Viral respiratory infections (VRIs) are the most common infectious diseases that cause seasonal epidemics and pandemics. Climatic changes often influence the transmission of these diseases.

To date, the relationship between VRIs and climate change is not well understood. In a recent eBioMedicine study, scientists review existing literature to understand how changes in weather conditions, meteorological conditions, and global warming have affected seasonal outbreaks, epidemics, and pandemics of VRIs.

Study: Viral respiratory infections in a rapidly changing climate: The need to prepare for the next pandemic. Image Credit: crystal light / Shutterstock.com

The relationship between VRIs and climate change

There are hundreds of types of viruses that are identified as causative agents of VRIs. In the 21^st century, several large-scale outbreaks and pandemics of VRIs have occurred, including severe acute respiratory syndrome (SARS) in 2003, Middle East Respiratory Syndrome (MERS) in 2012, and the coronavirus disease 2019 (COVID-19) pandemic caused by SARS-CoV-2 in 2019. Each of these outbreaks has led to significant human mortality, morbidity, and considerable economic disruption.

Some of the common viral pathogens that cause respiratory infections are respiratory syncytial viruses (RSV), Influenza viruses, human metapneumoviruses (HMPV), rhinoviruses (RV), human bocaviruses (HBoV), enteroviruses (EV), parainfluenza viruses (PIV), human coronaviruses (HCoV), and adenoviruses (ADV). In this review, the association between VRIs and climate change has been explored based on long-term warming, extreme weather events, and meteorological factors. 

Climate change has both direct or indirect effects on the emergence and transmission of VRIs. Several meteorological factors, such as temperature, precipitation, wind speed, humidity, and solar radiation, influence the incidence of seasonal epidemics of VRIs.

In the northern hemisphere winter, low temperature, solar radiation, and humidity are linked to seasonal epidemics. Likewise, increased precipitation results in a VRI surge in tropical and subtropical regions.

An indoor microclimate is often artificially regulated by indoor heating and air conditioning systems, which influence the indoor temperature, as well as indoor relative humidity (RH) and absolute humidity (AH). Individuals living in homes with indoor heaters, which increase indoor RH levels, lower viral infection rates by decreasing virus viability, comparable to an air-conditioned room with poor ventilation that enhances viral transmission.

Based on biological and epidemiological evidence, humidity and temperature are the two most significant meteorological factors that impact VRI seasonality. Climate change, particularly high temperatures, and abnormal rainfall patterns, contributes to spatial and temporal shifts in seasonal epidemics of VRIs.

People, particularly those residing in resource-limited regions, become vulnerable to extreme temperatures, as they increase the risk of displacement and food insecurity. Climate change increases the risk of zoonotic spillover, which leads to the emergence of novel pathogens that have the potential to cause future pandemics. 

To understand the complex interactions between climate change and VRIs, a conceptual framework was established. VRIs with pandemic potential that emerged from animal-human interfaces could be influenced by climate change through multiple processes related to social, ecological, and environmental mechanisms, each of which interacts with each other in a complex manner and reshape the environment.

At present, the risk of emergence and wide-scale transmission of VRIs is particularly high due to multiple anthropogenic factors, including glowing population, urbanization, civil conflict, migration, deteriorating ecological environments, and the rapid expansion of global travel.

The rapid rise in global temperatures with the increased frequency of extreme weather has severe consequences for humans. These factors, directly and indirectly, increase the frequency of human-animal-environment interactions and, as a result, the risk of emerging and re-emerging VRIs due to climate change.

Conclusions

The One Health approach investigates the interaction between humans, animals, and the environment, while also considering the interconnection of human health, climate change, environmental sanitation, and biodiversity. Understanding this complex interplay is instrumental in determining the regional and global health threats of climate change. 

In the future, these interconnected mechanisms must be considered, and more interdisciplinary collaboration should be established. This could enable the development of a robust surveillance system that could provide early warning of viral diseases and ultimately manage future pandemics more effectively.

Currently, the compound effect of climate change and the incidence of VRIs has gained significant research attention. It is imperative to assess the risk from compound events, such as exposures to certain ranges of temperature and humidity that causes a higher incidence of VRIs. 

Multi-source data and advanced technologies can be utilized to make accurate predictions about a disease's progression. Traditional epidemiological models for disease prediction and early warning have limited application, as their generalizability is affected by the diverse climatic conditions across regions.

Climate data and forecasting techniques can be incorporated into existing climate-based models to improve their overall prediction accuracy of early warning. Collaborative research, particularly involving epidemiologists and atmospheric scientists, can effectively improve the prediction of seasonal VRIs in the future.

Written by

Dr. Priyom Bose

Priyom holds a Ph.D. in Plant Biology and Biotechnology from the University of Madras, India. She is an active researcher and an experienced science writer. Priyom has also co-authored several original research articles that have been published in reputed peer-reviewed journals. She is also an avid reader and an amateur photographer.