The lingering threat of future pandemics from deforestation
We often speak of the importance of protecting the Amazon rainforest, as a large contributor to planetary health in regulating the Earth's climate. Whether directly, or indirectly, we are all susceptible to the status of the rainforest. Largely forgotten, however, until recently, is the control of zoonotic diseases, and vector-borne diseases that lay wait in the forests that we continue to destroy.
Wildlife of the rainforest are hosts to a huge diversity of well known, and unknown pathogens some of which could likely lead to future epidemics. The climate of the rainforest is fragile, and where we have identified issues with global warming on a global scale, the Amazon rainforest will experience exponentially higher effects, by at least 2 degrees (IPCC 2013). These environmental changes will act as a catalyst, creating favourable settings for pathogens to survive, reproduce, and evolve. For example, mosquitoes where previously may have been confined to a particular area could colonize new geographical regions as the temperatures are more favourable for them, spreading malaria and other infections in humans.
Agricultural practices in Africa led to an increase in a form of malaria. The geographic origin of falciparal malaria may have expanded due to the changing environment, where the habitat became more suitable for arthropods (invertebrate with an exoskeleton, segmented body and paired joined appendages) through fire-fallow cultivation, where natural vegetation is cut and burned down, clearing the land for more cultivation (Coluzzi, 1994).
A particularly serious result of global warming is the success of pathogens which cause diarrheal diseases, a concern particularly in urban areas, where open defecation, latrines and other unsanitary conditions for excrement are used, and clean water sources are scarce. This is particularly worrying for countries where many of the infectious diseases begin.
Whilst tracing the protein sequence of diseases to its exact origins is difficult, it has been determined that most of the infectious diseases we have encountered, and continue to encounter are from wild and domestic animals, and many current emerging diseases are associated with modification of the environment. In fact, the Eco Health Alliance (2019) stated that HIV/AIDS, Ebola, and the Zika virus all originated in forest landscapes that had been altered by human interaction.
Whilst source tracing is difficult, we can trace back to a point where humans may have first begun having an effect and encouraging the development of diseases. Our part in the development can be linked back to some of the earliest civilisations, where the spreading of diseases occurred following the behavioural change of our ancestors (Pearce-Duvet, J. 2006)..
Early human populations were susceptible to parasites that could establish in small groups of 50-100 people (Dobson and Carper, 1996) such as hepatitis B, herpes, cytomegalovirus, all of which are still found in primitive tribes within largely isolated areas. Following human movement into a more sedentary lifestyle and farming, diseases became more abundant, as communities developed and life cycle bacterial and viral infections were able to be sustained. Most and probably all of the distinctive infectious diseases of civilization transferred to human populations from animal herds. It is suggested that domestication is linked to the development of agriculture and with that, the close- proximity of domesticated animals. As population growth occurred, human density increased, and agriculture had to expand to support this, allowing herd pathogens to develop and spread amongst humans.
The population continues to grow and we are looming towards a count of 8 billion people, by 2023. As our population grows, just as it did many civilizations ago, we continue to harvest the resources of the Earth to provide food, in a system that filters large quantities of nutrition able to feed the World, into smaller packets for the few. Deforestation is usually accompanied by larger groups of livestock, used to indulge populations around the World. With this, an increase in rabies outbreaks in animal and human populations become more common (Fisher, Streicker and Schnell, 2018) A study by Andrade et al, (2016) stated that the areas with the highest risk for the transmission of bovine rabies are concentrated in extensive deforested areas, as well as those with the large herds of cattle and the largest numbers of highways.
Unfortunately, the impact doesn’t stop once the tree is cut.
Deforestation opens the forest floor to flooding, causing eutrophication of the soil and movement of nutrients and bacteria into water bodies. Increased rainfall encourages the spreading of diseases such as leptospirosis, a bacterial infection, and gastroenteritis, commonly known as infectious diarrhea. Wind direction changes, altering the movement patterns of insects, many of which, carry diseases. Roosting sites of bats change as the tree canopy is reduced, and primates, rodents, and other disease-spreading animals move closer to urban areas.
Many countries feed off of the meat of wild animals for sustenance, and this is often reported as the source of many pandemics and diseases. Being within close proximity to, and eating wild animals has direct links between the development of pathogens and the spreading of diseases.
The Ebola Virus, which once dominated our headlines is sourced from bats, which can transmit it to other animals such as primates and antelope (CDC, 2019). These animals are a normal source of food in many countries, and upon eating, or coming into contact with a host, a human is infected. Human to human transmission occurs, spreading the disease amongst family and health workers. Had better management of forest areas been in place, and eating a non-meat diet been the norm, these outbreaks may not have happened.
As these diseases become abundant in humans, they can become established and mutate to thrive in new environments. Now more than ever, we are more densely populated and packed in, creating an abundance of hosts for diseases to cross between.
Covid-19 was thought to first infect a human host from meat at a wet market in China, where all types of wild animals are sold for food. These include squirrels, scorpions, turtles, and rats, all of which provide a perfect opportunity for cross-species transmission of pathogens.
However, it is important to note that the wet markets are not responsible for the problem, but we should be looking instead at the root, and stopping wild animal trade from their natural environments.
But it’s not just in the forests, whilst many of the diseases we have faced and will face are a result of deforestation, we need to consider further, the environmental implications and the dormant diseases that come with that.
Earth's system is particularly fragile, but more than that, it is connected. As global warming increases, encouraged by deforestation, the permafrost of the Arctic melts. Hidden dormant within these capsules of ice could be diseases unknown to us, that could unleash devastation on our species.
It is more important now, than ever before, that we use our new-found understanding of the impacts of pandemics to fight for the protection of our Earth. Despite this, deforestation continues to soar and the Earth is bled dry.
We have a new opportunity to start anew and re-enter the World following this pandemic to have positive impacts upon the Earth. It is a time for action against inaction, and to voice our demands upon the governments which continue to privatise land, degrade forests and raise infrastructure.
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