Entomological Aspects of the 1959 Outbreak of Eastern Encephalitis in New Jersey

Summary An investigation was made of the entomological aspects of the 1959 epidemic and epizootic of EE in New Jersey. Extremely heavy rainfall during July resulted in a record production of mosquitoes, the three most abundant species being Aedes sollicitans, Aedes vexans, and Culiseta melanura. Change in the average wind direction from southwest to south probably increased the contact of salt marsh mosquitoes with humans in the epidemic area. A serum survey of 22 farm chicken flocks indicated that about ⅔ had HAI antibodies to EE and that high rates of EE transmission occurred in both the coastal and inland areas of southern New Jersey. About ⅓ of 92 wild bird sera also had HAI antibodies to EE. All available information supports the hypothesis that: (1) The swamp mosquito, C. melanura, served as the primary sylvan vector which carried EE virus from enzootic swamp foci to peridomestic wild and domestic avian reservoir hosts in both the epidemic (coastal) and episootic (inland) areas; (2) A. sollicitans served as the primary epidemic vector in the coastal area where most of the human cases occurred, obtaining its infection from peridomestic avian reservoir hosts (including chickens) and subsequently transmitting the infection to man; (3) A. vexans served as the primary epizootic vector in the inland area of the equine outbreak, obtaining its infection from peridomestic avian hosts and subeequently transmitting the infection to horses; and (4) A. vexans may also have served as a vector for occasional human cases that occurred in the inland area.