Study finds climate hazards can aggravate over half of known human infectious diseases

A recent article posted to the journal Nature Climate Change demonstrated that climate change could aggravate about 50% of recognized human pathogenic illnesses.

Study: Over half of known human pathogenic diseases can be aggravated by climate change. Image Credit: Sepp photography
Study: Over half of known human pathogenic diseases can be aggravated by climate change. Image Credit: Sepp photography

Background

The continual release of greenhouse gases (GHGs) is escalating several climatic risks, which, in turn, worsen human pathogenic illnesses. The severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, which amply demonstrated the social upheaval driven by infectious diseases, offers alarming hints to the possible outcomes of impending health crises caused by climate change.

Although it is well-established that climate change influences pathogenic illnesses, the degree of human susceptibility to the pathogenic diseases impacted by climatic alteration is not entirely known. With few outliers, previous research on the relationship between climatic hazards and human pathogenic illnesses has typically concentrated on certain classes of pathogens (such as bacteria or viruses), climatic hazards (such as warming, precipitation, or floods), or transmission modes (like vector-, food-, waterborne). Hence the measurement of the complete threat to humans caused by climate change as it connects to pathogenic illnesses is prevented by the inability to combine available information.

About the study

In the present study, the investigators methodically searched for empirical evidence of the effects of 10 climatic changes sensitive to GHG emissions on each recognized human pathogenic illness. The 10 GHG-sensitive climatic hazards analyzed in the research were drought, warming, wildfires, heatwaves, floods, precipitation, sea level rise, storms, land cover change, and ocean climate change.

The team conducted three interdependent literature searches to identify case reports of pathogenic illnesses impacted by climate hazards. In the first search, they performed separate investigations for each combination of the term "disease" with each of the 10 climate hazards identified as GHG emission-sensitive. In the second search, the researchers conducted separate searches for scientific articles combining each illness name from two reliable databases of infectious illnesses with each of the 10 climatic hazards. 

The authors then undertook additional queries for diseases and climatic risk combinations in which the previous two searches did not provide any case instances. They first generated a table showing all illnesses identified by searches 1 and 2 as rows and each climatic risk as columns. Additionally, the team utilized alternative names for the pathogens and diseases in the third search. Besides, they used Google Scholar for all queries.

Results

The authors found 3,213 empirical cases in which climate hazards were connected to pathogenic illnesses. These case examples were linked to 286 distinct pathogenic diseases, 277 of which had a minimum of one climatic risk making them worse. While some climatic hazards diminished 63 illnesses, 54 among them were exacerbated occasionally by other climatic risks. Indeed, climatic hazards uniquely lessened only nine pathogenic diseases.

The scientists documented illnesses that climatic hazards worsen. The collection of pathogenic diseases that climatic hazards aggravate accounts for 58% of all infectious illnesses identified to have affected humanity globally. In detail, climatic hazards exacerbate 218 of a reliable list of 375 pathogenic diseases noted to have influenced human beings. 

The team identified 1,006 distinct routes by which climate hazards, through various modes of transmission, led to occurrences of pathogenic illness. They noted 76, 69, 45, 24, 23, 12, and nine diseases caused by viruses, bacteria, animals, fungi, protozoans, plants, and chromists, respectively, were influenced by warming, precipitation, floods, drought, storms, land cover change, ocean climate change, fires, heatwaves, and sea level rise associated with 160, 122, 121, 81, 71, 61, 43, 21, 20, and 10 unique diseases, respectively.

Vectors mainly spread pathogenic illnesses, namely 103 distinct diseases. However, the researchers also found 78, 60, 56, and 50 unique disease case examples for the waterborne, airborne, direct contact, and foodborne transmission channels, respectively. There were 19 common illness names (such as gastrointestinal infections) lacking data on the causative pathogen among all case examples of pathogenic illnesses adversely affected by climate hazards. In addition, there were no details regarding the transmission mechanism for 116 diseases.

Conclusions

Overall, in the current research, the team discovered that climatic hazards exacerbate 58% (i.e., 218 of 375) of infectious illnesses experienced by humans globally at some point. On the other hand, it diminished 16% of pathogenic diseases occasionally. Empirical cases demonstrated 1,006 distinct ways that climatic risks led to pathogenic illnesses through various transmission methods. 

Notably, climate risks exacerbate too many human pathogenic diseases and transmission modes, surpassing the capacity of societal adaptations, underscoring the urgent need to address the root cause of the issue, which is lowering GHG emissions.

Journal reference:
Shanet Susan Alex

Written by

Shanet Susan Alex

Shanet Susan Alex, a medical writer, based in Kerala, India, is a Doctor of Pharmacy graduate from Kerala University of Health Sciences. Her academic background is in clinical pharmacy and research, and she is passionate about medical writing. Shanet has published papers in the International Journal of Medical Science and Current Research (IJMSCR), the International Journal of Pharmacy (IJP), and the International Journal of Medical Science and Applied Research (IJMSAR). Apart from work, she enjoys listening to music and watching movies.

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