fact that
horses are dead-end hosts and can’t pass on
the virus.
A bit of history:
West Nile Virus was first identified in the blood
of a woman in 1937 in Uganda. It spread to
cause outbreaks in Egypt and Israel during the
1950’s. In the 1990’s, the way the virus
behaved seemed to change: a number of
outbreaks occurred in the Middle East and
southern Europe with a higher percentage of
people getting neurological disease than
before. In 1999, West Nile Virus reached
New York City in the USA, causing a huge
epidemic that spread across the whole country
over the next few years. It affected birds,
horses and humans. Since 1999, over
25,000 cases of West Nile Virus encephalitis
(inflammation of the brain) have been reported
in US horses. Fortunately, the situation in horses
in the USA has improved greatly since the
introduction of vaccines against the virus.
Prevention:
There are vaccines available that are licensed
for horses in the UK and Europe. These pro-
vide good immunity against the virus. Presently
there is no need to routinely vaccinate horses
in the UK. However, it would make sense to
vaccinate horses travelling to areas where
West Nile Virus is common.
EXOT I C D I SEASES
Veterinary surgeon
Andrea Kilduff-Taylor
XLEquine practice
608 Farm and Equine