Throughout history, humans have been afflicted by diseases transmitted from animals, with the current coronavirus outbreak the latest to have taken place in recent years, from the 1998 Nipah virus in Malaysia, to the 2014 Ebola virus across West Africa.
The World Health Organization has declared four global health emergencies over the past decade and research reveals outbreaks are becoming more common. Why are we seeing this increase around the world?
Tim Benton: The fundamental job of pathogens throughout evolution has been to maximize their chances of infecting susceptible organisms. Pathogens can live in lots of different host organisms and so they are continually looking for an opportunity to jump from one species to another. Some pathogens are particularly good at this like the coronavirus.
Certain species of animals, like bats, appear to have immune systems that harbour a lot of organisms living inside of them naturally but their immune systems can cope with it and they become reservoirs of diseases.
These pathogens then seek the opportunity to jump to another species. But where are they going to find a new host? Well, from an environmental perspective, when humans change the environment, such as by changing the climate, we cause animals to move around the landscape, often migrating northwards towards the Northern Hemisphere, which drives different animals to come into contact with us.
Similarly, when we degrade habitats, animals are forced to squeeze together with other animals into smaller areas. If we then come into contact with these animals, then we risk the pathogens living inside of them, jumping across to us.
The same is true when humans migrate to urban centres which are reservoirs of diseases too. Rats are a prime example of an animal which hosts a lot of pathogens and are common to find in cities, and people, particularly low-wage people, often come into contact with them.
So, climate change, habitat change and our own societal changes are creating new ecologies which are leading us to mix with those new ecologies in new ways and giving the perfect opportunity for pathogens to make a leap across to us.
Richard Kock: 100 years ago, we didn’t have the tools to understand what viruses were so part of the apparent increasing emergence of these diseases is the fact that we’re better able to detect them.
But the movement of a virus from an animal to a human is important. Pathogens jumping to another species is actually an extremely rare event. HIV, for example, was a rare event in the 1950s that led to a disease that spread throughout the human population. Measles, too, is a common disease among humans but was believed to have spilt over from cattle to humans in the 15th century.
But this is what evolution is all about. This crisscrossing is happening all of the time but the chance of you or I getting a zoonosis directly from an animal is actually extremely rare. In fact, the most likely zoonosis that humans might get would be from a domestic animal. Dogs, for example, can give us rabies and there are around 50,000 cases of rabies a year around the world.
We should remember that wildlife is not a threat to us. We are a threat to it, and to ourselves, because we create the conditions for spill-overs of diseases to happen. How do we do this? By invading their environment and, in that process, there is a risk that the pathogens that they carry see an opportunity to jump into us as a new host. So the only person at fault here is us.
Scientists have warned human activities are creating a ‘perfect storm’ for a spill-over of diseases from animals to humans, as you mentioned, and that humanity’s ‘promiscuous’ treatment of nature needs to change or there could be more pandemics like the coronavirus in the future. How far has humanity’s changing relationship with the environment contributed to the likelihood of pandemics, like the coronavirus, occurring?
Tim Benton: The coronavirus outbreak is another example of the fact that, increasingly, as we change our environment, we are creating the conditions for society to get hit by diseases whether it’s the coronavirus or something like bluetongue, which is an animal disease impacting livestock, or Ug99 which is a disease impacting wheat.
But it’s not just about pandemics occurring but the subsequent impacts they can have on human health, for example, the impacts to our livestock systems and our crop systems and, therefore, food availability and the nutrition that underpins our ability to fight diseases like the coronavirus.
When you put all of these pieces together, we shouldn’t just be worried about pandemics occurring, but the increasing shocks to society that could happen in all sorts of ways as a result.
Richard Kock: Yes, human activities, such as deforestation, agriculture and mining, have led to a greater risk of pathogens transmitting from animals and humans.
Population demography is also a problem. There are a lot more people now than there used to be and they increasingly migrate to urban centres where they live alongside a large population of domestic animals – in fact the biomass of domestic animals is about three times the biomass of humans – it’s massive. This is a huge problem because it creates a close connection between us.
Take a rat, a crow, a seagull or a fox. They basically feed off of human waste because we consume all of the natural resources. Bats fly and rats hide but they’re very good at surviving very close to human habitation. That’s why certain domestic species are a greater threat to us because they’re able to occupy the same space as we do and therefore spill-overs of pathogens from them to us are much more likely.
MERS-CoV, which has been developing since 2012, came from a camel which is also a domesticated animal often found in farms in the Middle East. These farms become like pathogen factories where the virus can spill over to humans, and then human-to-human, until we get an outbreak which is what I suspect happened with COVID-19.
Similarly, if you look at the evidence for SARS, we had the civet cat and the raccoon dog which are both domesticated ex-wild animals used for the fur and meat trades in Asia. So, if you put the bats and the rats to one side, it’s also the animals that we’re exploiting directly that are the greatest threat to us but, ultimately, the threat is caused by us.
Human activities have significantly altered three-quarters of all land and two-thirds of all of the ocean on Earth leading to a changing climate and unprecedented global biodiversity loss. In light of a recent warning from the UN that multiple famines of ‘biblical proportions’ could be seen within months following the pandemic, what can we expect to happen if we continue along our current trajectory?
Tim Benton: We can’t continue as we are because it’s taking us to a situation where we are undermining the ability of our species to survive.
The coronavirus crisis is interesting because it is a wake up call for governments and it’s generating much more hard-headed thinking about the challenges of the future.
I’ve been working on these issues for decades now and I remember having conversations with the UK government in the past about the risk of environmental breakdown to our food system. The UK government’s response then was that the market will sort everything out but I think there is very different thinking now. I just hope that we make the changes needed fast enough.
Richard Kock: One of the most interesting things that I have experienced in my career was in 2015, when I was in Kazakhstan, which has a beautiful steppe habitat with very extreme weather. This is where historically the mammoths and the sabre tooth tigers come from and also a species called the saiga antelope. It’s a fast-reproducing antelope that still lives in Central Asia having survived the Pleistocene, unlike many species, although they’re now a critically endangered species.
We started seeing a phenomenon there – a disease wiping out the population – over an area the size of the UK. 230,000 animals died over a period of about three weeks. It was extraordinary. We found out there was a bacteria that is quite common around the world called Pasteurella multocida which was, for some reason, suddenly able to invade each individual saiga antelope across the landscape. But there had been no transmission of the bacteria meaning the bacteria must’ve been present in the animal beforehand.
We then found that a recent change in the weather had caused the bacteria to become activated inside of the animals. I’m not saying it was climate change but it’s amazing what happened with a change in the climate: a warm-blooded mammal was affected by a pathogen due to a change in the environmental conditions and had a 100 per cent mortality rate. Climate change, however, will bring these types of conditions about more often which could lead to a 100 per cent mortality rate of the human population.
COVID-19 has a 1-2 per cent mortality rate which is extremely mild yet look what it does to our economy. We must wake up as humans and realize that there are existential threats out there, through our own fault, which could eliminate us as a species, and the sooner we wake up, the better.