Evidence from the tragic death of a 5-year-old boy in 2008 may finally settle the debate over a mysterious polio-like condition that’s been paralyzing children for years. Researchers this week say they’ve found clear traces of enterovirus D68 in the nerve cells of the child, who likely died from acute flaccid myelitis. Many scientists have long suspected EV-D68 to be the root cause behind recent outbreaks of the rare illness.
Acute flaccid myelitis (AFM) is characterised by inflammation along the spinal cord and tends to affect very young children. This inflammation leads to neurological symptoms, most commonly a sudden weakness of the arms and legs and the loss of reflexes. AFM can sometimes cause permanent paralysis, and, in the most severe and often fatal cases, people’s breathing muscles stop working completely. Importantly, this same sort of illness rarely happens to people who contract polio, which was responsible for paralyzing tens of thousands of American children during the mid 20th-country.
In 2012, a group of doctors in California began noticing a small but alarming increase in the number of children who developed these symptoms. Polio was quickly ruled out as the cause, since it’s become nearly eradicated from the world. But a viral infection remained at the top of the suspect list, in part because most victims reported a fever or other signs of a respiratory infection soon before their AFM began. Since then, outbreaks of AFM have regularly been reported in the U.S. and have affected hundreds of children at a time.
Many scientists have settled on EV-D68 as being the leading cause of this spike in AFM. It’s a close cousin of the polio virus, and it’s sometimes been spotted in the spinal fluid of victims. And though EV-D68 has historically been seen as a mild common cold bug, there is some evidence that it’s recently evolved in ways that might allow it to cause AFM more often.
Even health authorities like the Centres for Disease Control and Prevention now explicitly state that EV-D68 is likely causing these peaks of AFM, though there may be other related enteroviruses to blame as well. But much of the case for EV-D68 is circumstantial, and there is still much we don’t understand about how it’s actually causing AFM. This new research, presented Wednesday in the New England Journal of Medicine, appears to provide the most direct proof yet for its role.
Researchers were able to find a case study, published in 2011, about a 5-year-old boy who died from an AFM-like illness in 2008, back when AFM wasn’t formally recognised. As part of the study, the family had allowed an autopsy of the child, which found EV-D68 in his spinal fluid. The team went back and reexamined preserved spinal cord samples. This time, they found EV-D68 RNA and proteins in the motor neurons of the boy, further indicating infection. And they also identified clear evidence of inflammation in these infected cells.
All together, the authors say, it’s solid evidence that AFM is caused by “a combination of the direct effects of viral infection of spinal cord motor neurons and damage resulting from local inflammation.”
Though AFM is a serious condition that can have lifelong effects, most children don’t die from it, and it’s simply not safe to take these kinds of samples from living patients. So the rediscovery of this case allowed researchers a rare opportunity to look for the virus where it was most likely to be causing trouble in its victims.
“This is exciting. It’s the best evidence we’ve had in humans,” Megan Culler Freeman, an infectious disease specialist at Children’s Hospital of Pittsburgh who isn’t affiliated with the research, told Healthday.
There remain many mysteries about AFM and EV-D68, including when the next major outbreak will strike next. Since AFM was first identified, outbreaks have usually arrived every two years on schedule. Experts did expect a summer 2020 surge, but pandemic-related precautions reduced the incidence of many other infectious diseases, EV-D68 included. With these precautions largely going away, though, it’s likely that another peak will eventually arrive.