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By Maggie Fox
The Centers for Disease Control and Prevention say they do not know what causes a sudden increase in cases of scary, polio-like illness that leaves children paralyzed or weakened.
Suspect # 1 was a virus called Enterovirus D68 or EV-D68. In 2014, a wave of cases of acute flaccid myelitis coincided with epidemics of EV-D68 across the country.
But the CDC says that it has not consistently found the EV-D68 in cases confirmed since then. Officials say they are studying a range of possible causes.
However, doctors who have studied children with acute flaccid myelitis say they have gathered a growing body of evidence showing that EV-D68 is the leading cause and that the virus may have changed in recent years so to make the side effects paralyzing. more likely.
They documented an increase in the number of EV-D68 cases surrounding outbreaks of acute flaccid myelitis. Experiments have also shown that EV-D68 can invade nerve tissue, including the spine, and there is also evidence of genetic changes in the virus itself.
A team of university researchers has formed its own network to try to determine why very few children develop paralytic syndrome from a harmless virus for over 99% of those infected.
"It's amazing that four years later, the CDC has not confirmed the etiology of these cases," said Dr. Ali Khan, Dean of the Epidemiology Department at the University of Nebraska Medical Center.
"To continue to consider this as a mystery after so many years does not do justice to public health," said Khan, former director of CDC's Office of Public Health Preparedness and Response.
State health services have reported at least 155 possible cases of acute flaccid myelitis at the CDC this year, and the agency confirmed confirmation of 62 of them. Other cases may also be related to a viral infection, but they do not have the exact same symptoms of acute flaccid myelitis, including sudden onset and specific lesions of the spinal cord.
For doctors who have treated many cases, it is clear that some viruses are responsible and that most cases are probably due to EV-D68.
"I think we are seeing the emergence of a new paralytic disease resembling polio. His model and most of the evidence we have suggests that it's likely a viral illness, "said Dr. Ken Tyler, a neurologist at the Faculty of Medicine's Department of Medicine. University of Colorado, at NBC News.
"I think the main candidate is enteroviruses in general and the EV-D68 in particular."
Many different viruses are circulating at the same time, and one strain will be common one season and another strain next.
Increases in cases of acute flaccid myelitis have been documented in 2014, 2016 and now in 2018. The CDC reported that there is not much evidence that EV-D68 cases also increased in 2016.
But Dr. Gregory Storch of Washington University in St. Louis and his colleagues discovered an epidemic of EV-D68 in their area in 2016, claiming that they would have been missed if they did not actively researched it in Louis Children's Children's Hospital samples with respiratory symptoms.
"It seems that the enterovirus D68 is present every two years," said Storch. "Each time, there was an increase in the flaccid acute myelitis that occurred at the same time as the activity of the EV-D68."
Dr. Kevin Messacar of the Colorado Children's Hospital and his colleagues also found an increase in the number of EV-D68 cases in Colorado in 2016.
And Guiqing Wang, a pathologist at New York Medical College, and his colleagues performed genetic tests to identify a new strain of EV-D68 that had circulated in 2014 and 2016. This disease caused an epidemic of 160 confirmed cases in the Lower Hudson Valley of New York in 2016, they reported.
"It seems that new strains are more able to affect human motor neuron-like cells than older strains," Tyler said.
European researchers reported 29 cases of EV-D68 infection in children and adults with acute flaccid myelitis in 2016.
Tyler and his colleagues infected mice with EV-D68 and showed that it could affect the nervous system. "We know that enterovirus D68 in mice can cause a disease very similar to that seen in children," Tyler said. "You can see enterovirus particles in motor neurons."
This is not proof, Tyler says. "This means that you have established that it is plausible that a virus behaves this way," he said.
What is missing is the surveillance needed to show that outbreaks of EV-D68 were large enough to account for the increased number of AFD cases in 2016 and now in 2018, and that most patients with AFD were also infected with EV-D68.
Test quickly to catch the virus
It is also necessary to know what other viruses could cause cases. Messacar noted that a virus called EV-A71 had caused outbreaks of foot-and-mouth disease during Colorado's fall, and that this virus had also been associated with neurological effects.
This means that doctors must act faster to test children who are starting to show signs of weakness or paralysis. This may not be the first priority if a child arrives in the emergency room with difficulty breathing or an arm that suddenly does not work.
But a virus can damage the nervous system and disappear when the immune response goes into action – leaving a crime scene without much evidence from the perpetrator. This adds to the mystery.
"Other 2014 data suggest that the faster the swabs are, the higher the yield," said Tyler. After about a week, it was difficult to find a virus in patients, he said.
"One of the things we need to do more to move forward is active surveillance," said Messacar.
It is also possible that the damage is not directly caused by the virus, but by an abnormal immune response to the infection. It is therefore even more important to catch the virus in the act.
A few days can make all the difference, said Dr. Aaron Milstone, pediatrician at Johns Hopkins Medicine, who is part of an informal network of researchers who are trying to shed light on what has caused the proliferation of cases of MY.
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