Study shows: Greater spread of diseases due to climate change

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Back in 2017, researcher Camilo Mora looked at the effects of heat waves on human health. Together with his team, he described 27 ways in which a heat wave can kill a person. Mora, who researches biogeography, biodiversity and the environment at the University of Hawaii, has now extended this approach and examined the spread of many pathogens in the context of climate change. The result: climate change can exacerbate 58 percent of the ailments caused by pathogens.

The study, published in the journal "Natural Climate Change", not only focused on the general warming caused by increasing greenhouse gas emissions, but also on the extreme weather events such as droughts, floods or heat waves. A total of 830 studies were evaluated for Mora's study, which looked at 286 diseases resulting from ten climatic hazards. 277 of these diseases spread faster or worsened in severity due to at least one climatic hazard.

Transmission by mosquitoes, ticks and wild animals

The authors then examined a list of health authorities documenting 375 infectious diseases that affect people. For 218 diseases, 58 percent, the researchers conclude that they are aggravated by climate hazards. The triggers here are pathogens such as viruses, bacteria, but also plant pollen or fungi. The pathogens were primarily transmitted by mosquitoes, ticks or other (wild) animals. Global warming promoted 160 diseases, floods 121 diseases, drought 81 diseases.

There are many ways in which natural extremes can expose humans to infectious diseases: For example, the probability of zoonoses, i.e. the transmission of pathogens from animals to humans, increases when they come together in one area, which is the case when, for example, droughts push wild animals closer to residential areas. But humans are also forced to look for new places to live during floods, for example, and in the process move to areas where they are confronted with new pathogens. The risk of virus transmission from animals to humans in the course of rapid environmental changes was recently calculated by a team of researchers from Georgetown University in Washington DC. According to this, even with a warming to the targeted 2 degrees, at least 10,000 virus species could potentially become dangerous to humans by 2070.

The spread of certain mosquito species that feel at home in warmer areas is another link between climate change and the spread of disease. The President of the Robert Koch Institute (RKI), Lothar Wieler, had already pointed out this impending danger. "Climate change is leading to an expansion of habitats for mosquitoes and ticks in Germany," Wieler told the newspapers of the Funke Mediengruppe. "Many mosquito and tick species can transmit viral, bacterial and parasitic infectious agents," Wieler said. These could be Zika or dengue viruses, for example. "It is also possible for malaria to return, which is caused by plasmodia." An important concern of the RKI is therefore to sensitise doctors to these diseases.

1,006 different connections due to climate change

Renke Lühken, ecologist at the Bernhard Nocht Institute for Tropical Medicine in Hamburg, also sees the spread of insects as problematic: "In Germany and in Europe, we are already observing the influence of climate change-related events on pathogens. Pathogens transmitted by vectors (editor's note: such as mosquitoes or ticks) also play a major role here," Lühken told the Science Media Center. "Exotic mosquito species like the Asian tiger mosquito are becoming established in large parts of Europe. The Asian tiger mosquito is particularly responsible for outbreaks of chikungunya virus and dengue virus in the Mediterranean region."

The researchers from Hawaii identified a total of 1,006 different pathways, i.e. connections, between climate change-related events and the spread of diseases. Camilo Mora has published an interactive overview of the pathways on gitHub. The diversity makes it so difficult to prevent the spread and worsening of diseases. The researchers' plea is therefore simply to reduce greenhouse gas emissions.

(pavb)