DPH raises alert for West Nile virus

Risk statewide but no human cases found

The risk level for West Nile virus was raised statewide for the second time in Massachusetts history.

The Department of Public Health announced it was raising the risk level from low to moderate in every city and town yesterday, urging residents to take precautions against mosquito bites.

Of the 351 cities and towns in Massachusetts, 162 communities are already considered to be at moderate risk for West Nile virus. There have been no reported human cases of West Nile virus in Massachusetts.

“We’ve come to expect this in Massachusetts because we know that mosquitoes do carry a number of diseases,” said Dr. Daniel Kuritzkes, chief of the Division of Infectious Diseases at Brigham and Women’s Hospital. “On the spectrum of things, West Nile virus is not as concerning as Eastern Equine Encephalitis virus, which we see from time to time. Fortunately we haven’t seen that recently here.”

Public Health Commissioner Monica Bharel said she hasn’t seen any mosquitoes positive for Eastern Equine Encephalitis virus either, also known as triple E.

“What we’re seeing now is we’re seeing more West Nile virus activity in mosquitoes across the state,” Bharel said. “That caused us to raise the risk level.”

This year, in mid-August, they’ve already found 256 positive mosquito samples that tested positive for West Nile, according to Bharel. They found 290 positive mosquito samples in the entire season in 2017, which extends from mid-June through mid-October.

“We want to make sure everyone is aware of the best things to do to avoid mosquito bites as much as possible,” Bharel said. “Most human infections occur in the months of August and September.”

“That’s why we are taking this step today so together we can help keep people from getting sick.” DPH state epidemiologist Dr. Catherine Brown added.

A recent spate of high temperatures and humidity, along with abundant rain contributed to the problem, Bharel said.

“The hot, humid weather in Massachusetts combined with frequent heavy rainfall has provided perfect conditions for mosquito species carrying West Nile virus to breed,” Bharel said.

Though West Nile can infect people of all ages, people over the age of 50 are at higher risk for severe illness. The virus is usually transmitted to humans through the bite of an infected mosquito. Most people infected won’t show symptoms, but one in five will. When present, the symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.

“West Nile virus causes a range of diseases in people,” Kuritzkes said. “They can vary in severity and the most severe manifestations of the infection tend to occur more often in elderly people. … It’s the rare complications that we worry about the most.”