As equine encephalitis viruses spread from their natural hosts, they generally infect horses 1 or 2 weeks before the first human cases appear. Cases in horses provide a warning to increase protection against mosquitoes. Sentinel chickens serve the same function. They are stationed in cages with free access of mosquitoes, and their blood is tested periodically for evidence of arbovirus infection. A positive test would trigger an encephalitis alert, as for St. Louis encephalitis in Florida:
■ Avoid outdoor activity during evening and night, the peak hours of biting for the Culex mosquito vector. If outdoors, wear long sleeves and pants.
26.3 Viral Diseases of the Nervous System 677
■ Make sure windows and porches are properly screened.
■ Use insect repellents and insecticides.
A vaccine against eastern equine encephalitis is approved for use in horses and has also been used to protect emus, a domesticated meat-producing fowl that is highly susceptible to this virus. There is no proven antiviral therapy for arbovirus encephalitis.
The main features of epidemic viral encephalitis are presented in table 26.6.
Infantile Paralysis, Polio (Poliomyelitis)
The characteristic feature of poliomyelitis is selective destruction of motor nerve cells, usually of the spinal cord, resulting in permanent paralysis of one particular group of muscles, such as those of an arm or leg. The two individuals most responsible for control of this terrifying disease will not see its imminent elimination from the world; Albert Sabin died in 1992, Jonas Salk in 1995. The two men were bitter rivals, both of whom expected, but did not receive, the Nobel Prize.
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