How does losing biodiversity actually make zoonotic diseases more likely?
The key mechanism is called the 'dilution effect.' In a healthy, diverse ecosystem, many different animal species are present, but only a few of them are good at carrying and transmitting a particular pathogen to humans. When biodiversity is high, these 'reservoir hosts' are diluted by many other species that are poor hosts, which reduces the chance that a pathogen will spill over into people [4][5]. A 2021 review explains that in less-disturbed areas, non-reservoir species predominate, keeping pathogen transmission low [5].
When biodiversity is lost—through deforestation, urbanization, or intensive farming—the species that tend to disappear first are often the poor hosts. Meanwhile, the animals that thrive in human-dominated landscapes, like rats, certain bats, and some primates, are often the very species that carry zoonotic pathogens [5]. This shift increases both the abundance of reservoir hosts and the frequency of human contact with them, directly raising spillover risk. For example, a study in Uganda found that 29% of people living near forest fragments hunted wildlife like chimpanzees, and 45.8% hunted cane rats, creating direct pathways for pathogen transmission [2].
How strong is the link between biodiversity loss and disease outbreaks?
The evidence is strong and comes from multiple angles. A 2025 survey of 172 health professionals in Nigeria identified biodiversity loss as a major driver of zoonotic disease emergence, with an odds ratio of 8.27—meaning it made the emergence of new zoonotic diseases more than eight times more likely, after accounting for other factors like urbanization and climate change [1]. This is a very large effect, comparable to or larger than other well-known drivers like intensive livestock farming (odds ratio 6.86) or international travel (6.14) [1].
At a global scale, a 2021 study analyzing outbreaks from 1990 to 2016 found that increases in zoonotic and vector-borne disease outbreaks were linked to deforestation, especially in tropical countries [3]. The same study also found that reforestation in temperate regions and the expansion of oil palm plantations were associated with more outbreaks, suggesting that any major change in land cover—not just loss—can disrupt ecosystems and increase risk [3]. Another 2021 review concluded that biodiversity loss appears to increase the risk of human exposure to both new and established zoonotic pathogens, reconciling earlier conflicting views [5].
Can restoring biodiversity reduce the risk?
Yes, restoring biodiversity is considered an important strategy for managing zoonotic disease risk. The same mechanisms that make intact ecosystems protective—the dilution effect—can be rebuilt by conserving and restoring natural habitats [4][5]. A 2023 review notes that higher biodiversity markedly reduces pathogen transmission rates, lowering the risk of spillover events [4]. This means that protecting forests, wetlands, and other natural areas isn't just good for wildlife—it's a direct investment in human health.
However, restoration must be done carefully. A 2021 global study found that reforestation in temperate countries was also linked to increased outbreaks, likely because newly planted forests can create new interfaces between wildlife and humans if not managed properly [3]. The key is to restore ecosystems in a way that maintains high species diversity and minimizes human encroachment. Experts recommend a 'One Health' approach that integrates human, animal, and environmental health, with strong surveillance and public education to reduce risky behaviors like hunting and bushmeat consumption [1][2].
Sources used in this answer
Perceptions and knowledge of frontline health workers on emerging zoonotic diseases in Nigeria
A 2025 survey of 172 health professionals in Nigeria found that biodiversity loss was a major driver of zoonotic disease emergence, with an odds ratio of 8.27 (95% CI: 2.87–23.81), meaning it made outbreaks more than eight times more likely.
A descriptive study of zoonotic disease risk at the human-wildlife interface in a biodiversity hot spot in South Western Uganda
A 2021 study in Uganda found that 29% of 370 respondents hunted wildlife like chimpanzees and 45.8% hunted cane rats, creating direct pathways for zoonotic spillover, though only 37% were aware of disease risks.
Outbreaks of Vector-Borne and Zoonotic Diseases Are Associated With Changes in Forest Cover and Oil Palm Expansion at Global Scale
A 2021 global analysis of outbreaks from 1990 to 2016 found that increases in zoonotic and vector-borne disease outbreaks were linked to deforestation in tropical countries and to reforestation and oil palm expansion in temperate regions.
The Link between Biodiversity Degradation and Zoonotic Diseases
A 2023 review explains that higher biodiversity reduces pathogen transmission through the 'dilution effect,' and that anthropogenic degradation of biodiversity increases spillover risk.
Impacts of biodiversity and biodiversity loss on zoonotic diseases
A 2021 review synthesizes evidence that biodiversity loss increases zoonotic risk because reservoir hosts proliferate in human-dominated landscapes while non-reservoirs decline, and recommends restoring biodiversity to manage disease risk.