Habitat destruction increases human vulnerability to pandemics

Understanding the connection between biodiversity and human health

The Covid-19 pandemic has heightened people’s awareness of our connection to nature. Humanity’s heavy footprint has destroyed and fragmented important ecosystems and landscapes, reducing the biodiversity those landscapes support and altering the delicate natural buffer that separates wildlife, pathogens and people. When habitat and biodiversity disappear and the buffer between humans and the natural world weakens, pathogens “spill over” to human populations, causing pandemics, such as Covid-19. At This is My Earth (TiME), we believe that the devastating loss of biodiversity and habitat that the planet has experienced in the last 30 years has set this disease in motion and will likely cause additional pandemics in the future, if not addressed.

Viruses like SARS-CoV-2, which causes Covid-19, most likely originate in animals, thus the diseases these viruses cause in humans are classified as zoonotic. In zoonotic diseases, viruses, bacteria and parasites that are generally present in a vertebrate (in most cases, a mammal) “jump” or “spill over” to humans when there is ongoing contact between the hosts of the pathogens and humans. Most infectious diseases that emerge in humans are zoonotic (Olival et al. 2017), and their occurrence has quadrupled over the past fifty years (Smith et al. 2014) due to habitat destruction and fragmentation (Acevedo-Whitehouse & Duffus 2009), which results in increased contact between humans and wildlife and potentially infectious pathogens. While further research is required to fully understand how to best prevent the spillover of pathogens to humans, TiME believes that the reduction of habitat loss can significantly diminish the likelihood of future pandemics.

Habitat destruction increases human vulnerability to pandemics

Habitat destruction and fragmentation around the world is occurring at an astonishing rate (Haddad et al 2015). Forests are among those ecosystems that are particularly hard hit. According to the Global Forest Watch initiative of the World Resource Institute (WRI), on average a forest the size of a football field is lost every two seconds (WRI, 2019). More importantly, most forest destruction is uncoordinated, such that the resulting patches of degraded, fragmented forest threaten the ability of species to survive. As a result, species’ genetic pools are split into small fragments, or genetic puddles. These puddles can become breeding grounds for pathogens, such as SARS-CoV-2, which can infect humans who come into close contact with the pathogen-carrier.

Fragmented habitats also favor and support species that are considered generalists (Devictor et al 2008). Generalists can thrive in disturbed lands, whereas specialists (often rare and endangered species, dependent on specific habitats) often do not survive, becoming either locally or globally extinct. A decrease in the total diversity of species within a specific area may also interfere with the “dilution effect” of a broader population that helps reduce opportunities for pathogens to infect hosts (Civitello et al 2015). Many pathogens thrive only in specific species (“competent hosts”), whereas other species may serve as “incompetent hosts,” harboring the pathogen but not allowing for its proliferation. As a result, a fragmented land left with only — or mostly — competent hosts, enables the pathogens to survive and develop (Chivan & Bernstein 2008). Many generalist species, such as rodents and bats, thrive along the borders between human and natural habitats and often carry the pathogens that can spill over.

Pathogen spillover threats

viruses cause in humans are classified as zoonotic

Spillover is a dynamic process, as pathogens mutate and adapt to fill new niches. The evolution of pathogens in fragmented landscapes often amplifies spillover. In a study published last year, Zohdy and her colleagues (2019) suggested a co-evolution effect that explains pathogen spillover: Increased habitat isolation allows the hosts, the parasites that survive only in these hosts, and the pathogens to co-evolve within each fragment. Thus, multiple fragments increase the general genetic diversity of pathogens across the landscape and increase the likelihood that a pathogen with zoonotic potential will evolve and spill over into a human community.

Habitat destruction also leads to increased human activity on those degraded lands, such as hunting and capturing wildlife for food. Bringing infected wildlife to markets in population centers lowers the dependency of pathogen transmission on additional agents (mosquitoes or ticks, for example), thereby cutting short the chain of pathogen transfer, and expediting spillover. In 2007, a group of researchers warned that such “wet markets” constituted a threat to human health (Cheng et al 2007). Scientists now believe that Covid-19 arose in the wet market of Wuhan, China, where wild-caught terrestrial and marine species are slaughtered for food.

Join the TiME community and become a member today

The increasing frequency of pandemic outbreaks require us — now more than ever — to increase efforts to halt habitat destruction and fragmentation. To address these challenges, TiME was established in 2015 to protect biodiversity hotspots around the world. Our non-profit organization is unique in its approach to biodiversity and habitat protection: TiME enables people of all ages, from every corner of the world, to support our mission. For as little as $1, members of our community can participate in biodiversity protection and restoration. TiME members vote online to select the habitats that we purchase and protect in a fully transparent process.

At a time when hundreds of millions of people are in quarantine and sheltering-in-place, TiME offers hope and action as an alternative to retreat and helplessness. Hiding in our homes will not help us solve the problem in the long term. To help prevent future pandemics, we need to engage and work to protect, preserve, and restore the integrity of critical ecosystems around the world.