The disease of deforestation

The more forests we destroy, the greater the chance of new pandemics.

Photo: Araquêm Alcântara/Rainforest Foundation Norway

Most of us have by now suffered under the consequences of the coronavirus pandemic. Whether we have had personal experience of the disease Covid-19, or felt the effect of the measures that followed. From the impossible combination of homeschooling and working from home, to not being able to spend time with the people we love or exercise the freedom to go wherever we want.

Who is holding the key to the next lockdown? The bats, pangolines, pigs and rats that we will meet later in this article, have only one part of the answer

Diseases from animals

“This sort of pandemic comes as a consequence of how we have capitalised on nature, as well as our frenetic traveling,” says biology professor Dag O. Hessen.

Originally these diseases emerged from keeping livestock close to where humans live, according to Hesssen, but recently they are linked to our overconsumption of nature.

Professor of Biology Dag O. Hessen says that human over consumption of nature cause disease. Photo: Anne Valeur

"We eat wild, rare animal species often sold at game markets, and we are constantly penetrating areas that destroy nature, pushing animals out of their natural habitats and providing closer contact with wild animals," he says.

So-called zoonoses, diseases transferred from animals to humans, are not new. Black Death, Spanish Flu, HIV, Rabies, Malaria, Salmonella, Sars and Ebola. They are all examples of diseases in humans that originated from animals.

What is new, is that the occurrence of this type of disease is on the increase world over. With the rapid destruction of nature and modern travelling habits, they are spreading much faster than before. According to the UN Environment Programme (UNEP), 75 percent of all new infectious diseases in humans originate in animals. On average, one new infectious disease emerges in humans every four months.

UNEP links the increase in zoonoses to the loss of nature and biodiversity, illegal hunting and trade in wild animals and the destruction of their habitats. Climate change, intensive agriculture and industry, the demand for meat, urbanisation and travel are considered to be the drivers.

Rainforest is cut down to make space for large scale palm oil production. Photo: Rainforest Foundation Norway

A Malaysian Mystery

Several studies point to encroachment on pristine forests as an underlying and common denominator for many of the zoonoses. According to a report from EcoHealthAlliance, almost a third of new infectious diseases are linked to changes in land use, such as deforestation and resource extraction in previously untouched nature.

In order to better understand how this happens, we will time travel to Malaysia in the late 90s, and look at the mystery of coughing pigs and dead pig farmers. At that time there was a rise in both pig farming and palm oil production with large areas of rainforest in western Malaysia being chopped down.

Bats who previously lived in the forest started eating from the farmer’s fruit trees, and moved in under the roofs of the pigsties that were built on the forest frontiers. Chewed off fruit bits and faeces from the bats fell into the pigsty.

In 1998, some of the pigs developed a bad cough, but they were otherwise fine. After a while their piglets started dying. In order to secure as much income as possible the parent pigs were sold. By the time the first pig farmers started getting ill, the pigs had already been sold and consumed all over the country.

The first outbreak of the Nipah virus was a fact. After a while, the virus spread from human to human with symptoms from fever and vomiting to pneumonia, meningitis and permanent personality disorders. The mortality rate of the Nipah virus is high, from 40 - 75 percent depending on where the outbreak is. Other Nipah virus outbreaks have later emerged in Bangladesh and in India.

The outbreak of the deadly Lassa virus in West Africa is another example of how bad things can go when profit is put before nature. Large areas of forest are cut down to meet the global demand for palm oil, and rodents are pushed out of the forest to find food elsewhere. Rats eating food meant for human consumption transmits the contagion, which presents in humans as a fever and internal bleeding.

Several scientists say that pangolins have incorrectly become scapegoats for the outbreak of Covid-19. Destruction of nature may be the real reason. Foto: Alexis Huguet/Rainforest Foundation Norway

Some scientists now wonder whether the real cause of Covid-19 is also linked to the destruction of nature. Professor Thomas Gillespie of Emory University said to the newspaper Mongabay that the development of the Three Gorges Dam, the world’s largest hydroelectric power station, could be a contributing factor. The dam is situated about 400 kilometres from Wuhan, further up the Yangtze river. The dam project has killed off most of the animals that lived there, but bats may have flown out of the area and brought contamination to Wuhan, where the first case was registered.

Forest protection as a health measure

“When we destroy forest, we reduce biodiversity. Healthy ecosystems are made up of a great deal of species diversity and when we lose that, pathogens can invade,” says professor of biology Mary C. Pearl. She is Dean of Macaulay Honors College of the City University of New York and has worked with conservation and ecology since the 80s.

Biology professor Mary C. Pearl says that when there are fewer animals, pathogenic viruses will try to look for new hosts.
Photo: private.

“We know from agriculture that when we have monoculture, the pests arrive to be more destructive than if we had a mixed crop. The same is true with wild animals,” she says.

Pearl explains that pathogens are more likely to move across to new species when the population of their original host species is severely reduced. The disease-causing agents either die off or find new or additional hosts.

This way they can cause further health deterioration in natural ecosystems. If species reduction is due to human incursion with their livestock, new pathogens can arrive from both humans and livestock causing new disease outbreaks in wildlife.

Pearl thinks that the protection and rebuilding of forest is a protection against diseases. Large areas of connected forest are important.

“When we build corridors between fragmented areas of forest, you can have that kind of resilience that goes away when ecosystems are disrupted. These are all health measures,” she says.

Health measures that can span further than current global health services. It is often poor people that are more exposed to zoonoses. They are the ones working with livestock, harvesting, mining and logging on the frontiers between original and changed forest. Lack of water and sanitation makes virus prevention harder and many live far away from public health services.

Poor people are often more exposed to zoonotic diseases, as they are the ones working with livestock, harvesting, mining and logging in the frontier between original and changed forest. Foto: Araquêm Alcântara/Rainforest Foundation Norway

Viral chatter

So, destructive viruses can jump from species to species before transmitting to humans, in a process referred to as viral chatter. After that they may jump back to animals and cause pandemics in animals. Or they may mutate and return to humans in a much more dangerous form.

“The strategy of the virus is to mutate fast and get hold of a population which can give the largest possible spread. Humans are many and they travel at a frenetic pace. Although it is not in the virus’ interest to kill off their hosts, there is an imminent danger of new outbreaks that may cause more severe symptoms than Covid-19. It is really just a question of time,” says biology professor Dag O. Hessen.

He calls for better prevention against future zoonoses and pandemics. And he is not alone. Recently, the UN released a report that not only looks at strategies for identifying, diagnosing and treating new zoonoses, but also looks at what the underlying causes are. The UN calls on authorities the world over to have a unified approach, called One Health, that forges closer ties between experts on human, animal and ecosystem health.

Even to the biology professor, the connection between pandemics and natural loss has been a wake-up call. Had he written his recent book “Verden på vippepunktet” (The world at tipping point) a few months later, he would have added some paragraphs about pandemics.

“We have had our eyes opened to how the economy works and had time to think about where we are going, both in terms of climate and degradation of nature. I sincerely hope that this makes the consequences of cutting rainforest very clear,” he says.


Zoonoses are infectious diseases in the form of viruses, bacteria, parasites and fungi that are transmitted from animals to humans.

Examples of zoonoses are Covid-19, HIV, Ebola, Sars, Nipah, Malaria, Dengue and Salmonella.

Transmission occurs through direct contact with animals, animal body fluids and feces, animal products (meat, eggs and milk) and bites.

The incidence of such diseases is increasing.

Causes and drivers: Loss of nature and biodiversity, illegal hunting and trafficking of wild animals and destruction of their livelihoods. Climate change, intensive agriculture and industry, the demand for meat, urbanisation and travel.

Sources: Centre for Disease Control and Prevention, EcoHealth Alliance, UNEP, Sustaining Global Surveillance and Response to Emerging Zoonotic Diseases