Frequently Asked Questions about West Nile Virus and Wildlife
in the United States has West Nile Virus (WNV) been detected in
A. Since the virus was first
detected in 1999, WNV has been detected in wildlife, primarily birds,
in 45 states and the District of Columbia. A regularly updated map
of regions reporting WNV in dead birds can be found at:
Are crows and raptors the only bird species with
A. Since 1999, WNV has been
detected in over 225 wild and captive bird species. This list is
based on reports from public health, wildlife and veterinary diagnostic
laboratories across the United States. To see a list of those species,
Are birds the only species that are susceptible to WNV infection?
A. Birds are the natural host and
reservoir of WNV. Although other animals, including several mammals
and captive alligators, are susceptible to WNV infection, there
is currently no evidence that animals other than birds naturally
develop a high enough virus load to transmit the infection to an
The list of animal species in which WNV infection has been detected
has continually increased since 1999 and can be found
Which bird species are responsible for maintaining the virus
in the environment?
A. There are theories that crows
or house sparrows are the primary reservoir for WNV in the environment.
However, these have not yet been substantiated, and it is not known
which birds are the primary reservoirs circulating the virus in
I’m not seeing the numbers of birds that I have seen in
previous years. Is this because of WNV?
A. The National Wildlife Health Center
(NWHC) has been receiving reports from several regions of the United
States about decreased numbers and species of birds being observed.
Because WNV activity in the U.S. is associated with bird mortality,
it is possible that the decline in bird sightings is due to WNV
If birds are the natural host for WNV, why is WNV being detected
in so many dead birds?
A. Since this virus was not detected
in the Western Hemisphere until 1999, it is likely that native bird
populations in the U.S. were not previously exposed to the virus.
It is not unusual for a new disease to cause high rates of infection
or death because they do not have natural immunity to the infection.
It is not known if or how long it will take for populations to develop
sufficient immunity. Surveys of wild birds completed in the last
three years have shown that some birds already have antibodies to
Most bird testing and surveillance programs for WNV in the U.S.
have been focused only on testing for the presence of the virus
in the birds. Testing for other possible causes of death was not
being conducted, so it is unknown if all of the bird deaths are
due to WNV infection.
What is the effect of WNV on bird populations? Are these
bird species, particularly the crows and blue jays, going to disappear
at this time, we do not know if WNV is having an impact on bird
populations. While we do know that the virus kills some species
of birds, it is difficult to document the effect WNV has had on
wild bird populations. Based on Christmas Bird Counts, Breeding
Bird Surveys, and reports from bird enthusiasts, we know there have
been declines in observations of many local bird populations. However,
we do not know if this is a true decline or if the decline can be
attributed to WNV. There are surveys of bird populations underway.
It is not anticipated that the commonly seen species, such as crows
and blue jays, will disappear from the United States.
What is the threat to endangered and threatened
A. This is an issue of great concern,
as these populations are already struggling to survive in the current
environment. If some of these species are more vulnerable to fatal
WNV infection, WNV may ultimately lead to their extinction or significantly
set back the progress of the recovery programs.
Could the local mosquito control efforts, particularly the spraying
of pesticides for adult mosquitoes, be killing the birds?
A. Based on
safety reports available from the EPA, many of the pesticides being
used by local agencies for mosquito control are considered to have
very low toxicity to birds. For more information, contact your local
health department for information on the mosquito control methods
being used in your area.
There have been many reports of increasing numbers of
non-avian species infected with WNV. Has the virus changed?
A. It is possible
that there may have been a mutation in the virus that is causing
a higher number of species to be affected. There is currently no
evidence of significant mutation in the U.S. strain of WNV since
its discovery in 1999, but many studies are still underway.
How do I know if an animal has WNV infection?
A. Signs of infection in wildlife,
like in humans, can range from no symptoms to severe symptoms of
neurologic illness. Commonly reported signs in animals have included:
weakness, stumbling, trembling, head tremors, inability to fly/walk,
and lack of awareness that allowed them to be easily approached
and handled. These signs do not necessarily indicate WNV infection,
and the only way to confirm WNV infection is by laboratory testing
of tissues for the presence of virus.
What should I do if I find sick or dead wildlife?
A. A cluster of sick or dead animals
in an area are not likely to indicate WNV infection, but may indicate
other wildlife diseases of concern.
If you find sick or dead wildlife, contact your closest state or
federal wildlife agency that may want to investigate some of these
Since many local health departments use dead bird reports to estimate
WNV activity in an area, the wildlife agency may request that you
contact your local health department to report a sick or dead bird
How do I handle a sick or dead animal?
A. There is no evidence to indicate
you can be infected with WNV by handling a sick or dead animal.
However, there are a number of other potential infections that could
result from handling an animal. To protect yourself from any such
exposure, it is recommended to wear gloves or to put a plastic bag
over your hand before touching the animal and to wash your hands
with soap and water immediately afterward.
I have a bird feeder and/or a birdbath on my property. Am I at increased
risk of catching WNV?
A. At this time, there isn’t
evidence to indicate that humans can get infected directly from
an infected bird. However, it is recommended to always follow general
hygienic procedures. Birdbaths and feeders should be washed or disinfected
regularly. Wash your hands with soap and water after touching the
To prevent mosquitoes from breeding on your property, empty and
clean birdbaths at least once a week and eliminate any other standing
water in your area. Contact local health officials if you are concerned
about potential mosquito breeding sites in your area.
By having the feeder/birdbath, am I increasing the exposure
of other birds to infection by attracting them to a common place?
A. Preliminary studies in the laboratory
have shown the potential for direct bird-to-bird transmission, but
there is no evidence that transmission in nature occurs among birds
by routes other than by mosquito. Information on other diseases
that can be transmitted at bird feeders and recommended measures
to prevent transmission of these diseases can be found
I am a wildlife biologist/birdbander/rehabilitator and handle
live birds on a regular basis. Should I be concerned about exposure
A. Measures to protect from mosquito
exposure are recommended. There is no evidence indicating direct
The NWHC has developed an information sheet that may provide guidance
to those handling wildlife. The guidelines can be found
here. Consult with your supervisor and/or physician about measures you
may want to take to prevent transmission of disease to yourself
and to other animals.
What about game birds? Should hunters be concerned about eating
the game they catch?
A. Some game birds have tested positive
for WNV. However, there is no evidence of human infection by consumption
of properly cooked infected game. Hunters are likely at higher risk
of infection by mosquito exposure, particularly in wetland environments.
Protective measures should be taken to prevent mosquito exposure
Also, WNV transmission to humans has been documented to occur by
accidental injury in the laboratory and by blood transfusion. It
is recommended that hunters wear gloves when dressing (cleaning)
the birds to protect against accidental injury and exposure to blood.
Immediately consult with a physician should an injury occur to discuss
the risk of WNV exposure from the injury.
Other protective measures recommended to hunters are those that
prevent exposure to any infectious organisms carried by game species,
including washing hands with soap and water after handling carcasses
and cooking the meat thoroughly.
Can my dog or cat get WNV by eating an infected animal?
A. Experimentally, it was found that
this may be possible. However, there has been no evidence to indicate
transmission of WNV to cats or dogs that carry or consume infected
animals has occurred naturally. Dogs and cats can get infected by
the bite of a mosquito, thus minimizing their exposure to mosquitoes
Is there a vaccine available for birds?
A. At this time, there is not a WNV
vaccine approved for use in birds. Many zoos and wildlife centers
have been using the Fort Dodge horse vaccine (West Nile-Innovator®)
in birds. The vaccine has not been tested for use in birds by Fort
Dodge, and therefore, the safety and efficacy of use of this vaccine
in birds is neither known nor guaranteed by Fort Dodge or the USDA.
There are currently several studies underway investigating the use
of this vaccine in captive bird populations. The recently licensed
WNV vaccine by Merial (Recombitek Equine West Nile virus®) has
been approved by the USDA for use in horses only. Similar to the
Fort Dodge vaccine, the safety and efficacy of the Merial vaccine
in birds is neither known nor guaranteed by Merial or the USDA.