Presently, diagnosis of virus infections is usually made by conventional diagnostic techniques.
Serology is the mainstay of virus diagnosis.
An acute infection can be made by the detection of virus-specific IgM or rising titres of IgG or total antibody. However, in the latter case, the diagnosis is usually retrospective because paired acute and convalescent sera are required. In addition, many viruses such as diarrhoeal and respiratory viruses, cause clinical disease before the development of antibodies and thus a serological diagnosis would be retrospective. Many virus infections can be diagnosed by virus isolation. However, it may take up to several weeks before viral induced changes such as cytopathic effect to become apparent and therefore, again the diagnosis is usually retrospective.