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West Nile Virus

What is West Nile virus?      

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

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. Although extremely rare, WNV can also be spread through blood transfusions, organ transplants, and from mother to child during pregnancy or breastfeeding.

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 lasting a few days to several weeks.  WNV can cause more serious symptoms, including high fever, severe headache, confusion, lack of coordination, and permanent muscle weakness/paralysis.

Is West Nile virus in Boston?

WNV has been detected in Boston mosquitoes during the summer and fall months (June – November) every year since 2000, but WNV in people is rare. In 2012, there were six confirmed cases of WNV in Boston. Occasionally, WNV does cause serious illness or death. WNV is expected to re-appear every summer.

When am at risk for getting West Nile virus?

Mosquitoes are most active and most likely to carry WNV in Boston during July through 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 when mosquitoes are most active, is at risk for getting WNV. People who are over 50 years old are more likely to develop severe illness if they get WNV.

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.  Cases that are more serious may require hospitalization. If you think you may have WNV, contact your health care provider immediately.

How is the Boston Public Health Commission (BPHC) tracking and controlling WNV?

BPHC works with the Suffolk County Mosquito Control Project to trap and test mosquitoes around Boston for WNV during the summer and fall months. Mosquito control measures are also implemented during summer and fall months. Wetlands, storm drains, and other areas around the city are treated to limit the number of mosquitoes. Click here to learn more about mosquito control in Boston. 

How can I help prevent WNV?

Follow these steps to help prevent mosquito bites:

  • Use a mosquito repellent. Repellents approved by the EPA include those containing DEET, oil of lemon eucalyptus, Picaridin or IR3535. Read the directions on the product label to find out about precautions that need to be taken and how long the product is effective. After returning indoors, wash off repellent 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 (mosquito netting can be used over infant carriers) or oil of lemon eucalyptus to 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. Items that do collect water should be cleaned once a week.

  • Containers: Turn over or cover unused flower pots, buckets, garbage cans, and wheelbarrows.  Change water in birdbaths 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.​

    mosquitoes and containers.jpgView our video to learn more about preventing WNV in Boston:


Additional Resources:

Boston Public Health Commission
1010 Massachusetts Ave, 6th Floor, Boston, MA 02118.
Phone:(617) 534-5395 Email: