West Nile Virus (WNV)

What is West Nile virus?

West Nile Virus (WNV) Disease is spread by the bite of a mosquito infected with the virus. Mosquitoes become infected when they feed on infected birds. The infected mosquitoes can then spread the virus to humans and other animals. In humans, WNV may cause a mild illness but may also cause encephalitis (inflammation of the brain) or meningitis (inflammation of the lining of the brain and spinal cord).

Who gets WNV?

Anyone who lives in or travels to areas where West Nile virus activity has been identified is at risk of getting the disease. WNV is considered endemic (native) in New York State and is generally found in at least part of the state each summer. See the New York State weekly arboviral surveillance report. Most people are infected in summer to early fall. While chances of anyone becoming seriously ill are small, people over 50 years of age are at the highest risk for severe illness.

How is WNV spread?

WNV is usually spread through the bite of an infected mosquito. While there are about 70 different species of mosquitoes in New York State, only certain species have been associated with WNV. It is not spread from person to person through casual contact or from handling dead infected birds, although gloves should always be worn when handling any dead animal. In a small number of cases, WNV has been spread by blood transfusion, which has resulted in the screening of blood donations for the virus in the US, or by organ transplantation. WNV can also be spread from mother to baby during pregnancy, delivery, or breast-feeding in a small number of cases. Pregnant women should consult their health care provider for more information.

What are the symptoms of WNV?

Most people (70-80%) who are infected with WNV do not show symptoms. It is estimated that 20% of the people who become infected will develop less severe symptoms including fever, headache and body aches, nausea (the feeling of sickness in the stomach), and occasionally a skin rash and swollen lymph glands. These symptoms typically last a few days - but may last several weeks.

The symptoms of severe infection (West Nile encephalitis or meningitis) can include headache, high fever, neck stiffness, muscle weakness, stupor, disorientation, tremors, seizures, paralysis, and coma. WNV can cause serious illness, and in some cases, death. Usually, symptoms occur from 3 to 14 days after being bitten by an infected mosquito. There is no specific treatment for viral infections, other than to treat the symptoms and provide supportive care. Individuals with concern should consult their health care provider for more information.

How is WNV diagnosed?

Health care providers diagnose WNV based on the patient's clinical symptoms and laboratory diagnosis by testing blood or spinal fluids, which will show if the virus or antibodies against the virus are present in the person.

What is the treatment for WNV?

There is no specific treatment for WNV. Health care providers will usually attempt to relieve the symptoms of the illness. In severe cases, patients may need to be hospitalized and closely monitored. Currently there is no West Nile virus vaccine available for humans.

Does past infection with WNV make a person immune?

It is likely that people with past infection of West Nile virus will be protected from getting the disease again.

Can my pet be infected?

Pets occasionally get WNV from mosquito bites, but very rarely get sick. Horses are more susceptible to serious illness from WNV than are dogs and cats; however, a vaccine is available for horses. Natural infection of a pet by contacting or eating an infected dead bird has not been documented.

What can be done to prevent the spread of WNV?

Protecting yourself from mosquito bites will help prevent the spread of WNV. Use of repellents may be helpful in minimizing exposure. To minimize exposed skin, people spending time outdoors in mosquito-infested areas can use insect repellents containing DEET. Consider wearing long sleeves and tucking pants into socks and shirt into pants when outdoors at dusk or dawn, the time of day when mosquitoes are most active. More information on repellents go to Environmental Protection Agency- insect-repellents. In addition:

  • Be sure to follow label directions.
  • Try to reduce the use of repellents by dressing in long sleeves and pants tucked into socks or boots.
  • Children should not handle repellents. Instead, adults should apply repellents to their own hands first and then gently spread on the child's exposed skin. Avoid applying directly to children's hands. After returning indoors, wash your child's treated skin and clothing with soap and water or give the child a bath.
  • Do not apply near eyes, nose or mouth and use sparingly around ears.
  • After returning indoors, wash treated skin with soap and water.

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.
  • Landscape to eliminate standing water that collects on your property.