Mink, like people, often die from infection with the virus, and nobody knows why. “This is a key thing,” Dr. Perlman said. “Why do people get sick? Why do we react so differently to these viruses.” He said he had thought about studying mink, but the challenges, involving their genetic diversity and the lack of an established set of biochemical tools for studying infections in them, made the prospect difficult.
Some parts of the mink puzzle fit easily together. They live in crowded conditions in rows of cages on mink farms, like people in cities, and are in constant contact with the humans who care for them. No surprise then, that they not only caught the virus from people, they passed it back to us.
And the infection of mink and the potential danger they pose is a reminder that it isn’t only wild animals that are the cause of spillover events. The livestock humans housed in close quarters have always given diseases to humans, and acquired diseases from them. But it required big human settlements for epidemics and pandemics to appear.
In a 2007 paper in the journal Nature, several infectious disease experts — including Jared Diamond, the author of “Guns, Germs and Steel: The Fate of Human Societies” — wrote about the origins of diseases that spread only in relatively dense human populations. Measles, rubella and pertussis, they wrote, are examples of crowd diseases that need populations of several hundred thousand for a sustained spread. Human groups of that size did not appear until the advent of agriculture, around 11,000 years ago.
The authors listed eight diseases of temperate regions that jumped to humans from domestic animals: “diphtheria, influenza A, measles, mumps, pertussis, rotavirus, smallpox, tuberculosis.” In the tropics, more diseases came from wild animals, for a variety of reasons, the authors wrote.
Diseases move from wild animals to farmed animals and then to people. Influenza viruses jump from wild waterfowl to domestic birds and sometimes to pigs and then to people who are in close contact with the farmed creatures. As occurred with the mink, the viruses continue to mutate in other animals.
There may have even been an earlier coronavirus epidemic that came from cattle. Some scientists have speculated that one of the coronaviruses that now causes the common cold, OC43, may have been responsible for the flu epidemic of 1889, which killed a million people.