To multiply, a virus must first infect a cell. Susceptibility defines the capacity of a cell or animal to become infected. The host range of a virus defines both the kinds of tissue cells and the animal species which it can infect and in which it can multiply.

Which stage of virus occurs first?

Attachment is the first stage in the infection process in which the phage interacts with specific bacterial surface receptors (e.g., lipopolysaccharides and OmpC protein on host surfaces).

How does viruses multiply?

Viruses cannot replicate on their own, but rather depend on their host cell's protein synthesis pathways to reproduce. This typically occurs by the virus inserting its genetic material in host cells, co-opting the proteins to create viral replicates, until the cell bursts from the high volume of new viral particles.