By Francesco Dernie
Walking through a typical suburban neighbourhood, you might expect to come across any number of unassuming animals – birds, cats, dogs, and perhaps even the odd nocturnal fox. Running into a venomous snake on your driveway, however, might come as a bit of a shock. The natural habitats of snakes, whilst diverse, tend not to include areas where tarmac and brick predominate over grass and trees. However, the combination of rapid urbanisation and climate change that has characterised the 21st century is causing an unexpected development in the global ecological relationship between snakes and humans, with important consequences for public health.
The risk of snakebites has been of increasing concern in the global public health community in recent years, given their potential to cause life-long disability or death if not treated promptly, and the relative difficulty of providing effective antivenoms. In 2017, mounting pressure led the World Health Organisation to add snakebite envenoming to its priority list of neglected tropical diseases. Despite this rising international interest, snakebites have predominantly been regarded as an issue that solely affects rural communities, where people live in close proximity to the natural habitats of snakes, and where healthcare resources are scarcer. This traditional viewpoint is now being challenged, however. In August 2019, the Wall Street Journal reported a steady rise in snakebites being recorded in Texas, North Carolina and Georgia, with record numbers seen over the past year. A high proportion of these took place in the rapidly-expanding suburbs of major cities in these states, as new neighbourhoods encroach into what was, until recently, the natural habitat of several native snake species. This unprecedented urban growth has brought snakes into direct contact with people who are unfamiliar with their behaviour, escalating the risk of snakebites and adding a new dimension to the scale of the challenge facing global health authorities.
Snakes are cold-blooded reptiles, relying on sunshine and the ambient temperatures of their habitat to survive. The hotter, lengthier summers caused by climate change allow snakes to stay active for longer and shorten their periods of dormancy, a change already being seen in the mildly-venomous Montpellier snakes that inhabit the Mediterranean basin. Alongside these behavioural adaptations, temperature changes caused by climate change will also open up new habitats previously too cold for snakes to inhabit. The Burmese python, which currently inhabits a small region of the Florida Everglades, has recently been found populating regions much further north, due to a combination of their own adaptation to cooler temperatures as well as warming climates generally. Indeed, predictive studies have suggested that some previously Southern-dwelling snake species could reach Canada by 2050, and have already begun moving northwards in other countries such as China.
Flooding, wildfires and other extreme weather events also affect snake behaviour. In California, a recent 20-year study has shown that snakebite cases rise following rainfall, possibly because of the increased availability of prey. The USA recently experienced its wettest recorded winter, and the frequency of extreme weather events will only continue to increase, allowing more snakes to move into new regions as they search for prey.
In tropical countries such as Sri Lanka, which sees more than 80,000 snakebites per year and hundreds of deaths, increasingly intense heatwaves alongside decreasing humidity mean that the annual number of snakebites could rise by up to a third over the coming decades. Venomous bites typically require treatment with antivenom, but this process can often trigger allergic reactions. Antivenoms are highly specific to individual species, so if the species is unknown, then medical workers are typically unable to choose the right antivenom. Recently however, polyspecific antivenoms, which are effective against multiple snake species, have been developed, presenting a potentially revolutionary new weapon for combatting snakebite related disease across the world. If increasing urbanisation and climate change lead to increasing numbers of suburban snakebites, these new antivenoms will be a crucial tool for urban healthcare providers.
The ability of some snakes, such as the Burmese python, to survive and adapt as their habitats are changed by urbanisation and climate change challenges the commonly held viewpoint that human expansion and globalisation will simply and inevitably overpower the rest of the natural world. Indeed, in the ever-evolving interaction between humans and the natural systems we inhabit, such unexpected twists will continue to challenge public health infrastructure, highlighting a critical need to better understand the implications of climate change and urbanisation on human health. In the case of snakebites, the ability to harness technology and reporting systems to map both rural and urban at-risk areas, and in doing so identify populations who would benefit from education about snakebites, will be crucial in preventing a further rise in cases. For healthcare providers, the development of effective, affordable and accessible antivenoms will also be invaluable in treating snakebites, especially in rural and urban areas that are at high risk.
The relationship between snakebites, climate change and urbanisation provides a single snapshot of a new challenge facing global public health. Ultimately, our ability to sustainably address such unexpected challenges lies in our willingness to combat their root causes, and in doing so mitigate the pressures facing our public health systems from a changing world in the years to come.
Francesco Dernie is a fourth year medical student at the University of Oxford. He is interested in how climate change can impact human health, and how medicine and climate science can be combined to meet these challenges.
Art by Maya Adams
This article is an online feature of Anthroposphere Issue V.
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