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West Nile Virus

West Nile Virus Fact Sheet: English | Spanish | Portuguese | Chinese (traditional) | Haitian Creole

The Cambridge Public Health Department leads the city's response to the risks posed by West Nile virus, eastern equine encephalitis, and other mosquito-borne diseases.

WEST NILE VIRUS UPDATE:  Week of October 22–26, 2018

Human Infections

State health officials have announced 42 human cases of West Nile virus among Massachusetts residents in 2018, including three Cambridge residents. Most of the cases were hospitalized with serious West Nile virus symptoms. For more information, see the Aug. 24Aug. 27, Sept. 4, Sept. 7, Sept. 17, Sept. 18, Sept. 21, Sept. 24, Sept. 28Oct. 5, and Oct. 12 media releases from the Massachusetts Department of Public Health.

Mosquito Samples

  • West Nile virus-infected mosquitoes have been reported locally in Arlington, Bedford, Belmont, Boston, Braintree, Brookline, Burlington, Cambridge, Concord, Everett, Framingham, Lexington, Malden, Medford, Melrose, Natick, Newton, North Reading, Quincy, Waltham, and Watertown.
  • Positive mosquito samples in Cambridge were reported on July 26 (one sample) and August 23 (three samples). 

What is the current risk?

On August 27, the Massachusetts Department of Public Health (MDPH) raised the risk of West Nile virus infection from "moderate" to "high" in Cambridge and 10 nearby communities due to the fact that at least two of people diagnosed with West Nile virus were exposed in the Greater Boston area. See MDPH media release

On August 21, MDPH raised the risk level for West Nile virus from low to moderate in every Massachusetts city and town. It was only the second time since West Nile virus was first detected in the Commonwealth in 2000 that public health officials have raised the risk level statewide.
The majority of human West Nile virus infections in Massachusetts occur during August and September.  People at greatest risk for serious illness are people over 50 and those who are immunocompromised. 

To learn more about risk of West Nile virus in Cambridge and the state, see the risk map and testing results from the Massachusetts Department of Public Health.

What You Can Do

Avoid Mosquito Bites

  • Apply Insect Repellent when Outdoors. Use a repellent with DEET (N, N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus [p-methane 3, 8-diol (PMD)] or IR3535 according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30% or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.
  • Be Aware of Peak Mosquito Hours. The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning.
  • Clothing Can Help Reduce Mosquito Bites. Wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.
  • For more information on how to protect yourself, see the Cambridge Public Health Department's Prevention Tips.

Reduce Mosquito Breeding Areas

In New England, the mosquitoes that carry West Nile virus are "container breeding" species.  These mosquitoes lay their eggs in still or stagnant water found in catch basins, roof gutters clogged with leaves, old tires, flower pots, bird baths, swimming pool covers, buckets, cans, barrels, and other places where water can be trapped. Tenants, property managers, and homeowners can greatly reduce the city's mosquito population by removing mosquito breeding areas on their property.

Remove stagnant water from your property

  • Empty or treat any items that hold water, such as flower pots, birdbaths, swimming pool covers, buckets, cans, and barrels.
  • Clean rain gutters, leaves in downspouts, and pooled water on flat roofs.
  • Remove unused tires and other items that could collect water.
  • Remove containers that may hold water in places that are hard to see, such as under bushes, porches, decks, or stairs.

When you can't get rid of stagnant water by sweeping or other methods (such as Mosquito Dunk, a product sold in hardware stores), please report the address or location of the puddle or still water source to the appropriate city department:

  • Private property: Cambridge Public Health Department, 617-665-3838
  • Public property (roads, parks): Cambridge Dept. of Public Works, 617-349-4800
  • Construction sites: Cambridge Inspectional Services, 617-349-6100

If you have questions or local concerns about West Nile virus or stagnant water, please contact the Cambridge Public Health Department’s Environmental Health Division at 617-665-3838 or contact Environmental Health staff at slipson@challiance.org.

For general information, visit the Massachusetts Department of Public Health's mosquito-borne diseases website and the CDC's West Nile virus website.

Last updated on October 23, 2018


For general questions about West Nile virus and eastern equine encephalitis, please call 617-665-3838. 

Join the Cambridge WNV listserv and receive seasonal updates on West Nile virus and eastern equine encephalitis.

October 12, 2018

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August 27, 2018

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June 26, 2018