Viral entry

Viral entry is the earliest stage of infection in the "viral life cycle", as the virus comes into contact with the host cell and introduces viral material into the cell. The major steps involved in viral entry are:
 * 1. Attachment, when receptors on the viral envelope become connected to complementary receptors on the cell membrane. This attachment causes the two membranes to remain in mutual proximity, favoring further interactions between surface proteins.
 * 2. Membrane Fusion or Hemifusion State or Viral Adsorption, as the cell membrane is punctured and made to further connect with the unfolding viral envelope.
 * 3. Entry Pore formation, which results from viral proteins establishing a stable opening in the cell membrane.
 * 4. Viral Pentration as the viral capsid is injected into the host cell's cytoplasm.

After the introduction of the viral capsid, unpacking of the contents (viral proteins and the viral genome via some form of nucleic acid) occurs as the next stage of viral infection.