Humans pass more viruses to animals than they do to us – 03/27/2024 – Science

Some of the deadliest diseases to hit humanity have come from pathogens that jumped from animals to people. The virus that causes AIDS, for example, came from chimpanzees. And many experts believe that Sars-Cov-2, which caused the Covid-19 pandemic, emerged from bats.

However, as a new study demonstrates, this exchange is not a one-way street. An analysis of all publicly available viral genome sequences produced a surprising result: humans pass more viruses — almost twice as much — to animals than they do to us.

The researchers looked at nearly 12 million viral genomes and detected nearly 3,000 examples of viruses jumping from one species to another. Of these, 79% involved viruses moving from one animal species to another animal species. The remaining 21% involved humans. In the latter case, of the total, 64% were human-to-animal transmissions, known as zooanthroponosis, and 36% were animal-to-human transmissions, known as anthropozoonosis.

Animals affected by zooanthroponosis include pets (cats and dogs), domesticated animals (pigs, horses and cattle), birds (chickens and ducks), primates (chimpanzees, gorillas and howler monkeys) and other wild animals (raccoons, marmosets black-tufted and African soft-haired rats).

Wild animals are much more likely to undergo human-to-animal transmission than vice versa.

“This really highlights our enormous impact on the environment and the animals around us,” said Cedric Tan, a PhD student in computational biology at the University College London Genetics Institute, lead author of the study published Monday in the journal Nature Ecology. & Evolution.

People and animals are hosts to countless microbes that can jump to another species through close contact. The study observed viral transmissions involving all vertebrate groups: mammals, birds, reptiles, amphibians and fish.

“Viruses can jump between different species through the same modes of transmission that apply to humans, including direct contact with infected fluids or bites from other species, among others,” Tan said.

“However, before a virus jumps to a new host, it needs to either already possess the biological toolbox or acquire host-specific adaptations to enter the cells of the new host species and exploit its resources,” Tan added.

Over the millennia, pandemics that have killed millions of people have been caused by pathogens such as viruses, bacteria and fungi that crossed from animals to people. Anthropozoonosis has been the main concern regarding dangerous emerging infectious diseases.

“The biggest current threat is probably H5N1 avian influenza, which is circulating in wild birds. The main reason recent host jumps are so dangerous is that the host species population has no pre-existing immunity to the new disease,” said the biologist computational and study co-author, François Balloux, director of the UCL Genetics Institute.

Most species-to-species transmissions are inconsequential.

“In most cases, these infections don’t go anywhere because the virus is poorly adapted and there is no onward transmission in the new host,” Balloux said.

“In some cases, the virus may begin to circulate, causing a disease outbreak, an epidemic, a pandemic, or even become established as an endemic pathogen. Small outbreaks of anthropozoonosis diseases are probably quite common, even if we don’t realize the large most of them, but full-blown epidemics tend to be rare events, from an evolutionary perspective,” Balloux said.