(CNN) - Researchers found evidence of what might cause acute flaccid myelitis, known as AFM, a rare polio-like illness that affects children. According to a study published Monday in the journal Nature Medicine, a virus seems to be the culprit.
Since the first cases were documented in 2012, scientists have debated how children get AFM, which can cause weakness and paralysis. Some thought the cause was an autoimmune disorder, while others suspected a virus. Until recently, evidence of a virus was only circumstantial and couldn't be found in 98% of AFM patients who had their spinal fluid tested, according to the study.
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.
"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," Dr. Ryan Schubert, a clinical fellow in neurology at the University of California, San Francisco and an author of the new study, said in an emailed statement.
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.
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.
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.
"It's always good to see reproducibility. It gives more confidence in the findings for sure," said Dr. W. Ian Lipkin, director of the Center for Infection and Immunity in the Mailman School of Public Health at Columbia University, a co-author on the study in mBio. "This gives us more support of what we found."
He, along with Dr. Nischay Mishra, an assistant professor of epidemiology at Columbia University, said in the study the virus most clearly implicated was D68, and that is where research investments should focus.
"We are very eager to understand why. It seems by the time a child hits adolescence, almost everyone has been exposed to this virus, we want to know why these very few kids develop this awful outcome," Lipkin said. "There may be a genetic predisposition, we don't know. We also need to uncover another piece of the puzzle that is why there is this sort of periodic outbreak. It seems to be every other year. We don't understand a lot about how EV D68 circulates and we want to know more."
Another recent paper, published in October in the journal Pediatrics, also said that AFM was likely caused by viruses, including enterovirus.
The studies aren't conclusive, though, and more research is needed. But "because of the public health urgency of understanding the etiology of AFM" it was important to publish these results, the current study authors said.
For most patients with AFM, symptoms begin between August and October. There have been 20 confirmed cases in the United States in 2019.
There is no proven treatment for AFM, but knowing how AFM starts can be a first step for scientists to develop better diagnostic tools and one day, perhaps, a vaccine to keep children safe.
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