Our forests, long considered a vital shield against environmental degradation, are increasingly recognized for another crucial role: protecting human health. The COVID-19 pandemic, which has placed enormous pressure on health systems and caused massive losses of life and economies, is a stark reminder of the interconnectedness of human and environmental health. With every diversion of forest areas for human habitation, agriculture, development projects or urbanization, humanity is tearing down the natural barrier that has long kept dangerous diseases at bay.

Pandemics are not new; documents show the occurrence of at least eight pandemics, from the 14th century plague to the COVID-19 pandemic. A significant 60 percent of newly emerging infectious diseases in humans, such as HIV, Ebola, and Nipah, have been transmitted through various animals, mostly wildlife.. Over the past three decades, more than 30 new pathogens have been identified in humans, 75 percent of which originate from animals. Up to 80 percent of pathogens of biological warfare/bioterrorism concern are zoonotic organisms. Forests, in addition to providing medicinal plants and products, have functioned as natural disease regulators for millennia.

Their rich biodiversity supports complex ecosystems where pathogens exist in a delicate balance, often confined to forests and wildlife populations far from human contact. Countless viruses co-evolve and live harmlessly in their animal hosts in forests. However, when humans interfere with or alter forest habitats, they can unwittingly become hosts to these pathogens. In fragmented and degraded forests, pathways for disease transmission to human populations are created, and the potential for exposure intensifies with each new human intervention.

In addition to the heightened global danger of the release of potentially deadly microbes locked away for millennia in polar ice caps, The likelihood of transmission leading to the spread of zoonotic diseases – those that jump from animals to humans – also increases with climate warming..

One of the primary ways that deforestation causes the spread of zoonotic diseases is by supporting the influx of human populations. These areas of intervention often lack health care infrastructure, which increases the risk of disease outbreaks. At the same time, as habitats shrink, wildlife is forced closer to human settlements in search of food and shelter. This proximity creates more opportunities for zoonotic diseases to emerge and spread.

Deforestation alters microclimates and creates new breeding grounds for disease vectors. Clearing 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 itself can also release long-dormant pathogens deep in forest soils and organisms, potentially exposing human populations to unforeseen health risks.

The economic drivers behind deforestation exacerbate the problem. Unsustainable agricultural practices and over-harvesting of forest products not only destroy forests, but also create environmental conditions conducive to disease transmission. Poaching, fueled by the illegal wildlife trade, also gains momentum when forest areas are easily accessible. Loosely controlled global trade, including wildlife smuggling, also provides a platform for the spread of zoonotic diseases.

Analysis of zoonotic disease outbreaks shows that fires in the Indonesian rainforest in 1997, caused by land clearing for agriculture and drought, drove bats searching for food into Malaysian orchards. These bats carried the Nipah virus, which they passed to pigs via contaminated fruit, ultimately leading to the first known human outbreak of Nipah virus in 1999. Deforestation has created the conditions for the transmission of deadly pathogens such as Nipah, Lassa, malaria parasites and Lyme disease bacteria from wildlife to humans. In Liberia, the clearing of forests for palm oil plantations attracted rodents that carried viruses and infected people, causing hemorrhagic fever. In Brazil, a simultaneous increase in malaria cases has been observed with deforestation and agricultural expansion.

In India, deforestation has been primarily driven by encroachment, which has been further supported from time to time by legalization and, more recently, by the flawed implementation of the Forest Rights Act. Forest habitats are fragmenting due to conversion of forest land to agriculture, infrastructure projects, urbanization, etc. Kyasanur Forest Disease (KFD) or Monkey Fever, a tick-borne viral disease, has been linked to forest fragmentation caused by the expansion of agriculture. The altered landscape, which brought humans and livestock closer to infected ticks carried by monkeys and other mammals, has spread the disease. Again, deforestation in areas of Kerala has altered the habitat of bats (the natural reservoir of Nipah virus) and brought Nipah virus into human settlements and domestic animals. Studies in other tropical regions have shown a link between deforestation and increased incidence of malaria.

The dependence of indigenous peoples’ health on the health of biodiversity is highlighted in a survey of the Shompen tribes of Nicobar Island, which revealed alarmingly high rates of chronic malnutrition, coupled with the decline of traditional nutritional sources and medicines provided by wild foods – all due to habitat destruction.

Deforestation is not just an environmental issue; it is a natural public health crisis. By protecting our forests, we are not only conserving biodiversity and mitigating climate change, but we are also investing in a healthier future for ourselves and future generations. Containing disease is a new ecosystem service, similar to carbon sequestration and pollination. India's One Health Mission recognizes that the health of humans, domestic and wild animals, and the wider environment (including ecosystems) are closely linked and interdependent. Balancing and optimizing human, animal, and environmental health through forest conservation is of paramount importance, as the benefits will always outweigh the gains from deforestation. Spring

Glossary of key terms

• Zoonotic diseases: Diseases that are transmitted from animals to humans.
• Pathogens: Microorganisms, such as viruses and bacteria, that can cause disease.
• Outbreak: A sudden, unexpected increase in the number of cases of a disease in a particular area.
• Disease vectors: Organisms (such as mosquitoes or ticks) that transmit pathogens from one host to another.
• Biodiversity: The diversity of life in a particular environment.
• Habitat fragmentation: The division of large, continuous habitats into smaller, isolated parts.
• Encroachments: The gradual disturbance or encroachment on forest areas, often for human settlement or agricultural purposes.
• Spillover: The process by which a pathogen jumps from one host species to another.
• Microclimate: Local climatic conditions in a small, specific area.
• One Health: An approach to health that recognizes the interdependence of human, animal and environmental health.
• Ecosystem services: The benefits that humans derive from ecosystems, such as disease regulation, carbon storage, and pollination.
• Kyasanur Forest Disease (KFD) or Monkey Fever: A tick-borne viral disease associated with forest fragmentation in India.
• Nipah virus: A deadly virus carried by fruit bats that can jump to pigs and humans.
• Lyme disease: A tick-borne disease linked to deforestation in certain regions.
• Malaria: A disease transmitted by Anopheles mosquitoes, often associated with altered watercourses due to deforestation.