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Anonymous
Presumably, all of the lentiviruses trace back to a common ancestor- one of the more interesting questions. The phylogenetic trees are today drawn without any identifiable root.We go to great lengths to imagine how humans may have picked up a monkey virus, by tribes drinking monkey blood,etc. It is even more interesting to imagine the link that spread a virus between say, cattle and monkeys. It conjures slightly humorous images of Farmer Brown inviting his brother, Jungle Jim, out to the farm, where his pet monkey, Bonzo, got into a fight with Bessie the cow. Blood was everywhere. It must have been awful.After all, we are talking about viruses that do not spread by casual contact,even if the animals had casual contact,which they do not. They are not predators of each other, they do not have sex with each other. You might imagine some common vector such as insects, but we have been assured that insects cannot transfer HIV, and are not likely to do so in the future, even if HIV were to mutate significantly.You might suppose that humans are the most common link among all the animals, but we supposedly got our virus variant as the last in line. Another interesting observation is that most of the mammal lentviruses are spread by milk, sometimes, spread primarily by milk. Humans, consumers of goat's milk, sheep's milk, cow's milk, sometimes unpasteurized, have presumably been exposed to other animal lentiviruses many times. If the viruses are truly ancient, it is rather odd that we never became infected with deadly disease, until very recently.
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