How researchers can track how a virus circulates

DETROIT – When it comes to tracking the way a virus circulates, researchers use many traditional methods, such as contact tracking.

While that’s important, it only gives a narrow window on transmission among a limited number of people. Local 4 Dr. Frank McGeorge explains how epidemiologists can get a 10,000 foot view of the spread.

Update June 26, 2020: Michigan coronavirus cases (COVID-19) up to 62,695, death toll now at 5,888

Viruses mutate naturally, often in a minor way. But every time a change occurs and the virus is transmitted to another person, the newly created difference links those two individuals and by studying sequential changes it is possible to follow a virus that travels across the country or the world.

The SARS-CoV-2 virus genetic code is made up of approximately 30,000 base pairs. Like words in an instruction manual that the virus copies every time it spreads. When the virus copies itself, errors occur naturally. But these mutations are generally inconsequential, except for the trail they leave.

The value of these errors is that they act as a signature, exclusive of the virus at that time. That signature is passed to each descendant of that virus. Researchers have been sequencing or reconstructing the genetic signatures of different SARS-CoV-2 viruses worldwide. In doing so, they have created an ancient tree.

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The tree shows how each successive change was transmitted and where it branched out with different mutations. Thinking of it as a family tree, when you see the same signature changes on different branches, you know they must be related.

By mapping the genome of the virus that infected different people, in different places, at different times, and with matching signatures, we can infer relationships.

The researchers believe that after the initial identification of the viruses in China, it began to show differences as it traveled to different parts of the world. The signature of the virus identified in Washington state suggests that it was imported directly from China.

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The viral genomes of the SARS-CoV-2 samples from people infected in Michigan months ago are more directly related to the firms that are also found in Canada and Europe. Suggesting that the virus did not come to Michigan directly from China, but was imported from Europe.

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Michigan firms also have a relationship with viruses found in several other states. It is important to mention that this only suggests a transmission relationship, it does not say in which direction the virus traveled.

Click here to visit the Nextstrain data website