In several states there are reports of children developing cases of a mysterious polio-like syndrome known as Acute Flaccid Myelitis (AFM).
A cluster of six cases in Minnesota has prompted Sen. Amy Klobuchar (D-Minn.) to request an investigation by the Centers for Disease Control and Prevention (CDC). In total 16 states are reporting cases.While it is understandable that the news of a polio-like illness appearing, seemingly, in clustered outbreaks across the United States is concerning, it is important to emphasize how rare such cases are and how they occur.
What is AFM?
Acute flaccid myelitis is a clinical syndrome that is characterized by the rapid onset of weakness in one or more limbs with characteristic changes seen in the spinal cord on MRI imaging. AFM is usually caused by a viral illness and chief among them, historically, was polio, which is only circulating in its wild form in Afghanistan and Pakistan, exclusively.
Other viral causes notably include West Nile Virus and a group of viruses known as enteroviruses. There are no vaccines available for West Nile Virus or non-polio enteroviruses. Though AFM is typically associated with children, it can occur in adults as well.
Enteroviruses are a diverse group of viruses, related to common cold viruses, that notably includes polioviruses. Polio is no longer a threat to the U.S. due to the famed success of vaccination programs. However, non-polio enteroviruses are ubiquitous and cause many different illnesses including common colds, viral meningitis and hand-foot-and-mouth disease (HFM).
AFM is something that occurs in about 1 in 1,000,000 people per year and is extremely rare. It likely has to do with a complex genetic and immunologic interaction with the virus that have not been completely characterized.
AFM in its most severe form can lead to paralysis of many muscles, including those essential for breathing. This could result in a person requiring mechanical ventilation to survive. There are no specific treatments for AFM and supportive care is the mainstay of therapy. Most people with AFM never fully recover the strength in their limbs.
Enterovirus D68 and AFM in 2014
AFM really grabbed headlines in 2014, when a sudden increase in cases was noted and tied to the appearance of enterovirus D68 (EV-D68). From August to December of that year 120 cases of AFM were reported.
Since 2014 the annual number of U.S. cases has ranged from 22 to 149. Through September 2018, 38 cases had been reported. This number will increase significantly as new cases are added to the tally. This includes three in Pittsburgh and 41 in Colorado linked to enterovirus D71 (EV-D71), a strain notorious for severe disease.
What this isn’t
While there is some mystery around these cases — why are they geographically clustered, which viruses are responsible, what are the risk factors for severe illness — one thing the cases are not related to is vaccines. Vaccines, on the contrary, have basically rid the world of what historically was the most important cause of AFM: polio.
This simple fact, unfortunately, has not prevented those who cast doubt on the tremendous value of vaccines from trying not to let the crisis represented by AFM clusters go to waste. Seizing on a 2014 historical perspective piece on a phenomenon known as “polio provocation” in the highly respected medical journal, The Lancet, anti-vaccine forces have attempted to link the recent AFM cases (as they attempt to do with many other medical occurrences) to childhood vaccinations.
Polio provocation is a phenomenon by which injections cause tissue injury and, if during the time of injection, wild poliovirus happens to be circulating in the community it has an easier route to the spinal cord. However, as the piece notes, this is applicable only when the poliovirus is circulating — which it hasn’t in the U.S. for decades — and that robust vaccination rates that keep wild polio at bay are the means to end polio provocation. Thus, the article they cite affirms the power of vaccination against polio and supports the opposite conclusion the anti-vaxxers are trying to foist on the public.
What do we do?
Because most viruses that cause AFM are common cold viruses, it is very hard to avoid infection especially as respiratory virus season approaches. The main means to limit one’s exposure is good hand hygiene with frequent hand-washing. In addition, since West Nile Virus is also a cause, mosquito avoidance and robust vector control is helpful as well.
AFM is very rare. Not every cough or cold that a person experiences is a harbinger of a more severe illness. The vast majority of coughs and colds are just that. However, if someone develops weakness in a limb or difficulty breathing it is essential that they seek medical attention.
It is also important for the medical and public health communities to thoroughly investigate the causes of the AFM cases, cataloging the various viruses that are responsible.
As my colleagues and noted in our recent report on pandemic pathogens, aggressively pursuing specific microbiological diagnoses of unknown syndromes provides much insight, enhances situational awareness of potentially dangerous pathogens and helps to prioritize pathogens for vaccines and therapeutics.