Malaria, yellow fever, coronavirus, ebola, monkeypox, and influenza in all its forms came to humans because of close contact with animals. These diseases have killed untold millions, if not billions, over the course of human history.
But now, a new study from University College London suggests that, as big a disease threat as animals have always posed to humans, humans may pose an even bigger disease threat to animals. Rather than simply being an incubation sink for a variety of zoonotic diseases diseases, study co-author and UCL Professor Francoi Balloux suggests that humans may actually be a key source in the network of creatures that pathogens use to stay alive.
The study sifted through public databases to examine the genomes of tens of thousands of viruses. This approach allowed a look at all the hidden information within the viruses, revealing clues about inter-species transmission in the virus’s history. This forensic approach works because when viruses interact with host immune systems, they mutate readily to survive, and these mutations comprise genetic tell-tales of where the virus has been. The UCL researchers used these clues to determine whether a given virus had originated in animals, or in humans.
Researchers examined over twelve million viral genomes. In nearly two-thirds of their samples, the viruses analyzed originated in humans.
Forming an accurate understanding of how viruses get passed around between species across the entire tree of life may help experts better predict what diseases thought to be eradicated in humans might come surging back, and what factors might enable cross-species transmission.
Changing current disease surveillance measures to search also for pathogens that move from humans to animals may allow civilization to prepare better for future outbreaks of novel illnesses, Balloux says. Previously, human-to-animal transmission has received little attention.
If the conclusions of this study withstand scrutiny, it marks a turning point in the history of epidemiology, and will forever shape the discipline going forward.
