CDC Doctors Say Mysterious Illness, Acute Flaccid Myelitis, Is on the Rise

And they still don't know what causes it.

Just as flu season begins, a strange new disease is rising in numbers in the US, and doctors still don’t know what causes it. While officials at the US Centers for Disease Control and Prevention have confirmed a spike in cases of acute flaccid myelitis this year, they are still tracking down the toxin, bacterium, or virus responsible for this polio-like illness. AFM mostly affects children, causing limb weakness and, in some cases, partial paralysis. And CDC officials say they’re working hard on an explanation.

On Tuesday, doctors at the CDC addressed the public to explain what they know — and what they still don’t know — about AFM.

Nancy Messonnier, M.D., the director of the CDC’s National Center for Immunization and Respiratory Diseases, told reporters that there have been 252 suspected cases of AFM and 90 confirmed cases as of November 9. And since they don’t know what causes it, there’s currently no vaccine and no cure.

She also said the CDC has broadened the scope of its investigation. Initially, they suspected that an enterovirus was causing the condition, but now they think AFM may be caused by an autoimmune response to a pathogen. In other words, it may not be the bacterium or virus itself that’s causing paralysis, but rather the body’s response to it. What pathogen? They don’t know.

“As a mom, I know what its like to be scared for your child. And I know parents want answers,” Messonnier told reporters. “We’ve learned a lot about AFM since 2014, but there are things we still don’t understand.”

CDC graphic on spotting AFM


Children who have the illness suddenly experience weakness in their muscles and joints, and this weakness can turn into flaccid paralysis, which means their limbs are floppy.

Messonnier noted that in many cases, the children had experienced respiratory illness, fever, or both prior to reporting AFM symptoms.

And while the CDC isn’t ready to nail a culprit, the health office’s data do point to a prime suspect: enterovirus D68, which has been found in the cerebrospinal fluid of a number of AFM patients. While Messonnier was extremely cautious about claiming EV-D68 as the cause of AFM, she did recognize that when a patient is sick and a pathogen is found in their cerebrospinal fluid, that pathogen is usually the cause of their illness. Her hesitation comes from the simple fact that many AFM patients haven’t had any pathogen in their cerebrospinal fluid.

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


But some doctors have found independent support for the EV-D68 hypothesis.

In April, Lydia Marcus, M.D. a pediatric neurologist at the University of Alabama at Birmingham’s School of Medicine, first-authored a paper in the journal Neurology, in which she and her co-author suggested that EV-D68 could be contributing to the rise in AFM cases. They noticed that as AFM spiked in 2014, the first year it was recognized nationally, EV-D68 cases spiked too.

“We at our institution have had around 10 cases of acute flaccid myelitis since 2014, and that’s pretty much consistent with what the CDC and people nationwide have seen, which is that it’s typically every other year,” Marcus told Inverse. As shown in the graph above, AFM cases spiked in 2014, 2016, and 2018, with lulls in 2015 and 2017. So far there’s no solid explanation for this 2-year pattern, though five years is hardly enough to even call it a “pattern.”

Marcus does note, though, that even though most institutions started tracking AFM in 2014 when it first made itself know, looking back at cases in her hospital reveals that at least seven children fitting the symptoms of AFM had presented to her hospital alone. It’s just that doctors hadn’t known what to call their condition.

For now, the best advice that doctors have is to wash your hands to avoid transmitting infections — a small precaution to avoid the long-term after-effects of AFM.

“We have had a couple people who’ve had some pretty good recovery,” Marcus says. “Most people have had a little bit of recovery, but unfortunately, we haven’t seen anybody who’s had a full recovery from this. It’s really discouraging.”

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