Opinion: 70% of new human diseases since 1990 originated from wildlife, and the rate of pandemic-level emergences has been rapidly increasing

By David Duffy, University of Florida and Jenny Whilde

What links an Irish A&E nurse to a poultry and pig farmer, a subsistence hunter and an primate conservation ranger? Not only are each of these people susceptible to being infected by a human pandemic, but they are all part of an interconnected web, from the origin of human pandemics to the frontline workers attempting to combat them.

The unfortunate fact is that human pandemics like Covid-19 originate in animals, and the rate of occurrence of human pandemics has been accelerating due to some unlikely human activities. Such diseases, which involve the transfer of novel pathogens from other species to humans, are known as zoonotic diseases.

From NPR's Short Wave, tracing the origins of the coronavirus

A whopping 70% of new diseases that have emerged in humans since 1990 ultimately originated from wildlife, and, worryingly, the rate of human pandemic level emergences have been rapidly increasing. There are many recent examples of such epidemics and pandemics, including Covid-19 (originating in bats, likely with pangolins as an intermediary host, before reaching humans), AIDS (originating in chimpanzees), bird flu (multiple wild aquatic bird species), swine flu (pigs), SARS (small mammals, possibly bats) and Ebola (bats and other bushmeat). The list goes on and on.

Although originating in animals, it is human destruction of the natural world which initiates a chain of events leading to global pandemics. The blame for this increase in human diseases therefore lies squarely at our own feet and not those of our animal counterparts. It is no coincidence that, as the human population grows (currently standing at 7.8 billion people, up from 2.6 billion in 1950), our intensive agricultural practices have expanded exponentially and have unrelentingly pushed wildlife populations to the brink.

We have forced wild animals onto marginal lands and into increasingly fragmenting habitats, and dramatically reduced their number on the planet. The effects of a burgeoning human population on wildlife are also being exacerbated by the ongoing human-induced climate emergency. 

Mother Bornean orangutan and its baby. Conflicts with humans, including clearing of rainforest for palm oil plantations, bring these great apes into close contact with humans, greatly reducing their available habitat and leaving many babies orphaned (as the mothers are often killed)

While species loss is an enormous tragedy in its own right, this is not just a stand-alone species conservation issue. Aside from serious ecosystem collapse problems, including biodiversity loss, reduced carbon sequestration, lack of pollinator species for our crops, and lack of clean air and water, environmental destruction brews trouble on the health front that even the most human-centric 'enviro-phobes' among us cannot readily avoid.

When wild animals are so severely maligned, the remaining animals in the population are weakened, unable to thrive, living on increasingly polluted, sub-optimal land, with limited food availability. This compromises their immune systems, leaving them more vulnerable to pathogens like bacteria and viruses and increases their rate of diseases, including cancers.

Poor creatures...but poor us, too. The increased contact and conflict between weakened wild animals and the human populations squeezing them from all sides means there are now vastly more opportunities for their emboldened pathogens to cross the species barrier and transmit into humans and seed new pandemics. Not only that, but other human activities facilitate zoonotic disease transmission (transmission from animals to humans) still further.

A lilac-breasted roller (Coracias caudatus) in Kruger National Park, South Africa. Birds can often be a potential source of zoonotic disease

For example, we have unwittingly constructed bridges to facilitate transmission into humans through our intensive animal agricultural practices and ever increasing numbers of farm animals. Right now, there are 23 billion farmed chickens and over a billion cattle on the planet. That's three chickens for every human at any one time, with 66 billion chickens produced every year. In what is essentially an animal monoculture (small numbers of breeds kept at high densities), the limited genetic diversity and extremely close quarters offer an ideal pathogen breeding ground, greatly facilitating the spread of pathogens from wildlife to humans, via our slaughtered and consumed stock animals that act as intermediate hosts.

The convergence of threatened wildlife, over-intensification of animal agriculture, human encroachment on wild habitats and increases in the bushmeat trade and poaching has led to accelerating incidences of human pandemics which show no sign of slowing down. As the world grapples with the current pandemic, it will not be enough to only focus on the Herculean tasks of crushing the curve, developing vaccines and reviving economies. We must also look to a green recovery, which addresses the underlying causes of pandemics, globally and locally.

Increased contact and conflict between weakened wild animals and humans means there are now more opportunities for pathogens to cross the species barrier

We must return more of our planet back to the care of nature, allowing wilderness and wildlife to thrive, which can only benefit us all. We must make it financially feasible for farmers to return to less intensive and more sustainable practices. We must continue to diversify our forestry (the vast majority of which is non-native, biodiversity-poor, commercial conifer species), decarbonise the economy and encourage marine protected areas. The urgent necessity of such practices is being recognised by international bodies such as the UN, WHO, EU and WWF and increasingly also by corporations and investors

Dr David Duffy is an assistant professor of Wildlife Disease Genomics at the Whitney Laboratory for Marine Bioscience and Sea Turtle Hospital at the University of FloridaDr Jenny Whilde hold a PhD. in Behavioural Ecology from Trinity College Dublin


The views expressed here are those of the author and do not represent or reflect the views of RTÉ