Some zoo animals contracted SARS-CoV-2 from humans
Sergei Supinsky/AFP/Getty
Animals such as rats are often thought to be disease carriers. But when it comes to the spread of disease, it turns out other animals have more reason to fear us than we do.
An analysis of the virus’s genome found that when the virus spread between humans and other animals, 64 percent of the time it was the humans who infected the other animals, rather than the other way around.
“We give animals more viruses than they give us,” says Cedric Tan at University College London. For example, after the SARS-CoV-2 virus spread from bats to humans (possibly through another species), humans spread it to many other species.
Tan and his colleagues have been using a global database of sequenced viruses to study how they jump between species. There are nearly 12 million sequences in the database, but many are incomplete or lack data on when they were collected and from which host species.
So the researchers narrowed the 12 million high-quality sequences down to about 60,000, with complete data attached. They then created a “family tree” of related viruses.
In total, they identified nearly 13,000 viral lineages and 3,000 jumps between species. Of the 599 jumps involving humans, most were from humans to other animals, not the other way around.
Tan said the team wasn’t expecting this to happen, but in retrospect it makes sense. “Our population is massive. Our global distribution is basically everywhere.”
In other words, a virus that circulates in humans will have many opportunities to spread to many other species around the world, while a virus that circulates in non-human species restricted to one region will have much less chance.
Research has found that SARS-CoV-2, MERS-CoV and influenza viruses are the viruses most commonly transmitted from humans to other animals. This is consistent with other studies showing, for example, that SARS-CoV-2 has spread from humans to pets, zoo animals, farmed animals such as minks, and wild animals such as white-tailed deer.
However, even when SARS-CoV-2, MERS-CoV and influenza viruses were excluded from the analysis, the team still found that 54% of viral transmissions were from humans to other animals.
Tan said the spread of viruses from humans to other species poses a threat to many endangered animals. For example, several wild chimpanzees have died in Uganda due to outbreaks of human metapneumovirus and human respiratory viruses.
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