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Neurology => Nervous System => Encephalitis
Encephalitis
INTRODUCTION
Encephalitis, any infectious disease of the human central nervous system characterized by inflammation of the brain. The typical symptoms are headache, fever, and extreme lethargy, which lead eventually to coma; double vision, delirium, deafness, and facial palsy often occur in the acute stage of the disease. After effects of encephalitis may include deafness, epilepsy, and dementia.
Several types of encephalitis are caused by viral infection of the central nervous system. These types fall into two main groups, primary neurotropic-virus infections and secondary infections occurring as complications of a primary virus infection elsewhere in the body.
NEUROTROPIC-VIRUS ENCEPHALITIS
The neurotropic-virus encephalitis group comprises several epidemic diseases that primarily affect wild and domestic animals and birds. The disease is transmitted to human beings from these animals by insect carriers. St Louis encephalitis, first recognized in 1933 during an epidemic in St Louis, Missouri, United States, is transmitted to humans by mosquito bites. Other mosquito-borne types of encephalitis are Japanese B encephalitis, California encephalitis, and equine encephalitis. Ticks are the insect carriers of Russian spring-summer encephalitis.
SECONDARY VIRUS INFECTIONS
The group of secondary virus infections includes two types, postinfective encephalitis and postvaccinal encephalitis. The first type occurs as an occasional complication of certain viral diseases, including mumps, measles, influenza, and yellow fever. Occasionally infections with the herpes virus involve the brain and cause brain damage or death. The second type may occur, although very infrequently, following the first vaccination with such attenuated-virus vaccines as those against smallpox and yellow fever.
OTHER TYPES
Encephalitis may occur as a result of an infection from a sporozoa called Toxoplasma, which is parasitic in animals, birds, and human beings. It can also be due to trypanosomiasis infection with the protozoan Trypanosoma cruzi, transmitted by the bite of the tsetse fly. In addition, forms of apparently non-infectious encephalitis occur occasionally as a complication in cases of poisoning from contact with heavy metals, particularly lead.
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