Scientists have linked a specific strain of the respiratory illness enterovirus D68 to the previously-unexplained rash of childhood paralysis and muscle weakness that struck dozens of children between 2012 and 2014.
Researchers found the genetic imprint of a relatively new strain of enterovirus D68 -- B1 -- in children who developed acute flaccid myelitis (paralysis or muscle weakening) after having a fever or respiratory illness. After checking patients' respiratory secretions, blood and cerebrospinal fluid for a variety of different pathogens, they couldn't find any other probable cause of the paralysis in these children.
While this study strengthens the link between EV-D68 and sudden paralysis or muscle weakening in pediatric patients, it doesn't definitively establish the virus as the cause of acute flaccid myelitis. Nor does it explain by which mechanism EV-D68 may cause paralysis. But the finding points to the urgency for further research of EV-D68 and a possible vaccine, said lead researcher Dr. Charles Chiu, director of the Abbott Viral Diagnostics and Discovery Center at University of California, San Francisco.
"Given that none of the children have fully recovered, we urgently need to continue investigating this new strain of EV-D68 and its potential to cause acute flaccid myelitis," said Chiu in a statement.
Chiu also found that among siblings who caught a genetically identical strain of EV-D68, only one of them went on to develop acute flaccid myelitis, which indicates that not everyone who contracts this certain strain of EV-D68 will have the same reaction.
"This suggests that it's not only the virus, but also patients' individual biology that determines what disease they may present with," explained Chiu.
The study examined 48 pediatric patients: 23 had confirmed enterovirus-related diseases and 25 had acute flaccid myelitis. Chiu found genetic traces in EV-D68 in 12 out of the 25 who had been struck by acute flaccid myelitis, and saw they were all part of the same B1 strain. He speculated that they were only able to find trace amounts of EV-D68 in some patients because fluid samples were taken from the children about one week after the onset of respiratory symptoms, which may have been too long to wait for more robust samples.
The B1 strain of EV-D68 emerged around four years ago, and is similar to other viruses like EV-D70 or poliovirus, which cause nerve damage and paralysis. It was the most dominant strain of EV-D68 circulating during the 2014 outbreak, and only a small minority of children -- 115 across 34 states -- went on to develop paralysis or muscle weakening between Aug. 2014 and Mar. 2015, according to the Centers for Disease Control and Prevention.
Babies, children and teens, particularly those with asthma, are especially susceptible to the disease because they're less likely to have built up immunities against the disease. Symptoms can start out mildly (fever, cough, sneezing, body aches) and progress to wheezing or difficulty breathing. Currently, there is no vaccine for EV-D68.