Covid & the Environment - Part 1: The Origins
A tale of biodiversity loss and ecosystem destruction
This is the first part of three, exploring the link between the Covid-19 pandemic and the environment.
Part 1 — The origins of Covid-19: a tale of biodiversity loss and ecosystem destruction
Part 2 — The consequences of the pandemic on the environment
Part 3 — Connecting the dots: the aftermath of the pandemic will be what we make it
It looks like the Covid-19 pandemic took the world by surprise. Actually, it did not.
Since the disease originally jumped from bats to humans, an animal metaphor is a good way to start. Covid-19 has been described as a “black swan”: an event of low probability, that no-one can predict based on current data, and with world-changing implications. That is not quite right. Instead, it was more akin to a charging “gray rhino”. A disaster, that is, which was looming with high probability and high impact and yet, felt always distant and blurry enough to choose to ignore it before it was too late. Eerily enough, the World Health Organization included in its register of priority diseases a so called “Disease X” with putative characteristics rather similar to Covid-19. SARS-CoV-like viruses from bats, the group the Covid-19 virus belongs to, were already called “a time-bomb” in a paper published in Clinical Microbiology Reviews in 2007 (Cheng et al., 2007). So although there was no way to predict when it would materialize, this threat was already well identified. Why is that?
Three fourth of new infectious diseases in people come from animals — they are called zoonotic diseases. New strains of influenza have emerged from livestock farming. HIV, Ebola, SARS, MERS and now Covid-19 have been linked to wildlife. Epidemics usually begin as pathogens in animals that jump to people when we make contact with them. And industrial societies have three key aspects that act as threat amplifiers: industrial farming, global warming and ecosystem destruction.
Industrial farming represents a perfect incubator for deadly pathogens that can decimate livestock, and cross over to the people who rear them: in large industrial farms, thousands of animals are kept at high density and often in poor sanitary conditions, with widespread use of antibiotics, which speed up the evolution of resistance (Dhingra et al., 2018).
Global warming, which we owe to the greenhouse gas emissions from the fossil fuel and cement industries as well as some agricultural practices, is expected to have two main effects on infectious diseases. The first one is by making species change their geographic ranges, coming into new contacts with one another (Carlson et al., in press). By expanding the warm climatic zone where most vector diseases thrive (i.e. diseases spread by mosquitoes, ticks and the like), global warming also puts a bigger and bigger share of the global population at risk from diseases such as malaria and dengue. The second infectious threat of global warming comes from pathogens trapped in permafrost, the frozen soil of high latitudes which is now melting at an alarming rate — a threat that materialized for the first time as a small but deadly anthrax outbreak in 2016 in Siberia.
Finally, the destruction of ecosystems, and the disruption of the fragile networks of relationships between the species that compose them (humans included), is at the root of the emergence of diseases like Covid-19.
It is now clear that preserving biodiversity is a major way to prevent the emergence of infectious diseases (Keesing et al., 2010). In 2014, a study on biodiversity and infectious diseases made two important findings. First, the overall richness of infectious diseases in a region is positively correlated with its biodiversity. Second, the number of zoonotic disease outbreaks increases with the number of threatened species, and the extent of deforestation. This shows that while biodiversity is a source of pathogens, which are indeed themselves an integral part of this diversity, it is the destruction of biodiversity and the disruption of ecosystems that make the infection of humans likely (Morand et al., 2014). Mechanisms underlying this relationship are many, but one of them is the decrease in the numbers of top-predators and scavengers, animals which are often under a significant pressure from humans, but play a major role in controlling diseases, in temperate regions just as much as in the tropics (Estes et al., 2011).
Covid-19 originated in bats
In the case of Covid-19, although it will be hard to ever be certain of the precise chain of events that led to the outbreak, the favoured scenario so far is that the virus originally afflicts bats, and was transferred to humans possibly via an intermediate host. It is still unsure whether the pangolin might be the one (Cyranoski, 2020). This final contagion step probably happened in a seafood market in Wuhan. There, wild animals destined to human consumption were detained in small cages, stressed,with depressed immune systems, conditions that boost the likelihood of interspecies contamination (Lam et al., 2020). The existence of such markets selling a variety of live animals and bushmeat, especially in tropical Africa and Asia, has already been associated with emerging infectious disease (Kurpiers et al., 2015). Some outbreaks killed many people locally, but were eventually contained, and none had yet developed into a pandemic of that scale. The more connected the region to the outside world, the more likely the pathogen is to spread outside of its original range.
Wildlife trade is now under worldwide scrutiny due to the Covid-19 outbreak
China has already announced a ban on all wildlife trade for consumption. Are such sweeping measures the solution?
Be they in Asia or Africa, they might not be the perfect fix. First, banning bushmeat markets without addressing related socio-economic aspects would be detrimental to the local folks, often already poor and living in relatively marginal communities, and who depend on wild-caught animals for protein or income (Kurpiers et al., 2015). Second, it could drive the trade underground, a very counterproductive outcome since it would now be impossible to enforce hygiene norms, nor to monitor for early warnings of viral emergence, which is believed by some scientists to be the most efficient epidemic prevention tactic (Holmes et al. 2018). As it happens, illegal wildlife trade is already the second largest black market worldwide (including trade for medicinal or recreational purposes, and illegal, unreported and unregulated fishing).
Despite these important social caveats, rethinking and regulating bushmeat markets and wildlife trade is clearly necessary, as advocated by the United Nations biodiversity chief. This is especially pressing since the commodity chain supply is currently getting longer due to growing urban demand for bushmeat (Ahmed et al., 2019), the trade even becoming international, which is both adding pressure on the hunted species and enhancing the risk of international outbreaks (Kurpiers et al., 2015).
Wildlife markets are only the easy target
Hunting wild animals for food is only one of the activities increasing the risk of disease emergence in the tropics. Biodiversity loss and habitat fragmentation are causing increased contact between humans and other animals, and disrupting the subtle balance of relationships between hosts and pathogens within ecosystems. And this disruption and increased contact favour pathogens jumping hosts.
Bats are a particularly plentiful reservoir of diseases and a particularly efficient spreader due to their flying abilities. Sadly, environmental destruction often compels them to move from their natural habitats to agricultural areas, where they can infect people or farmed animals, as we now know was the case during the Nipah outbreak in Malaysia, for instance (Kulkarni et al., 2013).
In the wake of the Covid-19 pandemic, the global sanitary threat paused by the link between environmental destruction and infectious diseases is finally getting more widely recognized. This is for instance the case of the United Nations, or the German Environmental Ministry who recently asked the IPBES (Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services) to investigate the links between infectious diseases and the destruction of nature, and to outline policy options to help prevent pandemics.
Activities causing biodiversity loss and habitat fragmentation in the tropics are multiple: aside from legal and illegal wildlife trade, they include clear cuts, logging, mining, oil extraction, and agricultural intensification (Kurpiers et al., 2015). They have in common to be in large part driven by growing international demands for commodities like wood, cattle feed, meat, palm oil, petroleum, or metals. This means that non-tropical countries also have the means and responsibility to directly decrease the risk of disease emergence in tropical areas, especially the richest importer countries: by reducing demand for those commodities to what is truly essential, they have the power to stop much of the associated environmental disaster.
Towards a concept of planetary health
Future outbreaks need to be prevented by integrating emerging infectious disease prevention into sustainable development goals, and by understanding the relationship between biodiversity, ecosystem disruption, climate change, and emergent diseases (Di Marco et al., 2020). This program forms a new integrative field of study called planetary health (Whitmee et al., 2015), which will help policymakers take a holistic view of public health that includes the health of the natural environment, and respond with “planetary consciousness”. Hopefully the current pandemic acts as a wake-up call for some political leaders, making them realize that everything is connected in the Earth system, and that their policies must reflect just that.
As we have seen, the Covid-19 pandemic, and possible future similar epidemics, are made more likely by environmental degradation. But is the current pandemic, which has brought human activities worldwide to a standstill, a “good thing” for the environment?
Find out more in Part 2 & 3:
Part 2 — The consequences of the pandemic on the environment
Part 3 — Connecting the dots: the aftermath of the pandemic will be what we make it
To be continued!
NB: should you find any inaccuracy in this piece, or have comments, please write to atilquin@ethz.ch!
