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Vital Signs

Viral marketing: Spreading the word of a new threat

By Laura Stephenson Carter

Ahundred years ago, a devastating illness—polio—swept the world. It could invade the central nervous system (CNS), paralyzing and even killing some victims. Thanks to vaccines developed in the 1950s, polio has now been nearly wiped out. But another equally devastating virus may be taking its place. Enterovirus 71 has polio's knack for attacking the CNS. And there have been several outbreaks, including some in the U.S.

Threat: Health officials need to prepare for this emerging threat, warns DMS's Dr. John Modlin, an international expert in enteroviruses and infectious diseases. The former chair of the national Advisory Committee on Immunization Practices, he spelled out the situation in a recent article in the New England Journal of Medicine.

"I'm one of a handful of people who are concerned about it," says Modlin. "Until we see larger outbreaks closer to our home soil, I doubt that we're going to interest a large number of people [in] looking at this virus."

Enteroviruses are almost as common as rhinoviruses, which cause the common cold. More than 90 types have been identified, including polioviruses, coxsackieviruses, and echoviruses. Since enteroviruses are excreted in stool, fecal contamination is the major way they're transmitted. They can also be spread by person-to-person contact within households. Most infected people do not become ill, and those who do usually develop only mild upper-respiratory symptoms, a flu-like illness with fever and muscle aches, or a rash.

Scary: "You can kind of look at these viruses as summer flu," according to Modlin. "Only a minority of those who are infected have any symptoms, and only a minority of those will have serious neurologic disease." Poliovirus and enterovirus 71 are the only enteroviruses known to attack the CNS. And the scary thing is that when enterovirus 71 does trigger neurologic symptoms, says Modlin, they can be worse than in polio and are more likely to be fatal.

Enterovirus 71 was first isolated in California in 1969. Since then, it has caused epidemics in Eastern Europe in 1975 and 1978 and in Southeast Asia between 1997 and 2000. "The most recent focus of increased incidence in the U.S. was in the Denver area a couple of years ago, where there were five or six cases of serious disease," says Modlin.

Outbreaks: What has him most concerned are some large outbreaks, such as one in 1998 in Taiwan; at least 130,000 people there were infected, 405 were hospitalized for CNS symptoms, and 78 died. "These outbreaks looked very much epidemiologically and clinically like the large outbreaks of polio that we saw 100 years ago in New York and Boston," says Modlin. Early symptoms of poliovirus include sore throat and fever. If the CNS is affected, a stiff neck and paralysis may soon follow.

Early symptoms of enterovirus 71 can include hand-foot-mouth syndrome. Common to other enteroviruses, too, the syndrome causes a fever; sore throat; and painful red bumps on the hands and feet, inside the mouth, and sometimes on the buttocks. As in polio, if neurologic illness does develop, enterovirus 71 begins to invade the ventral brain stem, cerebellum, and spinal cord; this can cause a number of serious neuromotor problems, such as paralysis of one or more extremities, as well as acute pulmonary edema, or fluid in the lungs.

Vaccine: There is now no vaccine for the virus, but the Soviet Union developed one in the 1970s when Bulgaria had a large outbreak. But the outbreak subsided and the vaccine was never used, so it's unknown whether it would have been effective.

Yet "it should be technically feasible to produce a vaccine," Modlin feels. For more with Modlin, see this article's Web Extras.

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