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West Nile Virus (WNV)

This fact sheet answers frequently asked questions about West Nile virus.

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West Nile virus (WNV) is a rare disease most often spread to people by the bite of an infected mosquito. WNV carrying mosquitoes appear in Boston every year during the summer and fall months.

The basics

How is West Nile virus spread?

WNV is most often spread to people when an infected mosquito bites them. Mosquitoes get WNV when they bite an infected bird. People cannot get WNV directly from birds. WNV can also spread through blood transfusions, organ transplants, and from mother to child during pregnancy or breastfeeding.

Is West Nile virus in Boston?

WNV in people is rare, but it does appear in Boston mosquitoes during summer and fall. Occasionally, WNV causes serious illness or death.

When am I at risk for getting West Nile virus?

Mosquitoes are most active and most likely to carry WNV in Boston from July to September. If the weather is warm, mosquitoes can carry WNV as early as June and as late as November.

Who is at risk for West Nile virus?

Anyone who is outside, especially during dawn to dusk is at risk. Mosquitoes are most active at dawn and dusk. People who are over 50 years old are more likely to develop severe illness if they get WNV.

Symptoms

What are the signs and symptoms of West Nile virus?

Most people who get WNV experience no signs or symptoms. A few people with WNV will experience headache, fever, nausea, vomiting, and body aches. These symptoms can last a few days to several weeks. WNV can cause more serious symptoms, including:

  • high fever
  • severe headache
  • confusion
  • lack of coordination
  • permanent muscle weakness/paralysis

Prevention

How can I help protect myself from mosquitoes?

  • Use a mosquito repellent. Repellents approved by the EPA include those containing DEET, oil of lemon eucalyptus, Picaridin or IR3535. Follow the directions on the product label. After returning indoors, wash repellent off with soap and water and wash treated clothes before wearing again. Do not use these products on pets unless the label approves
  • If you use a product containing DEET, do not use concentrations of more than 30% on adults and use low concentrations of DEET on children. Apply DEET to exposed skin (not eyes or mouth) and on clothes, but do not use on open cuts or wounds. Do not apply underneath clothes.
  • Do not let children apply repellants to themselves. Apply the repellant to your hands and rub it on your child. Do not apply repellants to children’s eye, mouth, or hands and use cautiously around ears. Do not apply DEET on infants. Instead use mosquito netting over infant carriers or oil of lemon eucalyptus on children under 3 years of age.
  • Wear protective clothing such as long sleeved shirts, long pants and socks whenever possible. Tuck your shirt into your pants to keep mosquitoes from going under your clothes.
  • Although mosquitoes can bite at any time of day, try to limit time outdoors between dusk to dawn when mosquitoes are most active.
  • Make sure window and door screens don’t have holes in them. Screens in good condition will help prevent mosquitoes from getting inside your house.

Follow these steps to help prevent mosquito breeding: Mosquitoes need water to breed. They can develop into adults in as little as a week. Make sure items around your home don’t collect water. Clean out items that do collect water once a week:

  • Containers: Turn over or cover unused flower pots, buckets, garbage cans, and wheelbarrows. Change water in bird baths once a week.
  • Gutters: Remove leaves and other debris that can clog gutters and trap water.
  • Pools: Cover unused swimming pools and turn over kiddie pools when not in use. Be sure to keep swimming pool covers clear of leaves and water. Keep large pools treated and circulating.
  • Old tires: Cover or dispose of them. They are a favorite mosquito-breeding site.

To learn more about EEE, click here. 

How is the BPHC tracking and controlling WNV?

BPHC works with the Suffolk County Mosquito Control Project to trap and test mosquitoes around Boston. They test for WNV during the summer and fall months. Mosquito control measures are also implemented during summer and fall months. They treat wetlands, storm drains, and other areas around the city to limit the number of mosquitoes.

Treatment

Is there a treatment for West Nile virus?

There is no specific treatment for WNV. 

Individuals who experience mild symptoms usually recover on their own. If experiencing mild symptoms, rest, fluids, and over-the-counter pain medicines may provide some symptom relief. Cases that are more serious may need hospitalization. If you think you may have WNV, contact your health care provider immediately.

For more information on treatment, please visit the CDC's page on symptoms and treatment. 

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