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How worried should we be about a new ‘polio-like’ virus?

California health officials have documented 20 to 25 recent cases of paralysis in kids that they believe are linked to a polio-like virus—but not caused by polio itself. While that sounds pretty frightening, paralysis caused by infectious diseases is quite rare.

Some, but not all, of the children tested positive for enterovirus-68, a respiratory virus that, in rare cases, has been associated with polio-like limb paralysis and breathing problems. The California children were all vaccinated against polio, but not against enterovirus-68 which has no vaccine.

“Enteroviruses are among the most common viruses causing respiratory tract illnesses in children,” said Dr. Al DeMaria, state epidemiologist at the Massachusetts Department of Public Health.

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Various strains can cause coughing, sore throats and sneezing and can also infect the gastrointestinal tract leading to diarrhea and vomiting. Far less commonly, this virus could, like polio, invade the bloodstream and attack nerve cells in the spine sometimes causing irreversible paralysis in the arms and legs.

“We found enterovirus-68 in two of out the five children we treated but detected it in a nasal swab, not in the blood or spinal fluid,” said Dr. Emmanuelle Waubant, a neurologist at the University of California, San Francisco, who has been involved in the investigation. “We have not been able to find the virus in our three other patients either because they weren’t infected or had already cleared the virus when they came to us.

As with polio, the paralysis cases seen by the California doctors have not responded to standards medical treatments like steroids.

“With polio, 1 in every 1,000 children who were infected developed paralysis,” DeMaria said, “and at its height, polio caused 20,000 to 30,000 cases of paralysis per year.” No one knows how common paralysis is with rare enterovirus-68 infections, but it’s likely far less common than with polio—perhaps between 1 in 10,000 to 1 in 100,000 infections, DeMaria estimated.

“It’s something we need to keep an eye on,” he said, although no cases of paralysis linked to these respiratory infections have been reported to the state health department.

While doctors must report measles and pediatric flu deaths to public health officials, they don’t need to report unexplained paralysis, so DeMaria said a handful of single cases might have occurred in the state that he hasn’t heard about.

Dr. Keith Van Haren, a pediatric neurologist at Lucile Packard Children’s Hospital at Stanford University, alerted the California Department of Public Health last year after he treated five children for paralysis that did not resolve with steroids and other treatments. The California Department of Public Health has since identified 15 to 20 more sudden paralysis cases occuring mostly in children, but health officials there have not yet found a common link between them.

“It sounds bad because it’s something that looks like polio,” Waubant said, “but the number of cases has been small considering how large California is. We don’t think it’s an epidemic and, if anything, it might have been a small outbreak of a rare infection.”

Enterovirus-71, which circulates widely in Asia, can also cause a polio-like paralysis, as can the enterovirus Coxsackie virus infection, which causes hand-foot-and-mouth disease. But the vast majority of children who get these infections have just a few days of symptoms that resolve on their own.

The best protection for now, DeMaria said, is prevention of the infection’s spread through frequent hand washing and by keeping sick kids home from school.

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