The disease is raising some serious red flags with the Centers for Disease Control and Prevention researchers.
Minnesota's health department has reported six cases of the illness, which is similar to polio, since last month.
The CDC says it starts as a common cold, but later partially paralyzes children.
"Weakness in your arms and in your legs, slurred speech, and facial drooping," Dr. Janette Nesheiwat said.
She said anyone with symptoms should see a doctor right away.
Right now, there is no cure for the illness.