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West Nile Virus


What is West Nile Virus?

West Nile virus (WNV) is a mosquito-borne infection that can cause serious illness, and in some cases, death. Although a person's chances of getting sick are small, there are some simple steps you can take to reduce your risk of being bitten by mosquitoes.

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What are the symptoms of West Nile Virus?

Most people who are infected with the West Nile virus will not have any type of illness. It is estimated that 20% of the people who become infected will develop West Nile fever: mild symptoms, including fever, headache, and body aches, occasionally with a skin rash and swollen lymph glands. In many individuals, these symptoms are so mild that they go unnoticed or undetected.

The symptoms of severe infection (West Nile encephalitis or meningitis) can include headache, high fever, neck stiffness, muscle weakness, stupor, disorientation, tremors, convulsions, paralysis, and coma. It is estimated that one in 150 persons infected with the West Nile virus will develop the more severe form of the disease. Usually, symptoms occur from three to14 days after exposure. There is no specific treatment for viral infections, other than to treat the symptoms and provide supportive care.

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Who is at risk for getting West Nile Virus?

All residents of areas where virus activity has been identified are at risk of getting West Nile virus; persons over 50 years of age are at the highest risk for severe disease.

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How is West Nile Virus transmitted?

West Nile virus is primarily transmitted through the bite of an infected mosquito. Over 30 species of mosquitoes have been infected nationwide. WNV has been transmitted by blood transfusion or organ transplantation in a small number of cases. As a result, U. S. blood collection agencies are screening blood donations for the presence of the virus.

These transfusion and transplant related cases make up a small percentage of those infected with WNV. Although persons needing blood transfusions or organ transplants should be aware of the risk of West Nile virus infection, the benefits of receiving needed transfusions or transplants outweigh the potential risk for infection.

Transplacental transmission (pregnant woman to unborn child), and transmission through breast-feeding, have also been documented. The number of these cases is small. Pregnant women should consult their health care provider for more information.

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Do all mosquitoes transmit disease?

No. Most mosquitoes do not transmit disease. While there are about 70 different species of mosquitoes in New York State, only certain species have been associated with West Nile virus.

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Where do mosquitoes live and breed?

Mosquitoes lay their eggs in moist areas, such as standing water. The eggs become larvae that remain in the water until the adults mature and fly off. Weeds, tall grass and shrubbery provide an outdoor home for adult mosquitoes. They can also enter houses through unscreened windows and doors, or broken screens. Many mosquitoes will breed in containers that hold water, such as flowerpots or discarded tires.

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When are mosquitoes most active?

Some mosquitoes are active between dusk and dawn, when the air is calm. However, others will feed at any time of day. Mosquitoes prefer a warm, moist environment. They are active from early summer until late fall in New York State. In southern states that have a warm year-round climate, mosquitoes that transmit West Nile virus are active year round. New Yorkers should take measures to protect themselves from mosquito bites when traveling to these states.

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Which birds can carry West Nile Virus?

In New York State, most West Nile virus-positive birds have been American crows. The State Health Department is using dead crow sightings to track West Nile virus, so it is important to report any dead crows to your local health department or to the toll-free dead bird hotline, 1-866-537-BIRD (2473). Not all dead crows need to be tested for West Nile virus. If the bird is not going to be collected, you may dispose of it. Wear thick gloves, double bag the bird, and place it in the trash. Barehanded contact with dead animals should always be avoided.

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Can my pet be infected?

Pets occasionally get West Nile virus from mosquito bites, but very seldom get sick. Horses are more susceptible to serious illness from WNV than are dogs and cats. Natural infection of a pet by contacting or eating an infected dead bird has not been definitively established, although it is safer to keep pets from contacting and eating dead animals.

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How can I protect myself and my family?

To reduce the mosquito population around your home and property, reduce or eliminate all standing water:

  • Dispose of tin cans, plastic containers, ceramic pots or similar water-holding containers.
  • Dispose of used tires. Used tires are a significant mosquito breeding site. Call your local landfill or Department of Public Works to find out how to dispose of them properly.
  • Drill holes in the bottoms of recycling containers that are kept outdoors.
  • Make sure roof gutters drain properly, and clean clogged gutters in the spring and fall.
  • Remove leaf debris from yards and gardens.
  • Turn over wading pools and wheelbarrows when not in use.
  • Change the water in birdbaths twice weekly.
  • Clean vegetation and debris from edges of ponds.
  • Clean and chlorinate swimming pools, outdoor saunas and hot tubs.
  • Drain water from pool covers.
  • Use landscaping to eliminate standing water that collects on your property.

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Should we stay indoors?

It is not necessary to limit outdoor activities. However, you can and should try to reduce your risk of being bitten by mosquitoes. In addition to reducing standing water in your yard, make sure all windows and doors have screens, and that all screens are in good repair. If West Nile virus is found in your area:


  • Wear shoes and socks, long pants and a long-sleeved shirt when outdoors for long periods of time, or when mosquitoes are most active.
  • Consider the use of mosquito repellent, according to directions, when it is necessary to be outdoors when mosquitoes are biting.

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Where can I get more information about West Nile Virus?

Click here for more information.

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Source: New York State Department of Health