A Key Difference Between Polio and the Polio-Like Disease Rising in the US

"This is actually a pretty dramatic disease."

Polio has been nearly eliminated in the United States for almost 40 years, but another disease, which doctors describe as “polio-like,” has sprung up. On Tuesday, officials at the CDC confirmed a spike in the number of cases of acute flaccid myelitis, a disease that affects the central nervous system and makes reflexes slow and limbs weak, mostly in children. So far, doctors don’t know what causes the disease. It could be viral, bacterial, or perhaps even caused by some kind of environmental toxin.

The CDC confirmed 386 cases of AFM between August 2014 and September 2018. Of the total number of cases, 62 of them occurred in 2018, across 22 states.

The condition’s symptoms — muscle weakness and slow reflexes — are very similar to those of poliomyelitis, which has led some to fear that the poliovirus is back after the US was declared “polio-free” in 1979. Nancy Messonnier, M.D., the director of the CDC’s National Center for Immunization and Respiratory Diseases, did her best to put these fears to rest on Tuesday.

“Right now, we know that poliovirus is not the cause of these AFM cases,” Messonnier told reporters. Though it’s not new, its sudden rise since 2014 has confounded experts.

“This is actually a pretty dramatic disease,” Messonnier said. “These kids have a sudden onset of weakness and they are generally seeking medical care and being evaluated by neurologists, infectious disease doctors, and their pediatricians, and coming to public health awareness.”

This chart shows how cases of acute flaccid myelitis have occurred from August 2014 to September 2018.


Similar Symptoms, Different Disease

The fact that none of the AFM patients have tested positive for the poliovirus indicates that it is a different disease. Symptoms of paralytic polio, the most serious disease caused by the poliovirus, can include loose and floppy limbs, a condition known as “flaccid paralysis.” It can also cause long-term, progressive muscle and limb weakness.

Similarly, AFM patients rapidly experience muscle weakness similar to that experienced by polio patients, and some require breathing assistance with ventilators, another similarity to polio. Some AFM patients have recovered their muscle functions quickly, but others have remained paralyzed, requiring ongoing care — much like polio patients.


The CDC emphasizes that in spite of the concern over AFM, it’s still a very rare disease, affecting fewer than one in a million people in the US each year. CDC doctors are still trying to figure out what causes it, so the recommendations for protection are about the same as any other illness: Wash your hands, get the recommended vaccines, and use mosquito protection — AFM cases seem to increase in the summer and fall months, leading some to believe it could be transmitted by mosquitoes.

A paper published in the journal Neurology in April suggested that a virus known as enterovirus D68 plays a role in AFM’s spread. There was an outbreak of the virus in 2014, the same year that AFM started appearing. With such a small number of cases, though, the connection was not considered conclusive.

What is clear is that all of the AFM patients seem to have the same disease, suggesting that a rare illness is indeed on the rise. Though there’s no cure, doctors can treat the most serious, life-threatening symptoms, like difficulty breathing.

“As a parent myself, I understand what it’s like to be scared for your child,” Messonnier told reporters. “Parents need to know that AFM is very rare, even with the increase in cases that we are seeing now. We recommend seeking medical care right away if you or your child develop sudden weakness of the arms and legs.”

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