West Nile Virus Alert

Some mosquitoes trapped throughout the region have, as expected, recently tested positive for West Nile Virus (WNV). Risk of infection to people and pets will increase as the season progresses, and as mosquito contact increases. We encourage you to take steps to reduce your risk of WNV and of other mosquito-borne infections.

Preventing Exposure to Mosquitoes

Consider reducing outdoor activities between dusk and dawn, when certain kinds of mosquitoes are most active. If you must be outdoors in the evening, cover up skin by wearing a long sleeved shirt, long pants and socks.


The Massachusetts Department of Public Health and United States Centers for Disease Control and Prevention (CDC) recommend using mosquito repellents to further reduce risks from mosquitoes. Refer to these resources to help guide your choice of product, and always read and follow label directions:

Eliminate Standing Water

Mosquitoes deposit their eggs in stagnant or standing water, and these may hatch and develop to the adult stage in less than one week. Water – even just a quarter of an inch – in roof gutters, buckets, trash containers, kiddy pools, tarps, disused tires, bird baths or other sites is sufficient to produce a surprising number of mosquitoes. So, inspect and drain these items frequently.

Keep Mosquitoes Outside

Whereas most mosquitoes will bite while outside, many will take every opportunity to enter into homes, apartments and offices through windows and doors. Keep windows and doors closed, or protect these openings with screens. Check the screens frequently to ensure that they fit tightly, and replace / repair any with holes or tears.

Community Efforts

The Commonwealth and many communities (including Boston and Cambridge) actively monitor mosquito populations and pursue efforts to reduce their abundance and the risks associated with mosquitoes and mosquito-borne infection. Harvard University cooperates in these activities on and around our campuses, and in manners that are environmentally appropriate.

Further insights and guidance regarding West Nile virus and other mosquito concerns are available:

Should you have additional questions regarding mosquitoes or other pest-related questions, please contact the EH&S Environmental Public Health program: