Several studies have found evidence of what might cause acute flaccid myelitis, known as AFM, which affects children. AFM is a rare polio-like illness which can cause weakness and paralysis. According to a study published Monday in the journal Nature Medicine, a virus seems to be the culprit.
According to Dr. Ryan Schubert, a clinical fellow in neurology at the University of California, San Francisco and an author of the new study, “When there’s an infection in the spinal cord, antibody-making immune cells travel there and make more antibodies. We think finding antibodies against enterovirus in the spinal fluid of AFM patients means the virus really does go to the spinal cord. This helps us lay the blame on these viruses.”
Using a virus hunting tool called VirScan, scientists were able to examine the spinal fluid of patients for an immune response to enterovirus and to thousands of other viruses simultaneously. Using this method, the team confirmed the presence of antibodies for enterovirus strains D68 and A71 in nearly 70% of the 42 AFM patients that they tested. They did not find antibodies against any other virus.
The new research is consistent with other recent studies. A study published in August in the journal mBio used another method and found antibodies to enteroviruses in 11 of 14 AFM patients. Dr. Nischay Mishra, an assistant professor of epidemiology at Mailman School of Public Health at Columbia University, and lead author, said in the study the virus most clearly implicated was D68, and that is where research investments should focus.
Another recent paper, published in October in the journal Pediatrics, also said that AFM was likely caused by viruses, including enterovirus. These studies aren’t considered conclusive, though, and more research is needed.
Enteroviruses are common; they cause about 10 million to 15 million infections a year in the United States, according to the US Centers for Disease Control and Prevention. Typically, enteroviruses cause cold-like symptoms such as fever, runny nose and body aches, and recovery is easy.
During late summer of 2014, several cases of AFP among children were identified in Colorado. The Centers for Disease Control and Prevention (CDC) developed a case definition for acute flaccid myelitis (AFM), which included persons 21 years or younger with acute limb weakness and an MRI demonstrating predominantly gray matter lesions of the spinal cord. The CDC says there have been nearly 600 cases since it began tracking. There have been 20 confirmed cases in the United States in 2019. For most patients with AFM, symptoms begin between August and October.
What’s still unclear is why the virus strains are linked to paralysis in some children when they don’t have the same impact on adults, and why fewer than 1% of infected children get AFM. Knowing how AFM starts is perhaps the way to protecting children in the future.