David Rosen, PhD Physics & Solid State, City University of New York Graduate Center (1985)
Answered Mar 9 · Author has 8.9k answers and 3.4m answer views
One has to be very general with the word ‘kill’, since the virus is hardly alive. However, a virus can ‘kill’ another virus in a very general sense.
One species of virus can parasitize another species of virus by being injected in the host cell at the same time. One of the species of hepatitis parasitizes the other species this way. While the host virus could have taken over the host cell entirely by itself, it has to share the host cell with the parasitic virus. Thus, the parasitic virus is preventing the host virus from reproducing rapidly.
Some virus species are so closely related that the same antibodies can work against both. So a host infected with one virus builds up immunity to both viruses. The second virus never gets a chance to infect the host. This is the basis of many vaccines.
Cowpox is a virus related to small pox. People who got cowpox are resistant to small pox. So Jenner discovered that by infecting people with cowpox, he was preventing the spread of smallpox.
Cowpox is less virulent than small pox. However, this makes many people carriers without symptoms. So it spreads in populations (e.g., mil maids), making the population reject all cowpox AND small pox viruses that are introduced later. So cowpox effectively kills both members of its own species and smallpox. People actually learned to infect people with cowpox, which is sometimes called Jenners vaccine. In a way, the cowpox virus is manipulating people for its own benefit with regard to ‘killing’ small pox.
A virus infecting a host sometimes makes the host resistant to other viruses of its species. This in effect is killing any viruses that try to infect the host later, including its own species.
As I said, one has to be very general with the word ‘kill’. These ways of ‘killing’ other viruses may seem indirect to you. However, virus infection is an indirect process. So far as natural selection is concerned, preventing another virus from spreading is the same as killing the other virus. (Please do not hide my questions glaistig if you have no idea what the question is about. I understand that you rather like questions about sex with minors and stuff. I am trying to talk about science and have no ambition to disturb your kindergarten. Pleas do not disturb my questions)