A Mysterious Polio-Like Illness Is on the Rise in Kids. Scientists Don't Know Why.
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Dozens of children across the United States have developed a rare polio-like illness, but the reason for this spike in cases remains a mystery, according to health officials.

Today (Oct. 16), the Centers for Disease Control and Prevention (CDC) announced it had received reports of 127 cases of people with the condition, called acute flaccid myelitis (AFM), in 2018. Of these, 62 cases have been confirmed in 22 states.

Most of these cases began in August and September, and 90 percent are in children, Dr. Nancy Messonnier, director of the CDC's National Center for Immunization and Respiratory Diseases, said at a news conference today.

AFM is a condition that affects the nervous system and causes muscle weakness, according to the CDC. In particular, the condition can cause weakness in the arms and legs along with loss of muscle tone and problems with reflexes. Other symptoms include facial drooping, difficulty moving the eyes, difficulty swallowing and slurred speech. [27 Oddest Medical Cases]

The condition is not new, but officials started to see a rise in cases in 2014; and there was another spike in 2016. So far, the number of cases in 2018 is similar to the number reported in 2014 and 2016, Messonnier said.

"We know this can be frightening for parents," Messonnier said. But she stressed that despite the increase in cases, the illness is still very rare, occurring in fewer than 1 in a million people in the U.S. each year. Still, if a child experiences sudden weakness or loss of muscle tone in their arms or legs, parents should seek medical care right away, she said.

However, officials have not been able to identify the cause of most of the AFM cases, or the reason for the spikes in 2014, 2016 and now 2018.

In a few cases, it appears that the illnesses were linked to viruses, including enterovirus. But officials haven't been able to find a single agent that would explain the clusters of cases that occur around the same time.

"[There's] nothing that provides the unifying diagnosis that we'd expect to explain these peaks of disease," Messonnier said.

And despite the resemblance to polio, officials have ruled out poliovirus as a cause of the illnesses.

Besides viruses, officials are also considering environmental toxins as a possible cause, but so far, they have no evidence that a particular toxin is behind the cases.

The outlook for patients with AFM can vary from a quick recovery to ongoing paralysis, Messonnier said. One child died from AFM in 2017.

Because officials don't know the cause of AFM, they can't recommend a specific way to prevent it. But Messonnier said that, in general, parents can help protect their children from diseases by washing their hands, making sure their children are up to date with vaccinations and applying insect repellent to protect against mosquito bites, which can spread viruses.

Originally published on Live Science.