The Rural Voice, 2003-05, Page 32More than a
pest now
With the invasion of West Nile Virus into Ontario,
a mosquito bite holds the potential to be more than
just an itch to be scratched.
By Keith Roulston
Of all farm livestock. horses are in most..
-danger from West Nile Virus':,
So the warm weather finally
arrives and so does the breeding
season for mosquitoes. In the
past this has just been a nuisance but
with the arrival of West Nile Virus,
the pesky insect has also become a
potential source of illness for farmers
and their livestock.
The disease, which mosquitoes get
by biting infected birds and then pass
on to humans, has swepted across
North America like a hurricane since
it first appeared in the New York
area in 1999. While WNV had first
been recorded in Uganda in 1937,
and eventually spread throughout
Africa and Europe, this early version
of the disease did not kill birds. But
in 1998 a new, more virulent strain
showed up in Israel that did kill
birds. By the next summer it had
somehow reached New York, first
showing up in birds, then humans.
By August 2001 Ontario had its
first confirmed case in birds when a
dead bird was found in Essex County
and tested positive. By last year the
28 THE RURAL VOICE
disease had been confirmed in dead
birds throughout most of southern
Ontario.
Worse, the spread to the human
population was more serious than
anyone realized. Public health
officials tried not to exaggerate the
dangers of the virus and ended up
being accused of not giving it enough
attention. As of April 11 this year,
they have confirmed 307 cases of
WNV in humans in Ontario with a
further 83 probable cases. Three
deaths have been attributed to WNV
while four others are listed as having
been from the virus contributing to
other problems in the death while
five others may be linked to
problems associated with the disease
and five deaths remain under
investigation.
Almost as frightening are the
stories of lingering effects of the
infection for some survivors,
including paralysis.
In midwestern Ontario, one case
each of human infection were
reported in Bruce -Grey and Perth and
three cases in Waterloo. But then it
wasn't until mid -summer last year
that deaths of birds were even
reported in these areas.
Health officials admit the rapid
spread of WNV caught them by
surprise but they're determined not to
be unprepared for the summer of
2003. More monitoring of
mosquitoes will be done and the
provincial government will fund
spraying of larvacides to kill off the
young hatched mosquitoes before
they can become airborne.
Ontario Ministry of Agriculture
and Food has been providing regular
updates to veterinarians and horse
owners, since horses are the animal
that seems to be most affected by
WNV.
Last year there were 107 cases of
equine West Nile Virus infection
confirmed in Ontario, clustered in the
Niagara, Haldimand and Essex areas.
Mortality in unvaccinated horses is
25-30 per cent.
The virus attacks the spinal
system of the animals, causing a
sudden lack of co-ordination. The
animals remain mentally alert and
ready to eat but are so unco-ordinated
they can't. They suffer twitching
muscles and often their nose starts
shaking. They don't know where
their feet are. Eventually the animals
may go down and the survival rate
among those that do is not good.
The good news for horse owners
is that there is a program of
immunization they can undertake to
protect their horses. The bad news is
that time is running out for effective
protection for 2003.
Ontario Ministry of Agriculture
and Food veterinarian Dr. Leslie
Woodcock told 100 horse owners
from across midwestern Ontario
attending a meeting in Brussels in
March that the immunization, which
requires two shots, three to six weeks
apart, needs to be done four to five
week.s prior to exposure to
mosquitoes that carry the West Nile
Virus. Since the first mosquitoes
appear in May there's no time to
waste, she advised.
Those horses that have had two
shots at least 30 days previous to
being exposed to the virus have 94
per cent protection, Woodcock said.
"All equines need to be vaccinated,"
including donkeys and mules, she