Slouching to Armageddon: Covid and climate change

Plague and pestilence have deep historic links to climatic disruption. We need to understand better the links between human health and the ecosystems we depend on.

Pestilence and environmental upheaval are ancient bedfellows. It is likely that the periodic waves of ‘Black Death’ that decimated Europe were linked to Asiatic climate change. Research suggests that fifteen years or so after successive climatic fluctuations rendered the Karakoram mountains inhospitable to rodents, outbreaks of plague hit European harbours. With rodent numbers decimated, fleas carrying Yersinia pestis sought other hosts, including human populations, the disease then sauntering the slow medieval trade routes to Europe.

Although COVID seemed to fall from a clear sky, there is evidence linking it – and other recent zoonotic outbreaks of disease including MERS-CoV, Sika and Ebola – to anthropogenic  environmental change.

Progressive global destruction of habitat forces birds and animals ever closer to human populations. Deforestation is known to displace bat populations – which may be linked to COVID – forcing them into gardens and increasing the likelihood their viruses will shift to human hosts. As we are unlikely to have natural immunity, the consequences, as we know first hand, can be devastating. Global temperature change pushes natural populations from their traditional environments, taking their viruses with them. Malaria is expanding beyond its traditional range. The disruption of balanced ecosystems undoes natural constraints on pathogens: the explosion of Lyme’s disease in the US is associated with the loss of habitat for opossums and chipmunks – both highly effective at keeping tick populations in check.

COVID-19 – a zoonotic infection probably jumping from bats to humans

Food production

Intensive modern farming, particularly the pressure to produce inexpensive meat at scale, is a powerful driver of zoonotic spillover – viruses jumping the species barrier. Although spillover is probably as old as humankind – and was intensified with the shift to agriculture some 12,000 years ago – modern farming creates particularly fertile conditions for viruses to species-shift. Among the major sources include overcrowding of farmed livestock, appalling rearing conditions and widescale use and misuse of antibiotics. Intensive poultry production in China and elsewhere has been convincingly linked to the emergence of dangerous avian influenzas. A 2015 US study showed that Europe and the US are the world’s leading exporters of swine flu. Other critical sources of virus spillover are smallholders – many forced into the traffic and cultivation of wild animals by competition from large-scale agribusiness.

As COVID demonstrates, increases in human mobility and population density further facilitate the spread of zoonotic viruses, and magnify the challenges of response.

Poverty compounds the problem: overcrowding, multi-occupancy, poor ventilation, difficulty social distancing and unsanitary conditions combined with generally worse underlying health speed up transmission and exacerbate health burdens.

The glamour and genius of biotech

The rapid development of vaccines for COVID has been a triumph, both of biotech and oversight – delivering a safe and effective vaccine to market in the twinkling of a regulatory eye was breath-taking. It showcased our technological sophistication, our ability deftly to respond to serious human threats.

But there is a danger in relying exclusively on biomedical responses. 

Pathogenic bacteria. Image by kalhh from Pixabay

They risk shrinking our vision to the micro-dot of a pathogen, tempting us to focus on the disease, forgetting the conditions that enable it to spillover and flourish. In doing so we menace our ability to understand the critical links between human health and the complex natural and man-made systems on which it depends.

If COVID has taught us anything it is that we are links in long chains of wellbeing. Until we change our relationship to the global ecosystems on which we depend, we will lurch from crisis to global crisis.

Among the impediments routinely trotted out to environmental change are financial – that such a global transformation is improbably, unachievably expensive. But The Economist has recently put the global economic cost of COVID in GDP foregone at $10 trillion for 2021-21, surely a figure big enough to focus the minds of a few world leaders. There will be many lessons learnt from COVID. Few aspects of our lives will be unaffected. But now is the time to think long and hard about our dependency on our global environments. One-health is a trans-disciplinary movement designed to promote optimal human health through acknowledging the strength of our connection to animals, plants and their shared ecosystems. In addition to zoonotic diseases such as COVID, foci of concern include food safety and security, antimicrobial disease, pollution, mental health and even noncommunicable diseases.  We have never needed it so much.

Julian Sheather

This is a slightly longer version of a blog originally posted over at The British Medical Journal.

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