Scientists identify virus behind polio-like illness AFM which causes paralysis in children
A common seasonal virus has now been discovered as the culprit that is causing a polio-like illness in children. The first case of the mysterious polio-like illness called acute flaccid myelitis (AFM) - that causes permanent, sometimes life-threatening paralysis in young children - surfaced in 2012. Over the years, the disease has continued to baffle the scientific community and has been a matter of considerable debate, until now.
A team of researchers has identified the culprit enterovirus (EV), known to cause blisters in hands, feet, and mouth. The findings provide direct evidence that AFM is caused by an enterovirus that invades and impairs the central nervous system, and is the strongest proof to date that the disease is viral.
But this is not the first time that the virus has been linked to AFM. Scientists had initially pinned their suspicions on EV: they noted that a spike of AFM cases happened during EV outbreaks.
Furthermore, the CDC detected strains belonging to a subtype of EV in the spinal fluid of 4 out of 590 confirmed cases of AFM, since 2014. Tests in mice also pointed fingers at the virus. But not everyone was convinced. The virus was not found in 98 percent of the cases, a few scientists were more inclined towards believing the theory that AFM was either an autoimmune disease or was being caused by a virus that hasn't been discovered yet.
Putting all speculations to rest is the study that provides evidence against EV. They could detect the elusive virus by adopting a different approach. Instead of directly hunting for the virus in patient samples, the group of scientists relied on a more indirect method.
This indirect method stems from our very own immune system. When it detects the presence of a foreign agent, in this case, EV, it releases antibodies to neutralize it. It is these antibodies that the scientists were after.
"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," said Ryan Schubert, a clinical fellow in UCSF's Department of Neurology, a member of Wilson's Lab, and lead author of the new study.
Using this technology, they tested spinal fluid samples collected from 42 children with AFM and 58 with other neurological diseases for the study. The results were on expected lines: scientists found antibodies against EV in nearly 70 percent of AFM patients and in less than 7 percent of non-AFM patients.
To rule the role of other viruses, the scientists tested samples from AFM patients against other viruses, from those affecting humans and other vertebrates to those attacking ticks and mosquitoes. They found that none of AFM patients had developed antibodies against other viruses.
"The strength of this study is not just what was found, but also what was not found. EV antibodies were the only ones enriched in AFM patients. No other viral family showed elevated antibody levels", said Joe DeRisi, PhD, professor of biochemistry and biophysics at UCSF, co-president of the Chan Zuckerberg Biohub, and co-author of the new study.
However, there is one question that scientists haven't addressed yet. They are still trying to understand why AFM affects fewer than one percent of those with EV infection. "We don't know for sure why children get paralysis and adults don't", Schubert said. "The thinking is that young children have low immunity to the virus that increases as they get older, so we see the most severe effects in children around the age of two. But more work needs to be done to understand AFM."
Co-author Riley Bove is hopeful that the study can open doors to developing better diagnostic tools and vaccines. For now, he said, there's no way to prevent or treat AFM. But if it follows the biennial pattern first established after the 2012 outbreak, AFM cases may spike again next year.
The study was published in Nature Medicine.