WNV was first introduced into North America in New York USA in
1999.
Since this time, WNV has been detected in 150 different
species of wild and
domesticated birds, squirrels, cats, dogs, horses,
camelids, amphibians, reptiles,
mosquitoes, ticks, and sheep.
Those species hit especially hard by WNV are
humans, horses (equids)
and birds of the corvid family (crows, ravens, blue
jays and
magpies). Transmission is primarily by being bitten by the culex
mosquito, however in cats and other carnivores, it is suspected that
oral
transmission is highly effective leading researchers to believe
that infected prey
animals may be a significant source of infection for
these animals. By the end
of 2000 the Center for Disease Control
and Prevention had reports of 21 human
cases, 63 equine cases, 4 304
infected dead birds and 6 other species of mammals
in 7 different
northeastern states. Since this time, WNV has been confirmed or
suspected in All 50 continental states, and in 2002 WNV was declared
endemic in
the USA.[1]
In Canada, WNV was first identified in August 2001 in a bird from
Windsor-Essex Ontario. Since then, WNV
has
been identified in birds over many
parts of Canada, including Ontario,
Nova Scotia, Quebec, Manitoba, Saskatchewan
and Alberta. The first
cases of equine WNV infection in Canada were reported in
Manitoba in
2002. 2002 was also the 1st year in which cases of West Nile
virus
encephalomyelitis in the horse was identified in Canada.
It is imperative that horses
with an acute onset of neurological
disease be tested for West Nile virus to better
understand this
emerging disease [5]. In 2003, WNV was declared a reportable
disease
by the Canadian Food Inspection Agency (CFIA) [15]. It is
believed that between 10
and 40% of horses infected by WNV will develop
clinical disease, and of those,
the
www.ci.greenfield.ca.us/Public_Health_Info.htm
fatality rate is roughly 30% [1].
http://wildlife1.usask.ca/en/west_nile_virus/current_maps/canada06en.jpg
Map indicates areas where corvid birds
which are considered a sentinal species for WNV have been found to be
infected with the West Nile Virus. This may
indicate an increased risk for horse and humans, however, it must be
remembered that positive tests in birds is not necessarily indicative of large
populations of infected mosquitoes.
WNV was first introduced into North America in New York USA in
1999.