In the past half-century, the global production of meat has undergone a seismic shift. While meat was once mostly raised on small farms, today almost all the meat we eat comes from industrialized “factory” farms, known as “concentrated animal feeding operations,” or CAFOs. More than 90 percent of the world’s meat supply comes from CAFOs. And in the US, that figure is closer to 99 percent.

Animals in CAFOs are often packed closely together, which makes the facilities efficient and, for many, ethically dubious. There are also environmental concerns around these industrial farms. But infectious disease experts worry about CAFOs for a different reason: They’re an ideal environment for virus and bacteria mutations that human immune systems have never seen. In other words, they’re a highly likely source for the next pandemic.

Watch the video above to learn how humans have created the ideal environment for pandemic-causing pathogens.

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