Ever since it emerged from a wet market in Wuhan, China, the coronavirus disease (COVID-19) has been linked to the wildlife trade. Experts have posited the zoonotic disease is carried by bats and pangolins, but few have followed the transmission any further to find the source of their infection.
It may be humanity’s endless assault on the world’s tropical forests.
According to the Conversation, diseases like Yellow fever, malaria, Venezuelan equine encephalitis, and Ebola all originated from animals living in threatened habitats. When humans have settled in these habitats, displacing the native ecosystem to produce beef, soy, palm oil or wood products, the affected animals find themselves in greater contact with humans, increasing the risk of a transmission event.
It’s happened before, resulting in the spread of some of the worst diseases in recorded history.
Humans and mosquitoes transmit Malaria and dengue fever
There is growing evidence that malarial mosquitoes infect humans at a greater rate around deforested areas. This relationship was studied in the Amazon rain forest by NSF-funded scientists Andy MacDonald at UC Santa Barbara and Erin Mordecai at Stanford.
“Deforestation is a huge issue in the Brazilian Amazon because of the political and economic pressures pushing up against environmental health, biodiversity, social justice and indigenous rights,” Mordecai told Phys.org. “We found that deforestation is not only an ecological disaster but also a major threat to human health.”
“People have been really interested in the effect of deforestation on malaria transmission,” adds MacDonald, a disease ecologist at UCSB. “In the 1970s, Brazil started to incentivize settlement of the Amazon, and we saw a huge increase in malaria transmission associated with that.”
A nexus of species transmit Yellow Fever
Yellow Fever is most commonly transmitted by mosquitoes that move between monkey populations in the jungle and humans who live nearby.
According to Inverse, Yellow Fever infections were behind the delay of the Panama Canal’s construction in the 1900s before a vaccine was developed 30 years later. However, even with a treatment, Yellow Fever still infects more than 200,000 people every year, killing one out of every three.Most of these deaths are reported in West Africa where mosquitoes transmit the disease between Howler monkeys and humans.
“Shrinking habitat has been shown to concentrate howler monkeys – one of the main South American yellow fever hosts. A study on primate density in Kenya further demonstrated that forest fragmentation led to a greater density of primates, which in turn led to pathogens becoming more prevalent,” Wuyou Sui reports for the Conversation. “Deforestation resulted in patches of forest that both concentrated the primate hosts and favored the mosquitoes that could transmit the virus to humans.”
Rodents at the root of Venezuelan equine encephalitis
Also spread by mosquitoes, the Venezuelan equine encephalitis virus (VEEV) is responsible for thousands of cases of life-threatening disease every year. According to the Center for Food Security and Public Health, VEEV causes “severe encephalitis in horses and humans. It can also occasionally cause disease in other mammals and birds.”
In South America, in and around its namesake country, VEEV may originate in small rodents. A study conducted during a VEEV outbreak in Darien, Panama, found that populations of Tome’s spiny rat and the short-tailed cane mouse were both extremely likely to carry the virus in their bloodstreams. The short-tailed cane mouse has also been linked to serious diseases like hantavirus and Madariaga virus.
These rodents thrive in the clear cut forests and farms that agriculturalists and corporations have annexed from the dwindling rain forest. Meanwhile, mosquitoes thrive on the rodents, and then introduce the disease to humans with each sting.
How Zika moved from Brazil to Africa
As Yale Environment 360 reports, deforestation removes shade from forest streams, reduces water acidity as tannins from leaves are flushed out, and increases turbidity, ideal conditions for mosquitoes to grow. Meanwhile, as tree roots are no longer absorbing surface water, the ground of former forests can become swampy.
The Zika virus may have emerged from the same conditions in Uganda’s Zika forest in the 1940s.
Though human carriers may not exhibit symptoms immediately, the disease most notably causes microencephaly, a shrunken cranium, in newborn babies. A human carrier who traveled to a favela in Brazil was stung by a mosquito, which passed it on to others that swarm standing water in buckets and old tires.
The tragic result was a spike in microencephaly cases at hospitals near impoverished areas in Brazil.
Pinpointing the spread of Ebola
In humans, the Ebola virus causes fever, uncontrollable diarrhea, body aches and both internal and external bleeding. But it wasn’t until humans began cutting down sub-Saharan forests for farmland and
The first human-borne Ebola outbreaks in history occurred in 1976 in Sudan and Zaire, now Democratic Republic of Congo. Since then, thousands more have died of Ebola in villages of Guinea, then Sierra Leone, Liberia, Nigeria, Senegal and Mali, according to the New Internationalist.
“Scientists have recently discovered that an outbreak of Ebola is most likely to strike villages in Sub-Saharan Africa that are near areas that have experienced deforestation within the previous two years, a finding which could have profound implications for predicting outbreaks,” writes Katie McQue. “There is also some suggestion that the likelihood of an outbreak may peak at two years after deforestation has taken place, although researchers are unclear what the mechanism for this is.”
Is Coronavirus found in the forest?
The coronavirus disease 2019 did not originate on the border of a rain forest, but it has been linked to wildlife trafficking operations that deal in animals from those environments. Worldwide demand for those products, namely spurious folk medicines and exotic charms, has only amplified the spread.
According to Forbes, coronavirus has been traced back to Chinese Horseshoe bats and civets, also implicated in the spread of SARS. If the disease mutated in the bodies of civets to the point of zoonotic transmission to humans, contact with those animals in a public market may have prompted the first cases of COVID-19.
“Deforestation and the sale of live wild animals or bushmeat, such as bats and monkeys, make the emergence of new viruses inevitable, while population growth, dense urbanization and human migration make their spread easier,” wrote Dr. Seth Berkley, head of the GAVI Alliance, a non-profit international vaccine initiative, in Scientific American.
The bottom line is, encroaching on natural habitats is not a sustainable practice at this point. Not for the earth, and not for humans.
Matthew Russell is a West Michigan native and with a background in journalism, data analysis, cartography and design thinking. He likes to learn new things and solve old problems whenever possible, and enjoys bicycling, going to the dog park, spending time with his daughter, and coffee.
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