The hearts of the world’s oldest and most intact forests are the global centers of evolution and biological diversity, and most of this diversity is unknown and microscopic. To a biologist, these “primary forests” are natural cathedrals that still contain untold numbers of undiscovered species. To an epidemiologist, they contain a primordial soup of novel and dangerous pathogens. Biological diversity does not only refer to the cutest or most charismatic of creatures.
These places, which we value for their inherent cultural, medicinal, and economic benefits also contain millions of undescribed microbial species—and this is a good thing since some of our most potent antibiotics come from these areas too. With so many bacteria and viruses in one place, they must compete against each other for resources, and it is this diversity itself that prevents outbreaks of the more harmful of the lot. It is often when natural diversity is lost, or these pathogens encounter new hosts in livestock or people as their ecosystems are disturbed, that some of them escape and harm people.
The emergence and spread of pathogens from these places and into people can be separated into three distinct risk components¹:
- Risk 1 (Hazard): Are animals sick or dying from disease and where?
- Risk 2 (Exposure): Is there more contact between people and wildlife leading to increased exposure to new pathogens?
- Risk 3 (Susceptibility): Are there types of animals whose pathogens can transfer to humans more easily or human situations that weaken immune systems?
Forest loss and degradation already pose a significant threat to global health, climate, security, and economic growth. Research also shows that the emergence of novel disease is elevated in tropical, biodiverse, and historically forested regions that are experiencing land-use changes.² As landscapes are changed and natural areas are destroyed, degraded, and repurposed for people, these pressures heighten each of the elements of risk:
- Wildlife with degraded habitats tend to crowd into forest or habitat fragments with more individuals. This higher relative population density is a hazard that increases disease among individuals in wildlife populations.
- As land is deforested and degraded, more people exist in areas that expose them to diseased animal populations or the vectors of those diseases, like mosquitos. These communities are often in remote areas opened by new roads and rely on hunting for sustenance.
- The susceptibility of people to infections from other animals increases, both because common disease vectors, such as rodents, bats, and livestock, tend to survive well in the presence of people, and because a community’s susceptibility to the spread of pathogens and mortality from disease is further amplified by many of the impacts of deforestation and environmental degradation—poverty, malnutrition, respiratory illness, and poor water and air quality.
Scientists have long raised concerns about the conditions that increasingly enable outbreaks of diseases like COVID-19. Mitigating the risk of another novel coronavirus will require concerted efforts to connect the conservation and public health disciplines, and to conserve and restore forest intactness and understand how land-use planning, particularly road building and infrastructure, can maintain nature’s disease regulation. Until the conditions that align these three mechanisms of emergent infectious disease risk are addressed, a point outlined well by WWF-US’ CEO Carter Roberts, we’ll need to start preparing for the next pandemic now.
¹ Hosseini, P.R., Mills, J.N., Prieur-Richard, A.-H., Ezenwa, V.O., Bailly, X., Rizzoli, A., et al. (2017). Does the impact of biodiversity differ between emerging and endemic pathogens? The need to separate the concepts of hazard and risk. Philosophical Transactions of the Royal Society B: Biological Sciences, 372, 20160129. https://doi.org/10.1098/rstb.2016.0129
² Allen, T., Murray, K.A., Zambrana-Torrelio, C., Morse, S.S., Rondinini, C., Marco, M.D., et al. (2017). Global hotspots and correlates of emerging zoonotic diseases. Nat Commun, 8, 1–10. https://doi.org/10.1038/s41467-017-00923-8