Viral respiratory infections (VRIs) are the most common infectious diseases causing seasonal epidemics and pandemics. Climate change often affects the transmission of these diseases. There are hundreds of types of viruses identified as causative agents of VRI. Some of the common viral pathogens that cause respiratory infections are respiratory syncytial viruses (RSV), influenza viruses, human metapneumoviruses (HMPV), rhinoviruses (RhV), human bocaviruses (HBoV), enteroviruses (EnV), parainfluenza viruses (PIV), human coronavirus viruses (HCoV) and adenoviruses (ADV). Several large-scale epidemics and pandemics of these viruses have occurred in the 21st century, including severe acute respiratory syndrome (SARS) in 2003, Middle East respiratory syndrome (MERS) in 2012, and the 2019 coronavirus disease pandemic (COVID-19) caused by SARS-CoV2 in 2019.
Each of these outbreaks has led to significant human mortality, morbidity, and considerable economic hardship. Warming of the Earth’s atmosphere is occurring at an unprecedented rate and is largely driven by greenhouse gas emissions from human activities. Climate change has both direct and indirect effects on the emergence and transmission of VRI. Several meteorological factors, such as temperature, precipitation, wind, humidity and solar radiation influence the incidence of seasonal epidemics. In the northern hemisphere, winter, low temperature, solar radiation and humidity are linked to seasonal epidemics. Similarly, increased precipitation causes an increase in VRI in tropical and subtropical regions. An indoor microclimate is often artificially regulated by indoor heating/air conditioning systems, which affect indoor temperature as well as indoor relative and absolute humidity.
Individuals living in homes with indoor heaters reduce viral infection rates by decreasing virus viability, comparable to an air-conditioned room with poor ventilation enhancing viral transmission. Based on biological and epidemiological evidence, humidity and temperature are the two most significant meteorological factors influencing the seasonality of VRIs. Climate change, particularly high temperatures and abnormal precipitation patterns, contribute to spatial and temporal changes in seasonal VRI outbreaks. People, especially those residing in regions with limited resources, become vulnerable to extreme temperatures, as food insecurity and the risk of displacement increase. Climate change increases the risk of zoonotic fallout, which leads to the emergence of new pathogens that have the potential to cause future pandemics. But it’s not just microorganisms being affected by the issue.
Allergic respiratory diseases such as allergic rhinitis and asthma are considered to be adverse effects of climate change on human health. The underlying mechanism for this association is increases in atmospheric carbon dioxide and air temperature, which affects airborne allergens such as fungal spores and pollen. Climate change affects airborne allergens and consequently allergic respiratory diseases, such as allergic rhinitis and allergic asthma. In many countries and regions, these diseases already pose serious public health challenges, with asthma affecting at least 30 million children and young adults in Europe and more than 350 million people worldwide. Pollen allergies can affect the quality of life of sensitized people, for example, by reducing the opportunity for outdoor activities during periods of greatest risk of pollen exposure.
However, high concentrations of pollen can also cause symptoms and discomfort in normal people. In addition to acute effects, pollen exposure has been associated with changes in lung function and inflammation, childhood asthma risk, cardiovascular outcomes, and cognitive performance. Symptoms, including runny nose, itchy eyes and sneezing, which are caused by pollens and other allergens in sensitized people, are well documented. Overall, pollen not only induces allergy but has a broader impact on human health. Not only local pollen, but also long-distance transported pollen could be relevant to health effects. Furthermore, the allergen-independent mechanisms are not yet well understood. The release of lipid mediators from pollen after contact with mucous membranes may be a potential initiator of inflammation. There are suspicions that it can trigger sensitivities to substances one is not allergic to, even food components that were routinely tolerated at some point in life.
Last but not least, pollen itself can act as a vector for infectious microorganisms, obviously including respiratory viruses. This is a hypothesis that is still under investigation and does not directly indicate that pollen can carry infectious viruses. It is much more likely that pollen and viral agents in specific periods of the year can play a synergistic role together, amplifying respiratory problems in the general population. After having exposed all this information, this scientific editorial board feels like concluding that even before it becomes the responsibility of international health systems, it is the undisputed responsibility of the planetary economic and political authorities to opt for changes that prevent voluntarily causing damage to public health, as effectively it’s already happening.
- Edited by Dr. Gianfrancesco Cormaci, PhD, specialist in Clinical Biochemistry.
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