Massachusetts health officials announced Tuesday they were raising the risk level for West Nile virus from low to moderate statewide.
Department of Public Health officials said of the 351 cities and towns in Massachusetts, 162 communities are already considered to be at moderate risk for the virus.
Since the virus first appeared in Massachusetts in 2000, the department tells NBC10 Boston this is only the second time the risk level has been increased statewide. The only other such instance came in 2012, when 33 human cases were confirmed in the Bay State.
The DPH is urging residents to take precautions against mosquito bites due to the recent hot and humid weather combined with heavy rainfall the region has received which they say provide perfect conditions for mosquitos carrying West Nile to breed.
"I strongly encourage everyone to keep using insect repellant and to be especially aware of mosquito activity at dusk and dawn when the risk of being bitten by mosquitoes is greatest. Move indoors if you are getting bitten," said Public Health Commissioner Monica Bharel, MD, MPH.
In early July, mosquitoes in Boston's Jamaica Plain neighborhood tested positive for West Nile virus for the first time this season.
"This year, pretty much everywhere we look for the virus, we're finding it in mosquitoes," said DPH State Epidemiologist Dr. Catherine Brown.
Health officials say West Nile can infect people of all ages but people over the age of 50 are at higher risk. The disease is usually transmitted to humans through the bite of an infected mosquito.
While there have been no confirmed human cases of the virus this year, Brown says the weather conditions not only increase mosquito breeding, but also the likelihood that they could spread the virus.
"We know that heat and the amount of rain that we've had this summer, those certainly contribute to the problem," Brown said. "When the weather is warmer, they develop the ability to transmit that virus, to give it to a person faster."
Most people infected with West Nile will have no symptoms but when present, symptoms tend to include fever and flu-like illness. In rare cases, more severe illness can occur.
"August and September are the months when most human cases occur," said Brown. "That’s why we are taking this step today so together we can help keep people from getting sick."