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Zoonotics and Climate Change


René F. Najera, DrPH

April 11, 2020

This blog post is authored by at the University of Pennsylvania. Oscar Serpell is a Research Associate there.

Storm surge, wildfires, and pandemics: How climate change is increasing the risk of zoonotic disease outbreaks

As we all self-quarantine and dutifully follow “socially distancing” protocol for a third week in order to protect ourselves and others from COVID-19, one could conclude from our sluggish response and lack of preparedness that this pandemic was a freak occurrence that no one could have predicted. This, sadly, could not be further from the truth. For years epidemiologists and public health experts have us that the majority of countries are not ready for a global outbreak, and that it was not a question of if but when a deadly pandemic would occur.

Of course, bacterial and viral outbreaks have always occurred periodically throughout human history and no matter what steps we take today, we will always have to contend with future outbreaks. The severity and frequency of these outbreaks, however, can be influenced by , and right now, unrestrained carbon emissions are making us more vulnerable than ever to pathogens like COVID-19.

To understand this relationship, it is important to consider one of the primary causes of outbreaks like COVID-19. Many of the most threatening outbreaks of recent years (SARS, EBOLA, MERS, swine flu, and COVID-19) were caused by zoonotic viruses – viruses that originated in other animal species and at some point, successfully infected and were able to replicate in a human host. These “” expose humans to an unfamiliar virus for which we have very little immunity. If that virus is then able to spread between humans, it can easily trigger a widespread epidemic or, in the case of swine flu and COVID-19, a global pandemic. Climate change increases the likelihood of these spillover events for : changes in species distribution and changes in viral load and infection rate.

To some extent, climate change is altering patterns of rainfall and average temperature in every region of the world. These changes can have profound effects on the delicate equilibrium of ecosystems. Some species’ may benefit from these changes and multiply, increasing in density and/or range. When this happens, pathogens being carried by pre-adapted species will have greater opportunity to spread within the population because of increased density and will be more likely to ‘spillover’ to humans or another intermediary species because of the pathogen’s increased range. On the other hand, some species may be less well-adapted to these changes and will be less able to compete for resources. This could lead to a higher rate or disease within the population and therefore a higher risk of transmission to other species.

Once a virus enters the human population, climate change can significantly affect a pathogens ability to . For one, people tend to gather in confined indoor spaces during more extreme weather, increasing the likelihood of transmission. Our immune systems are also impacted by weather, so living in more extreme conditions can make us more susceptible to contracting a disease to which we are exposed. There is also evidence that temperature, humidity, and sunlight can impact how long viruses are able to survive outside of the body, for example on frequently touched surfaces. Lastly, warmer weather conditions can cause an increase in ; invertebrates capable of transmitting viruses or bacteria between humans or other animals (e.g. ticks spreading Lymes disease or mosquitos spreading malaria). 

Right now, we most urgently need to look at COVID-19 as a public health crisis, the solutions for which are social distancing, careful sanitization, widespread testing and access to safety equipment, and competent medical care. However, as we rebuild our faltering economy and prepare for the future, the COVID-19 outbreak needs to be recognized for what it is - another natural disaster made more severe and more likely by unsustainable resource and energy use practices. The only way to reduce ecosystem disruption and the subsequent spreading of pathogens is to reduce global carbon emissions and rapidly halt catastrophic climate change.    


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