Database Reference
In-Depth Information
Chapter 5
Encephalitis
A virus transmitted between hosts, most commonly by mosquitoes and ticks, causes
encephalitis. The disease is kept extant by a complicated transmission process be-
tween 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 them-
selves. 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 Adminis-
tration 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.
5.1 St. Louis Encephalitis
St. Louis encephalitis is the most common form of this disease in the United States,
occurring in 48 states. Few infected people display symptoms, yet nearly 3,000
cases are reported annually. The older one is, the more likely one is to suffer or die
from the infection, with an overall death rate of around 10 percent. Surveillance and
