The COVID-19 crisis has been a shock to our system. In the past few months, the world has faced unprecedented health challenges ranging from overrun hospitals and delayed testing to a shortage of personal protective equipment (PPE). No one could have predicted exactly what 2020 would have in store for us, but perhaps we shouldn’t be so surprised. Scientists have been warning us of the growing possibility of a pandemic for years.
How did this global pandemic come about? As it turns out, humans are partially to blame. No, it does not have anything to do with the biowarfare or 5G network conspiracy theories taking over the internet. Researchers have analyzed the virus’s genome and are confident the novel coronavirus has not been engineered or manipulated by humans.
It is the human interaction with wildlife and the natural environment that has a role to play in producing pandemics.
SARS-CoV-2 is the name of the novel coronavirus that causes COVID-19, which is a zoonotic disease that occurs due to contact between humans and wildlife.
Coronaviruses describe a large collection of viruses, including those causing severe illnesses such as the 2003 Severe Acute Respiratory Syndrome (SARS) epidemic and the 2012 Middle East Respiratory Syndrome (MERS). Both of these outbreaks occurred when humans were exposed to animal hosting or carrying the virus. In the case of SARS, these hosts were civets, and with MERS, they were camels. Bats are natural carriers of similar coronaviruses, and scientists believe they are the most likely reservoir for SARS-CoV-2. However, there has not been reports of humans contracting the virus after direct interaction with bats. This leads scientists to infer that there must be an intermediate host.
Most experts agree that COVD-19 arose from a live animal market involving traded wildlife. In January 2020, COVID-19 spread out from its epicenter in Wuhan, China, where there was a wildlife water market. Scientists expect that while the SARS-CoV-2 virus originated in bats, it was then passed to pangolins, small, spiny animals that have long snouts and tongues to help them eat ants. These animals, found in Asia and Africa, are described as shy, and when they feel threatened, they roll up into a ball.
Scientists have compared the protein structure and genetic make-up of a coronavirus carried by the pangolin and the virus causing COVID-19. They found a 91% overlap, which is “high enough to confirm an evolutionary relation between the two viruses.” Still, there is room for uncertainty. This overlap is lower than it was in SARS and MERS, which were both over 99% identical to the viruses carried by their respective intermediate hosts. Current evidence indicates that the pangolin is the most likely intermediate host of SARS-CoV-2, but it is possible that there are additional hosts in the mix or perhaps even another one entirely.
Before you start directing blame at pangolins or other potential hosts, it is important to realize why humans have been experiencing direct contact with these wild animals in the first place.
According to wildlife experts, pangolins are the most trafficked non-human mammal in the world, with tens of thousands of pangolins being poached annually. Their scales are made of keratin, but unlike human hair or fingernails, which are also made of this structural protein, pangolin scales are highly valued in some cultures. They are often dried and ground to powder to be used in traditional Chinese medicine. Pangolin meat is also served as a delicacy to those wealthy enough to pay for it. Between illegal trade, habitat loss, and low reproduction rates, pangolins continue to face a declining population and are considered critically endangered.
Since the COVID-19 outbreak, China has placed a restriction on the trade and consumption of non-aquatic wild animals. Critics were quick to point out some obvious loopholes in the ban. For example, there are no restrictions on wildlife trade for the purpose of fur and traditional medicine, meaning trade for animals like pangolins can continue. Wuhan and other provinces have set up their own local bans and many have developed programs to pay Chinese farmers to stop breeding exotic animals.
Illegal wildlife trade is a significant part of the story, but humans have an impact even further upstream in this process. Land use change is known to be a significant driver of infectious diseases. According to Dr. Jonathan Patz, a professor at the University of Wisconsin–Madison and the John P. Holton Chair in Health & the Environment, it is the human incursion and disruption of nature that is inducing pandemics.
Land use change, or the process of converting natural landscapes into agricultural land or development for human use, poses multiple threats. Not only is it a major threat to conservation and a significant driver of climate change, but it is also strongly linked to the emergence of diseases, as Patz reported 16 years ago. The land use changes humans have caused may bring economic growth, but they also bring diseases like malaria, Ebola, the Hendra Virus, and now COVID-19.
When looking at trends of various viruses, a pattern starts to emerge. In Australia, the 1994 Hendra Virus was responsible for killing over a dozen horses and their handler. The cause was discovered to be bats roosting in trees above horse pastures. The bats excreted the virus in their urine which fell onto the pasture, and the horses ate the contaminated grass. The horses became infected and even passed the infection on to their human handlers. The outbreak can be identified as a result of widespread deforestation and fires across Indonesia. Researchers reported that bats were migrating to urban and agricultural areas outside of their typical range because they faced a lack of food in their destroyed natural habitat.
The Nipah virus outbreak, which resulted in hundreds of deaths in Bangladesh, Malaysia, and India, emerged with a similar story. Humans were tapping trees to collect date-palm sap, and fruit bats were visiting the sites to eat out of the sap-collecting pots. When this sap was collected and sold for human consumption, the virus left by the bats was passed along with it. Research again points to a disruption of these bats’ natural habitat as the root cause of their appearances in human-managed spaces. Further supporting this reasoning, scientists found that areas of land with this particular virus consisted of more fragmented forests.
Malaria outbreaks in the Amazon Rainforest are also linked to rapid deforestation. Researchers found that a mere 1% increase in deforestation was associated with an 11% increase in malaria incidence. Even after adjusting for human populations, access to health care, and other factors, malaria hotspots were located in regions with the most destruction of rainforests. In the case of malaria, the mosquito vector, Anopheles darlingi, prefers open, sunny spaces, which led to an increase in larvae and biting rates in deforested sites.
“When you are thinking about preventing the next pandemic, It’s not just about early surveillance. It’s about stopping the degradation of ecosystems and our disturbance of natural systems,” said Patz.
Unfortunately, we have another, increasingly concerning issue that continues to fuel the likelihood of the next pandemic: climate change. Increasing temperatures, rising sea levels, and greater hydrological extremes are all alarming factors.
An increase in infectious diseases, especially vector- or water-borne diseases, are part of the consequences our world will face due to climate change. Scientists have known this danger for decades. Patz and his colleagues published a paper 24 years ago stating that climate change would directly affect disease transmission. For vector diseases, the changing climate shifts the vectors’ geographic ranges and influences their reproductive and biting rates. Changes to sea temperature and level can also increase the incidence of water-borne infectious illnesses.
The Zika virus, which hit South America in 2015, is one example of how closely viruses are linked to environmental conditions. The El Niño of 2015, a naturally occurring pattern of above-normal temperatures in the Pacific Ocean that causes extreme weather around the world, was one of the strongest in recent historical records. Aedes aegypti, the species of mosquito that carries Zika along with yellow fever and dengue, flourished under these new conditions. There were other factors influencing Zika transmission, including travel and trade, but scientists warn that temperature played a key role in igniting the outbreak.
Temperature surely impacts other viruses as well, and with the exacerbation of climate change and increasing global temperatures, future pandemics appear to be more likely to occur. The COVID-19 pandemic has been and continues to be an unprecedented challenge. With such immediate struggles, it is hard to imagine battling another global crisis as soon as this one ends, but scientists urge the public to not lose sight of the climate emergency. As Patz said, “Why don’t we treat climate change like an infectious disease, because after all, climate change is a global health emergency.”
As Peter Dasak, a disease ecologist and the president of EcoHealth Alliance, said, “Pandemics are on the rise, and we need to contain the process that drives them, not just the individual diseases. Plagues are not only part of our culture; they are caused by it.”
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