07/08/2015 14:25 EDT | Updated 07/08/2016 01:12 EDT

Genetics help disease trackers follow measles

TORONTO — You could call it CSI: Disease Detectives.

Scientists in British Columbia have used the genetic signatures of viruses to trace the source and path of a measles outbreak that occurred after the 2010 Vancouver Olympics.

The research brought into focus what is generally invisible: the path that the highly contagious virus took as it moved from person to person across wide expanses of British Columbia.

The measles virus is so infectious you can catch it on a bus, in a public space, even by being in a room an infected person has already left. That often makes it impossible to know how individuals became infected.

In this circumstance, the study — the largest of its kind involving measles — shows that after two different strains of measles were introduced into the Vancouver area during the 2010 Winter Olympics, one strain headed north along a single highway.

"Highway 97. All of the affected communities were located on that highway," said Dr. Jennifer Gardy, lead author of the article, which is published in the Journal of Infectious Diseases.

"All of those cases, even though they occurred in towns that were thousands of kilometres apart, they were all the result of one single introduction of virus into that region. They all had this one mutation that said: 'Hey, these came from one person.' Very interesting."

It was happy happenstance that Gardy — a molecular epidemiologist at the B.C. Centre for Disease Control — and her colleagues were able to do the research.

It was assumed leading up to the Vancouver Games that H1N1, the flu virus that caused the 2009 influenza pandemic, would make an appearance. An event like the Olympics — or this month's Pan Am Games in Toronto — provides terrific opportunities for viruses and bacteria to move around the world, with athletes and spectators from various parts of the globe converging and then dispersing.

Gardy and her colleagues were going to study flu viruses isolated from people who contracted influenza during the Games. But the flu was a no-show. 

There were, however, 82 people diagnosed with measles, in an outbreak that first came to light shortly after the Olympics ended.

The genetic sequences of viruses from 27 of those cases showed two people had actually brought measles to Canada. The outbreak was caused by two different strains of the virus.

By checking the sequences against those recorded in an international database of measles viruses, Gardy and her colleagues concluded one of the viruses was probably from China. The source of the second was less clear: viruses identical to it had been spotted in a number of places, including Italy, India and the United States.

The technique she and her team used is called whole genome sequencing, comparing the genetic data for the entire virus to all the other available viruses in the outbreak.

Since Gardy and her colleagues started this work, the science has evolved substantially, allowing for more rapid generation of the type of data that took this team several years to publish. She noted that whole genome sequencing has helped show how Ebola spread across borders in the ongoing West African outbreak.

The advances mean this type of tracking can be used during an outbreak to help public health officials figure out how a disease is spreading.

"For the first time ever, we can really draw important, useful epidemiological conclusions about virus transmission from genomics. We did it retrospectively but it's now being done in real time in West Africa," Gardy said.

The equipment needed to do the work has shrunk to the point that a person with a backpack can head out to the field and start to analyze what's going on, she said.

"I think that's a big game-changer in what we're calling digital pathogen surveillance. Sequencing in real time ... sharing it online and using that (information) to draw epidemiological conclusions."

Helen Branswell, The Canadian Press