Tropical Areas Concentrate the Risks of Animal-to-Human Disease Transmission

The massive transformation of land on a global scale is profoundly altering interactions between humans and their environment, thereby fostering the emergence of major health risks. Among these, the transmission of pathogens from animals to humans, known as zoonotic spillover, represents a growing threat. This phenomenon occurs when infectious agents cross the species barrier, often due to the destruction of natural habitats and the expansion of agricultural areas.

Tropical regions, particularly Southeast Asia, Latin America, Africa, and to a lesser extent Eastern Europe, are the most affected by this issue. These areas host a significant portion of large-scale land transactions, where vast expanses of land are acquired for intensive agriculture, biofuel production, or livestock farming. These changes in land use disrupt ecosystems and increase contact between humans, wildlife, and domestic animals.

Passerine birds, bats, and rodents play a key role in this process. These species, often tolerant to environmental disturbances, thrive in human-modified landscapes, such as agricultural lands. They serve as natural reservoirs for numerous pathogens capable of infecting humans. When their habitats are fragmented or destroyed, these animals move closer to inhabited areas, multiplying opportunities for disease transmission.

The data reveal that high-risk areas for zoonotic spillover are characterized by large expanses of still-intact forests, as well as low population density and few roads. This is because these regions, although sparsely urbanized, are undergoing rapid changes in their vegetation cover, creating interfaces between natural environments and cultivated areas. However, there are exceptions: in Ghana, Nigeria, Malawi, Brazil, and Indonesia, high-risk areas combine both high human population density and a developed road network, which exacerbates the potential for disease spread once a pathogen is transmitted to humans.

Land investments are not solely transnational. More than one-third of transactions involve local actors, and an additional 17% occur within the same region. The main investment flows come from countries such as China, the United States, Malaysia, or the Netherlands, which often target biodiversity-rich areas. In Southeast Asia, for example, Chinese investments are concentrated in regions like Indonesia or Myanmar, where the diversity of pathogen reservoir species is particularly high.

The countries most affected by these dynamics are Brazil and Indonesia, which combine vast acquired land areas and a high presence of disease-carrying species. In contrast, countries like Russia or Ukraine, despite receiving significant investments, have a lower risk of spillover due to a lower diversity of reservoir species and a smaller proportion of natural land converted.

To mitigate these risks, it is essential to rethink current agricultural models, which are often based on the chemical and mechanical intensification of crops. Alternatives exist, such as agroecology, which promotes more diverse and resilient landscapes, thereby reducing opportunities for contact between humans and wild animals. Maintaining the ecological integrity of habitats—that is, their connectivity and natural state—helps strengthen what scientists call landscape immunity: a concept referring to the ability of ecosystems to limit pathogen spread through their complexity and balance.

Governments and investors must integrate these issues into their decision-making. This involves systematically evaluating land projects by cross-referencing data on local biodiversity and areas of land conversion. Precautionary measures, such as preserving portions of natural land within agricultural projects or implementing biosafety protocols for local communities, could mitigate risks. International coordination is also necessary, as cross-border investments link geographically distant actors whose actions have local repercussions.

Lessons from the past, such as the Ebola epidemics in Africa or Nipah in Asia, show that reactive responses are often too slow. Pathogens can circulate for weeks before being detected, as was the case with Ebola. A proactive approach, combining ecological surveillance, land-use planning, and cross-sectoral cooperation, is therefore essential to anticipate and prevent the next health crises.

Credits and Attributions

Primary Source

DOI: https://doi.org/10.1038/s44458-026-00102-1

Title: Global land rush concentrates potential zoonotic spillover risk in the tropics

Journal: Communications Sustainability

Publisher: Springer Science and Business Media LLC

Authors: Chuan Liao; Seongmin Shin; Katie Rohrbaugh; Nabin Pradhan; Elizabeth Ludwig; Zhenci Xu; Manuel Ruiz-Aravena; Shuai Zhou; Arun Agrawal