Laboratory diagnosis of viral infections

In the diagnostic laboratory virus infections are confirmed by several methods that include:

Diagnostic virology has changed rapidly due to the advent of molecular techniques and increased clinical sensitivity of serological assays.

A wide variety of samples can be used for virological testing. The type of sample sent to the laboratory often depends on the type of viral infection being diagnosed and the test required. Blood is used for serological testing for antibody and antigen detection in a variety of different infections as well as monitoring viraemias. Sputum, gargles and bronchial washings are used to detect respiratory viruses such as Influenza. Faeces are usually sent to determine the presence of viral gastroenteritis agents. Other samples include swabs (usually in viral transport medium), cerebrospinal fluid, biopsies and post mortem tissues, dried blood spots and others.

Proper sampling technique is essential to avoid potential pre-analytical errors.

When growing virus in a cell culture, the cells affected with virus will evolve morphologic changes, often specific for the type of virus involved.

When the adaptive immune system of a vertebrate encounters a virus, it produces specific antibodies which bind to the virus and render it non-infectious. This is called humoral immunity. Two types of antibodies are important. The first called IgM is highly effective at neutralizing viruses but is only produced by the cells of the immune system for a few weeks. The second, called, IgG is produced indefinitely. The presence of IgM in the blood of the host is used to test for acute infection, whereas IgG indicates an infection sometime in the past. Both types of antibodies are measured when tests for immunity are carried out. Antibody testing has become widely available through automated panels.

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Wikipedia