Massachusetts announces first human case of West Nile virus, risk moderate in Bristol county

BOSTON (September 1, 2021) – The Massachusetts Department of Public Health today announced the first human case of West Nile virus in the state this year. The individual is a female in her 80s who was likely exposed to the virus in Middlesex County, an area known to be at moderate risk. The risk of human infection with WNV is moderate in the Greater Boston area, and several towns in Bristol and Worcester counties. There are no risk level changes associated with this finding; there have been no deaths this year associated with WNV.

“This is the first time that West Nile virus infection has been identified in a person in Massachusetts this year,” said Acting Public Health Commissioner Margret Cooke. “Risk from West Nile virus has been slow to increase this year. This is an important reminder that we all need to continue to take steps to protect ourselves and our families from mosquito bites.”

Although late in the season, the substantial amount of rain in the region in July and the recent hot weather have resulted in an increase in the population of the Culex species of mosquitoes, known to spread West Nile virus and breed in places where standing water accumulates.

In 2020, there were five human cases of WNV infection identified in Massachusetts. WNV is usually transmitted to humans through the bite of an infected mosquito. While WNV can infect people of all ages, people over the age of 50 are at higher risk for severe disease. Most people infected with WNV will have no symptoms. When present, WNV symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.