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LITTLE ROCK, Ark. — Three Arkansas children have been diagnosed with a rare, polio-like illness that can cause paralysis in the arms and legs, according to federal and state health officials.

The U.S. Centers for Disease Control and Prevention confirmed the diagnoses following an investigation into an increase in reported cases of acute flaccid myelitis, or AFM, the Arkansas Department of Health announced on Monday.

AFM was first discovered in 2014 and its symptoms include sudden arm or leg weakness, facial droop, difficulty swallowing and slurred speech.

Health authorities still don’t know how the condition is spread, what causes it or how to prevent it, said state epidemiologist Dr. Dirk Haselow.

The illness targets children between ages 4 and 5, Haselow said. It’s rare for those with the condition to completely regain their strength or mobility.

Haselow said the CDC “identified that the number of cases exceeds what has occurred in the previous couple years, and now they are putting a lot of resources to this to get to the bottom of it as fast as feasible.”

The CDC has confirmed that about 80 acute flaccid myelitis cases have been reported in 25 states this year. There were 33 reported cases last year, down from the 149 cases in 2016, according to the CDC.

Haselow said the condition has been linked with the West Nile virus and certain enteroviruses, with cases increasing in the fall and winter. But there hasn’t been one virus that explains the large cluster, he said.

“That’s sort of what makes this such a dramatic and frankly scary syndrome,” Haselow said. “There’s not a vaccine against this. It isn’t entirely clear how people are getting it and why it’s focusing on children.”