Microcheck 263

Many different kinds of viruses can attack the nervous system, but they generally do so in only a small percentage of the people they infect. At least half of viral meningitis cases are caused by the enterovirus subgroup of picornaviruses, which are generally spread by the fecal-oral route. Viral meningitis is usually benign, but viral encephalitis often causes permanent disability. Arboviruses maintained in nature in a mosquito-bird or -rodent cycle are a leading cause of epidemic viral encephalitis. Sporadic viral encephalitis is usually due to herpes simplex virus. Poliomyelitis, characterized by paralysis of one or more muscle groups, is caused by three other enteroviruses. Rabies is a widespread zoonosis, almost uniformly fatal for humans, usually transmitted by animal bites.

Table 26.8 Rabies

Symptoms

Fever, headache, nausea, vomiting, sore throat, cough at onset; later, spasms of the muscles of mouth and throat, coma, and death

Incubation period

Usually 30 to 60 days; sometimes many months or years

Causative agent

Rabies virus, single-stranded RNA, rhabdovirus family; has an unusual bullet shape

Pathogenesis

During incubation period, virus multiplies at site of bite, then travels via nerves to the central nervous system; here it multiplies and spreads outward via multiple nerves to infect heart and other organs

Epidemiology

Bite of rabid animal, usually a bat. Inhalation is another possible mode

Prevention and treatment

Avoid suspect animals; immunize pets. Effective post-exposure measures: immediately wash wound with soap and water and apply antiseptic; inject rabies vaccine and human rabies antiserum as soon as possible. No effective treatment once symptoms begin

■ Name one cause of viral meningitis that is preventable by vaccination.

■ Discuss the likelihood of person-to-person spread of viral encephalitis.

■ Why is rabies now rare in humans when it is so common in wildlife?

■ Why is the Sabin vaccine against poliomyelitis the preferred vaccine to use in countries where polio is still prevalent?

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