At least two unexplained cases of sudden, partial paralysis in young children have been confirmed in Canada, and doctors believe the cases could be linked to the return of a virus that in 2014 sent hundreds of North American children to hospital with severe respiratory illness.
The two children who turned up in hospital with polio-like symptoms – one in British Columbia, the other in Alberta – both tested positive this month for enterovirus D68, a relative of the common cold that was rarely identified in Canada and the United States before a high-profile outbreak two years ago.
"We're interested in this virus because it has some fairly unique features," said Danuta Skowronski, the lead epidemiologist for influenza and emerging respiratory pathogens at the B.C. Centre for Disease Control (BCCDC). "Most enteroviruses will just cause mild or no symptoms, and that's likely for D68 as well. But it has been found in association with severe respiratory symptoms, particularly in people with asthma, and also with some neurological complications."
EV-D68 disappeared in 2015, but this year it's back, giving epidemiologists like Dr. Skowronski the opportunity to better understand what link, if any, there is between this enterovirus strain and the sudden onset of paralysis in children.
The Public Health Agency of Canada sent out a bulletin late last week warning that EV-D68 has re-emerged this year and that physicians ought to be on the lookout for it.
So far, British Columbia has confirmed 16 cases of EV-D68, Alberta has confirmed one and Ontario has identified at least 32. None of the Ontario patients has displayed paralysis or muscle weakness.
EV-D68 is almost certainly present elsewhere in the country. In the vast majority of cases, the virus causes only mild cold-like symptoms, meaning patients do not visit their doctors or hospitals where they might be flagged for testing.
"It's the tip of the iceberg," said Bryna Warshawsky, a public health physician with Public Health Ontario. "These numbers are … just a tiny piece of the picture."
As well, there is no formal requirement that cases be tracked and reported, as there is with some other communicable diseases in Canada. Until the 2014 outbreak, there was little point in determining the exact strain of a non-polio enterovirus because there is no vaccine or anti-retroviral treatment to combat such viruses.
Now, though, epidemiologists are following EV-D68 more closely in hopes of unravelling its connection to the paralysis cases.
"It's hard to advance in your understanding when there aren't additional cases to be able to clarify or investigate," Dr. Skowronski said. "I think [EV-D68] likely does play a role, but what kind of role?"
During the 2014 EV-D68 outbreak, five people in B.C. who tested positive for the virus also developed partial paralysis. The BCCDC checked in on those cases one year later and found none had regained full mobility. Three of the patients had been on ventilators at the hospital at some point.
One, a child under the age of 5 with no underlying health problems, arrived at the hospital unable to lift his or her head, and wound up spending more than six months in the hospital.
This year, B.C. has found one case of a child under the age of 2 with partial arm paralysis. The Alberta case, which was described in detail on ProMED, where doctors around the world can report infectious disease updates, involved an otherwise healthy two-year-old who arrived at the hospital with vomiting and paralysis in the right side of the face that eventually progressed to "flaccid paralysis" of the right arm and weakness in the left arm.
Marek Smieja, the head of microbiology for the Hamilton Regional Laboratory Medicine Program, said his lab has so far confirmed 28 cases of EV-D68 from the 12 Southern Ontario hospitals it covers, far fewer than at this point in the 2014 outbreak.
"Now, even if our numbers double, we'll be nowhere near the amount [from 2014]," he said.