Mosquitoes in five more Connecticut towns have tested positive for eastern equine encephalitis since the first case of the rare but serious disease was detected in Thompson last week.

Data shared by the Connecticut Agricultural Experiment Station, the state agency that handles mosquito trapping and testing, shows EEE has surfaced in Hampton, Killingly, Thompson, Tolland, Voluntown and Woodstock as of Tuesday. In total, nine mosquitoes have been found to be infected: one in Hampton, one in Killingly, one in Thompson, two in Tolland, three in Voluntown and one in Woodstock. The Thompson case was reported on Sept. 4.

In contrast, 117 mosquitoes have tested positive for the much more common West Nile virus statewide as of Tuesday, according to the same data. While West Nile virus is perhaps the most well-known mosquito-borne disease in the country, EEE is significantly more deadly. Roughly one-third of those infected will die, and the majority of the survivors will be left with severe permanent neurological damage.

Of the nine mosquito EEE cases detected in Connecticut so far in 2023, seven have involved Culiseta melanura, the black-tailed mosquito, CAES data shows. The species, a major vector for the virus, has a habitat preference for the hardwood swamps of rural southeastern Connecticut, Philip Armstrong, director of the CAES mosquito monitoring program, previously told Hearst Connecticut Media. A map provided by CAES shows most of the nine EEE cases have occurred in the state's northeastern corner.

Cases of EEE in humans tend to occur in clusters every four to five years, according to Armstrong. During the most recent outbreak in 2019, four human cases were reported in Connecticut, three of which proved fatal, Armstrong said.