West Nile Virus (WNV)


Commonly Infected Wildlife

Birds are the main reservoir; some mammals may be infected.

Is This Animal Infected?

WNV primarily infects and multiplies in birds, which serve as reservoirs (a persisting group of carriers) for the virus.

Corvids (crows, blue jays, and ravens) and birds of prey are the most susceptible to this disease.

Affected birds may exhibit weakness, lethargy, tremors, and abnormal head posture.

Many mammalian species are also known to be susceptible to WNV but are not necessarily a source of infection to other animals or people.

Crow perched on tree branch
Jim Rathert

Can I Get It?

Yes, but a majority of people (80 percent) will have no noticeable symptoms, while about 20 percent may show flu-like symptoms.

How bad can it get?

  • Although symptoms are rare, WNV can be fatal.
  • About 1 out of 150 persons with WNV disease develops illness affecting the brain; it may take a long time to recover and some people never totally recuperate.
  • Any person can suffer from this severe illness, but people over 50 years of age and those with underlying health conditions are at greatest risk.

Symptoms in humans

  • The incubation period is usually 2 to 6 days but ranges from 2 to 14 days.
  • Some people may have mild flu-like symptoms, with a stiff neck and muscle weakness.
  • Rare cases result in neurologic illness such as encephalitis or meningitis.

Protect Myself and Others

Prevent mosquito bites:

  • wear light-colored, long-sleeved clothing;
  • use insect repellents with DEET, picaridin, or IR3535;
  • avoid going outdoors when mosquitoes are most active (dawn and dusk); and
  • eliminate standing water around your home or workplace to reduce the number of mosquitoes.

Safe for Pets?

Horses may become infected with WNV, and the disease can be fatal. A vaccine for horses is available; contact your veterinarian for more information. Infection in other pets is very rare.

What Causes It?

WNV disease is caused by a virus transmitted by mosquitoes.