State public health officials announce season’s first West Nile virus-positive mosquito sample

BOSTON (July 9, 2020) – The Massachusetts Department of Public Health (DPH) announced today that West Nile virus (WNV) has been detected in mosquitoes in Massachusetts for the first time this year. The presence of WNV was confirmed today by the Massachusetts State Public Health Laboratory in two mosquito samples collected July 7 in the town of Belmont in Middlesex County. No human or animal cases of WNV or Eastern Equine Encephalitis (EEE) have been detected so far this year. There is no elevated risk level or risk-level change associated with this finding.

“The first WNV positive mosquito sample has been identified this year in Massachusetts,” said Public Health Commissioner Monica Bharel, MD, MPH. “It is important to remember that WNV can cause very serious illness, especially in individuals over 50 and those who are immune compromised.”

WNV is usually transmitted to humans through the bite of an infected mosquito. There were 5 human cases of WNV in 2019. In 2018, there were 49 human cases of WNV infection acquired in Massachusetts – the greatest number of cases the Commonwealth has ever had in a single year. 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.

“People have an important role to play in protecting themselves and their loved ones from illnesses caused by mosquitoes,” said State Epidemiologist Dr. Catherine Brown. “The tools for prevention include using a mosquito repellent with an EPA-registered ingredient according to the directions on the label, wearing clothing to reduce exposed skin when weather permits, draining standing water to prevent mosquito breeding and repairing window screens to keep mosquitoes out of your home,” she said.

Information about current mosquito activity in Massachusetts is updated daily and can be found here.

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-methane 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 either draining or discarding items that hold water. Check rain gutters and drains. Empty any 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 of your 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.