for years, scientists warned about the possibility of a deadly pandemic brought about by climate change like the one we are facing now. if we do not learn from this pandemic and take strong steps against climate change, we will face even more pandemics.
Between the surrealism of studying for an online exam at home and the constant stream of frightening pandemic-related news, I found myself needing a distraction. There are few better distractions than a good adventure story. So I picked up a book I had long wanted to read: Douglas Preston’s The Lost City of the Monkey God. I was exhilarated by Preston’s account of traveling as a National Geographic writer with a team of archaeologists to find a lost Mesoamerican city in the middle of the Mosquitia region of Honduras. It was an intersection of all the dreams I have ever had of being Dora the Explorer and Indiana Jones. That is, until I got to the last section of the book where Preston and his team become infected with a disease known as leishmaniasis (also known as leish).
This interaction is similar to what caused the COVID-19 pandemic: humans interfered with the balance of nature and wildlife, and brought wild animals into the world of humans without proper caution.
Leish comes from an infected sand fly, which is called a “vector”, because it is the organism that transmits a pathogen to an animal. The vector then finds a mammal to act as the pathogen’s host, whether they are human or not. SARS-CoV-2 most likely was transmitted to humans from bats, which were brought to a wet market in Wuhan, China. At the market (a large open-air market that sells fresh food and occasionally wild animals), the virus jumped from the bats (their reservoir hosts) to humans. Dr. Theodore Nash, the chief clinical researcher of leishmaniasis at the United States National Institute of Health (NIH), told Preston that the valley in Mosquitia had been removed from humans for so long that sand flies and mammals there had been “locked in a cycle of infection and reinfection” for generations. There was an established relationship between those who infected others and those became infected, and humans were not a factor at all.
This interaction is similar to what caused the COVID-19 pandemic: humans interfered with the balance of nature and wildlife, and brought wild animals into the world of humans without proper caution. Similar to how Preston describes his team’s encounter with leishmaniasis, “we were like clueless civilians wandering into a battlefield and getting shot to pieces in the crossfire.”
According to a recent report from the UN Environment Programme and the International Livestock Research Institute infectious diseases have the potential to spread across the world and become pandemics like the COVID-19 pandemic. This is because of several major anthropogenic contributors, such as: increasing demand for animal protein, increased use and exploitation of wildlife and unsustainable urbanization. Dr. Anthony Fauci — the top infectious disease expert in the United States and fixture of American cable news — told Preston’s team that they had received “a cold jolt of what it’s like for the bottom billion people on earth.” With increased deforestation and urbanization, humans are destroying natural habitats and creating urban areas out of these areas where viruses like leish thrive, bringing these infectious diseases that feel so far away right to our doorstep.
In 2016, Yale University’s School of the Environment released an article hypothesizing how pathogens jump from their vectors to humans during deforestation events. It argues that deforestation is a major contributor to rising diseases in humans because of how forests act as “incubators” for insect-borne and other infectious diseases. What happens, Robbins says, is that pathogens in these areas (i.e. the Amazon rainforest or Borneo) have been passed between vectors and mammals for ages, evolving together. Humans, because of the lack of similar contact and evolution with those pathogens, don’t have the same type of familiarity or immunity. Therefore, when humans come into the rainforest to clear the trees, they expose themselves to many of the pathogens that were only passed to the other mammals in the rainforest.
Humans complicate disease infection with deforestation by creating suitable environmental conditions for vectors to thrive. The article focuses on mosquito-borne diseases like malaria, arguing that once sunlight reaches the forest floor, water temperature increases, which mosquitoes love for breeding. Any flowing water will also dam up and pool, creating a swampy area on the forest floor and more standing water, which mosquitoes favor for their breeding as well. Once deforestation has created these conditions for vectors to breed, there are more vectors to infect hosts. However, deforestation is also habitat destruction. This means that mammals (monkeys, for instance) have acted as pathogen hosts for a long time, and then when their trees are cut down, they are forced to live where there are any trees left.
With more hosts in one area, mosquitoes have the ability to infect them at a higher rate. Unfortunately, a consequence of humans working in close proximity to animals and mosquitoes is that they have a higher risk of infection. In the case of the COVID-19 pandemic, when humans take animals out of their habitats and into an area largely inhabited by humans, even more people face the risk of infection.
As climate change makes global temperatures rise and natural disasters become stronger and more frequent, the entire globe is becoming increasingly vulnerable to these potentially fatal diseases.
The UN Environment Programme’s report adds to this theory of habitat destruction contributing to viral infection. It suggests that as humans alter habitats, fragments of forests are created. These fragments will act as islands for wildlife that are hosts for pathogens. These pathogens undergo “rapid diversification”, meaning that the pathogens are multiplying and changing to increase the probability that they reach other hosts, including humans who are coming into those areas. The report also writes that many zoonoses (infectious diseases caused by pathogens that have jumped from non-human animals to humans, like COVID-19) are climate sensitive and prefer warmer, wetter, disaster-prone areas. Many current environmental policies — such as Brazilian president Jair Bolsonaro’s opening of the Amazon to miners and loggers — drive climate change rather than mitigate it. Therefore, these policies are making humans more vulnerable to diseases rather than protecting them.
As climate change makes global temperatures rise and natural disasters become stronger and more frequent, the entire globe is becoming increasingly vulnerable to these potentially fatal diseases. With deforestation, pathogens that have not encountered humans now have new hosts to infect and can infect more very quickly because of how globalized our world is. Richard Preston wrote in The Hot Zone that a virus from the rainforest “lives within a twenty-four-hour plane ride from every city on earth.” We have seen this scenario play out with our current pandemic, and it will continue to happen if we do not take strong action against climate change and change many current environmental policies that destroy habitats. Scientists warned of a possible pandemic like the current one for years, and the world did not listen. If we fail to learn from the COVID-19 pandemic, we will likely suffer more under the next one.
Art by Alex Rive
UnEarth Magazine 
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