Immunologic Manifestations of Rubella infection
المؤلف:
Mary Louise Turgeon
المصدر:
Immunology & Serology in Laboratory Medicine
الجزء والصفحة:
5th E, P317-318
2025-09-10
389
Acquired Rubella Infection
In a patient with primary rubella infection, the appearance of both immunoglobulin G (IgG) and IgM antibodies is associated with the appearance of clinical signs and symptoms, when present.
The IgM antibodies become detectable a few days after the onset of signs and symptoms and reach peak levels at 7 to 10 days. These antibodies persist but rapidly diminish in con centration over the next 4 to 5 weeks, until antibody is no lon ger clinically detectable. The presence of IgM antibody in a single specimen suggests that the patient has recently experienced a rubella infection. In most cases, the infection probably occurred in the preceding month.
Production of IgG is also associated with the appearance of clinical signs and symptoms. Antibody levels increase rapidly for the next 7 to 21 days and then level off or even decrease in strength. IgG antibodies, however, remain present and protective indefinitely. Detection of IgG antibody is a useful indicator of rubella infection only when the acute and convalescent blood specimens are drawn several weeks apart. Optimum timing for paired testing in the diagnosis of a recent infection is 2 or more weeks apart, with the first (acute) specimen taken before or at the time signs and symptoms appear, or within 2 weeks of exposure.
Paired-specimen testing may demonstrate that the antibody levels are the same. In these cases, either the patient was previously immunized or the acute sample was taken after the anti-body had already reached maximum levels. Demonstration of an unequivocal increase in IgG antibody concentration between the acute and convalescent specimens suggests a recent primary infection or a secondary (anamnestic) antibody response to rubella in an immune individual. In cases of an anamnestic response, IgM antibodies are not demonstrable, but IgG pro duction begins quickly. No other signs or symptoms of disease are exhibited.
If both IgM and IgG test results are negative, the patient has never had rubella infection or been vaccinated. Such patients are susceptible to infection. If no IgM is demonstrable but IgG is present in paired specimens, the patient is immune.
When evaluating of the immune status of patients, IgG antibodies present in a dilution of 1:8 or higher indicate past infection with rubella virus and clinical protection against future rubella infection. The clinical significance of lower levels is not currently known. Titers of 1:16, 1:64, 1:512, or higher may be found in acute and past infections; however, the diagnosis of acute infection requires an IgM antibody titer on the same specimen or a paired-specimen comparison. It should be noted that IgM also appears for a transient period after vaccination.
Congenital Rubella Syndrome
Because IgG antibody is capable of crossing the placental barrier, there is no way of distinguishing between IgG antibody of fetal origin and IgG antibody of maternal origin in a neonatal blood specimen (Fig. 1).
Fig1. Natural history of congenital rubella: pattern of virus excretion and antibody response. (Adapted from Krugman S et al: Infectious diseases of children, ed 9, St Louis, 1992, Mosby.)
Testing for IgM antibody is invaluable for the diagnosis of congenital rubella syndrome in the neonate. IgM does not cross an intact placental barrier; therefore, demonstration of IgM in a single neonatal specimen is diagnostic of congenital rubella syndrome. In the newborn, serologic confirmation of rubella infection can be made by testing for IgM antibody for at least the first 6 months of life. This is especially useful when clinical evidence of congenital rubella is slow in emerging or is of uncertain origin.
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