In August 2022 a study in Nature concluded that 58% of infectious diseases we face are “aggravated by climatic hazards”. The authors identify “global distress” caused by “human vulnerability to pathogenic diseases”. 

This literature study describes how “empirical cases revealed 1,006 unique pathways in which climate hazards, via different transmission types, led to pathogenic diseases”. Among the research were different links between climate hazards and disease, some of which are highlighted below. 

Climate hazards bringing pathogens closer to people: 

The study reflects that “shifts in the geographical range of species are one of the most common ecological indications of climate change”. For example, “warming and precipitation changes” can be linked to the “range expansion” of a variety of vectors. These include “mosquitoes, ticks, fleas, birds and several mammals” as well as “bacteria, animals and protozoans”. Expansions were also perceived in aquatic systems.  

Disruptions to natural habitats caused by factors such as drought, wildfires, floods, and land cover change are also “bringing pathogens closer to people”. Viral spillovers were linked to wildlife moving over “larger areas” in search of resources or habitats. In a dystopian conclusion, warming was related to “melting ice and thawing permafrost exposing once-frozen pathogens”.  

Climate hazards bringing people closer to pathogens: 

Climate hazards push the global population closer to pathogens in a variety of ways. For example, heatwaves increase instances of “recreational water-related activities”, associated with “rising cases of several waterborne diseases”. Human displacement, caused by floods and storms, has seen an increase in cases of Lassa fever, typhoid, and pneumonia, among others. Furthermore, land use changes provoke “human encroachment into wild areas”. This brings people “into closer proximity to vectors and pathogens”. 

Pathogens strengthened by climatic hazards: 

Climatic hazards also provide enhancement to certain aspects of pathogens. These include “improved climate suitability for reproduction, acceleration of the life cycle, increasing seasons/length of likely exposure, enhancing pathogen vector interactions, and increased virulence”. For mosquitoes, increased temperatures saw positive effects on population development and viral replication. Consequently, the “transmission efficiency” of West Nile virus was increased.  

Virulence is also linked to climatic hazards in the study. The researchers consider heat, which was “related to upregulated gene expression of proteins affecting transmission, adhesion, penetration, survival, and host injury by Vibrio spp”. Furthermore, heatwaves are considered a “natural selective pressure” towards viruses that are heat resistant. These viruses are thought to then be better able to respond to fever in the human body.  

People impaired by climatic hazards: 

Our ability to respond to pathogens has been affected by climatic hazards as well. The study identifies “stress from exposure to hazardous conditions”, weakened infrastructure, unsafe conditions, and reduced access to treatment. Citing “body malnutrition and condition” as an example, it reflects that “immunocompetence” is greatly impaired by increased exposure to hazards.  

Although the examples above paint a very alarming picture, the study includes some diseases that were “diminished” by climatic hazards: 16%. For example, warming “appears to have reduced the spread of viral diseases probably related to unsuitable conditions for the virus or because of stronger immune system in warmer conditions”. However, many diseases that were “diminished by at least one hazard” were sometimes “aggravated by another and sometimes even the same hazard”. The is exemplified in malaria, which was reduced through drought decreasing breeding grounds. At the same time, drought can lead to “increased mosquito density” in bodies of water.  

The conclusion is overwhelmingly negative, and the authors conclude that collaborative and proactive efforts must be increased. As attempts to tackle climate change continue, some are preparing for the many pathogens that follow.

“The sheer number of pathogenic diseases and transmission pathways aggravated by climatic hazards reveals the magnitude of the human health threat posed by climate change and the urgent need for aggressive actions to mitigate GHG emissions.”

To hear from industry and thought leaders on how we can prepare for increasing pathogen exposure come to the World Vaccine Congress in Europe in October 2022.