When Denmark announced plans to exterminate all farmed mink across the country in response to confirmation by a state research institute that a mutated strain of coronavirus had jumped back to humans and could hinder the effectiveness of any impending vaccine, media publications — even reputable ones — were quick to proclaim fears of a "new pandemic."
As overblown as these fears may seem, they reflect both a heightened sensitivity to, and growing understanding of, the risk posed by zoonoses — pathogens like Sars-COV-2 (the virus causing COVID-19) that are transmitted from animals to humans, or passed back and forth between them.
"The question is not 'if,' it is 'when,' the next pandemic will be," Delia Randolph, a global leader in the spread of animal diseases, told DW when asked what zoonoses mean for humanity. "Ever since we have been keeping good records, we have seen one new human disease emerging every four months, many from animals [...] and this is accelerating."
To be precise, three out of four of those "new diseases" come from animals, and the frequency with which they have emerged has been accelerating for over 40 years.
Randolph was the lead author of a joint International Livestock Research Institute and UNEP report published in July looking into the reasons for this acceleration. Research from dozens of scientists spanning the globe came to one conclusion: human behavior, i.e., the way we interact with and consume animals, is the main driver increasing the prevalence of zoonotic disease.
The report lists seven "human-mediated factors" behind the emergence, with numbers one through three as follows: 1) increasing human demand for animal protein, 2) unsustainable agricultural intensification, 3) increased use and exploitation of wildlife.
In other words, it's safe to say our desire for meat and other animal products will most likely be responsible for the next pandemic. But what kind of animals are we talking about?
Hygiene measures make livestock safe
If you ask leading infectious disease experts in Germany, such sweeping generalizations with regard to meat production and the increase of new epidemic events must be made with great care; one must be very clear, for instance, what kind of meat production is implied — and what kind of pathogens lead to such events.
"I don't think you can blame factory farming for zoonotic diseases," said Paul Becher, director of the Institute of Virology at the Hannover University of Veterinary Medicine. "The hygiene standards are simply too high in the industrial agricultural sector. And livestock such as pigs, cattle, goats or sheep are generally not receptive for these kinds of exotic pathogens. It's a complex issue, but new zoonotic diseases usually originate from wild animals."
Despite the immense number of animals required for intensified industrial meat production, and that they are kept in close proximity, veterinary epidemiologists appear to agree that these animals are not responsible for the genesis and spread of new diseases.
"Factory farming is a perfect breeding ground for the transmission of infectious agents," said Marcus Doherr, head of the Institute for Veterinary Epidemiology at Berlin's Free University. "If an infection were to happen in this closed system, there would be nothing to stop it from spreading to all the animals. However, the hygiene practices in place make this very uncommon."
Germany's Friedrich Loeffler National Institute for Animal Health points out that several zoonotic diseases have been introduced through factory farming in the past, among them bovine tuberculosis, brucellosis, avian influenza, campylobacter, and salmonella, but that "mankind is quick to forget this because these infections are easily avoided by following hygiene measures."
Biodiversity loss weighs in
The risks posed by bushmeat and backyard farming, common methods of meat production in developing countries, including humid tropical forest regions in Africa and Asia, are higher not only because of lacking hygiene measures. One must also take into consideration the heightened conduciveness for microorganisms where these practices are taking place.
"If you have a high biodiversity with things you see, you have an even higher biodiversity with things you don't see," said Fabian Leendertz, epidemiologist of highly pathogenic microorganisms at Germany's Robert Koch Institute.
Leendertz told DW it was "amazing how many viruses, bacteria and parasites exist in nature and how so few of them have made it to humans," adding, however, that as human beings encroach more and more into animal habitats and eradicate biodiversity, pathogens will have a better chance of making that jump and creating new zoonotic diseases.
"If you destroy diversity of species, suddenly you have shifts in the mammal composition, and these shifts can result in certain species becoming very abundant. If they then carry a highly infectious pathogen, the likelihood of a jump over to humans is much higher."
Overpopulation the root problem?
Increased backyard farming and the trade of bushmeat are likewise due to population growth, as meat is often the only reliable source of sustenance in parts of the developing world.
Of the veterinary epidemiologists and virologists DW contacted for this article, all of them stressed that population growth coupled with our greater mobility as a species was just as problematic as our desire for meat when it comes to the rise of zoonotic diseases.
"The pathogens have always been there," said Fabian Leendertz. "What has changed and what I think is really worrying is the great connectivity of the globalized world we live in today. The risk of a small, exotic pathogen reaching the next capital city from where it can easily spread across the world is now much greater than it ever was before."
"I’m not saying we're going to have a COVID-19 every year," said Marcus Doherr, who has already been asked by insurance companies whether the next big outbreak can be predicted. "What I'm saying is that the possibility of it happening again is definitely there. Given our current population size and the interaction with wildlife that is very intense in some regions of the world, it will be impossible to prevent transmission of pathogens between animals and humans. But the question of whether it spreads among humans on a pandemic level is driven by nothing other than our travel behavior, our global mobility."