Laboratory diagnosis of virus
Encyclopedia
In the diagnostic laboratory virus
infections are confirmed by several methods that include:
, the cells affected with virus will evolve morphologic changes, often specific for the type of virus involved.
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.
in tissues and fluids.
Other techniques are:
s.
. Nucleic acid hybridization with virus-specific probes detects specific viruses.
Virus
A virus is a small infectious agent that can replicate only inside the living cells of organisms. Viruses infect all types of organisms, from animals and plants to bacteria and archaea...
infections are confirmed by several methods that include:
- Growth of the virus in a cell cultureCell cultureCell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
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 by electron microscopy.
- Hemagglutination assayHemagglutination assayThe hemagglutination assay is a method of quantification for viruses or bacteria by hemagglutination...
Cell culture
When growing virus in a cell cultureCell culture
Cell culture is the complex process by which cells are grown under controlled conditions. In practice, the term "cell culture" has come to refer to the culturing of cells derived from singlecellular eukaryotes, especially animal cells. However, there are also cultures of plants, fungi and microbes,...
, the cells affected with virus will evolve morphologic changes, often specific for the type of virus involved.
Antibody detection
When the adaptive immune systemAdaptive immune system
The adaptive immune system is composed of highly specialized, systemic cells and processes that eliminate or prevent pathogenic growth. Thought to have arisen in the first jawed vertebrates, the adaptive or "specific" immune system is activated by the “non-specific” and evolutionarily older innate...
of a vertebrate
Vertebrate
Vertebrates are animals that are members of the subphylum Vertebrata . Vertebrates are the largest group of chordates, with currently about 58,000 species described. Vertebrates include the jawless fishes, bony fishes, sharks and rays, amphibians, reptiles, mammals, and birds...
encounters a virus, it produces specific antibodies which bind to the virus and render it non-infectious. This is called humoral immunity
Humoral immunity
The Humoral Immune Response is the aspect of immunity that is mediated by secreted antibodies produced in the cells of the B lymphocyte lineage . B Cells transform into plasma cells which secrete antibodies...
. Two types of antibodies are important. The first called IgM
IGM
IGM as an acronym or abbreviation can refer to:* Immunoglobulin M , the primary antibody against A and B antigens on red blood cells* International Grandmaster, a chess ranking* intergalactic medium* Intragroup medium - see: Intracluster medium...
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
Immunity (medical)
Immunity is a biological term that describes a state of having sufficient biological defenses to avoid infection, disease, or other unwanted biological invasion. Immunity involves both specific and non-specific components. The non-specific components act either as barriers or as eliminators of wide...
are carried out.
Antigen detection
Detection of virus antigens can be done by ELISAELISA
Enzyme-linked immunosorbent assay , is a popular format of a "wet-lab" type analytic biochemistry assay that uses one sub-type of heterogeneous, solid-phase enzyme immunoassay to detect the presence of a substance in a liquid sample."Wet lab" analytic biochemistry assays involves detection of an...
in tissues and fluids.
Other techniques are:
- immunofluorescenceImmunofluorescenceImmunofluorescence is a technique used for light microscopy with a fluorescence microscope and is used primarily on biological samples. This technique uses the specificity of antibodies to their antigen to target fluorescent dyes to specific biomolecule targets within a cell, and therefore allows...
- immunoperoxidaseImmunoperoxidaseImmunoperoxidase is a type of immunostain used in molecular biology, medical research, and clinical diagnostics. In particular, immunoperoxidase reactions refer to a sub-class of immunohistochemical or immunocytochemical procedures in which the antibodies are visualized via a peroxidase-catalyzed...
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 assayAssay
An assay is a procedure in molecular biology for testing or measuring the activity of a drug or biochemical in an organism or organic sample. A quantitative assay may also measure the amount of a substance in a sample. Bioassays and immunoassays are among the many varieties of specialized...
s.
Nucleic acid detection
Detection of virus encoded DNA and RNA is done with polymerase chain reactionPolymerase chain reaction
The polymerase chain reaction is a scientific technique in molecular biology to amplify a single or a few copies of a piece of DNA across several orders of magnitude, generating thousands to millions of copies of a particular DNA sequence....
. Nucleic acid hybridization with virus-specific probes detects specific viruses.