Marilyn J. Roossinck
Every time there is a major disease outbreak, one of the first questions scientists and the public ask is: “Where did this come from?”
In order to predict and prevent future pandemics like COVID-19, researchers need to find the origin of the viruses that cause them. This is not a trivial task. The origin of HIV was not clear until 20 years after it spread around the world. Scientists still don’t know the origin of Ebola, even though it has caused periodic epidemics since the 1970s.
As an expert in viral ecology, I am often asked how scientists trace the origins of a virus. In my work, I have found many new viruses and some well-known pathogens that infect wild plants without causing any disease. Plant, animal or human, the methods are largely the same. Tracking down the origins of a virus involves a combination of extensive fieldwork, thorough lab testing and quite a bit of luck.
Viruses jump from wild animal hosts to humans
Many viruses and other disease agents that infect people originate in animals. These diseases are zoonotic, meaning they are caused by animal viruses that jumped to people and adapted to spread through the human population.
It might be tempting to start the viral origin search by testing sick animals at the site of the first known human infection, but wild hosts often don’t show any symptoms. Viruses and their hosts adapt to each other over time, so viruses often don’t cause obvious disease symptoms until they’ve jumped to a new host species. Researchers can’t just look for sick animals.
Another problem is that people and their food animals aren’t stationary. The place where researchers find the first infected person is not necessarily close to the place where the virus first emerged.