State Health Officials Announce Fourth Human Case of West Nile Virus (WNV) and Risk Level Changes in Massachusetts
Residents Should Continue to Take Precautions to Avoid Mosquito Bites
Date of Record: October 5, 2023
The MA Department of Public Health (MDPH) today announced the fourth human case of West Nile virus (WNV) in a MA resident this year. The individual is a male in his 60s who was exposed in Norfolk County.
The risk of human infection with WNV is already moderate in the Greater Boston area (Middlesex, Norfolk, and Suffolk counties), and in parts of Berkshire, Bristol, Hampden, Hampshire, Plymouth, and Worcester counties. Twelve additional municipalities - Ashland, Holliston, Hopkinton and Sherborn in Middlesex County, and Dover, Medfield, Medway, Millis, Norfolk, Norwood, Walpole, and Westwood in Norfolk County - are now also considered to be at moderate risk.
“This is the fourth person identified with West Nile virus infection in a Massachusetts resident this year,” said Public Health Commissioner Robert Goldstein, MD, PhD. “With the weather getting cooler, mosquito activity will start to be reduced and the risk of West Nile virus will decrease, though some risk of mosquito-borne disease will continue until the first hard frost.”
Risk from Eastern Equine Encephalitis (EEE) virus is moderate or high in southern parts of Hampden, Norfolk, and Worcester counties and there have been EEE infected animals identified in both Rhode Island and Connecticut. Based on recent EEE positive mosquitoes in Massachusetts, thirteen additional municipalities are now considered to be at moderate risk. Those municipalities are: Easton, Norton, Raynham, Rehoboth, and Taunton in Bristol County; Agawam, Chicopee, Holyoke, Longmeadow, and West Springfield in Hampden County; Bridgewater and West Bridgewater in Plymouth County; and Warren in Worcester County.
In 2022, 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, WNVsymptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.
EEE is a rare but serious and potentially fatal disease that can affect people of all ages. EEE is generally spread to humans through the bite of an infected mosquito. There were 12 human cases of EEE in Massachusetts in 2019 with six deaths; there were five human cases with one death in 2020. There were no human cases of EEE in Massachusetts in 2021 or 2022.
People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes.
Avoid Mosquito Bites
Apply Insect Repellent when Outdoors. Use a repellent with an EPA-registered ingredient (DEET (N,N-diethyl-m-toluamide), permethrin, picaridin (KBR 3023), oil of lemon eucalyptus [p-Menthane-3,8-diol (PMD)] or IR3535) according to the instructions on the product label. DEET products should not be used on infants under two months of age and should be used in concentrations of 30 percent or less on older children. Oil of lemon eucalyptus should not be used on children under three years of age.
Be Aware of Peak Mosquito Hours. The hours from dusk to dawn are peak biting times for many mosquitoes. Consider rescheduling outdoor activities that occur during evening or early morning in areas of high risk.
Clothing Can Help Reduce Mosquito Bites. Wearing long-sleeves, long pants and socks when outdoors will help keep mosquitoes away from your skin.
Mosquito-Proof Your Home
Drain Standing Water. Mosquitoes lay their eggs in standing water. Limit the number of places around your home for mosquitoes to breed by draining or discarding items that hold water. Check rain gutters and drains. Empty unused flowerpots and wading pools and change the water in birdbaths frequently.
Install or Repair Screens. Keep mosquitoes outside by having tightly fitting screens on all windows and doors.
Protect Your Animals
Animal owners should reduce potential mosquito breeding sites on their property by eliminating standing water from containers such as buckets, tires, and wading pools – especially after heavy rains. Water troughs provide excellent mosquito breeding habitats and should be flushed out at least once a week during the summer months to reduce mosquitoes near paddock areas. Horse owners should keep horses in indoor stalls at night to reduce their risk of exposure to mosquitoes. Owners should also speak with their veterinarian about mosquito repellents approved for use in animals and vaccinations to prevent WNV and EEE. If an animal is suspected of having WNV or EEE, owners are required to report to the Department of Agricultural Resources, Division of Animal Health by calling 617-626-1795, and to the Department of Public Health by calling 617-983-6800.
More information, including all WNV and EEE positive results, can be found on the Arbovirus Surveillance Information web page at Mosquito-borne Diseases | Mass.gov, which is updated daily, or by calling the DPH Division of Epidemiology at 617-983-6800.
West Nile Virus Fact Sheet