Mink, like humans, often die from infection with the virus, and no one knows why. “This is a key thing,” said Dr. Perlman. “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 involved in their genetic diversity and the lack of an established set of biochemical tools to study infections in them made the prospect difficult.
Some parts of the mink puzzle fit together easily. They live in overcrowded conditions in rows of cages on mink farms, just like people in cities, and are in constant contact with the people who take care of them. No surprise, as they not only caught the virus from humans, they sent it back to us.
And the infection of mink and the potential danger they pose is a reminder that it is not only wild animals that are the cause of overflow events. The livestock people who are close by have always given diseases to humans and acquired diseases from them. But it required large human settlements for epidemics and pandemics to emerge.
In a 2007 article in the journal Nature, several infectious disease experts – including Jared Diamond, author of “Guns, Germs and Steel: The Fate of Human Societies” – wrote about the origins of diseases that spread only in relatively dense populations . Measles, rubella and pertussis, they wrote, are examples of human diseases that need populations of hundreds of thousands for a sustained spread. Human groups of that size first appeared before agriculture came about 11,000 years ago.
The authors mentioned eight diseases in temperate regions that spread to humans from domestic animals: “diphtheria, influenza A, measles, mumps, pertussis, rotavirus, smallpox, tuberculosis.” In the tropics, several diseases came from wild animals for various reasons, the authors wrote.
Diseases move from wild animals to farmed animals and then to humans. Influenza viruses jump from wild waterfowl to domestic birds and sometimes to pigs and then to humans who are in close contact with the farmed creatures. As with mink, viruses continue to mutate in other animals.
There may even have been a previous coronavirus epidemic that came from cattle. Some researchers have speculated that one of the coronaviruses now causing the common cold, OC43, may have been responsible for the 1889 flu epidemic that killed one million people.