The diseased mosquitoes all were found in the same sample in North Dorchester.
Julia Gunn, the commission’s director of the Communicable Disease Control, said the city has put larvicide in targeted locations and has done some spraying, but has no plans to take additional steps at this time.
West Nile virus is spread to humans by mosquito bites and can cause serious illnesses, including meningitis. No humans have tested positive in the state since 2008. People are advised to stay in after dark or cover up and use bug spray