Infectious diseases: humans have transmitted diseases to other animals many times

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A review found ample evidence of wild and captive animals contracting diseases through close contact with humans

The life


March 23, 2022


White-tailed deer in Minnesota – covid-19 is now spreading among North America’s deer population

Stan Tekiela Author/Naturalist/Wildlife Photographer via Getty Images

Covid-19 originally jumped from animals to humans, but people have passed other diseases to animals as well – such ‘throwback’ events being described in almost 100 studies. And the documented reports are probably the “tip of the iceberg,” says Anna Fagre at Colorado State University.

Fagre’s team searched previously published research for any papers describing disease transmission between humans and animals that did not involve the novel coronavirus. They found 97 reports, involving bacteria, viruses, fungi and parasites; 57 of the cases involved transmission to primates – likely because it is easier for pathogens to jump from humans to these relatively closely related species.

Many transmission events involved zoo animals – for example, a cheetah that caught a strain of human flu – but they also involved wild animals, such as mountain gorillas in Uganda catching several bacterial infections that cause diarrhea.

There have been no confirmed cases of the disease jumping to an animal species and continuing to spread between individuals. But several wild skunks have been found infected with human flu, suggesting there could be ongoing transmission. And the virus that causes covid-19 is now spreading widely among white-tailed deer in North America.

In addition to harming affected animals, another danger is that the human pathogen mutates in the animal host and becomes more dangerous to humans if it crosses paths again.

“I think there’s a lot more transmission than we’re currently picking up,” Fagre says. “When we don’t sample robustly, there are so many pathways we could miss.”

The original animal host of Covid-19 appears to have been bats, although there may have been an intermediate stage in pangolins. From humans, the coronavirus appears to have jumped to pets such as cats and also farmed mink, necessitating a massive cull in Denmark in 2020 over fears the mink virus could turn into a more dangerous.

Tourists on gorilla-watching trips are supposed to wear face masks, to reduce the risk of transmitting infections, but many do not.

Journal reference: Ecology Letters, DOI: 10.1111/ele.14003

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