Preventing Viral Zoonotic Spillover Events


The STOP Spillover project is aiming to prevent remerging infectious disease outbreaks.

The emergence of zoonotic spillover events that develop into human infectious disease is a significant health issue. More than two-thirds of human viruses are zoonotic.1

There have been a number of zoonotic diseases such as Ebola virus, rabies, Zika virus, African swine fever, and severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) that have emerged into people through an intricate and complex biological process known as spillover.2 And although not proven definitively, the ongoing leading theory on how COVID-19 emerged was due to a zoonotic spillover event.

Zoonotic spillover is determined by interactions among several factors, including disease dynamics in the reservoir host, pathogen exposure, and the human factors that affect susceptibility to infections.3

In response to the COVID-19 pandemic as well as the potential of other spillover events, the United States Agency for International Development (USAID) announced the launch of the Strategies to Prevent Spillover (STOP Spillover) project in September 2020. It is designed to be a five-year, $100 million project to anticipate and address threats posed by viral zoonotic diseases.

Tufts University is leading the STOP Spillover project, along with a consortium of wildlife and human-disease experts including: AFROHUN, SEAOHUN, Bangladesh (ICDDR,B), Right Track Africa, JSI Research & Training Institute, Tetra Tech, University of Washington Institute for Risk Analysis and Risk Communication, University of Glasgow Institute of Biodiversity, Animal Health and Comparative Medicine, University of California, Los Angeles, the Broad Institute of MIT and Harvard, University of Nebraska Medical Center, Humanitarian OpenStreetMap Team, and Internews.

The consortium is trying to reduce future outbreaks from known zoonotic viruses by having partners on the ground in various parts of the world to monitor, analyze, and characterize the risk of priority zoonotic viruses spilling over from animals to people.

STOP Spillover is in 5 countries including Uganda, Liberia, Cambodia, Bangladesh, and Vietnam with the long-term goal to be in 10 countries across Asia and Africa, explains STOP Spillover Project Director Deborah Kochevar, DVM, PhD.

An important distinction in this project is that it is not only monitoring for outbreaks, but will create actionable interventions in those vulnerable areas that can prevent or reduce potential outbreaks.

“A really important starting point is to speak to the stakeholders who live in the highest risk areas, places where interfaces between animals and humans are most likely to yield spillover,” Kochevar, said. “Our project focuses on empowering stakeholders, asking them where they think the interventions would be most effective, and then assisting in bringing expertise and working together to put in place interventions and assess them.”

Kochevar spoke to Contagion recently about the consortium’s aims, the specific families of viruses they will be observing, and the importance of understanding and mitigating risks in potential spillovers.


1. Woolhouse M, Scott F, Hudson Z, Howey R, Chase-Topping M. Human viruses: discovery and emergence. Phil. Trans. R. Soc. B (2012) 367, 2864–2871

2. Rohde R, McNamara R. Virus spillover and emerging pathogens pick up speed. Contagion. 2021; 6 (2): 1, 12-13

3. Plowright, R., Parrish, C., McCallum, H. et al. Pathways to zoonotic spillover. Nat Rev Microbiol 15, 502–510 (2017).

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