BY HANNAH BUDROE
When people typically think of climate change, they picture droughts, rising sea levels, devastating forest fires, and other environmental phenomenons. They do not, however, fully consider all of the implications of our warming planet and, in particular, how it will impact the future of infectious diseases.
In the past century, there has been a huge increase in the incidence of infectious diseases globally, with more disease outbreaks and emergent diseases. This can be attributed to a variety of factors, including population growth, globalization, and changes in our lifestyles. Geographical and environmental shifts, as well as the interconnectedness of society and increased human interaction, have created greater potential for disease emergence and transmission in a population. Climate change, however, also plays a large role in accelerating the emergence of infectious diseases and their spread.
In general, environmental changes affect diseases and their transmission. For example, flooding or increased rainfall in areas can create new breeding grounds for waterborne diseases, such as cholera. A warmer temperature could be preferential to some pathogens, allowing them to thrive and better infect hosts. Changes to a landscape could change animal migration patterns or life cycles, potentially causing new populations of animals to meet and transmit pathogens. These are just a few examples of how even the smallest change in an environment can have multifold impacts.
Specifically, climate change will greatly affect the incidence of vector-borne diseases, which are diseases caused by infectious pathogens that are carried in a variety of living organisms (typically insect hosts) before spreading to humans. Even small shifts in temperature could shift the geographical distribution of these vectors, causing them to spread to new locations. As the world becomes warmer, tropical vectors such as mosquitos may be able to thrive in larger parts of the world that were previously inhospitable to them, thus giving them a larger range of hosts to infect. Such a shift to a more densely populated region could lead to more interaction between the vectors and humans, thus allowing for increased transmission of the pathogen. In addition, this new shift could expose a new and unprotected population of people to a disease that they have no innate immunity towards, potentially leading to a rise in infections. Warmer temperatures could not only affect the geographic distribution of a vector, but also impact their survival and breeding rates, behavioral patterns (such as interactions with humans), and the rate of pathogen incubation within hosts, which may all lead to changes in the spread of the vector and the pathogens they carry.
A case study of this can be seen in how climate change could affect mosquito-borne diseases, such as malaria, Dengue fever, Zika, and more. Mosquitoes thrive in warmer temperatures - they reproduce faster and have more biting activity. An increase in rainfall, humidity, or drought could create areas of standing water ideal for breeding mosquito larvae. However, heavy rainfall could potentially wipe out mosquito breeding grounds, while an increased geographic range could potentially expose mosquitoes to new predators. With all these varying factors, more modeling and research is needed to demonstrate the interplay between them and what it means for mosquitoes and the pathogens they carry.
In addition to focusing on how climate change will impact the transmission of vector-borne diseases, the spread of disease between humans could be accelerated by increased interpersonal contact, increasing the probability of an epidemic. As seen with intensifying natural disasters, many people have become displaced from their homes, living in temporary emergency camps or migrating to new areas. As sea levels continue to rise, forest fires burn, and floods and/or droughts make previously inhabited areas inhospitable, livable areas may become more densely populated to accommodate for an influx of climate refugees. This higher population density and overcrowding seriously exacerbates the potential for disease transmission. People are less isolated and come into contact with each other more frequently, allowing disease to more rapidly spread throughout a population. A virus will not only spread faster within a larger, more dense population, but also has the potential to mutate with each host it infects, thus leading to issues of immunity and the efficacy of vaccination. A virus may also have the potential for greater lethality, as there is no end of hosts to limit their spread if they quickly kill their hosts, compared to a virus in more rural areas that may incubate in hosts longer to have the chance to spread to other people.
While we know that climate change will definitely impact the spread of disease and the potential emergence of new diseases, there is much more research needed to know exactly how all of the varying factors will play out on the world stage. As climate change continues to mount and become more serious, knowing all its potential implications, particularly concerning public health, will be direly important. There is an ever increasing need for us to evaluate our actions and take steps to prevent the coming climate catastrophe.