ABSTRACT
In 1952 above-normal snowpack in the Sierra Nevada, a cool, wet spring, and a strong earthquake centered in the Tehachapi Mountains combined to produce conditions that led to the largest epidemic of mosquito-borne encephalitis in California history (Reeves and Hammon, 1962). The elevated snowpack and wet spring led to flooding along the Kern River and the emergence of a large mosquito population — while the earthquake destroyed most of the city of Bakersfield, forcing the population into temporary shelters and thereby increasing human contact with mosquitoes. Morbidity rates for western equine encephalomyelitis virus (WEE) were as high as 100 per 100,000 population in infants (<1 year age group), and many of these patients experienced serious neurological sequelae requiring institutional care (Finley et al., 1955; Longshore et al., 1956). Additional clinical cases were diagnosed with a second virus, St. Louis encephalitis virus (SLE). This epidemic occurred when the size of the human population residing in the southern San Joaquin Valley was relatively small and residents in rural high-risk communities had acquired immunity rates >75% (Reeves and Hammon, 1962). Clearly, an epidemic of this magnitude under current conditions would be devastating and overwhelm the health care system, because population size has increased dramatically and the current population is essentially nonimmune (Reeves and Milby, 1989), with seroprevalence rates <1% (Reisen and Chiles, 1997).
