Infectious diseases spreading as the result of deforestation

Outbreak of infectious diseases linked to deforestation increased between 1990 to 2016

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.

Change in natural forest cover due to deforestation or afforestation and increase in commodity plantations like oil palm was correlated with outbreaks of infectious diseases globally, found a new study.

Outbreaks of both vector-borne and zoonotic diseases linked to deforestation increased between 1990 and 2016, the study noted, proving right past theories. The report published in Frontiers in Veterinary Science March 24, 2021 said:

Deforestation has caused malaria epidemics in South America and that forest clearing had favored the mosquito vector Anopheles darlingi in Southeast Asia for the species complex A. Any disease caused by a virus, bacteria, parasite or fungi turns zoonotic if the infection jumps from animals to humans, like was the case with the novel coronavirus disease (COVID-19). 

That's why Ana Lucia Tourinho wasn't surprised when she heard about the novel coronavirus, which was detected and has since spread around the world. 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, its 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.

Such virus in isolation and in equilibrium in their habitat does not pose threat to humans. When humans interfere in their forests and disturb the ecosystem, these viruses become a threat.  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.

The scenario is similar in the Amazon. In 2019, deforestation reached a record-breaking 9,762 square kilometers (3,769 square miles). The 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 center 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%.

Reforestation, especially in areas outside the tropical zone, also induced outbreaks of infectious diseases, the study confirmed. The research was the first of its kind on a global scale.

Here, reforestation refers to the kind where forest area is expanded to replace grasslands, savannas and open-canopy woodlands.

The authors of the report cited the example of case growth of a tick-borne disease in Italy:

The increase in incidence of tick-borne encephalitis in humans in Italy was explained by the ratio of coppice (low woodland) to high stand forest in Italy with natural reforestation that may favor the abundance of the small mammal reservoirs of tick-borne viruses.

They also found that in areas where palm oil monoculture increased, the residents were more exposed to infectious diseases. For instance, population of vectors for diseases like dengue, Zika, Chikungunya   , and yellow fever increased in oil palm and rubber plantations, the report showed.

Monoculture refers to the cultivation of a single variety of plant species in a large-scale, often replacing the natural growth of the area. The practice is known to cause loss of biodiversity and other ecological disturbances.

The researchers analysed three data sets to illustrate this correlation. They collated country-wise data on forest cover between 1990 and 2006 from the World Bank and data on human infectious diseases from GIDEON, a repository of information on infectious disease epidemics in each country. 

Data on area under oil palm plantation was gathered from the Food and Agricultural Organization of the United Nations, the report said. They juxtaposed the occurrences of the outbreaks with forest cover trends to arrive at the results.

                                                            The Editor