In 1872 the U.S. economy was growing as the young nation industrialized and expanded westward. Then in the autumn, a sudden shock paralyzed social and economic life. It was an energy crisis of sorts, but not a shortage of fossil fuels. Rather, the cause was a virus that spread among horses and mules from Canada to Central America.
Click here for original story, How a flu virus shut down the US economy in 1872—by infecting horses
Source: Phys.org