The research focused on two broad categories of pathogens that dominate concerns about emerging infections. The first are zoonotic diseases, those that spill over directly from animals into human populations, a group that includes some of the most feared pandemic threats of the modern era, such as coronaviruses, Ebola and mpox. The second are vector-borne diseases, which are transmitted to humans through the bites of infected mosquitoes, ticks and fleas, and which include major public health burdens such as dengue, Lyme disease and malaria. By analysing outbreak records for both groups at a global scale, the researchers hoped to identify whether a common set of environmental conditions underlies the well-documented rise in emerging infectious diseases over recent decades.

What they found was a clear anthropogenic fingerprint on the global geography of disease emergence, but one whose details differ sharply between disease types. For outbreaks overall, risk was generally higher in places where people and their livestock live in close proximity to highly fragmented forested ecosystems. Fragmentation, in this context, describes a familiar pattern of landscape change: a once-contiguous forest carved into many smaller woodlands, separated by farms, roads and human settlements. These patchwork landscapes tend to favour certain animal species that thrive at the edges between wild and human-dominated terrain, and many of those resilient species are more likely to carry pathogens. At the same time, people living in or near these fragmented habitats are more likely to encounter the animals, creating more opportunities for pathogens to make the jump into human populations.

For vector-borne diseases in particular, the evidence of human influence was especially clear. The analysis showed increased risks of outbreaks of diseases such as dengue and Zika in areas with fragmented ecosystems, and also in regions experiencing long-term declines in rainfall attributable to climate change. This connection between shifting precipitation patterns and mosquito-borne disease risk adds to a growing body of concern among public health researchers, because rainfall shapes the availability of the standing water that mosquitoes need to breed, and changing climate conditions can expand the geographic range and seasonal activity of vector species. The finding suggests that as climate change alters rainfall regimes across the tropics and subtropics, the threat from diseases like dengue and Zika may continue to grow in ways that are directly traceable to human activity.

Yet the picture for zoonotic infections proved far more complicated, and this complexity may be the study’s most consequential finding. For diseases that spill over directly from animals to people, including many of the pathogens considered the greatest pandemic threats, the researchers found no environmental factors that consistently helped to predict where outbreaks occur. The effects of deforestation, climate warming and agricultural intensification varied considerably from one disease to another, defying any attempt to draw a single map of global spillover risk. This variability challenges a widespread assumption that a common set of environmental drivers, such as forest loss or warming temperatures, lies behind the rise of emerging infectious diseases as a whole. Instead, the authors argue, meaningful progress will require disease-specific and region-specific data to monitor potential outbreak risks, an approach that is more demanding but far better matched to the messy reality of how pathogens actually move between animals and humans.

Lead author Dr Rory Gibb of the UCL People and Nature Lab emphasised this point in comments accompanying the release. Our findings show that no single environmental recipe can predict where emerging infectious disease outbreaks will occur, he said. Disease transmission from animals to people is common in human-modified habitats worldwide, but the exact human activities that drive outbreaks differ between diseases. He added that this variability makes it critically important to improve people’s access to healthcare and to strengthen disease monitoring systems, so that outbreaks of any disease can be detected early and stopped before they escalate into epidemics or pandemics. In other words, rather than betting on a predictive map of the next spillover, the safest strategy is to build systems capable of catching outbreaks wherever they arise.

One of the study’s most striking and potentially policy-changing results concerns not where outbreaks happen, but where they are noticed. The researchers found that the odds of an emerging disease outbreak being reported fell by an average of 32 percent for every additional hour of travel to the nearest healthcare facility. This finding demonstrates the critical role that healthcare access plays in determining where outbreaks are detected, and it carries an uncomfortable implication for how the world has understood disease emergence. Many of the apparent hotspots highlighted in previous global analyses may reflect less about where infections actually occur and more about where disease surveillance and healthcare systems are currently strongest. Regions with poor healthcare access, often the very places where ecological change is rapid, may be silently absorbing outbreaks that never enter the global record, leaving the international community with a distorted picture of the true geography of risk.

Co-author Professor Sadie Ryan of the University of Florida framed the broader lesson as a call for integration. Spillover disease outbreaks are multi-causal, shaped by the socioecological system, she said, adding that this really highlights the need for One Health integrated approaches to surveillance and intervention, because there is no single intervention strategy. The One Health framework, which recognises that the health of humans, animals and ecosystems are inseparably linked, has gained momentum in global health circles in recent years, and this study provides some of the strongest quantitative support yet for that perspective. If the drivers of emergence differ from disease to disease, then prevention cannot rely on any single lever, whether forest conservation, vaccination, or mosquito control alone, but must instead combine interventions tailored to local ecological and social conditions.

The authors of the Nature paper accordingly call for a more proactive and holistic approach to preventing epidemics and pandemics, one that combines the strengthening of health systems, global coordination of disease surveillance, and ecosystem-based interventions targeted at the most important diseases. Such an agenda would represent a significant shift from the reactive posture that has characterised much of the world’s response to emerging infections, in which resources flood toward a pathogen only after it has already caused a crisis. The study team was led by scientists at UCL, the University of Florida and Yale University, and the research was supported by a US National Science Foundation Biology Integration Institute grant to the Verena Institute, reflecting the interdisciplinary effort required to link ecology, climatology and epidemiology at a global scale.

As human populations continue to expand into fragmented habitats and climate change redraws the maps of rainfall and temperature, the pressures documented in this study are set to intensify. The research does not offer the comfort of a simple predictive rule, but it offers something arguably more valuable: a realistic account of how human activity shapes disease emergence, an honest accounting of the blind spots created by unequal healthcare access, and a clear argument that early detection and strong health systems are the most reliable defence available. In an era when the next outbreak may come from any of dozens of pathways, that message, that vigilance must be broad, locally informed and globally coordinated, may prove to be the study’s most enduring contribution to global public health.

Subject of Research: Environmental drivers of emerging zoonotic and vector-borne infectious disease outbreaks

Article Title: How human impacts increase risk of emerging infectious disease outbreaks

Article References: How human impacts increase risk of emerging infectious disease outbreaks. (n.d.). Original publication

Image Credits: AI Generated

DOI: Not provided

Keywords: emerging infectious diseases, zoonotic spillover, vector-borne disease, deforestation, ecosystem fragmentation, climate change, dengue, disease surveillance, One Health, healthcare access, Nature, global health