By Ashley Welch CBS News October 17, 2018, 12:40 PM Symptoms of mysterious polio-like illness parents should watch out for

Federal health officials have issued an unusual warning about a growing number of cases of a polio-like illness called acute flaccid myelitis, also known as AFM. The Centers for Disease Control and Prevention announced Tuesday that 62 cases have been confirmed in 22 states in recent weeks. Ninety percent of those affected are children.

"It's rare, but certainly when you hear about it it's very scary for parents," CBS News medical contributor Dr. Tara Narula told "CBS This Morning."

AFM affects the nervous system, specifically the area of spinal cord called gray matter, and causes the muscles and reflexes in the body to become weak or even paralyzed.

The disease is extremely rare, with the CDC estimating that less than one in a million people in the United States will get AFM every year.

Officials began tracking the disease in 2014 when they received reports of 120 cases nationwide. Outbreaks appear to follow an every-other-year pattern with another sharp rise in 2016, primarily in late summer and early fall. That pattern appears to be repeating this year. There have now been a total of 386 confirmed cases since 2014.

Symptoms of AFM

It's important for parents to know the symptoms so they can get their child immediate medical care and help doctors get a handle on the disease.

"Many times it can start with what looks like a respiratory illness, a little bit of a fever," Narula said. "The hallmark is sudden onset of weakness in the arms or the legs. Children can also have trouble swallowing, trouble with their speech, facial droop, trouble with their eye muscles."

The scariest and most severe symptom is when the disease affects the diaphragm, the muscle that helps us breathe.

"That's when children can really deteriorate and end up on a ventilator," Narula explains.

At a press briefing Tuesday, Dr. Nancy Messonnier, director of CDC's National Center for Immunization and Respiratory Diseases, said, "We want to encourage parents to seek medical care right away if you or your child develops symptoms of AFM, such as sudden weakness and loss of muscle tone in your arms or legs."

Doctors diagnose AFM based on a combination of the patient's symptoms and an MRI scan.

What's behind the rise?

Health officials do not know what's causing the increasing number of cases of AFM. It's also unclear why the illness seems to peak in the late summer and fall.

"This is truly a mystery disease," Messonnier told CBS News. "We actually don't know what is causing this increase. For some of the previous cases we've identified one pathogen or another, but we have no unifying diagnosis."

While the cause of AFM is not clear, experts say it can occur as a result of a variety of viral illnesses including the polio virus, enteroviruses, West Nile virus, and adenoviruses. None of the U.S. patients tested positive for polio, a crippling and often deadly disease which was eliminated in this country thanks to the polio vaccine.

Messonnier also said none of this year's cases have been linked to West Nile virus. Several cases have been linked to enteroviruses or other germs, but officials have not been able to find a cause for the majority of the cases.

Treatment for AFM

Unfortunately, there is no specific treatment for AFM, though the CDC says neurologists may suggest options on a case-by-case basis. Doctors may also recommend physical or occupational therapy to help with arm or leg weakness.

"Early intervention is definitely always helpful. Unfortunately there are no real treatments that have been proven to work, but early rehabilitation has been shown to help," Narula said.

Some patients recover completely, while others continue to struggle with muscle weakness.

All the uncertainties are frustrating for parents like Jenna Shumpert, whose son Hunter came down with AFM when he was just 15 months old. He suffered paralysis and had to be put on a ventilator.

"Nobody really knows treatment protocols, they don't know prognosis, and they can't really give parents an answer as to where this is coming from," she said.

Hunter was hospitalized with AFM when he was 15 months old.

Now 3 years old, Hunter has slowly recovered. He continues to get therapy to strengthen his muscles and uses electric stimulation pads to help rejuvenate his damaged nerves.

What parents can do to prevent AFM

The CDC says there are preventive measures people can take to reduce the risk of infections that could lead to AFM.

"Getting vaccinated, taking precaution against mosquitoes, washing hands — all of these things are recommended by the CDC," Narula said.

Vaccines and hand-washing help protect against the spread of viral illnesses, while insect repellent helps ward off the mosquitoes that transmit West Nile virus.