Some viruses accumulate inside of cells as inclusion bodies, arrays of hundreds to thousands of virions, usually very neatly packed, inside of cells. As inclusion bodies become too large or too numerous, cell structure is disrupted to the point of lysis. The presence of inclusion bodies in tissue samples taken from a site of infection often helps to diagnose a viral infection. Other outcomes are death, persistent infection, latent infection, or tumor formation. Examples of acute infections are cold and flu viruses, measles, mumps, etc.
Persistent infections result when the immune system is unable to completely eradicate an infection.
Persistent infections are also called chronic infections. These viruses usually cause an initial acute infection lasting a few weeks, followed by a persistent infection with few or no symptoms. During HIV infection, gradual depletion of immune system cells due to their chronic infection by the virus results in immunodeficiency and increased susceptibility to opportunistic infections. Death results from inability to fight off repeated opportunistic infections. Latent infections are hidden infections.