Humans are exposed continuously to the menace of viral diseases such as those caused by the Ebola virus, Zika virus and coronaviruses. Such emerging/re-emerging viral outbreaks can be triggered by cross-species viral transmission from wild animals to humans.
To achieve cross-species transmission, new hosts have to be exposed to the virus from the old host. Next, the viruses acquire certain mutations that can be beneficial for replicating in the new hosts. Finally, through sustained transmission in the new host, the viruses adapt further evolving as a new virus in the new host. However, at the outset of this process, the viruses have to overcome “the species barriers,” which hamper viral cross-species transmission. Mammals including humans have “intrinsic immunity” mechanisms that have diverged enough in evolution to erect species barriers to viral transmission.
HIV-1 most likely originated from related precursors found in chimpanzees and gorillas