Geographical and Ecological Drivers of Zoonotic Viral Spillover: A Review of Emerging and Re-emerging Outbreaks

Over the past two decades, outbreaks of zoonotic viruses have become increasingly frequent and severe, posing substantial threats to public health systems and the global economy. The viruses responsible for these outbreaks, such as SARS-CoV, MERS-CoV, Zika, Ebola, Nipah, avian influenza, and, most recently, SARS-CoV-2, typically originate in wildlife, highlighting the complex relationship between ecological systems and human activities. Human-wildlife interactions have markedly increased due to disruptions in environmental and geographic boundaries, primarily driven by urbanization, deforestation, intensified agricultural practices, and climate change. These factors contribute to an environment that facilitates zoonotic transmission spillover. This narrative review summarizes current research on the ecological, geographic, and human factors influencing zoonotic virus transmissions. It emphasizes how these viruses adapt to human hosts and cross species barriers via direct contact, vector-borne transmission, intermediate carriers, and environmental contamination. Moreover, the review discusses how the genomic plasticity of viruses enhances their transmissibility and facilitates adaptation to new hosts, thereby increasing the risk of epidemics and pandemics. The review further underscores the importance of ecological boundaries in mitigating spillover events and advocates for a One Health approach that integrates human, animal, and environmental health. This approach is essential for predicting, detecting, and preventing future outbreaks. In conclusion, the review emphasizes the importance of interdisciplinary research, proactive surveillance, habitat preservation, and policy interventions that address the underlying ecological factors contributing to zoonotic outbreaks. Restoring ecological barriers and implementing sustainable practices to minimize the interaction between wildlife and humans, while bolstering global biosecurity, are essential measures to mitigate the risk of future pandemics.