Local health officials announced Monday that Belmont, Arlington, Medford, Malden, and Melrose have been upgraded from low to moderate risk for West Nile Virus.
Monday's upgrade means that at least two dozen Massachusetts communities are now at moderate risk, according to the state Department of Public Health's website, including Boston, Brookline, Newton and Cambridge.
According to the state, risk level is moved from low - where human infection of West Nile is unlikely - to moderate when human infection is either likely or has already occurred.
No human cases have been reported in Massachusetts this year, according to state health department spokeswoman Anne Roach.
Belmont's health director, Stefan Russakow, said in an online statement that August is a hot month for West Nile.
"The first several weeks of August are frequently associated with occurrence of human infection with [West Nile], although the infections may not be identified until later," Russakow said in the statement. "While [West Nile] can infect people of all ages, people over the age of 50 are at higher risk for severe infection."
According to the US Centers for Disease Control, one in five people who have contracted West Nile Virus develop a fever, headache, body aches, joint pains, vomiting, diarrhea, or rash, but can usually be cured. Less than 1 percent of those with the disease will develop a neurological illness; about 10 percent of those cases can be fatal.
Last year, a Brookline woman in her 20s was infected with the virus, but recovered.
A Worcester man in his 60s died from the virus earlier last summer, the first death caused by the virus in Massachusetts since 2005.
Residents can avoid mosquito bites while outdoors by wearing insect repellant and sporting long sleeves from dusk to dawn. Since mosquitoes lay eggs in standing water, officials also advise residents to drain any outside their home, including in gutters, drains, or unused flowerpots and wading pools.
Residents can also keep mosquitoes out of their home by making sure all screens in their doors and window are tight-fitting.
For more information, visit the state's health website, or call the state's public health information line at 1-866-MASS-WNV (1-866-627-7968).
Jaclyn Reiss can be reached at firstname.lastname@example.org