Acute Flaccid Myelitis: The New Polio?
"It's like déjà vu all over again." (Yogi Berra)
When outbreaks of acute flaccid myelitis (AFM) surfaced in California and Colorado in 2014, it was highly reminiscent of poliomyelitis (the topic of the previous Germ Gems blog). Clinically, the diseases are similar: sudden onset of limb weakness or paralysis, mainly afflicting young children. While AFM is rarely fatal, complications include trouble breathing due to respiratory muscle weakness requiring ventilator support.
By the fall of 2019, outbreaks of AFM were reported in 41 states, and the total number of confirmed cases had reached 590. By then, the Center for Disease Control and Prevention (CDC) had ruled out polioviruses as the cause of the epidemic. As you would imagine, researchers at the CDC and elsewhere are focused on finding the etiology of AFM. Until this is accomplished, solid recommendations aren’t possible about prevention, and most importantly, the development of a vaccine with the potential of wiping the disease out, (as has almost happened with polio) isn’t feasible.
Polioviruses are members of the genus Enterovirus (entero means intestinal, reflecting their mode of transmission through the intestine). Specimens from many body sites of AFM patients have been tested for these and other pathogens. Notably, stool samples have routinely been negative for polioviruses.
There are more than 100 types of this genus of RNA virus, many of which cause disease in humans. Two enteroviruses: EV-68 and EV-71, were highest on the list of suspects as a cause of AFM because, just like polioviruses, they can attack the nervous system. But EV-68 and EV-71 have been detected by the CDC in the spinal fluid of only four of 590 confirmed cases since 2014. While this suggests they may be the cause of these patients’ AFM, for all other patients no pathogen (germ) was detected in their spinal fluid.
Whatever the cause of AFM turns out to be, it shares with polioviruses a predilection for grey matter in the spinal cord that is responsible for weak muscles (flaccid means limp) and loss of reflexes. A spinal magnetic resonance image (MRI) confirms the diagnosis. When cerebrospinal fluid is examined, white blood cells are often detected (myelitis means inflammation of the spinal cord).
Like many viral infections, AFM is seasonal; spikes of the disease occur between August and October. But one feature of the seasonality of AFM that is most unusual is that outbreaks mount every other year—2014 (120 cases), 2016 (140 cases), and 2018 (236 cases). So far in this odd-numbered year, only 22 cases have been confirmed. (But epidemiologists are holding their breath for 2020.)
Until the cause of AFM is discovered, what does every parent need to know? First, the disease is very rare (less than 2 per million children are affected in the U.S.), and with physical therapy, most kids recover muscle function over time. But, recognize the warning signs: sudden weakness in a muscle group, including facial drooping, difficulty moving the eyes, and challenges with swallowing or speaking. If your child develops a sudden weakness of any body part, contact your child’s doctor. Although evidence for the direct spread of the causative agent is lacking, frequent and careful handwashing is recommended.
It’s good to remember that it took three years of a concerted scientific effort to establish that a heretofore unknown virus (HIV) was the cause of the AIDS epidemic. We can only hope that such a scientific breakthrough is on the horizon for AFM.