subject: Rubella clinical features, pathogenesis and complications [print this page] Rubella clinical features, pathogenesis and complications
Postnatal rubella (German measles) is a mild illnessoccasionally complicated by arthritis or encephalitis. Bycontrast, infection in utero can have devastating effects onthe fetus.
Pathogenesis Rubella virus infects nasopharyngeal secretions, where it isfound during subclinical as well as overt infection. Duringthe viraemic phase it is disseminated widely and, as for1 MCQ 9.12 2 MCQ 9.13294measles, the clinical illness corresponds in time with the development of immunity. The incubation period for rubella is 14-16 days.Clinical featuresLike measles, rubella is associated with fever, lymphadenopathy,rash and conjunctival suffusion, but it is amild, short-lived illness which may be asymptomatic. The lymphadenopathy of rubella is characteristically suboccipital,postauricular and posterior cervical. It may persistlong after the rash has faded. Although, as in measles, therash starts on the face and behind the ears, spreadingdownwards and outwards over the trunk and limbs, thespots are paler red, circular macules which remain discreteand do not coalesce into brighter irregular blotches. Therash varies from hour to hour, fading and reappearing forup to 4 days. It is common to find petechiae on the softpalate (Forchheimer spots), but these are not diagnostic.ComplicationsArthritis is the only common complication of rubella.It usually affects young women, who develop polyarthritisof small joints, especially those of the fingers and wrists,although larger joints may be affected. It is easily confusedwith acute rheumatoid arthritis, especially in the absenceof rash. It usually subsides within a few days but can lastup to 3 months. Encephalitis and thrombocytopenicpurpura are very rare complications.Congenital rubellaBoth the risk and the severity of damage to the fetus areclosely related to the time of infection. Following infectionduring the first month of pregnancy over half of fetuses areaffected, whereas by the fourth month only 5% havedefects, although this is still twice the frequency in controlgroups. Minor damage can result from later infection.During the viraemic phase of the maternal illness rubellavirus invades the placenta, causing villous placentitis, andthen disseminates through the fetal circulation. The degreeof damage is variable, even in twins infected at the sametime.The common major abnormalities resulting from infectionin the first trimester are cataracts, patent ductus arteriosuswith or without pulmonary stenosis, and deafness.Rubella virus can be isolated from the baby's pharynx forseveral months, a much longer period than in acquiredrubella. The virus is present in all other secretions, andthese babies can readily infect nurses handling them.
Diagnosis Serology is the mainstay of diagnosis in both congenitaland acquired rubella. In the haemagglutination inhibition(HAI) test, the virus agglutinates chick red cells. Serumantibodies inhibit this agglutination. A rise in totalantibody titre or the presence of specific IgM antibodiesindicates recent infection.In acquired infection antibody is detectable by HAI14-16 days after infection and reaches a peak 6-12 dayslater. The fetus starts to produce IgM antibody at about the20th week of life, and as only IgG antibody can cross theplacenta the presence of IgM antibodies to rubella virus inthe fetus or infant implies active infection. Rubella viruscan be cultured from clinical specimens, but this is rarelyused for diagnosis.
Immunization Live attenuated virus vaccine is given routinely as part ofthe measles/mumps/rubella (MMR) vaccination to boysand girls aged 15 months. This was introduced in 1988 andreplaces the policy of immunizing girls aged between 11and 13 years. Vaccine virus can cross the placenta so itshould not be given during pregnancy, and pregnancyshould be avoided for 2 months after immunization
.Exposure to rubella during pregnancy Definite exposure to rubella of a non-immune pregnantwoman during the first trimester is an indication for terminationof pregnancy. If the woman does not knowwhether she is immune to rubella, the following course ofaction is recommended: If possible, establish by serology the diagnosis of rubellain the patient with whom the pregnant woman was incontact. Find out whether contact was close enough toallow transmission of virus. Test the pregnant patient for rubella antibodies:- // positive by HAI within 14 days of exposure torubella, the patient was immune previously and shecan be reassured.- // negative by HAI then test a further sample 2-3weeks from contact. If the second serum is positive orif IgM antibodies are detected, discuss risks and offertermination. Some women prefer to continue with thepregnancy despite the risk to the fetus. In this caseintramuscular rubella immunoglobulin should begiven as soon as possible after exposure.
