Western Encephalitis Virus in Massachusetts.

Summary The first recognized active infections of western encephalitis (WE) in Massachusetts are described. The virus was isolated from 15 pools of unengorged and 11 pools of engorged Culiseta melanura and from 1 pool of engorged Aedes canadensis collected in southeastern Massachusetts during 1959. and from 3 pools of unengorged C. melanura collected in 1960. The virus also was isolated from the brain of an infected 3-year-old Impeyan pheasant and from the blood of a 3-week-old chicken in 1959. WE and EE (eastern encephalitis) antibodies were detected in domestic fowl hatched and reared in widely separated areas in eastern Massachusetts during 1959. Although no human or equine outbreaks of WE have occurred in the eastern United States, the potential for such an outbreak apparently exists.