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Vector Control - West Nile Virus

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1. What is West Nile Virus?

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.

2. How do people become infected with West Nile Virus?

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 touching, kissing, or caring for someone who is infected.

3. How do mosquitoes become infected with West Nile Virus?

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.

4. What is "encephalitis"?

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

5. Who is at risk of getting sick from West Nile Virus?

The chance of getting sick from a mosquito bite is very rare even in areas where WNV is prevalent. Approximately 80 percent of people who are bitten by a WNV infected mosquito will not show any symptoms at all, but there is no way to know in advance if you will develop an illness or not. Persons over the age of 50 and the  Immunocompromised are generally at a higher risk for serious illness.

6. What are the symptoms of West Nile Virus infection?

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 fifteen 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.

7. Is there a treatment for West Nile Virus infection?

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

8. Is there a vaccine to prevent West Nile Virus infection?

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.

9. Can I get WNV from another person or an animal?

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

10. Can I get WNV directly from birds?

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, and place the bird in the outdoor trash.

Maricopa County Environmental Services

11. If bitten by a mosquito, should I be tested for WNV?

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.

12. What time of year are mosquito-borne viruses spread?

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

13. How can I help protect myself and my family from West Nile Virus?

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. - Scrub the sides and 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).

14. Which animals can get infected with West Nile Virus?

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.

15. Can a person get West Nile Virus infection by eating infected birds?

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

16. What is Maricopa County doing to prepare for West Nile Virus?

County and state health workers monitor mosquitoes 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.

17. Where can I get more information on West Nile Virus (WNV)?

Our dedicated Web site FightTheBiteMaricopa.org contains information about mosquitoes, prevention methods, a map with the routine trap information, such as location and times sprayed; a fogging calendar, and more. You can also call our WNV hotline 602-506-0700 or 602-506-6616.

Arizona Department of Health Services website.