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Alabama
Department of Public Health
West Nile Virus Host Range
October 9, 2002
WEST NILE
VIRUS, MAMMALIAN HOST RANGE - USA
A
ProMED-mail post
Date: Wed 9 Oct
2002
From: Bill Johnston <wjohnston@adph.state.al.us>
Recent media reports have prompted many questions regarding
West Nile virus (WNV) infection in species other than birds, horses, and
humans. As an "emerging disease" in the United States, WNV has
clinical and health effects on various animal species and populations
that have yet to be described or fully reported. The following
information is offered on the current knowledge of WNV infection in
other species.
It
is currently believed that any type of bird or mammal may be susceptible
to WNV infection, but very few species appear to develop clinical
illness due to infection. Since entering North America in 1999, WNV has
been reported in thousands of birds, horses, and humans (over 2768
people and 146 deaths, as of Wed 9 Oct 2002). Before this year, WNV
infection had been
reported in several bat species, chipmunks, gray squirrels, striped
skunks, a rabbit, and 3 cats. Laboratory trials had indicated that cats
would become viremic and ill, but that dogs were relatively resistant to
infection with WNV.
Serosurveys in New York following the 1999 outbreak
revealed that 8-11 percent of dogs had antibody titers to WNV, but had
not become ill. As WNV has moved across the country this summer,
infection and illness have now been reported in a domestic sheep, a
mountain goat, a dog, a 7-month-old wolf pup, a llama, and an alpaca.
Serologically positive black bears and white-tailed deer have also been
detected, but these animals did not develop clinical illness.
Some of the animals that became ill had another underlying
health condition and/or a compromised immune system predisposing them to
development of clinical disease. For instance, the one 8-year-old dog in
Illinois was immune-compromised. From what is currently known, WNV does
not appear to pose a significant health risk for species other than
birds, horses, and humans. The extremely small number of cases in other
species, the active surveillance conducted for the last 4 years, and
reports from 42 states that have detected WNV suggest that most of these
species are extremely resistant to developing clinical illness from
infection. There is also no current
evidence that any of these species are capable of serving as a reservoir
for the virus.
It is likely more cases in other hosts will be found as WNV
enters and becomes established in new areas. As additional information
becomes available, the relative health significance of WNV infection in
these populations will become more clearly established.
Bill Johnston, DVM, DACVPM
State Public Health Veterinarian
Alabama Department of Public Health
P.O. Box 303017
Montgomery, AL 36130-3017
wjohnston@adph.state.al.us
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