How do viruses attach to host cells?

Viruses attach to living cells by binding to the cell receptors. The receptor site is very much like a jig-saw puzzle and the virus must be shaped to fit the site and to lock in. The virus first sticks to the cell membrane of the host cell. The virus then inserts its DNA/RNA into the cell's cytoplasm. Once inside the host cell, the virus is uncoated, i.e. its capsid is dispersed, exposing the DNA/RNA. The DNA/RNA then takes over the host cell. The virus makes the cell produce new viral DNA/RNA and new capsomeres (proteins make up the capsid). The nucleic acid and the capsomeres are assembled in the cell to make new virus particles which escape from the cell. The cell might lyse and release new viruses to infect other cells.

Examples of viral infection are cold sore, measles and chicken pox.