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Chapter: Medical Microbiology: An Introduction to Infectious Diseases: Mumps Virus, Measles, Rubella, and Other Childhood Exanthems

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Rubella : Clinical Aspects

Rubella is commonly known as German measles or 3-day measles. The incubation pe-riod for acquired infection is 14 to 21 days (average, 16 days).

RUBELLA : CLINICAL ASPECTS

MANIFESTATIONS

Rubella is commonly known as German measles or 3-day measles. The incubation pe-riod for acquired infection is 14 to 21 days (average, 16 days). Illness is generally very mild, consisting primarily of low-grade fever, upper respiratory symptoms, and lym-phadenopathy, which is most prominent in the posterior cervical and postauricular areas. A macular rash often follows within a day of onset and lasts 1 to 3 days. This rash, which is often quite faint, is usually most prominent over the head, neck, and trunk. Petechial le-sions may also be seen over the soft palate during the acute phase. The most common complication is arthralgia or overt arthritis, which may affect the joints of the fingers, wrists, elbows, knees, and ankles. The joint problems, which occur most frequently in women, rarely last longer than a few days to 3 weeks. Other, rarer complications include thrombocytopenic purpura and encephalitis.

The major significance of rubella is not the acute illness but the risk of fetal damage in pregnant women, particularly when they contract either symptomatic or subclinical pri-mary infection during the first trimester. The risk of fetal malformation and chronic fetal infection, which is estimated to be as high as 80% if infection occurs in the first 2 weeks of gestation, decreases to 6 to 10% by the 14th week. The overall risk during the first trimester is estimated at 20 to 30%.

Clinical manifestations of congenital rubella syndrome vary, but may include any combination of the following major findings: cardiac defects, commonly patent ductus arteriosus and pulmonary valvular stenosis; eye defects such as cataracts, chorioretinitis, glaucoma, coloboma, cloudy cornea, and microphthalmia; sensorineural deafness; enlargement of liver and spleen; thrombocytopenia; and intrauterine growth restriction. Other findings include CNS defects such as microcephaly, mental retardation, and encephalitis; anemia; transient immunodeficiency; interstitial pneumonia; and intravascu-lar coagulation; hepatitis; rash; and other congenital malformations. Late complications of congenital rubella syndrome have also been described, including an increased risk of diabetes mellitus, chronic thyroiditis, and occasionally the development of a progressive subacute panencephalitis in the second decade of life. Some congenitally infected infants may appear entirely normal at birth, and sequelae such as hearing or learning deficits may not become apparent until months later. The spectrum of defects thus varies from subtle to severe.

DIAGNOSIS

Because of the rather nonspecific nature of the illness, a diagnosis of rubella cannot be made on clinical grounds alone. More than 30 other viral agents, which are discussed later, can produce a similar illness. Confirmation of the diagnosis requires laboratory studies. The virus may be isolated from respiratory secretions in the acute phase (and from urine, tissues, and feces in congenitally infected infants) by inoculation into a variety of cell cultures, or detected by reverse transcriptase polymerase chain reac-tion. Serologic diagnosis is most commonly used in acquired infections; paired acute and convalescent samples collected 10 to 21 days apart are used. Hemagglutination inhibition, indirect immunofluorescence, EIA, and other tests are available.

Determination of IgM-specific antibody is sometimes useful to ascertain whether an infection occurred in the past several months; it has also been used in the diagnosis of congenital infections. Unfortunately, there are certain pitfalls in interpreting this test. Some individuals ( 5%) with acquired infections may have persistent elevations of IgM-specific antibodies for 200 days or more afterward, and some congenitally infected in-fants do not produce detectable IgM-specific antibodies.

TREATMENT AND PREVENTION

 

Other than supportive measures, there is no specific therapy for either the acquired or the congenital infection.

Since 1969, a live attenuated rubella vaccine has been available for routine immu-nization. As a result of the widespread use of the vaccine in the United States, the num-ber of cases of rubella has declined dramatically. From 1990 through 1999, the median number of cases reported annually was only 232. The current vaccine virus, grown in human diploid fibroblast cell cultures (RA 27/3), has been shown to be highly effective.

It causes seroconversion in approximately 95% of recipients. Routine immunization is now recommended for infants after the first year of life and for other individuals with no history of immunization and lack of immunity by serologic testing. Target groups include female adolescents and hospital personnel in high-risk settings. The vaccine is contraindicated in many immunocompromised patients and in pregnancy. To date, more than 200 instances of accidental vaccination of susceptible pregnant women have been reported, with no clinically apparent adverse effects on the fetus; however, it is strongly recommended that immunization be avoided in this setting and that nonpregnant women avoid conception for at least 3 months after receiving the vaccine. Vaccine-induced immunity may be lifelong. Studies to date indicate that the duration of protection is at least 16 years.

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