Deforestation and COVID-19
Emerging understanding of planetary and human health linkages
by IEF Member Michael Richards
The evidence suggests that COVID-19 came from bats and was then passed to pangolins (scaly anteaters) and then, via wildlife traffickers in the Mekong region and a “wet market” in Wuhan, to people. COVID-19 is a “zoonotic” disease, i.e., it comes to people from animal hosts or vectors. Zoonotic diseases comprise up to three quarters of human infectious diseases according to expert estimates. COVID-19 is only the latest in a long line of zoonotics that can be traced back to birds or wild animals, and which seem to be increasing in frequency:
The 1918 Spanish flu pandemic, which infected about a third of the global population and killed 50 million people, is thought to have passed from birds to horses (in first world war trenches);
Asian avian flu from wild ducks killed about two million people in the 1950s and 1968;
The HIV pandemic, which has killed about 35 million, is thought to originate from chimpanzees hunted in Cameroon and eaten in restaurants, e.g., “smoked baby chimp”, in Kinshasa;
Severe Acute Respiratory Syndrome (SARS), which killed 770 people in 2003, came via horseshoe bats and civets;
Middle East Respiratory Syndrome (MERS), which has killed 850 people since 2012, passes from bats to camels to people;
Ebola, which has killed over 10,000 in West Africa, is linked to eating monkeys and bats;
Nipah virus, which kills a few people in India each year, is also traced back to bats;
Marburg Hemorrhagic Fever, which killed seven German lab staff working on green monkey tissue in 1967, is hosted by African fruit bats;
Kyasanur Forest Disease is a tick-borne virus from monkeys that annually affects 400-500 people in southwest India, resulting in occasional human deaths and high monkey mortality;
While not a zoonotic, African swine fever is a big killer of domestic pigs infected by ticks from wild pigs, bushpigs, and warthogs.
The link between deforestation and zoonotic diseases is being increasingly studied. In a recent blog, Kerstin Canby of Forest Trends notes that “without forests as a buffer, hunting, mining, and logging exposes people to animals. These interactions lead to the spread of animal diseases to humans. We’ve seen this with Zika, Avian Bird Flu, Ebola, and SARS, as well as Nipah, which leads to respiratory problems similar to those from COVID-19, and Kyasanur Forest Disease, spread by ticks.” Canby also points out the major role of poachers and others involved in wildlife trafficking; research shows that, at least in southeast Asia, the same actors are involved in illegal logging.
The loss of animal habitat, mainly due to deforestation, is forcing multiple animal species to crowd together in ever smaller areas, as well as bringing them more into contact with people, who are increasingly hunting and eating/selling them – especially as sustainable forest livelihood options are lost (also due to deforestation). Moreover it seems that at least some zoonotic diseases favour degraded environments: published research shows that Ebola vectors are mainly found in forest clearings and fringes, and that there is a statistical correlation between Ebola disease outbreaks and recent deforestation.
The problem is that in crowded (as regards bird/animal species) and degraded ecosystems, viruses are more likely to jump from one species to another. As noted by Dr Kate Jones of University College London: “we are creating habitats where viruses are transmitted more easily. Species in degraded habitats are likely to carry more viruses which can infect humans. Simpler systems get an amplification effect. Destroy landscapes, and the species you are left with are the ones humans get the diseases from.” Another researcher, Richard Ostfeld of the Cary Institute of Ecosystem Studies, New York, observes that “rodents and some bats thrive when we disrupt natural habitats. They are the most likely to promote transmissions. The more we disturb the forests and habitats, the more danger we are in.” David Quammen, author of Spillover: Animal Infections and the Next Pandemic, also expresses it succinctly: “We disrupt ecosystems, and we shake viruses loose from their natural hosts. When that happens, they need a new host.”
It can also be noted that some of the main drivers of climate change are also bad for human health. Apart from the role of deforestation, which causes 12-15% of greenhouse gas emissions, as a major indirect cause of zoonotic diseases, fossil fuel pollution is severely exacerbating the impact of COVID-19. Harvard University researchers have found a strong statistical correlation between exposure to fine particulates, which damage the lungs, and COVID-19 death rates: an increase in urban atmospheres of one microgram per cubic metre is associated with a 15% increase in deaths.
We don’t know where the next pandemic will come from, but it will almost certainly be another zoonosis, and it is quite likely to be associated with deforestation and illegal wildlife trafficking. If, as is the case with many zoonotic viruses, it affects the respiratory system, fossil fuel pollution will exacerbate the impacts. A glimmer of hope in all this is that perhaps there will be a greatly increased realization that what is bad for the planet is also bad for human health – and this could increase political will to combat climate change. In fact the links between environmental and human health are the focus of an emerging discipline called “planetary health”. And of course this is another example of the interconnectedness of all things.
Last updated 21 May 2020