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Epidemiologic Notes and Reports Arboviral Encephalitis -- United States, 1982

Sixteen cases of arboviral encephalitis in humans have been reported from four states (Florida, Georgia, New York, and Wisconsin) in 1982.

In Florida, a fatal case of eastern equine encephalitis (EEE) was confirmed in a 75-year-old resident of Orlando, with onset of illness on June 12. A second suspected case in a 14-year-old male from central Florida, onset July 23, is currently under investigation. Evidence of EEE viral activity was provided by seroconversions between May 31 and July 16 in 26 of 1494 sentinel chickens in nine counties. Approximately 150 clinical cases of encephalitis have occurred among horses in northern and central Florida; EEE virus has been isolated from the brains of four animals, and 58 cases have serologic evidence for EEE infection. The incidence of equine cases far exceeds that for 1981 (eight cases with serologic evidence).

In south Georgia, two human cases of EEE have been reported: one from Lowndes County (47-year-old female, with illness onset July 18, fatal outcome) and one from Brantley County (2-year-old male, onset July 10, recovered). Equine cases appeared in late June and continue to be reported from the southern part of the state; of approximately 50 cases recognized to date, 18 have been confirmed by virus isolation. EEE has affected penned quail and pheasants on six farms, resulting in over 4,000 deaths, principally among young birds.

Coincident with increased activity of EEE virus in Georgia is an unusual incidence of California encephalitis. In May and June, five serologically confirmed cases occurred in children 3 months to 10 years of age residing in Bacon County (one case), Coffee County (two), Crisp County (one), and Jeff Davis County (two). For three of the cases, La Crosse virus was identified by neutralization tests as the etiologic agent. Other cases are currently under investigation, and active surveillance has been initiated.

New York has reported one confirmed and six presumed cases of California encephalitis. One patient, a 3-year-old female from Rensselaer County, onset July 20, has been confirmed as having a case of La Crosse encephalitis. The other cases have been diagnosed presumptively (on the basis of antibody in a single serum sample) as Jamestown Canyon virus (two patients who died, ages 45 and 79, from Albany County, onsets June 1 and 2; one who died, age 86, from Suffolk County, onset July 8; one who recovered, age 4, from Niagara County, onset June 2; one who recovered, age 33, from Saratoga County, onset July 8; and one who recovered, age 70, from Ulster County, onset June 25).

In Wisconsin, one serologically confirmed case of La Crosse encephalitis has been reported in a 10-year-old girl from Prairie du Chien, onset July 10.

Other states have reported arboviral encephalitis in domestic animals but not humans. Single cases of western equine encephalitis (WEE) have occurred in Arizona, California, Colorado, and Texas; and seven cases of unspecified etiology (presumably WEE) have been reported from North Dakota. Equine cases of EEE have been documented in South Carolina.

Although no human cases of St. Louis encephalitis (SLE) have been recognized, low prevalences of SLE antibodies have been detected in juvenile wild birds in Kentucky, Mississippi, Ohio, and Tennessee. Reported by HL Rubin, DVM, Kissimee Diagnostic Laboratory, Florida Dept of Agriculture and Consumer Svcs, CL Campbell, DVM, Florida Dept of Agriculture and Consumer Svcs, E Buff, HT Janowski, JA Mulrennan Jr, PhD, FM Wellings, RA Gunn, MD, State Epidemiologist, Florida Dept of Health and Rehabilitative Svcs; DM Bedell, DVM, Extension Veterinarian, University of Georgia, Personnel of the Veterinary Diagnostic and Investigational Laboratory, College of Veterinary Medicine, Tifton; RK Sikes, DVM, State Epidemiologist, Georgia Dept of Human Resources; R Deibel, PhD, S Srihongse, MD, Virus Laboratories, State of New York Dept of Health; W Thompson, DVM, JP Davis, MD, State Epidemiologist, Wisconsin State Dept of Health and Social Svcs; JK Emerson, DVM, Colorado State Dept of Health; CR Webb, Jr, MD, State Epidemiologist, Texas Dept of Health; Viral and Rickettsial Disease Laboratory Section, Vector Biology and Control Section, and Infectious Disease Section, California Dept of Health Svcs; PM Hotchkiss, DVM, Acting State Epidemiologist, Arizona State Dept of Health Svcs; K Mosser, State Epidemiologist, North Dakota State Dept of Health; RL Parker, DVM, State Epidemiologist, South Carolina State Dept of Health and Environmental Control; JM Joseph, PhD, Bureau of Laboratories, Maryland State Dept of Health and Mental Hygiene; J McCammon, PhD, Louisville-Jefferson County, Kentucky Board of Health; Vector-Borne Disease Unit, Ohio Dept of Health; JG Hamm, JB Mullenix, JR Oates, WP Kelly, Memphis-Shelby County, Tennessee Health Dept; DL Sykes, Gulf Coast Mosquito Control Commission, Gulfport, Mississippi; Div Vector-Borne Viral Diseases, Center for Infectious Diseases, CDC.

Editorial Note

Editorial Note: EEE is a rare disease of man in the United States; in the past decade, the annual incidence has been less than or equal to eight cases (1). The disease occurs principally along the Atlantic and Gulf coasts, as well as inland near fresh-water swamps. The virus is maintained in a cycle involving Culiseta melanura mosquitoes and wild birds, but epidemic transmission to horses and humans may involve other vectors, including species of Aedes and Coquillettidia. The excess of cases in central Florida and Georgia in 1982 is believed to be due to heavy rains, resulting in high populations of mosquito vectors. A peculiar aspect of the epidemiology of EEE is the occurrence of epornitics in penned exotic birds (quail, pheasants, chukar partridges), with attack rates of up to 50% and serious economic losses. In these flocks, EEE virus is transmitted directly from bird-to-bird by pecking and cannibalism.

The high incidence of California encephalitis in Georgia due to La Crosse virus is also unusual. This virus is responsible for 50 to 150 cases annually in the United States; although previously reported in Georgia and elsewhere in the southern United States, La Crosse encephalitis predominantly affects the northcentral states. The principal vector is A. triseriatus, which breeds in tree-holes and peridomestic containers. Excessive rainfall in the area may be a factor in increased vector density and viral activity.

Jamestown Canyon virus, also a member of the California virus serogroup, has been clearly implicated as a human pathogen only since 1980. In addition to the reports from New York, isolated encephalitis cases have been found in Indiana and Ontario, Canada. Of interest is the age distribution of the New York patients (five of six cases among adults, three over 70 years of age) and the high case-fatality rate. In contrast, La Crosse virus principally affects children under 12 years of age and has a low case-fatality rate (under 1%). It should be emphasized that the New York cases were presumptively diagnosed on the basis of antibody in a single serum, a finding that may reflect remote infection unrelated to the current illness. In New York, Jamestown Canyon virus is transmitted by A. communis group mosquitoes; deer are the primary vertebrate host in the cycle, but transovarial transmission in the vector is important in maintenance of the virus.


  1. Monath TP. Arthropod-borne encephalitides in the Americas. Bull WHO 1979;57:513-33. NOTE: In Vol. 31, No.32

In the article, "Arboviral Encephalitis -- United States, 1982", three New York State presumptive cases of California encephalitis were reported in persons who died. Follow-up of these serologically presumptive cases has essentially ruled out California encephalitis: one had a 4-fold rise in diagnostic titer to herpes simplex; one had carcinomatous meningitis; and one presented with mental confusion secondary to pneumonia.

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