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West Nile Virus Frequently Asked Questions

    • West Nile Virus (WNV) is a mosquito-borne virus that can infect humans, birds, horses and other mammals. WNV was first detected in the United States in 1999. It is not known how the WNV was introduced into the United States but it may have entered in an infected traveler, bird, or mosquito. WNV has been present in Africa, West and Central Asia, and the Middle East for a long time. The majority of people and animals that are infected with WNV have no symptoms or only a mild illness. In rare cases, WNV can cause a more serious condition called encephalitis, or an inflammation of the brain.

    • People become infected with WNV only from the bite of an infected mosquito. Birds and other animals cannot transmit WNV to people. WNV is NOT spread by person-to person contact such as toughing, kissing or caring for someone who is infected.

    • Mosquitoes become infected with WNV when they feed on birds that are infected with WNV. Infected mosquitoes then can transmit WNV to other birds, humans and horses. Only certain species of mosquitoes carry the virus and very few mosquitoes are actually infected.

    • Encephalitis is an inflammation of the brain. In rare cases, WNV can cause encephalitis.

    • The chance of getting sick from a mosquito bite is very rare even in areas where WNV is prevalent. Less than 1 percent of all mosquitoes will carry WNV, and less than 1 percent of the people who are bitten by an infected mosquito will become ill. Persons over the age of 50 are generally at a higher risk for serious illness.

    • Most people who are infected with WNV have no symptoms or may experience mild illness, such as a fever and headache, before fully recovering. In some individuals, particularly in those over age 50, WNV can cause severe illness including encephalitis. Symptoms generally occur three to 15 days following the bite of an infected mosquito. It is estimated that 1 in 150 people who are infected with the West Nile virus will require hospitalization. Of the most serious encephalitis cases, approximately 3-15% may be fatal. If you think you maybe experiencing symptoms of WNV, please seek medical care as soon as possible.

    • There is no specific treatment for WNV infection. As with other viral illnesses, supportive care and symptomatic therapy are given.

    • There is no vaccine for humans for protection against West Nile virus infection. Currently several companies are working towards developing a vaccine. However, there is a vaccine available for horses.

    • No. WNV is not spread by person-to-person contact or directly from animals to people.

    • Currently, there have been no reported cases of WNV being spread directly from live or dead birds to the general public. However, dead birds can carry a variety of other diseases and should never be handled with bare hands. Use gloves or use the inverted plastic bag method to handle the birds. If the bird meets requirements for testing, please refrigerate and immediately contact Maricopa County Environmental Services for further instructions or place the bird in the outdoor trash.

    • No. Even in areas where mosquitoes and birds are known to carry WNV, very few mosquitoes are infected. The majority of people will not experience any symptoms if an infected mosquito bites them. Small percentages of people develop mild symptoms and recover without specific medication or laboratory testing. Those over age 50 are more likely to develop severe symptoms requiring medical care. Contact your health care provider for more information.

    • In Arizona, mosquito-borne viruses are most likely to be spread from May through October during the peak of mosquito activity.

    • The best way to protect you from WNV, or any other mosquito-borne illness, is to reduce the number of mosquitoes around your home and neighborhood and to take personal precautions to avoid mosquito bites. These are some of the preventative steps that you can easily take:

      • Eliminate standing water where mosquitoes can breed. Check for items outside the home that collect water, such as cans, bottles, jars, buckets, old tires, drums and other containers.
      • Change water in flower vases, birdbaths, planters and animal watering pans at least twice a week.
      • Repair leaky pipes and outside faucets, and move air conditioner drain hoses frequently.
      • Wear protective clothing such as long pants and long-sleeved shirts during peak mosquito activity.
      • Avoid shaded, bushy areas where mosquitoes like to rest.
      • Limit outdoor evening activity, especially at dusk and down when mosquitoes are most active.
      • Use insect repellent containing DEET (Please Read Instructions and use safely)

    • WNV infection has been reported in more than 70 bird species. The most severe illnesses are seen among crows, jays, ravens and magpies. Horses are susceptible to WNV infection but a vaccine is available for horses. No clearly defined clinical signs associated with WNV infection have been shown for dogs, cats, bats, chipmunks, skunks, squirrels, domestic rabbits, and domestic birds. Contact your veterinarian for information about pets and livestock.

    • If you find a dead bird, you should contact your local county health department for more information. In Maricopa County, please contact the Environmental Complaint line at 602-506-6616.

      Pigeons and baby birds will not be tested for WNV.  Crows, jays, ravens, sparrows, finches, quails and other wildlife foul are specimens of interest for testing.

      In order for a bird to be tested, the dead bird should be: 
      fresh (dead less than 24 hours)
      not scavenged or decomposed,
      no odor and no maggots
      Body should not be soft or mushy

      Always wear gloves when handling dead birds, or use the inverted plastic bag method. Refrigerate the dead bird until it is submitted for testing.  Do not freeze.

    • Proper cooking kills the WNV. Consequently, there is no danger associated with eating birds that have been properly cooked.

    • County and state health workers monitor mosquitoes, dead birds and 15 chicken sentinel flocks for mosquito-borne viruses. Mosquito surveillance involves trapping mosquitoes, counting them, identifying which species are present, and testing appropriate species for viruses. These surveillance methods are used to target areas where mosquito control efforts are needed. Detection and control of mosquito breeding sites depends upon integrated efforts among state, county, and tribal agencies as well as private citizens.

Where can I get more information on West Nile Virus?

Arizona's 24-hour bi-lingual Public Health Hotline
for the latest information about WNV
at (602) 364-4500 in Metro Phoenix

Or 1-800-314-9243 in other areas of the state.

You can also visit the Arizona Department of Health Service's Web site at

Or you can contact the Arizona Department of Health Services directly at (602) 230-5932.