Climate change: two articles warn of the dangers to human health
While we all know that global warming has an impact on the environment, it has also been shown to affect our health, and particularly our digestive health, not only because it puts our bodies through its paces, both directly and indirectly, but also because it causes the selection of pathogens better able to withstand our 37-degree body temperature.
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About this article
Climate change has caused a rise in the Earth’s average temperature of around 1.5°C since the pre-industrial period (1850-1900), in addition to (and especially?) extreme weather phenomena and record high temperatures. These exceptional phenomena apply selective pressure on all living beings, including humans. There are just two options to this pressure: suffer (and possibly perish) or adapt.
More than 50% of the infectious diseases affecting humans are aggravated by climate change. 1
Diarrheal diseases could increase by 10% by 2030, affecting mainly young children. 1
Pressure already at work
According to Mhairi Claire Donnelly and Nicholas J Talley, co-authors of a “Commentary” published in Gut 1, climate change is expected to significantly affect our digestive health, derailing its physiology and impacting our digestive and immune systems. According to the authors, this is due to: increased use of pesticides and fungicides to save weather-beaten crops, which cause dysbioses in consumers that result in digestive (Irritable Bowel Syndrome and colorectal cancer) and non-digestive (obesity and neurodegeneration) diseases; air pollution involved in inflammation, oxidation and insulin resistance; and so on. Mental health may also be affected, due to eco-anxiety.
Things are no better as regards infections: over 50% of infectious diseases are expected to be exacerbated by climate change, and a 10% increase in diarrheal diseases (contamination of drinking water during floods, high temperatures favoring certain viruses, etc.) is expected by 2030. The issue of digestive and liver cancers is also raised: rising temperatures are thought to induce the secretion of carcinogenic toxins, while microplastics from fossil fuels could be responsible for liver cancer. Paradoxically, treating these diseases also increases our carbon footprint, prompting the authors to conclude their article – which some will criticize for shortcuts and the non-separation of climate change and pollution – with a call for new practices, both at home and in hospitals.
Changes taking place
At the same time, some pathogens are adapting, warns Arturo Casadevall in his article in Nature Microbiology 2. He argues that successive heatwaves will result in the gradual natural selection of fungi most tolerant to high temperatures. Yet mammalian body temperature has been one of the weapons (along with immunity) used to defend against pathogenic fungi: Cryptococcus spp. blocked by a rabbit’s high body temperature cannot induce systemic cryptococcosis and is limited to the coldest parts of the body such as the skin and testicles.
But what will happen in the future if the greater number of very hot days results in the natural selection of fungi more tolerant to high temperatures that adapt more quickly to the heat? It would facilitate the infection of all mammals by fungi. So not only is global warming affecting the ecosystem, it could also be selecting pathogens adapted to higher ambient conditions.
Global warming has been linked to the simultaneous and unexplained emergence of different clades of C. auris on three continents in the 2010s. 2
Moreover, this selection may already be underway: global warming could explain the simultaneous and unexplained emergence on three continents, in around 2010, of different clades of Candida auris that are more thermotolerant than the phylogenetically related Candida spp. and display significant resistance to two of the three main classes of antifungal drug: azoles and polyenes.
