Encephalitis

A virus transmitted between hosts, most commonly by mosquitoes and ticks, causes encephalitis. The disease is kept extant by a complicated transmission process between humans and a vertebrate host such as a horse. Humans and domestic animals are terminal hosts. They suffer from the disease but do not spread the disease themselves. Several paths of transmission and several variants of the virus are known. Most often, the transmitting vector (mosquito or tick, for example) will pass the virus to his or her own offspring.

Four distinct types of mosquito-transmitted encephalitis are found in the United States: western equine, eastern equine, St. Louis, and La Crosse. The time period for appearance of the disease is from June through September and even into winter in the warm parts of the country. The virus causes flu-like symptoms that are seldom fatal. Currently, antibiotics and vaccines approved by the Food and Drug Administration are ineffective. The disease is best prevented in humans by the use of specific pesticides and protective clothing and by avoiding the transmitting insects.

Detailed data for this serious public health problem have been collected in many parts of the country. Yet, relatively few models of the disease have been made. We offer one such model of St. Louis encephalitis in Illinois. Models of this disease are useful as public health instruments as they enable better prediction of the conditions for its appearance, and because they can be used to evaluate the effectiveness of intervention programs.

The combination of good models, an aware public, and an alert and efficient public health service can combine to effectively control this disease.