Two Massachusetts residents are first human cases of West Nile virus this year

The Bay State has reported the first human cases of West Nile virus of the year, as health officials urge residents to take precautions to avoid mosquito bites.

The Massachusetts Department of Public Health on Tuesday announced the first two human cases of West Nile virus in state residents this year.

A man in his 40s was exposed to the virus in Middlesex County, which is an area already known to be at moderate risk for West Nile virus. The other case is a woman in her 70s who was exposed to the virus in another part of the country.

The risk of human infection is moderate in the Greater Boston area — Middlesex, Norfolk, and Suffolk counties — and in parts of Bristol, Plymouth, Worcester, Berkshire, Hampden, and Hampshire counties.

“This is the first time that West Nile virus infection has been identified in Massachusetts residents this year,” said Public Health Commissioner Robert Goldstein. “August and September are the months when most people are exposed to West Nile virus in Massachusetts.

“Populations of mosquitoes that can carry and spread this virus are fairly large this year and we have seen recent increases in the number of WNV-positive mosquito samples from multiple parts of the Commonwealth,” Goldstein added.

Last year, there were eight 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.

“We are coming to the unofficial end of summer but mosquitoes with West Nile virus will persist for several more months,” said State Epidemiologist Catherine M. Brown.

“To avoid mosquito bites, use a repellent with an EPA-registered ingredient, wear clothing to reduce exposed skin, drain standing water and repair window screens,” Brown added. “We also encourage everyone to regularly visit DPH’s mosquito-borne diseases web pages to stay informed on when and where WNV activity is occurring.”

Updated information on all WNV and EEE positive results can be found on the Arbovirus Surveillance Information website at www.mass.gov/mosquito-borne-diseases.