Spillover: Animal Infections and the Next Human Pandemic

The narrative opens with a description of Hendra virus, which was discovered in Western Australia. Though the disease infected very few people, and mostly harmed horses, the outbreak occurred suddenly and is a useful illustration of how diseases emerge, especially a phenomenon known as zoonosis: “an animal infection transmissible to humans” (14). Many well-known diseases, like AIDS and flu, belong in this category, and the phenomenon reminds us that human societies are closely connected to those of the animals around them.

The Hendra virus outbreak began in 1994, when racehorses in a Melbourne suburb of the same name became ill in large numbers. The first was a mayor named Drama Series, but many others became sick afterward, as did the horse’s human owner, who died. A stable hand survived and was never hospitalized. Necropsies (animal autopsies) revealed a new virus, unrelated to any known diseases. The researchers next had to determine where the virus typically resided—outside of horses and people—and how it was transmitted. When Quammen visited Melbourne, his guide showed him a fig tree in the horse’s pasture, where bats liked to roost. The bats were significant because diseases, like plants or people, have typical or preferred habitats.