Deforestation, a portal to infectious diseases

Scientists have been repeating the warning for at least two decades: As humans encroach upon forests, their risk of contracting viruses circulating among wild animals increases. That’s why Ana Lucia Tourinho wasn’t surprised when she heard about the novel coronavirus. An ecologist at the Federal University of Mato Grosso in Brazil, Tourinho studies how an environmental imbalance can cause forests and societies to become sick.

“When a virus that wasn’t part of our evolutionary history leaves its natural host and enters our bodies, it’s chaos. The new coronavirus is rubbing that in our faces,” she said. Before it infected the first humans and spread through the world by living in travelers’ bodies, the novel coronavirus,officially named SARS-CoV-2, inhabited other hosts in a wild environment — most likely bats.

When such viruses are isolated and in equilibrium in their habitat, for example a closed forest, they are not a threat to humans. The problem arises when this natural reservoir is cut down, destroyed and occupied.

Scientific studies published before the current pandemic had already showed a connection between deforestation, the proliferation of bats in the damaged areas and the family of coronaviruses, which includes the current lethal strain.

Aneta Afelt, a researcher at the University of Warsaw in Poland, conducted studies indicating that the next severe infectious disease would come from Asia due to the region’s high levels of deforestation over the past 40 years.

To reach this conclusion, Afelt tracked previous pandemics caused by other coronaviruses. These include SARS, which spread in 2002 and 2003 and had a 10% fatality rate, and MERS, which spread in 2012 and had a 38% fatality rate. “By being one of the regions of the world where population growth is the strongest, where sanitary conditions remain poor and where the deforestation rate is the highest, SEA (Southeast Asia) meets every condition to become the place of emergence or re-emergence of infectious diseases,” Afelt wrote in a 2018 article.

The scenario is similar in the Amazon. In 2019, deforestation reached a record-breaking 9,762 square km. Reports of deforestation increased by 51.4% between January and March 2020 in comparison to the same period the previous year. An analysis by Columbia University in New York showed that the region, which houses the biggest tropical forest in the world, is also considered a likely centre for epidemics. It also found that bats in Brazil carried at least 3,204 types of coronaviruses. 

Tourinho doesn’t even want to think about the public health impact that will occur if the Amazon rainforest continues being destroyed at this rate. “If the Amazon turns into a great savannah, we can’t even imagine what kind of diseases could come out of there. It’s unpredictable,” she said. “Besides being important to us because of the climate, the fauna, it is important for our health.” Studies in Brazil have already tracked the direct relation between deforestation in the Amazon and an increase in diseases. In 2015 the government-led Institute of Applied Economic Research (IPEA) found that for every 1% of forest that was cut down per year, malaria cases increased by 23%. The incidence of leishmaniasis, a disease transmitted by a sandfly-borne parasite, also seemed to relate directly to levels of deforestation.