The threat of climate change evokes certain scenes: Smoke rising from a burning forest. Stifling heat clings to the warped asphalt of a densely populated street. Glaciers are breaking in a rising sea. Another scenario should be equally terrifying but more difficult to contemplate: a virus leaving the animal that served as a blind host for an invading human.
For years, scientists have been warning us of a troubling reality: climate change will make pandemics more likely in our collective future.
Much like the effects of climate change on our environment, its effects on our health seem insidious, until they are not. A changing climate brings us closer to thousands of potentially destructive viruses – an obvious cause for concern, given that we reach nearly three years of life under COVID-19 and following the recent outbreak of monkeypox.
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Changes in temperature and precipitation shift the geographic ranges of animals – including mosquitoes, ticks, birds and small mammals – into the vicinity of humans. Storms and floods displace people from their land and bring them closer to animals that spread disease. This means that we will have more and more contact with wildlife, the organisms they carry and the diseases that come with them.
The recent floods in Pakistan after an unprecedented monsoon season are a stark example. The country was already experiencing a resurgence of cholera, caused by the Vibrio bacterium, which contaminates water sources. The floods have since disrupted vaccination, medical care and disease surveillance strategies essential to controlling the outbreak. Where large bodies of water stagnate, mosquitoes carrying dengue fever and other viruses as well as parasites like malaria proliferate and transmit them to humans. There are fears that the looming health crisis of waterborne diseases in Pakistan will worsen in the coming weeks.
Ebola, Lyme disease and Lassa fever have also reached humans via other species, and all three are expected to circulate more widely in a warming world. But the Lassa virus, a high-priority pathogen listed by the World Health Organization with the potential to cause a public health emergency, is particularly alarming because its presence in West Africa is entrenched and its spread is linked to the climate.
Under conditions of lower rainfall and longer dry seasons, the common African rat Mastomys natalensis carries the virus and has no choice but to forage for food in nearby human dwellings, leaving urine and saliva on rice, cassava and other crops stored in barrels or left in place. in the sun. When people ingest these foods or are directly exposed to them, it can lead to infection, usually leading to fever and general feeling of being unwell. But it can also produce worrisome symptoms such as eye, nose, and mouth bleeding, and even permanent hearing loss. The virus is estimated to infect nearly 500,000 people each year and kill 5,000. In parts of Liberia and Sierra Leone, it accounts for more than 10% of patients admitted to hospitals each year.
Climatic hazards can further enhance the virulence of a pathogen. Heat waves can make some viruses more resistant to fevers, the first onslaught of the body during an infection. Food shortages and droughts resulting from more heat, less rainfall and other changing weather conditions breed malnutrition and stress, leaving our immune systems weakened and our cells vulnerable. A recent study identified 1,006 unique ways climate change is driving the next global contagion.
As infectious diseases continue to emerge, so will efforts to suppress them. The US government has invested hundreds of millions of dollars in virus surveillance programs with dramatic names – DEEP VZN, STOP Spillover and PREDICT fire, to name a few. These groups of intrepid scientists are rooting deep in the hollow regions of Asia, Africa and Latin America – where the territories of human settlements, livestock and wildlife overlap – to gather data to model the pathways through which a zoonotic virus could spread within the fragile human being. biome, generating a new disease.
Such interventions can anticipate and even accelerate our response to an outbreak. But no matter how sophisticated these systems may be, they don’t prevent one from happening in the first place. While this research may help us predict and theoretically contain a virus about to spread to humans, it does not address the underlying factors that prime the microbial trampoline.
This is why our attention must focus more upstream, on climate change and the mitigation of its effects. Reducing emissions from the biggest culprits – such as the energy, transport and health industries – will stem the worsening of conditions conducive to disease, including floods, heat waves and droughts. And minimizing our carbon footprint will reduce air pollution and other environmental impacts, improving the basic health of our people. It could curb the chronic diseases – such as cardiovascular disease, diabetes and cancer – that made us vulnerable during the COVID-19 pandemic and make us vulnerable to the next threat.
But the biggest factor that would protect against a pathogen leap requires rethinking the way we change our landscapes. When forests are recklessly cleared for logging, road building and conversion to cropland, we lose the biodiversity that keeps the numbers of rats, bats and other disease-spreading wildlife in a careful balance. zoonotic. And when urban centers expand beyond reasonable limits, animal and human habitats are irrevocably linked.
The ecological networks that link us to our natural environment are clearer than ever. It is a relationship that we must honor. Failure to do so would aggravate biological collisions that we absolutely cannot win.
Arjun VK Sharma is an infectious disease writer and resident physician based in Ontario, Canada. @ArjunVKSharmaMD
