Ontario measles strain sequences offer a piece to the puzzle

The measles strain infecting people in Ontario is one that hasn’t been previously identified, and so far its origins remain mysterious.

Cases not connected to the Disneyland outbreak in California

The measles strain infecting people in Ontario is one that hasn’t been previously identified, and so far its origins remain mysterious.  

The origin of the measles cases in Ontario remain a mystery, but they are of a strain not previously seen in Canada. (U.S. Center for Disease Control and Prevention)

Scientists at the National Microbiology Laboratory in Winnipeg have received nine strains from Ontario with the same genotype, said Matthew Gilmour, the lab’s scientific director general.

"It's not to imply this is a new strain in Canada. Just one that hasn't been identified yet," Gilmour said Monday.

The public health investigation needs to continue to complete the puzzle.

The laboratory has confirmed the nine strains from Ontario all bear the D4 genotype, a trait that’s similar to but not identical to one in Europe, Gilmour said.

"If you have an exact match to a genotype in another country, the epidemiological information reveals the person travelled to that country, that's when the puzzle starts to come together."

To confirm the history of an outbreak requires two pieces: the genotype and a link to the originating location, such as a travel history.

What the genotype sequencing information eliminates is the possibility Ontario’s cases are connected to the Disneyland outbreak in California, which has been confirmed as the source in Quebec’s Lanaudière region, northeast of Montreal.

It also helps to rule out the possibility that this measles strain was introduced twice to Ontario by people travelling to the province independently of each other from different places.

"The fact they are related to each other brings you back to you've had some introduction of a virus into the system and now it's spreading locally," said Dr. Michael Gardam, an infectious disease specialist at Toronto’s University Health Network.

“What it does is it makes you ask more questions. You've got a strain that isn't related to anything else, so this is entirely a mystery as to where it came from. I think that's the really perplexing part of this."

It may be that the virus came from a part of the world that lacks the sophisticated ability do this type of viral sequencing, Gardam said. If so, the mystery may never be solved.

But in public health terms, the lab sequencing findings don’t change anything. Each measles case still needs to be followed and the vaccine offered to prevent spread, he said.

In hospitals, genome sequencing information "tends to blow up your preconceived notions" Gardam added, and serves as a reminder to check assumptions.

Measles is a highly contagious, vaccine-preventable disease. Symptoms develop about 10 days after exposure and include fever, a red blotchy rash, red watery eyes and white spots in the mouth.