West Nile Virus Risk Elevated to High as Fourth Case Announced in Greater Boston

BOSTON (August 27, 2018) - The Massachusetts Department of Public Health (DPH) today announced the fourth human case of West Nile virus (WNV) in the state this year. The person is a woman in her 50s from Middlesex County who was never hospitalized for her illness. Three other cases were reported on Friday.

Investigations conducted by state public health officials indicate that at least two of the four cases were exposed in the greater Boston area leading them to raise the risk level from moderate to high for 11 communities in the area. Those communities are Arlington, Boston, Belmont, Brookline, Cambridge, Chelsea, Everett, Medford, Newton, Somerville, and Watertown.

“Several individuals from the same area have developed West Nile virus,” said Public Health Commissioner Monica Bharel, MD, MPH. “That means that there is an increased risk in this specific area and that additional people could become infected. We are particularly concerned about people over 50 and those who are immunocompromised as they are the ones most likely to develop WNV disease.”

On August 21, DPH raised the risk level for West Nile virus from low to moderate in every Massachusetts city and town. It was only the second time since WNV was first detected in the Commonwealth in 2000 that public health officials have raised the risk level statewide.

For those 11 communities now at high-risk, DPH recommends that local health officials intensify messaging to raise awareness and promote personal protective behaviors, target outreach to high-risk populations, and increase surveillance for human disease.

People at high risk for severe illness are encouraged to consider avoiding outdoor activity at dusk and dawn. Local boards of health should continue to work directly with their Mosquito Control District to determine appropriate control measures.

“It is extremely important for people to take steps to avoid mosquito bites, including using repellents, wearing clothing to reduce exposed skin, dumping standing water, and moving indoors when you notice mosquitoes biting you,’’ said DPH State Epidemiologist Dr. Catherine Brown.

In 2017, there were 6 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.

People can take steps to protect themselves and their loved ones from illnesses caused by mosquitoes.

Avoid Mosquito Bites

• Apply Insect Repellent when Outdoors. Use a repellent with 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% 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.
• Clothing Can Help Reduce Mosquito Bites. Wear long-sleeves, long pants, and socks when outdoors to 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 diagnosed with WNV or EEE, owners are required to report to DAR, Division of Animal Health by calling 617-626-1795 and to the Department of Public Health (DPH) 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 www.mass.gov/dph/mosquito or by calling the DPH Epidemiology Program at 617-983-6800.