Cases of the polio-like disease  acute flaccid myelitis, or AFM, which causes paralysis in children, is on the rise in the United States.

The U.S. Centers for Disease Control and Prevention, which has been monitoring cases of this rare condition since 2014, reported a spike in this mysterious illness documenting 50 cases in 24 states from January to August this year, a significant increase from the number recorded last year. Of those affected, 90 percent were children.

What makes this rare condition very scary, according to Aaron Michael Milstone, from John Hopkins University School of Medicine, is that it is a polio-like disease that can show up even in healthy children.

Just like the crippling and potentially deadly polio, AFM affects the nervous system of the body particularly the spinal cord but unlike polio, which can be prevented with a vaccine, AFM does not have any available vaccine.

Much about the illness, particularly its exact cause, remains unknown but scientists think that the disease is likely the result of a viral infection. Health officials said that AFM can occur as a result of a variety of germs, which include the mosquito-borne West Nile virus, enteroviruses and adenoviruses.

"AFM is an illness that can be seen with a variety of different causes. The most famous one is polio, but there are also enteroviruses, which are circulating very broadly in the US and other countries," said Manisha Patel, CDC AFM team lead.

When initial cases of the condition were reported two years ago, many doctors believed it was associated with an outbreak of the respiratory virus Enterovirus D68, which hospitalized hundreds of children.

Although enteroviruses are known to cause only mild illnesses such as the common cold, it can have stronger effects in the immune system of younger individuals.

The CDC said that other potential culprits include genetic disorders, Guillain-Barré syndrome and environmental toxins.

Patel said that sudden limb weakness is a sign of the illness and that a limp may signal the presence of this mysterious disease.

Patel said that the key to identifying the disease is its sudden onset. Other symptoms include facial drooping and difficulty talking and swallowing. Urination may also be difficult in some patients.

When should parents seek help from pediatricians? Milstone suggested watching for certain symptoms.

"If they have weakness in the leg, the child may not walk right, they may limp a little or if they have trouble holding up their arms," Milstone said.