Deforestation: A looming public health crisis

From Nipah outbreaks in Southeast Asia to Monkey Fever in Western Ghats, the destruction of forests is accelerating the rise of zoonotic diseases, those that jump from animals to humans. Protecting forests is not just an environmental imperative — it’s a public health necessity

Our planet’s forests, long considered a vital shield against environmental degradation, are increasingly being recognised for another crucial role: safeguarding human health. The COVID-19 pandemic that challenged the healthcare systems of the world, put unfathomable pressure on health professionals, and caused massive losses to the world economy and humanity, is a stark reminder of the interconnectedness of human and environmental health. With every diversion of forests for human habitation, agriculture, development projects, or urbanisation, humanity is tearing down a natural barrier that has long kept dangerous diseases at bay. Pandemics are not new.

Documents show the occurrence of at least eight pandemics starting from the 14th Century Bubonic Plague or Black Death (in which 25 per cent of London’s population was killed) to the COVID-19 Pandemic with over 700 million cases worldwide and more than 7 million deaths. A significant 60 per cent of newly emerging infectious diseases in humans, such as HIV, Ebola, and Nipah, have travelled through various animals, predominantly wildlife. Over 30 new pathogens have been detected in humans in the last three decades, 75 per cent of which have originated in animals. Not surprisingly, 80 per cent of the pathogens of germ warfare/bioterrorism concern are organisms related to zoonoses. It is pertinent to note that while bird flu has been causing deaths of human beings infected through poultry, viruses are crossing the species barriers and infecting new species, even wildlife themselves. The bird flu virus has been reported to have infected big cats in the US since 2022; dozens of tigers and lions died in 2024 from bird flu in Vietnam; Antarctica seals tested positive for bird flu in 2024; and bird flu is on the increase in the avian species and even in wild animals like tigers and leopards, especially in Maharashtra and Gujarat, while a lion in Kanpur Zoo in India has died of bird flu on May 15, 2025. Forests, apart from providing medicinal plants and products, have acted as natural regulators of disease for millennia. 

Their rich biodiversity supports complex ecosystems where pathogens exist in a delicate balance, often confined within forests and wildlife populations far removed from human contact. Countless viruses co-evolve and live harmlessly within their animal hosts in forests. However, when humans encroach upon or alter forest habitats, they may unknowingly become hosts to these pathogens. In fragmented and degraded forests, pathways for diseases to spill over into human populations are created, and the potential for exposure intensifies with every new human encroachment. Notwithstanding the increased global danger of the release of potentially deadly microbes locked for millennia in polar ice caps, the probability of spillover events leading to the spread of zoonotic diseases — those that jump from animals to humans — also rises with climate warming. One of the primary ways in which deforestation causes the spread of zoonotic diseases is by promoting the influx of human populations. Encroachments lack healthcare infrastructure, which amplifies the risk of disease outbreaks. Simultaneously, as habitats shrink, wildlife is forced to venture closer to human settlements in search of food and shelter. This proximity creates more opportunities for zoonotic diseases to emerge and spread. Viruses are transmitted between people who become carriers, spreading them across the world in no time. Biotic interference and deforestation often lead to significant changes in local ecological conditions, inadvertently creating breeding grounds for disease vectors. Habitat destruction may reduce predator populations, leading to an increase in disease-carrying intermediate hosts.

Deforestation changes microclimates and creates new breeding grounds for disease vectors. The clearing of forests can alter water flow and create stagnant pools, ideal habitats for mosquitoes that transmit diseases like malaria, dengue, and Zika. The act of deforestation can also release long-dormant pathogens deep within forest soils and organisms, potentially exposing human populations to unforeseen health risks. The economic drivers behind deforestation exacerbate the problem. Encroachments, unsustainable agricultural practices, and over-harvesting of forest produce not only destroy forests but also create environmental conditions conducive to disease transmission. Poaching of wildlife, supported by illegal wildlife trade (one of the most profitable industries in the world today), also receives a boost if forest areas are provided easy access. Loosely controlled global trade, including the smuggling of wildlife, also provides a platform for the spreading of zoonotic diseases. The analysis of occurrences of zoonotic diseases shows that the 1997 Indonesian rainforest fires, driven by agricultural land clearing and drought, forced fruit bats to seek food in Malaysian orchards. These bats carried the Nipah virus, which they transmitted to pigs through contaminated fruit, ultimately resulting in the first known human Nipah virus outbreak in 1999, followed by a string of recurrent outbreaks in Southeast Asia.

Deforestation created conditions for deadly pathogens like Nipah, Lassa, malaria parasites, and Lyme disease bacteria to spill over from wildlife to humans. In Liberia, diverting forests for palm oil plantations attracted virus-carrying rodents and infected people, causing haemorrhagic fever, killing 36 per cent of infected people. Research has illuminated a compelling link between deforestation and the prevalence of Lyme disease in the north-eastern United States. In Brazil, there has been observed a simultaneous increase in the cases of malaria with forest clearance and expansion of agriculture. It is feared that the recent widespread forest fires and the consequent loss of Amazon habitat could lead to the emergence of another serious pandemic. In India, deforestation has primarily been driven by encroachments that have been further fuelled from time to time by regularisations, and unfortunately in recent times by flawed implementation of the Forest Rights Act.

Additionally, forest habitats get fragmented due to the diversion of forest lands for agriculture, infrastructure projects, urbanisation, etc. The Kyasanur Forest Disease (KFD) or Monkey Fever, a tick-borne viral disease in the Western Ghats, has been linked to forest fragmentation caused due to agricultural expansion favouring areca nut and cashew plantations. The altered landscape that brought humans and livestock closer to infected ticks carried by monkeys and other mammals spread the disease to neighbouring states like Kerala, Goa, and Maharashtra. Again, the deforestation in areas of Kerala altered the habitat of fruit bats (Nipah virus’s natural reservoir) and brought the Nipah virus into human settlements and domestic animals like pigs. Studies in other tropical regions have shown a link between deforestation and increased malaria incidence. The creation of stagnant water bodies because of altered land use patterns becomes ideal breeding grounds for Anopheles mosquitoes, the vector of malaria. Increased human intrusion into forest areas for activities like grass cutting, often in deforested or degraded lands, has been linked to a wider distribution of scrub typhus, a mite-borne disease.

The dependence of the health of Indigenous people on the health of biodiversity elements is highlighted in the survey of Nicobar Island’s Shompen tribes. It revealed alarmingly high rates of chronic undernutrition: 63 per cent of children exhibiting stunting, and 33 per cent being underweight despite medical support by the Government. This concerning trend appears to be linked to a decline in the traditional nutritional resources and medicines provided by wild foods — including fruits, tubers, honey, fish, and game — all due to habitat destruction. Deforestation is not just an environmental issue; it is a public health crisis in the making. By safeguarding our forests, we are not only preserving biodiversity and mitigating climate change but also investing in a healthier future for ourselves and generations to come. The containment of diseases is, in fact, a novel ecosystem service, akin to carbon storage and pollination. India’s One Health Mission recognises that the health of humans, domestic and wild animals, and the wider environment (including ecosystems) are closely linked and interdependent. Balancing and optimising the health of people, animals, and the environment by safeguarding forests is of paramount importance since its benefits shall always outweigh the profits made by cutting the forests down!

(The writer is a former Principal Chief Conservator of Forests, UP and Maharashtra. Views are their own)