Understanding Spillover: How Viruses Go from Wildlife to Livestock to Humans
Incautious farming practices and changes in natural habitats play a crucial role in species barriers’ crossing, with viruses potentially transmitted from wildlife to livestock to, sometimes, humans. How does the spillover work exactly? And how to prevent it?
The transmission of viruses from wildlife to domestic animals, known as spillover, is a concern for both animal and public health. Many emerging infectious diseases originate in wild species and can reach humans through intermediate hosts such as livestock, especially in areas where farming systems and wildlife habitats overlap.
Spillover is often favoured by a combination of ecological and human-driven factors: changes in land use, agricultural intensification, high animal densities, and insufficient biosecurity measures in livestock. When wild animals are attracted to farms by food resources, insects, or shelter, opportunities for indirect contact increase, creating pathways for pathogens to cross species barriers.
In this context, the recent study “A multi-disciplinary approach to identify spillover interfaces of bat coronaviruses to pig farms in Italy”(1), published by Istituto Zooprofilattico Sperimentale delle Venezie, investigates the potential risk of coronavirus spillover from bats to pigs in intensive farms in Northern Italy. Bats host a large diversity of viruses, including many coronaviruses, often showing no evident signs of disease. While several bat species are suffering the Anthropocene, few are thriving by taking advantage of human activities for food and sheltering. By combining ecological monitoring, landscape analysis and molecular virology, the researchers showed that pig farms from northern Italy provide a feeding ground and a shelter for several bat species. By using bat richness to infer viral diversity, the study estimated that eight CoVs potentially circulate in this setting, among which two were detected frequently. In turn, the study expresses challenges and opportunities at the interface between wild and domestic species. On one side, farms allow endangered species to survive in highly altered rural ecosystems; on the other side, the proximity of wildlife to animal productions pose a risk for the spillover of microorganisms. In this context, the study suggests that the implementation of physical barriers hampering the entrance of bats and bats’ dropping to animal shelters, currently rare in these settings, could allow bats to exploit farms’ resources while mitigating the risk for swine to be exposed to their viruses.
The spillover mechanism underlines even more the importance of adopting a One Health approach, fostered and promoted by the EU-funded project PAIR in pandemic prevention.
The PAIR project is indeed integrating veterinary science, human medicine, and environmental studies to analyse spillover events and strengthen preparedness against future emerging epidemics.
Both the pioneering technologies developed by the project help navigate in this direction. PANPOC, the portable point-of care system to detect RNA viruses, allows early detection in human and animal samples, and PANRISK, the platform based on a spillover and epidemiological model, facilitates data crossing, raising an alarm when viruses exceed the appropriate threshold.
Understanding when and how wildlife viruses may reach domestic animals and having highly technological tools to be used under the holistic One Health approach is therefore essential for preventing future outbreaks.
Learn more about the PAIR project: https://pairproject.eu/
With the collaboration of Istituto Zooprofilattico Sperimentale delle Venezie and University of Copenhagen, Department of Veterinary and Animal Sciences
(1) Festa F, Priori P, Chiarello G, Palumbo E, Zamperin G, Cosentino F, et al. (2025) A multi-disciplinary approach to identify spillover interfaces of bat coronaviruses to pig farms in Italy. PLoS One 20(10): e0332117. https://doi.org/10.1371/journal.pone.0332117
