The cause of a mysterious polio-like illness found predominantly in children might finally have been identified thanks to an 11-year-old case study. New research – published last week in the New England Journal of Medicine – provides the most substantial evidence yet that an enterovirus causes the condition, which is called acute flaccid myelitis (AFM) and has mystified scientists for years.
Fresh analysis of a 2011 study concerning the death of a 5-year-old boy may have finally put the debate to bed. Traces of enterovirus D68 (EV-D68) – a usually harmless respiratory virus – were found in the spinal cord of the child who likely died from AFM in 2008.
“[Our] findings support the view that EV-D68 infection is a cause of AFM,” the authors write in their paper.
“The pathogenesis of AFM may involve a combination of the direct effects of viral infection of spinal cord motor neurons and damage resulting from local inflammation.”
AFM is a rare but serious condition affecting the nervous system. It causes spinal cord inflammation, which can lead to muscles and reflexes in the body weakening. Sometimes, this can result in permanent paralysis, and in the most severe cases, it can impair breathing muscles and be fatal. The vast majority – 90 percent – of cases have been in very young children.
Since 2014, there have been spikes in cases every couple of years in the US, largely between August and October. In 2018, the Centers for Disease Control and Prevention (CDC) reported 238 cases. Another spike was predicted for 2020, but thanks to social distancing measures introduced as part of the COVID-19 pandemic response, cases were limited to just 33. So far in 2022, there have been just three confirmed cases.
In recent years, EV-D68 has emerged as the most likely cause of AFM, but until now evidence of that has been lacking. EV-D68 is a cousin of the poliovirus and “has [previously] been detected in respiratory specimens obtained from patients with AFM, but it has rarely been detected in the cerebrospinal fluid,” the new study’s authors write.
And there have been very few autopsy studies, they add. Children, thankfully, rarely die from the condition – since 2014 there have been just two deaths out of 682 US cases – although this means that there are fewer opportunities to study it as spinal cord biopsies are too dangerous to perform on living patients.
Fortunately, the team was able to find the 2011 case study and re-examine the autopsy tissues. Analyzing spinal cord cells, the team found EV-D68 RNA and proteins in motor neurons, as well as inflammation in the infected cells.
“This is exciting. It’s the best evidence [that EV-D68 causes AFM] we’ve had in humans,” Dr Megan Culler Freeman, an infectious disease specialist at Children’s Hospital of Pittsburgh, told HealthDay.
Hopefully, the discovery will help inform future research into the condition and potential treatment options.
“Unfortunately, we don’t have antiviral or antibody drugs available for treating EV-D68 infection in humans right now,” Dr Matthew Vogt of the UNC School of Medicine and lead author of the study said in a statement. Although he and colleagues are experimenting with monoclonal antibody therapies, like those used to treat SARS-CoV-2.
He remains optimistic: “If we can understand how this illness works, then we can work to understand how to prevent it from happening.”
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