In the Amazon rainforest, the seeds of the next disease outbreak could be quietly stirring.
Numerous ecologists, biologists, and epidemiologists have expressed concern that the next significant disease outbreak could come from the Amazon rainforest, not least because rampant deforestation and human development are bringing us into increasing contact with animal habitats and potential reservoirs of disease.
"The Amazon is a huge reservoir of viruses," David Lapola, a global change ecologist from the University of Campinas in Brazil, told AFP news agency.
Lapola described the Amazon rainforest as the "the world's biggest coronavirus pool," referring to the large group of viruses that includes the common cold, SARS, MERS, and Covid-19.
"That's one more reason not to use the Amazon irrationally like we're doing now," he said. "We'd better not try our luck."
Most of the diseases that have emerged in recent times – from HIV and Ebola to SARS and even Covid-19 – are zoonotic diseases, meaning they jumped from animals to humans. In fact, it’s estimated at least 60 percent of the 335 new diseases that emerged between 1960 and 2004 originated in non-human animals.
Primates are the most common source of viral spillover to humans because of our relatively close evolutionary links, but bats are also known to serve as viral disease hosts due to their high metabolism and supercharged immune system. In regards to Covid-19, the most likely candidate is a bat living in China, but other theories have also been suggested.
How, why, and when these pathogens jump from animal to human isn’t so clear, but recent research published in the Proceedings of the Royal Society B has shown that disrupting the environmental equilibrium can sharply increase the risk of virus spillover. This is especially true of human-driven environmental changes that are becoming increasingly common in the Amazon, such as hunting, wildlife trade, habitat degradation, deforestation, and urbanization, all of which are bringing wildlife and humans into close contact.
"Spillover of viruses from animals is a direct result of our actions involving wildlife and their habitat," lead author Christine Kreuder Johnson, a professor of Epidemiology and Ecosystem Health at the UC Davis School of Veterinary Medicine, said in a statement.
"The consequence is they're sharing their viruses with us. These actions simultaneously threaten species survival and increase the risk of spillover. In an unfortunate convergence of many factors, this brings about the kind of mess we're in now."
But increased contact with vertebrate animals isn’t the only concern. Previous research has shown that deforestation can help create the ideal conditions for mosquitoes to thrive, the vectors of disease such as Zika, malaria, dengue fever, and yellow fever. As one example, scientists discovered there was a boom in malaria cases in Malaysian Borneo following a spate of rapid deforestation driven by demand for palm oil. It’s also been speculated that the Zika virus epidemic that spread across the Americas in 2015–2016 was influenced by increased deforestation of the Amazon rainforest, which helped to foster conditions favorable to mosquitos.
There is no way to predict when or where the next disease outbreak might occur. However, it’s becoming increasingly apparent that the Amazon rainforest – along with the many other hives of biodiversity that are being overexploited by humans, like Southeast Asia and Central Africa – is becoming a ticking time bomb when it comes to viral spillover.