Deforestation, Climate Change And Disease Outbreaks: Is There A Link?

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The coronavirus is now telling the world what we have been saying for thousands of years—that if we do not help protect biodiversity and nature, then we will face this and worse future threats,” said Levi Sucre Romero, a BriBri indigenous person from Costa Rica who is the Coordinator of the Mesoamerican Alliance of Peoples and Forests.

Forests are key to climate, water, health and livelihoods. They are disappearing at an alarming rate. Ever since humans started cutting down forests, about 46% of the trees have been felled, according to a 2015 study in the journal Nature.

Ecosystem Services By Forests

Forests provide a diversity of ecosystem services including:

  • Convert carbon dioxide into oxygen and biomass.
  • Act as a carbon sink and help stop climate change.
  • Induce rainfall.
  • Purify water.
  • Mitigate natural hazards such as floods.
  • Act as a genetic reserve. 
  • Provide medicines. 
  • Additionally, serve as a source of lumber and recreational areas. 
  • Also, land food chains start from forests.  

An estimated 50% of modern drugs have been developed from natural products that are threatened by biodiversity loss. The decade 2011-2020 is the ‘UN Decade on Biodiversity’. The United Nations will observe 22nd May as the International Day for Biological Diversity (IDB) to increase understanding and awareness of biodiversity issues.

Deforestation, Climate Change And Disease Outbreaks

At the beginning of the 20th century, the Earth’s forest area was about 50 million square kilometers. This has since shrunk to less than 40 million square kilometers. Humans are deforesting the lands on a large scale, mostly for urbanization, agriculture expansion and industrialization. In the last 25 years, the world’s forests shrank by 1.3 million square kilometers. Since 1990, the world’s lost more forest area than the size of South Africa.

Fires, droughts, and tropical storms are also playing an increasing role in forest loss.

In the last 25 years, the world’s forests shrank by 1.3 million square kilometers. Image via Getty.

The frequency of disease outbreaks, deforestation, and biodiversity loss has been increasing fast since 1980. Between 1980 and 2013, there were 12,012 recorded outbreaks of 215 human infectious diseases, comprising 44 million individual cases in 219 nations.

Apart from the above factors, the other factors which are responsible for the disease outbreaks are high levels of travelling, trade and connectivity, and high-density population. But climate change and deforestation are the most important factors for disease outbreaks.

Climate change and deforestation have accelerated the transmission patterns of infectious diseases and have caused human displacement. Movements of large populations to new locations increase the vulnerability to diseases like measles, malaria, diarrhoea diseases and acute respiratory infections. 

The likelihood of spillovers to people may increase with the increase in global warming, and push the animals, which usually act as vectors or hosts to the viruses that they carry, into regions where they’ve never existed before. Such kind of migration cause disease outbreaks.

The health of the people living at the frontiers of such deforestation is always a great concern because deforestation destroys the natural habitats of wild animals and increases proximity to human populations. This creates a greater possibility for zoonotic diseases (diseases that spread from animals to humans).

Many viruses exist harmlessly with their vector or host in forests because that host has co-evolved with viruses they carry.

According to the WHO, climate variability has a direct influence on the epidemiology of vector-borne diseases. Image Credit: Quartz India

The majority of ‘new diseases affecting humans‘ are zoonotic. Among mammals, bats have a higher number of zoonotic viruses. Bats are notorious hosts for some of the world’s most deadly viruses, including Nipah, Hendra, Ebola, and severe acute respiratory syndrome (SARS). Bats fight with the viral infections but do not overreact to them and are safe from the many viruses they carry.

People and animals interacting with bats (or their urine, faeces or saliva) may catch these zoonotic viruses and then spread them into other animals or people. 

The problem of climate change is worsening this situation. At present, Earth is under severe pressure of GHGs. According to the ‘Global Carbon Project‘ atmospheric CO2 concentration in 2019 is 47% above the pre-industrial levels. One tonne of carbon is equivalent to 3.67 tonnes of carbon dioxide (CO2). 

According to the WHO, climate variability has a direct influence on the epidemiology of vector-borne diseases. By 2100, it is estimated that average global temperatures will have risen by 1.0–3.5 °C and will increase the spread of many ‘vector-borne diseases’ in new areas. Amongst these are fungi transmitted Cryptococcus gattii infection, algal transmitted Ciguatera fish poisoning, tick vector transmitted Lyme disease and mosquito vector transmitted West Nile Virus encephalitis, Chikungunya, Rift Valley Fever, Zika virus paralysis and Dengue fever, Bat-transmitted Ebola virus, Nipah virus, Coronavirus virus, etc.

Other equally important diseases, which will spread and prevail due to climate change and deforestation include respiratory allergies due to increased human exposure to air pollution and dust, and heat-related illness and deaths. 

The vector-borne infectious diseases are usually confined to wildlife that has spilt over to people in areas undergoing rapid forest clearing. About 60% of the new infectious diseases that emerge in people, including HIV, Ebola, and Nipah, originated in forest-dwelling animals. In Brazilian Amazon, between 2003 and 2015, on average, a 10% yearly increase in forest loss led to a 3% rise in malaria cases. 

In Liberia, forest clearings for palm oil plantations attracted typically forest-dwelling mice, lured there by the abundance of palm fruit around plantations and settlements. Humans contracted Lassa virus when they came into contact with food or objects contaminated with feces or urine of virus-carrying rodents or bodily fluids of infected people. In humans, the virus caused hemorrhagic fever—similar to Ebola virus—and killed 36% of infected people, in Liberia. 

A 4.3% increase in deforestation over a three-year timeframe was associated with a nearly 50%  increase of malaria incidence in a small patch of Brazilian Amazon. In a large-scale analysis in 2017, researchers found a positive association between the rates of deforestation and malaria prevalence in 67 countries.

Monkey malaria, caused by Plasmodium knowlesi, which proliferate in forest-dwelling macaques, has become the most common cause of malaria in Malaysia. Deforestation has been bringing humans into contact with forest-dwelling macaques and infected mosquitoes, as people move into cleared areas and macaques closer to human settlements. In addition, the clearing of trees may shift the locations of breeding sites for mosquitoes that thrive at forest edges. These mechanisms are thought to play a role in a range of vector-borne disease.   

The Ebola Virus Disease (EVD) outbreaks between 2004–2014 in West and Central Africa showing that in these EVD outbreaks the spillover from wildlife reservoirs occurred mostly in hotspots of forest fragmentation.

In the northeastern US, the bacterium causing Lyme disease, Borrelia burgdorferi, is transmitted via ticks but can infect many mammals in forest communities. Of these, only the white-footed mouse can truly sustain infections over long periods and pass them onto ticks.  

The past two coronavirus outbreaks, SARS and MERS, are examples of transmission of wild animal diseases to humans. In 2003, the SARS coronavirus jumped from bats to civets and then from civets to people. In the MERS outbreak, the MERS coronavirus jumped from bats to camels and then from camels to people.

It is expected that the novel coronavirus, causing COVID-19, was born in the wildlife market of Wuhan in China in late 2019.

Conclusion

We are living in the 21st century with the world population of about 7.6 billion today. Such a massive size is causing pressure on our ecology. Biodiversity and ecosystems are under stress. Humans are destroying their future to fulfill their current unsustainable needs and ambitions. The more we degrade and clear forest habitats, the more likely we’re going to find ourselves in those situations where epidemics of infectious diseases occur. 

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