One of the dire consequences of factory farming is that it encourages the spread of disease due to the close quarters in which the animals live. Thats why theyre fed antibiotics and other medicines when they arent sick. This overuse of antibiotics, while beneficial to the flocks and herds in the short term, leads to stronger and more drug-resistant bacteria in the long term. The effect has been widely reported by popular authors like Michael Pollan and Eric Schlosser. What we havent heard much about are how viruses can thrive in this environment.