Skip Navigation LinksSkip Navigation Links
Centers for Disease Control and Prevention
Safer Healthier People
Blue White
Blue White
bottom curve
CDC Home Search Health Topics A-Z spacer spacer
Blue curve MMWR spacer

Epidemiologic Notes and Reports Arboviral Encephalitis -- United States, 1983

Thus far in 1983, 22 cases of arboviral encephalitis in humans have been reported in the United States; additional cases have been reported in horses, chickens, and wild birds.

Eastern Equine Encephalitis (EEE): Nine human cases of EEE have been diagnosed by virus isolation or serology. Three cases occurred in Florida: a 12-year-old boy from Marion County developed symptoms on July 12 and has recovered with mild residual hemiparesis; a 66-year-old woman from Walton County had onset July 16 and died July 26; a 7-year-old girl from Pensacola had onset of a relatively mild illness July 14 and has recovered. Five confirmed cases have been reported from Massachusetts. Three had presumed exposure in the southeastern part of the state (Plymouth and Bristol Counties): a 64-year-old man with onset August 4 had a fatal case; a 28-year-old woman who developed symptoms about August 11; and an 11-year-old boy with onset August 12 have recovered. A fourth case occurred in a 53-year-old Massachusetts man from Randolph who had onset between August 15 and 17 and remains comatose. A fifth case occurred August 18 in a 58-year-old Norwood woman who recovered. A confirmed case occurred in a 49-year-old woman from Lowndes County, Georgia, who had onset July 14; she recovered but has neurological sequelae.

Cases of EEE in horses have been reported from Florida (55 cases), Louisiana (6), New York (6), New Jersey (5), Masssachusetts (4), Rhode Island (4), Michigan (3), Alabama (2), Mississippi (2), Tennessee (2), Georgia (1), and Maryland (1).

Western Equine Encephalitis (WEE): No human cases have been reported. Cases in horses have occurred in South Dakota (6 cases with laboratory evidence), North Dakota (3), California (2), Kansas (2), Minnesota (2), Montana (2), Texas (2), Arizona (1), and New Mexico (1). WEE virus transmission is at a high level, as reflected by isolations from Culex tarsalis mosquitoes in parts of Arizona, California, Minnesota, and North Dakota. Vector control efforts have been undertaken in some areas; aerial spraying of malathion has been initiated in a 29-county area of west-central and northwestern Minnesota.

St. Louis Encephalitis (SLE): Two serologically confirmed, non-fatal cases of SLE have been reported (one in a 24-year-old woman from near Yuma, Arizona, with onset June 20, and a second in a 3-year-old boy from Bard, California, with onset July 26). A high rate of SLE virus transmission in flooded areas of southern Arizona has been demonstrated by testing Cx. tarsalis collected in early August. In the central and southeastern United States (Alabama, Florida, Illinois, Indiana, Kentucky, Mississippi, Ohio, and Tennessee) SLE virus activity determined by serologic surveillance of wild birds and sentinel chickens has been minimal. In Texas, the virus has been recovered from Cx. pipiens mosquitoes in Harris County.

California Virus Group Encephalitis: Eleven confirmed and presumptive human cases have been reported. Five cases occurred in Illinois (an 11-year-old boy, Peoria County, onset June 14; a 6-year-old boy, Du Page County, July 12; a 4-year-old boy, Woodford County, July 20; a 14-year-old girl, Edgar County, July 22; and a 12-year-old girl, Marion County, July 24). Five cases occurred in Ohio (a 7-year-old boy, Liking County, onset July 13; a 6-year-old girl, Franklin County, July 16; an 8-year-old girl, Cuyahoga County, late July; a 9-year-old boy, Hawking County, early August; and a 5-year-old girl, Sandusky County, early August). One case occurred in Wisconsin (a 22-month-old boy from Vernon County, onset July 15). Reported by WE Birch, MD, State Epidemiologist, Alabama Dept of Public Health; ME Wright, RL Coppedge, MD, Acting State Epidemiologist, Arizona Dept of Health Svcs; R Roberto, MD, J Chin, MD, State Epidemiologist, California State Dept of Health Svcs; W Bigler, PhD, FE Sorhage, VMD, JJ Sacks, MD, Acting State Epidemiologist, Florida State Dept of Health and Rehabilitative Svcs; RK Sikes, DVM, State Epidemiologist, Georgia Dept of Human Resources; R Martin, DVM, C Langkop, BJ Francis, MD, State Epidemiologist, Illinois State Dept of Public Health; M Sinsko, PhD, CL Barrett, MD, State Epidemiologist, Indiana State Board of Health; DE Wilcox, MD, State Epidemiologist, Kansas State Dept of Health and Environment; L McFarland, MD, CT Caraway, DVM, State Epidemiologist, Louisiana State Dept of Health and Human Resources; E Israel, MD, State Epidemiologist, Maryland State Dept of Health and Mental Hygiene; MT Osterholm, PhD, AG Dean, MD, State Epidemiologist, Minnesota State Dept of Health; JK Gedrose, State Epidemiologist, Montana State Department of Health and Environmental Sciences; WE Parkin, DVM, State Epidemiologist, New Jersey State Dept of Health; J Montes, JM Mann, MD, New Mexico Health and Environment Department; M Jones, MD, R Rothenberg, MD, State Epidemiologist, New York State Dept of Health; JL Pearson, DrPH, Acting State Epidemiologist, North Dakota State Dept of Health; ED Peterson, TJ Halpin, MD, State Epidemiologist, Ohio State Dept of Health; R Keenlyside, MD, J Weisfeld, MD, Acting State Epidemiologist, Rhode Island State Dept of Health; KA Senger, State Epidemiologist, South Dakota Dept of Health; RH Hutcheson, Jr, MD, State Epidemiologist, Tennessee State Dept of Public Health; G Hunt, PhD, Harris County Mosquito Control District, C Reed, MPH, TL Gustafson, MD, Acting State Epidemiologist, Texas State Dept of Health; R Steketee, MD, JP Davis, MD, State Epidemiologist, Wisconsin State Dept of Health and Social Svcs; National Veterinary Diagnostic Laboratory, U.S. Dept of Agriculture, Ames, Iowa; Div of Vector-Borne Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: In 1982, there were 13 reported cases of EEE in the United States, the largest number since 1959 (when 36 cases occurred, most during an outbreak in coastal New Jersey). Increased EEE virus activity has often occurred in two successive years. In 1983, EEE virus transmission appeared earlier than in previous years in some areas. The first equine case in New Jersey, with onset July 8, was the earliest ever recorded in the state.

The area affected in southeastern Massachusetts is characterized by fresh-water marshes, wooded swamps, and small lakes and ponds, where EEE virus is transmitted every summer in its enzootic cycle involving birds and Culiseta melanura mosquitoes. Other vector species, including Coquillettidia perturbans and Aedes species, are responsible for spreading the virus from the enzootic cycle to clinical hosts (horses and humans). Climatologic factors appear important in amplifying EEE virus activity. In southeastern Massachusetts, the danger of an EEE outbreak is associated with the second consecutive year of excessive rainfall (1,2), and this pattern has been seen in outbreak years (1955, 1973, and 1983).


  1. Hayes RO, Hess AD. Climatological conditions associated with outbreaks of eastern encephalitis. Am J Trop Med Hyg 1964;13:851-8.

  2. Grady GF, Maxfield HK, Hildreth SW, et al. Eastern equine encephalitis in Massachusetts, 1957-1976. A prospective study centered upon analyses of mosquitoes. Am J Epidemiol 1978;107:170-8.

Disclaimer   All MMWR HTML documents published before January 1993 are electronic conversions from ASCII text into HTML. This conversion may have resulted in character translation or format errors in the HTML version. Users should not rely on this HTML document, but are referred to the original MMWR paper copy for the official text, figures, and tables. An original paper copy of this issue can be obtained from the Superintendent of Documents, U.S. Government Printing Office (GPO), Washington, DC 20402-9371; telephone: (202) 512-1800. Contact GPO for current prices.

**Questions or messages regarding errors in formatting should be addressed to

Page converted: 08/05/98


Safer, Healthier People

Morbidity and Mortality Weekly Report
Centers for Disease Control and Prevention
1600 Clifton Rd, MailStop E-90, Atlanta, GA 30333, U.S.A


Department of Health
and Human Services

This page last reviewed 5/2/01