A comprehensive review of the scientific literature revealed empirical evidence that more than 58% of human illnesses caused by pathogens, such as dengue fever, hepatitis, pneumonia, malaria, Zika and many others, have been – at one point – aggravated by the vagaries of the weather. This revealing and surprising discovery is the subject of a research article published on August 8 in Natural climate change by a team of researchers from the University of Hawaii at Manoa.

Researchers conducted a systemic search for empirical examples of the impacts of 10 climate hazards sensitive to greenhouse gas (GHG) emissions on each known human pathogenic disease. These hazards included global warming, drought, heat waves, wildfires, extreme rainfall, floods, storms, sea level rise, ocean biogeochemical changes, and land cover changes.

Combining two authoritative lists of all known pathogenic infections and diseases that have affected humanity in recorded history, the researchers then reviewed more than 70,000 scientific papers to find empirical examples of each possible combination of a hazard. climate having an impact on each of the known diseases.

Research has found that warming, precipitation, flooding, drought, storms, land cover change, ocean climate change, fires, heat waves and sea level changes all influence diseases triggered by viruses, bacteria, animals, fungi, protozoa, plants and chromists. . Pathogenic diseases were mainly transmitted by vectors, although case examples were also found for waterborne, airborne, direct contact and foodborne transmission routes. Ultimately, the research found that more than 58%, or 218 out of 375, of known human pathogenic diseases had been affected at some point, by at least one climate hazard, via 1,006 unique pathways.

“Given the widespread and widespread consequences of the COVID 19 pandemic, it was truly frightening to discover the massive health vulnerability resulting from greenhouse gas emissions,” said Camilo Mora, professor of geography at the College of Social Sciences ( CSS) and responsible author of the study. “There are simply too many diseases and transmission pathways for us to think we can truly adapt to climate change. This highlights the urgent need to reduce greenhouse gas emissions at scale. world.”

An interactive web page showing each link between a climatic hazard and a case of illness was developed by the research team. The tool allows users to query specific hazards, pathways and disease groups, and view available evidence.

The UH Manoa research team included experts from the CSS, the Department of Earth Sciences of the School of Ocean and Earth Science and Technology, the Marine Biology Graduate Program of the School of Life Sciences, the Department of Natural Resources and Environmental Management at the College of Tropical Agriculture and Human Resources and the Hawaiian Institute of Marine Biology at SOEST.

Other key findings include:

  • Climatic hazards bring pathogens closer to populations. Many climatic hazards increase the surface and duration of environmental suitability facilitating the spatial and temporal expansion of vectors and pathogens. Warming and changes in precipitation, for example, have been associated with the expansion of the range of vectors such as mosquitoes, ticks, fleas, birds and several mammals implicated in epidemics by viruses, bacteria, animals and protozoa including Dengue Fever, Chikungunya, Plague, Lyme Disease, West Nile Virus, Zika, Trypanosomiasis, Echinococcosis and Malaria to name a few.

  • Climatic hazards bring populations closer to pathogens. Climatic hazards have also been implicated with the forced displacement and migration of people causing or increasing new contact with pathogens. Heat waves, for example, have been associated with increased cases of several waterborne diseases such as infections associated with Vibrio (a type of bacteria), primary amoebic meningoencephalitis and gastroenteritis. Storms, floods and sea level rise have caused human displacement implicated in cases of leptospirosis, cryptosporidiosis, Lassa fever, giardiasis, gastroenteritis, legionellosis, cholera, salmonellosis , shigellosis, pneumonia, typhoid, hepatitis, respiratory diseases and skin diseases, among others.

  • Climatic vagaries have reinforced specific aspects of pathogens, including improving the suitability of climate for breeding, accelerating the life cycle, increasing likely seasons/durations of exposure, improving vector-pathogen interactions (e.g., shortening incubations) and increased virulence. For example, storms, heavy rains and floods have created standing water, expanding breeding and breeding grounds for mosquitoes and the range of pathogens they transmit (e.g. leishmaniasis, malaria, Rift Valley fever, yellow fever, St. Louis encephalitis, dengue and West Nile fever). The vagaries of the weather have also played a role in the growing ability of pathogens to cause more severe disease. For example, heat waves have been suggested as a natural selective pressure towards “heat-tolerant” viruses, the spillover of which into human populations results in increased virulence because the viruses can better cope with the human body’s primary defense. , which is fever.

  • Climate hazards have also diminished the human capacity to cope with pathogens by altering body condition; the addition of stress due to exposure to hazardous conditions; forcing people to live in dangerous conditions; and damaging infrastructure, forcing exposure to pathogens and/or reducing access to medical care. Drought, for example, was conducive to poor sanitation responsible for cases of trachoma, chlamydia, cholera, conjunctivitis, Cryptosporidium, diarrheal diseases, dysentery, Escherichia coli, Giardia, Salmonella, scabies and typhoid fever.

The researchers also found that while the vast majority of diseases were aggravated by climatic hazards, some were attenuated (63 out of 286 diseases). Warming, for example, appears to have reduced the spread of viral illnesses likely linked to conditions unsuitable for the virus or a stronger immune system in warmer conditions. However, most diseases that were mitigated by at least one hazard were sometimes aggravated by another and sometimes even by the same hazard.

“We knew that climate change could affect human pathogenic diseases,” said co-author Kira Webster, a doctoral student in geography at CSS. “Yet, as our database has grown, we have become both fascinated and distressed by the overwhelming number of case studies available that already show how vulnerable we are becoming to our growing greenhouse gas emissions. greenhouse effect.”


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