Does Enterovirus Cause Paralysis? Doctors Still Mystified

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Federal health experts issued another call Friday for doctors and hospitals to be on the lookout for a mysterious symptom that causes muscle weakness in some children who have had recent viral infections.

Two reports issued by the Centers for Disease Control and Prevention center on enterovirus-D68, which appears to be causing more infections than usual of late, and a potential link with a rare type of muscle weakness. Even so, the vast majority of infections are very mild and almost all children get better on their own.

That link is hard to pin down, said Dr. Daniel Feikin of the CDC’s National Center for Immunization and Respiratory Diseases. Only some of the children with the symptoms, which include characteristic lesions that show up on a magnetic resonance imaging or MRI scan, also have had infections with EV-D68. And the virus doesn’t turn up in the spinal fluid, which would have been expected if it was the culprit in the nerve and muscular symptoms.

And doctors and hospitals are not required to report cases of paralysis or muscle weakness, so it’s a little hard to paint a clear picture of what is or isn’t happening.

Feikin says he is concerned about a cluster of cases in Colorado affecting 10 children. This many cases in such a short time is not usual, he told NBC News. But doctors have only found EV-D68 in four of the children.

It’s possible to calculate how many cases there should be, says Karen Mason of the CDC’s Division of Viral Diseases. “Among children under 15 years of age, in the absence of polio, acute flaccid paralysis (AFP) typically occurs at a rate of at least 1 per 100,000 children annually,” she said.

“Since there are 62 million children under 15 years of age in the U.S., at least 620 cases of AFP in this age group are likely to occur each year throughout the country.”

But viral diseases are extremely common, so even if a viral infection caused the partial muscle weakness, it would be in only a fraction of a percent of children. "Enteroviruses circulate widely in the United States, causing an estimated 10–15 million symptomatic, mostly non-neurologic illnesses annually," the CDC team wrote in one report.

Polio is the worst cause of AFP. That’s been eliminated in the U.S. by vaccination, but the CDC says doctors need to be on the lookout for polio anyway, since it’s still circulating in Pakistan and some other countries.

Guillain-Barre syndrome, a disorder caused by an abnormal immune response, is another common cause. Enteroviruses, adenovirus and West Nile virus can also sometimes cause it, but it can be very hard to show a virus caused someone’s symptoms.

Also on Friday, California officials said they’d tracked down 35 patients with acute flaccid paralysis since 2012. “Of these patients, three have had infection with EV-D68, two in 2012 and one in 2014,” the California health department said in a statement. “Because EV-D68 was found in respiratory specimens from these patients, it is not known whether EV-D68 was a cause of paralysis or a coincidental finding.”