How do diseases like AIDS and HIV form? Why after thousands of years did it only show up in the 20th century?
In: Biology
A virus usually infects a particular host species of animal, but viruses can and often do jump from their primary host species to a new one. When a virus jumps to a brand new host species, that is called a “spill-over event”.
HIV was originally a virus that infected monkeys, but the virus spilled over from monkeys into chimpanzees sometime in the last couple hundred years, because chimpanzees hunt and eat monkeys and thus came into contact with infected monkey blood. Then the virus spilled over again, this time from chimpanzees into humans, sometime in the last hundred years, because humans hunt and eat chimpanzees and thus came into contact with infected chimpanzee blood. So HIV is the result of at least two spill-over events.
Many diseases that infect humans originally came from animals. New strains of Influenza often spill over into humans from pigs or birds. Tuberculosis originally spilled over into humans from cattle. COVID-19 spilled over from bats into humans only just last year.
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