Second human case of West Nile virus confirmed in Massachusetts

State health officials announced the second human case of West Nile virus in Massachusetts this year on Monday. A man in his 60s was exposed to the virus in Middlesex County, according to officials. The first case, announced on Aug. 20, involved a man in his 90s who was also exposed in Middlesex County.

As a result of these cases, the exposure locations, and ongoing mosquito testing, the risk level for West Nile virus has been elevated to high in Boston, Brookline, Cambridge, Everett, Newton, Somerville, and Watertown, officials said. Dozens of other communities in Suffolk, Middlesex, Essex, Worcester, Norfolk, Bristol, Plymouth, Barnstable, Hampden, Franklin, Hampshire, and Berkshire counties have a moderate risk level, according to state data.

Risk and peak season

Public Health Commissioner Robbie Goldstein emphasized the current danger, saying, "We are currently in peak season for WNV in mosquitoes, and the risk for many across Massachusetts is high." In a previous statement, he noted that "West Nile virus can be a [devastating] disease, especially for those who are older or have compromised immune systems." He added, "Those who are older or have compromised immune systems are especially at risk."

State Epidemiologist Dr. Catherine M. Brown recommended preventative measures: "People should use mosquito repellent with an EPA-registered active ingredient, clothing to reduce exposed skin, and consider rescheduling outdoor activities that occur during the evening or early morning when mosquitoes are most active," until the first hard frost.

Virus background and statistics

West Nile virus is a mosquito-borne illness that can cause flu-like symptoms, according to the Centers for Disease Control. Most infected individuals do not experience symptoms, but severe illness can lead to hospitalization or death. The virus was first identified in the United States in 1999, according to the Massachusetts health department.

The first West Nile virus-positive mosquitoes collected in the state in 2026 were announced on June 16, officials said. So far this year, the virus has been detected in 184 mosquito samples from every county except Nantucket County, according to state data. Another report cited 180 mosquitoes with the virus detected since June 16 across multiple counties.

In terms of symptoms, 80% of infected people show little to no symptoms. A smaller number—20%—may experience fever, headache, body aches, nausea, vomiting, and sometimes swollen lymph glands, the state health department said. People over 50 are most at risk for a serious case.

Treatment and prevention

The CDC notes there is no direct treatment for West Nile virus, as antibiotics do not treat viruses. Severe illness often requires hospitalization for supportive care, such as intravenous fluids, pain medication, and nursing care. About 1 out of 150 infected individuals may develop a severe, sometimes fatal illness.

Prevention tips from state health authorities include using EPA-registered repellents such as DEET, permethrin, picaridin, oil of lemon eucalyptus, or IR3535; avoiding peak mosquito activity hours between twilight and sunrise; repairing screen holes; and draining standing water. Residents are also advised to consult a veterinarian about mosquito repellents approved for animals.

Context

The announcement of the second human case follows news of the first case, which was accompanied by detection of Eastern equine encephalitis virus in mosquitoes. In Worcester and Bolton, mosquitoes also tested positive for West Nile virus earlier in the month. The state maintains an online map showing areas of high risk.