- Laboratory diagnosis of viral infections
In the diagnostic laboratory
virus infections are confirmed by several methods that include:
*Growth of the virus in acell culture from a specimen taken from the patient.
*Detection of virus-specific antibodies in the blood.
*Detection of virus antigens
*Detection of virus nucleic acids
*Observation of virus particles byelectron microscopy .
*Hemagglutination assay Cell culture
When growing virus in a
cell culture , the cells affected with virus will evolve morphologic changes, often specific for the type of virus involved.Antibody detection
When the
adaptive immune system of avertebrate encounters a virus, it produces specificantibodies which bind to the virus and render it non-infectious. This is calledhumoral immunity . Two types of antibodies are important. The first calledIgM 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. [Greer S, Alexander GJ. Viral serology and detection.Baillieres Clin Gastroenterol. 1995 Dec;9(4):689-721] Both types of antibodies are measured when tests for immunity are carried out. [Laurence JC. Hepatitis A and B immunizations of individuals infected with humanimmunodeficiency virus.Am J Med. 2005 Oct;118 Suppl 10A:75S-83S.]Antigen detection
Detection of virus antigens can be done by
ELISA in tissues and fluids.Other techniques are:
*immunofluorescence
*immunoperoxidase Hemagglutination assay
Many viruses attach to molecules present on the surface of red blood cells. A consequence of this is that - at certain concentrations - a viral suspension may bind together (agglutinate) the red blood cells thus preventing them from settling out of suspension. Usefully, agglutination is rarely linked to infectivity, attenuated viruses can therefore be used in
assay s.Nucleic acid detection
Detection of virus encoded DNA and RNA is done with
polymerase chain reaction .Nucleic acid hybridization with virus-specific probes detects specific viruses.ee also
References
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