Like other enteroviruses, polioviruses are quite stable under natural conditions, often surviving in swimming pools, but are inactivated by pasteurization and properly chlorinated drinking water. Control of poliomyelitis using vaccines represents one of the greatest success stories in the battle against infectious diseases (figure 26.18). Ironically, all cases of paralytic polio acquired in the United States between 1980 and 1999 were caused by Sabin's oral, meaning taken by mouth, attenuated polio vaccine introduced in 1961. Because of the small risk of developing paral-
ysis from the vaccine virus, approximately one case per 2.4 million doses given, routine use of the live vaccine was discontinued in the United States in mid-1999. On rare occasions one of the attenuated viruses in the vaccine has reverted to virulence and caused an epidemic of paralytic polio. This happened in July 2000 on the Caribbean island of Hispaniola. The epidemic was quickly controlled by immunizing the population with Sabin vaccine. Despite these drawbacks, the oral vaccine produces better local immunity in the throat and intestine, can spread from person to person, does not require an injection, and is less expensive. It is
680 Chapter 26 Nervous System Infections the preferred vaccine for completing the conquest of the disease in areas of the world where epidemic or endemic poliomyelitis continues to exist.
Poliomyelitis is summarized in table 26.7.
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