BOSTON — A woman in her 70s has been diagnosed with West Nile virus after she was exposed in Essex County, the Massachusetts Department of Public Health announced Wednesday.

Her infection and that a man in his 60s exposed in Middlesex County brings the total number of human cases of WNV in the state to six this year; there has been one animal case.

As a result of these new cases, Essex, Manchester, Boxford, Georgetown, Hamilton, Ipswich, Newbury, Rowley, and Topsfield are now considered at moderate risk. Twenty-seven communities in Essex, Middlesex, Norfolk, and Suffolk counties are at high risk.

As overnight temperatures get cooler, mosquito activity right around dusk and dawn may be more intense. Substantial rainfall and hot weather in July resulted in an increase in the population of the species of mosquito known to spread West Nile virus, the state health department said.

“There are large numbers of mosquitoes carrying West Nile virus right now in parts of Massachusetts due to a nearly perfect combination of periodic rain and warm temperatures,” said Acting Public Health Commissioner Margret Cooke. “All six of our human cases have been in people over the age of 50. It is especially critical that people at risk for severe disease, such as those over 50 and anyone with immune compromise, remember to take steps to prevent mosquito bites anytime they are outdoors.”

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 the virus have no symptoms, but some develop fever and flu-like illness, and in rare cases it can be fatal.

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