What you need to know about the 'polio-like' illness popping up around the U.S.

A rapidly progressing “polio-like” illness is leaving children in numerous states paralyzed – and experts aren’t sure what’s causing the kids to fall ill.

The rare disease, called Acute Flaccid Myelitis (AFM), causes an “inflammation of spinal cord” that resembles cases of polio from the 20th century, Johns Hopkins associate professor of neurology and pathology Dr. Carlos A. Pardo told the Daily News.

Cases of AFM have recently been reported in at least five states: Minnesota, Washington, Illinois, Colorado and Pennsylvania.

The exact cause of AFM is unknown — it may be a new virus that some children do not have enough immunity to combat and therefore have a bad reaction where the nervous system fails, or the virus attacks the spinal cord directly.

“The CDC found evidence of enterovirus D68 in respiratory samples in approximately 20% of patients affected, and other viruses in another 20%, though in the majority of cases a trigger was not identified,” Assistant Professor of Neurology at Columbia University Medical Center and neuroinfectious disease expert Dr. Kiran Thakur told The News. “Most patients presented with an acute febrile illness preceding the onset of weakness, so we think an infection triggered AFM, though we often cannot prove this by lab testing.”

The CDC estimates there are fewer than 1 million cases of AFM each year, with 362 cases identified in the U.S. since 2014.

The timeline from the onset of symptoms to loss of motor function is short.

“It shows with an upper respiratory infection with quick onset of a fever and paralysis,” Pardo said.

The disease rapidly progresses within 24 hours. Patients might begin to feel weak and have difficulty breathing. Paralysis of the limbs begins to set in.

In a study at Johns Hopkins, Pardo noted some patients had lost feeling in all four limbs in under six hours.

Parents should seek medical care immediately if concerning symptoms appear.

Patients often remain in intensive care for weeks after acquiring AFM and many will require mechanical ventilation.

“A small percentage have some recovery, but patients are left with severe neurological disability or paralysis,” Pardo said.

Pardo emphasized the short timeline between the onset of symptoms and the need to get medical care immediately. Patients may be given steroids or an IV, but so far there have been no proven treatments for the illness.

“Earlier recognition of the condition is essential for us to provide care and support for the patient, including monitoring for symptoms of respiratory involvement. Early supportive treatment can save lives.” Thakur said.

Families of those with AFM can find resources and information from The Transverse Myelitis Association (TMA).