There are just under 6,000 species of mammals. Around 500 may carry bacteria or viruses with the potential to cause human disease. The Plague, or Black Death, was transmitted from rats to people by flees. In Medieval Europe 25 million people may have died. It was the density of population and the lack of sewage that drove the rat population in ancient cities, and hence the plague. Globally, the Black Death may have killed 200 million.
Often, human beings have to do rather stupid things to facilitate diseases jumping from other mammals to people. Bush Meat markets are found in many parts of Africa. I have seen a variety of parts from wild animals for sale, including pangolins and chimpanzees. Pangolins are nocturnal ant eaters, and the only mammals with scales.
Thirty years ago, my African host in Chad asked it I wanted lunch in the African or French restaurant. I thought it polite to say African. Mistake! The menu was civet cat or a pangolin. I knew what a civet cat was so I ended up eating pangolin. Yes, you eat the scales. Millions of pangolins are exported to Vietnam and China where they are regarded as exotic foods. They can carry Covid-19.
A plausible origin for HIV/AIDs is that several decades ago someone was butchering a chimp for sale in a bush meat market. It was carrying the AIDS virus, The butcher cut themselves, becoming the first case of human HIV/AIDS infection. One person gave the disease to their sexual partner(s). Ultimately 30 million people were to die as the result of this single accident.
Occasionally, people do the right thing. In 1665, a tailor in Eyam, in central England, received a roll of cloth from London. He saw it carried some flees. The two village clergy understood how the infection spread. They replaced the Sunday services with a “socially distanced” congregation in a field.
The village boundary was defined and not one of the 800 population was allowed to enter or leave Eyam. They paid for food from their neighbors by dropping coins into vinegar. For all of two years, the village self-quarantined themselves. 260 members of the population died.
The plague was a horrible way to die. The self-control of this seventeenth century, often illiterate, population was remarkable. They were watching neighbors and family members die for two years. But no one broke ranks and tried to leave Eyam.
Those today who refuse to wear masks or deny the protection of vaccination might pause to learn from the brave, self-sacrificing villagers of Eyam four centuries ago.