The New Yorker:

Most new diseases have their origins in animals. So why aren’t we paying more attention to their health?

By Rivka Galchen

In the summer of 1999, a pathologist at the Bronx Zoo noticed an unusual number of dead crows in the vicinity of the zoo. Then, over Labor Day weekend, one of the zoo’s cormorants died, as did a pheasant, a bald eagle, and three flamingos. In Queens, physicians at Flushing Hospital saw six patients with encephalitis, all within a few weeks. Normally the city saw about ten cases a year, but now similar cases were turning up across the city. The disease presentation suggested a viral cause—but which virus? By the end of September, seven human patients had died, and others had had to be hospitalized for weeks. After the virus was identified as West Nile—a mosquito-borne virus that infects both birds and humans, and which no one expected to see in North America—the dead crows suddenly made sense. “I think it was really the West Nile virus that was the impetus for recognizing the value of having veterinarians work in public-health departments,” Sally Slavinski, a veterinarian at New York City’s Department of Health and Mental Hygiene, told me.

Slavinski focusses on zoonotic diseases—infectious diseases that can move from an animal to a human. Diseases cross over very rarely, with less than a tenth of one per cent of animal viruses ever successfully making the leap. And yet from another perspective the crossovers are common: more than two-thirds of emerging diseases in humans have animal origins. Diseases can also travel in the other direction, in what is called reverse zoonosis. “I’ll never forget the call from my colleague at the Bronx Zoo saying they had a tiger testing positive for sars-CoV-2,” Slavinski said. Her office worked on contact tracing for the big cats. She also does a lot of work with less regal urban friends, such as skunks, bats, and raccoons—“They’ve adapted incredibly well to urban life,” she said—which often means dealing with rabies, perhaps the only zoonotic disease so storied as to have its own adjective. Canine rabies was eliminated from the United States in 2004, but the disease persists in other animals. Slavinski recalled the 2009 outbreak of raccoon rabies in Central Park, in which some five hundred raccoons needed to be trapped, vaccinated, and released.

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