ToRCH & Childhood
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ToRCH & Childhood
A ToRCH test measures antibodies against five groups of chronic infections:
- Cytomegalovirus (CMV)
- Herpes simplex virus (HSV-1/2)
- Other infections (usually syphilis, hepatitis B, coxsackie virus, Epstein-Barr virus, varicella-zoster virus, and human parvovirus)
These infectious diseases are all associated with congenital abnormalities resulting from maternal infection. Although the organisms typically cause only asymptomatic or mild infection to the mother, they can have much more serious consequences to the fetus. If the infection occurs during the first three months of pregnancy and if it is a primary infection (newly acquired during pregnancy), the risk of congenital abnormalities is much higher compared to a secondary or reactivated infection. CMV, which is the most common cause of congenital infectious disease, also has a much higher rate of transmission from mothers with a primary infection (10%) compared to a reactivation (1%). An important part of prenatal care is to recognize these infections in the mother and the fetus and provide suitable care.
For most ToRCH organisms, the initial screening test is based on the detection of antibodies to the organism. Subsequent screening, if required, is carried out using a monoclonal antibody-based immunofluorescent assay (IFA). Assays are commercially available for the detection of IgG, IgM, or both IgG and IgM antibodies. In most cases, IgG reactivity in the absence of IgM reactivity is indicative of a past infection, while IgM reactivity in the absence of IgG reactivity indicates a current infection. However, for some ToRCH diseases such as toxoplasmosis and CMV, IgG avidity has recently been found to be useful for identifying primary infections. An IgG antibody produced in the first few months following an initial infection has a lower avidity than an IgG antibody produced several months or years later. Consequently, low-avidity antibody can be used to specifically identify high-risk mothers with a primary infection. To protect a fetus from ToRCH infection, early diagnosis through first trimester screening is critical.
TORCH IGG & IGM ANTIBODY SCREENING ASSAYS
A ToRCH serologic test must detect both IgM and IgG antibodies to the ToRCH panel of infectious diseases (Toxo, Rubella, CMV and HSV). IgM is the immediate antibody that is produced once a human is exposed to a bacteria, virus or a toxin and disappears within 2 to 3 weeks. It is then replaced by IgG which lasts for life and provides lasting immunity. All of Meridian’s ToRCH antigens are suitable for commercial IgG and/or IgM detection. They can be used in a range of immunoassay formats including, but not limited to, ELISA, LF, CLIA, rapid assays, and bead-based assays.
TORCH RAPID IGM CAPTURE ASSAYS
Rapid IgM capture assays are particularly sensitive in detecting IgM responses early in illness. The assay works by binding IgM antibodies in the patient’s specimen to a solid phase coated with an anti-IgM capture antibody. Soluble antigen is added in excess allowing the IgM antibody-antigen reaction to occur in the absence of competing IgG. Finally, a labelled detection antibody is added that has specific reactivity against the antigen. Assay sensitivity can be highly dependent on the purity of the antigen used.
TORCH IMMUNOFLUORESCENT ANTIBODY ASSAYS (IFA)
IFA is a traditional laboratory technique that utilizes fluorescent dyes to identify the presence of antibodies bound to specific antigens. Definitive diagnosis of a ToRCH infection, in particular HSV-1 or HSV-2, sometimes requires confirmation by IFA after a positive EIA result.
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