Genetic sequencing of a virus found in respiratory secretions of children in California and Colorado who suffered from paralysis or muscle weakness last fall reveals that they were infected with a mutated strain of enterovirus D68 that is closer to polio than other strains common in previous years.Much like the polio virus, EV-D68 (or whatever acronym is being used) does not affect all people the same way. Most people who got polio (and it is very rare now globally, and eliminated in the US) did not show symptoms beyond short term cold/flu. Only a minority suffered the devastating paralysis which was the reason the vaccines were such breakthroughs at the time. For polio, people were more likely to suffer the paralysis if they had escaped the disease while young, and protected by maternal antibodies. Thus, the poor, living with less sanitation suffered from it less than the wealthy, who were less likely to be exposed while young. My guess is that it will turn out to be true for EV-D68 as well.
The study, published Monday in Lancet Infectious Diseases, sheds new light on one of the most troubling medical mysteries of recent years. Amid a nationwide outbreak of severe respiratory illness, doctors at hospitals nationwide began to report that they were seeing an alarming number of children with unexplained weakness in an arm or a leg to complete paralysis that required them to be put on ventilators. Treating physicians noted that many of the children appeared to be infected with enterovirus D68, but researchers were cautious about drawing a causal link because virus had been bouncing around the world since the 1960s and had typically only caused breathing issues such as coughing and wheezing.
While the research does not provide a definitive link -- that would only be established if the virus were found in the spinal fluid and it was not -- it provides the strongest evidence to date of the link between enterovirus D68 and paralysis. The researchers theorize that the reason the virus was not found in the spinal fluid could be because the samples were taken too late. Scientists also tested the children for the presence of other pathogens capable of causing the symptoms but didn't find other viruses, bacteria, fungi or parasites.
The new research reveals that the children had a novel strain of the virus, called B1, which emerged about four years ago. That strain has only five to six coding differences from previous strains that were commonly found in the United States but each of those are mutated in the direction of polio or another nerve-damaging virus known as EV-D70.Now that a more dangerous strain has arrived (and the question of whether it originated in the US or was imported from Latin America is still of interest, but hardly germane to the treatment), perhaps the CDC and USDA should be thinking about funding vaccine development for this bug. Or now that we have so much more genetic knowledge than we did in the 1950s, maybe we could work out a vaccine for enteroviruses in general, or at least major groups of them.
"These are changes that may have made the virus more polio-like," said Charles Chiu, an associate professor at the University of California-San Francisco who worked on the study.