Emergence of Zoonotic Diseases and Associated Links with Deforestation

(Story Contributor: Kurian s Kurian, Advocate of sustainable tourism & green economy)

Year 1997. Rainforests of Indonesia which is approximately the size of Pennsylvania have been turned into ashes for agricultural purposes. Two years later, in 1999, severe brain inflammation and death cases were reported in Malaysia. Probably you might be wondering how the deaths reported in Malaysia are connected with the deforestation in Indonesia. Let’s rewind back to 1997 when the rainforest is being burned down. It is a natural phenomenon that forest habitats migrate to other places to save themselves from threats. Fruit bats carrying deadly viruses flew from the deep rainforest of Indonesia and settled on trees in the Malaysian orchard. First, this affected pigs who have eaten the fallen nibbled fruits and then humans. This is the first known emergence of Nipah virus in people.

Over the years, zoonotic diseases have been increasing at an alarming rate in numbers,frequency and diversity. According to the Centers for Diseases Control and Prevention “scientists estimate that more than 6 out of every 10 known infectious diseases in people can be spread from animals, and 3 out of every 4 new or emerging infectious diseases in people come from animals”.  A research titled Global trends in emerging infectious diseases reports emergence of 355 infectious diseases from global human population, between the years 1940 and 2004.

“We invade tropical forests and other wild landscapes, which harbor so many species of animals and plants. And within those creatures, so many viruses. We cut the trees, we kill the animals or cage them and send them to markets. We disrupt ecosystems and we shake viruses loose from their natural hosts. When that happens, they need a new host. Often, we are it.”

A thought provoking statement by David Quammen given in The New York Times ,which summarizes the activities that led to spread of the zoonotic disease.

It has been reported that 60% of emerging infectious diseases in humans are zoonotic. According to the World Health Organisation(WHO) zoonoses or zoonotic diseases are defined as those diseases and infections naturally transmitted between people and vertebrate animals. Some of the examples of the Zoonoses are Rift Valley fever, SARS, pandemic influenza H1N1 2009, Yellow fever, Avian Influenza (H5N1) and (H7N9), West Nile virus and the Middle East respiratory syndrome coronavirus (MERS-CoV).

One of the substantial reasons that explains the disturbing trend of such infectious diseases is deforestation. The research titled “Amazon Deforestation drives Malaria transmission, and Malaria burden reduces Forest Clearing ”, confirms the “intimate ties between environmental change and human health”. The research explains that “a 10% increase in deforestation leads to a 3.3% increase in malaria incidence (~ 9,980 additional cases associated with 1,567 additional square km lost in 2008, the study midpoint, Amazon-wide). The research estimated a 1% increase in malaria incidence results in a 1.4% decrease in forest area cleared (~219 fewer square km cleared associated with 3,024 additional cases in 2008). 

Over the years similar studies have been carried out in various parts of the globe to study the relation between spread of zoonotic diseases and human factors that lead to such spread. Recently, India is also witnessing “emergence and reemergence of high priority and neglected Zoonoses” says a Medical Reports and Case Studies titled Emergence of Zoonotic Diseases in India: A Systematic Review.  

One prime example which illustrates the association of zoonotic disease and deforestation in India is Kyasanur forest disease (KFD) or ‘Monkey Fever’. A tick-bone infection seen in the Western Ghats region of the country’s south-western states. It was first identified in 1957 in the Kyasanur forest area in the Shimoga District of Karnataka from which it got its name. The research named Forest loss shapes the landscape suitability of Kyasanur Forest disease in the biodiversity hotspots of the Western Ghats, India cites that forest loss is  one major suitable factor for kyasanur forest disease (KFD). According to the research 83% increase in KFD outbreak risk is calculated to each decile increase in forest loss.

An article titled The increase in zoonotic diseases: the WHO, the why and the when? explains the origin of zoonoses diseases. It states that “when natural ecosystems like forests remain intact, interactions between human populations and wild host species are limited. As a result, viruses circulate with limited crossing over into humans. Similarly, wild host species have fewer interactions with domesticated animals and livestock, which generally live in close proximity to humans. It is, therefore, less likely for domestic animals and livestock to become intermediate hosts of these diseases. But once the forests start to disappear, populations come in closer contact and disease spreads”.

The research named “Sustaining Global Surveillance and Response to Emerging Zoonotic Diseases” reports “the drivers of zoonotic disease can be quite complex—individually and collectively”. One of the ways to prevent such pandemics, according to the research Global capacity for emerging infectious disease detection is to “highlight the need for improvements in global outbreak surveillance”. The research also adds the need for two directional communication between the local government and the international community. 

An essay published in Science titled Ecology and economics for pandemic prevention illustrates “a sketch of the key components of an economically feasible set of ecological pandemic prevention strategies”. In short, preventing pandemics by investing in the environment. 

A Special Volume of UNEP’s Frontiers Report Series titled “Preventing the next pandemic : Zoonotic diseases and how to break the chain of transmission” recommends “One Health”,as the most promising way to manage and prevent zoonoses”. UNEP’s Frontiers Report recommends “EcoHealth”, “a closely related approach, that has been defined as a set of systemic, participatory approaches necessary to understanding and promoting both health and well-being in the context of social and ecological interactions”. 

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Featured photo credit:  Andre Moura , COURTESY via pexels