In 2014, a series of polio-like cases, which left patients suffering from sudden paralysis, were reported across the United States. The condition was dubbed acute flaccid myelitis, or AFM, and it appeared to primarily affect children. The number of cases surged once again in 2016. Now, we are in the midst of yet another outbreak, as Michael Nedelman reports for CNN.
According to the Centers for Disease Control and Prevention, there have been 72 confirmed cases of AFM so far this year, with the illness occurring in 24 states. A total of 191 reports were received, and some are still under investigation. Since the 2014 outbreak, the illness seems to have been surging every other year. In 2014, there were 120 confirmed cases, but in 2015 there were only 22. The 2016 outbreak saw 149 people diagnosed with AFM, compared to 33 in 2017.
More than 90 percent of confirmed cases have occurred in children 18 years old and younger. The average age of affected patients is four years old. Parents shouldn’t panic, Kevin Messacar, an infectious disease pediatrician and researcher at the University of Colorado, tells Tanya Basu of the Daily Beast. AFM remains exceptionally rare, with the chances of getting it about one in a million. But with that being said, AFM is a serious disease, one that has left medical professionals mystified.
AFM affects the nervous system, specifically the spinal cord, and it can cause weakness in one or more limbs. The condition's symptoms are similar to those caused by polio, but poliovirus has not been found in any AFM patients. Some children who contract the disease experience relatively mild paralysis and recover well. Others are left paralyzed from the neck down, and need to be supported with ventilators and breathing tubes. The outbreaks have not been clustered in any specific region, and there is no “unifying factor to explain the peaks,” Nancy Messonnier, director of the agency's National Center for Immunization and Respiratory Diseases, recently told reporters, according to Nedelman.
Health officials have not yet confirmed the cause of AFM. As Soumya Karlamangla of the Los Angeles Times reports, the CDC says it is investigating several possible culprits, including environmental toxins. But a more likely explanation may be that AFM is caused by viruses—specifically two strains of enterovirus called EV-D68 and EV-71.
According to the Atlantic’s Ed Yong, the 2014 outbreak of AFM coincided with a surge of respiratory illnesses caused by EV-D68. Parents of children affected by AFM have reported that their children began showing signs of paralysis after experiencing cold-like symptoms, and in 2014 and 2016, EV-D68 was the most commonly found virus in people affected by AFM.
The virus has not, however, been detected in every AFM patient. Just one child was found to have EV-D68 in his or her spinal fluid, which is where paralysis-inducing viruses might be expected to lurk. The CDC discovered EV-D68 in fewer than half of stool samples or nasal swabs that it tested from AFM patients.
But, Messacar noted in an interview with Yong, that isn’t reason to discount EV-D68 as a cause of AFM. For one thing, the virus can move through the nerves and is destroyed in the gut, so it might not appear in spinal fluids or stool. And “[i]n many neurological infections, the worst symptoms aren’t caused by the virus itself, but by the body’s disproportionate immune response, Yong writes. “That response can continue even after the virus has been cleared, which means that patients often test negative for whatever first triggered their illness.”
The other enterovirus, EV-71, is endemic to East Asia and has been linked to a polio-like illness there. It also surfaces in periods of two to three years. Messacar and his team of researchers have thus far found EV-71 in 11 AFM patients.
Though it has not confirmed the source of AFM, the CDC recommends a number of prevention measures: staying up to date on vaccines, washing hands, and taking measures to protect oneself from mosquitoes. At the moment, there is no national system for hospitals to share information and treatment outcomes pertaining to AFM. Messacar tells Basu of the Daily Beast that improving surveillance methods should be a priority.
“We don’t know what’s going to happen in 2020,” he says, “but seeing the pattern every other year for the past four years means we need to prepare.”