Viruses must be produced in a host cell. They can be produced in vitro (in glass) if there are host cells in there first.
A virus does not need a crystal to reproduce, as they are not living organisms and do not have cellular machinery to perform reproduction. However, a virus does need a host cell to replicate and produce new virus particles.
There is no other living thing that requires a virus in order to reproduce.
Schizophrenia is not caused by a virus or bacteria--it does not and cannot "reproduce". Because it is not caused by a virus or bacteria, it is also not "contagious".
a Cell
Nothing reproduces inside a virus. It has to latch on the a host cell and insert its' DNA or RNA and then make the host cell reproduce virus particles.
artificially acquired passive immunity
All viruses do that. That's what makes a virus a virus.
A virus cannot reinvent itself without the help of a 'hosts' living cell. Once the virus invades the living cell it takes over the mechanism of reproduction using the cells enzymes and other chemical to reproduce. Therefore a virus cannot reproduce independently. Once the host cell is compromised the virus is free to infect other cells in the living organism.
Virus
I believe its the saliva glands.
A foodborne virus can only reproduce inside the body of a living host, such as a human or animal. Once ingested, the virus can multiply in the host's cells and cause illness.
A virus is an organism that can reproduce only inside a host cell. They hijack the cellular machinery of the host cell to replicate their genetic material and produce new virus particles.