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Rubella
Rubella is associated with congenital abnormality in pregnancy. There is only one serotype however re-infection with different strains is not uncommon.
Transmission Transmission is through respiratory route. The virus can be isolated from respiratory secretions and urine.
Incubation period- 2 to 3 weeks. Infectious period- 1 week before the onset of rash to 4 days after. Clinical presentations
Malaise, anorexia Fever- mild Skin rash- macular Lympadenopathy in sub-occipital region. Arthritis involving small joints. Encephalitis
Complications in pregnant mothers In the first 20 weeks of pregnancy Missed abortion Congenital abnormality- teratogenic The common defects are on
Some of these complication can be identified in the second or third trimester of pregnancy with the help of ultrasound.
ü Infection after 20 weeks of pregnancy does not cause congenital defects.
In the newborn Congenital infection can present at birth with
Detecting hearing defect at the early age is important. Those infants with CMV infection should have a follow up.
Investigation
Depending on the clinical presentations. Ultrasound is useful to detect physical abnormalities in fetus.
Diagnostic tests Relevant test on pregnant women Primary infection Blood test for Rubella IgM is useful. This test has low specificity and additional tests should be done before any intervention. Booking blood and recently taken blood sample should be tested for Rubella IgG. Seroconversion indicates recent infection. If booking blood is not available, IgG avidity test is valuable to make a diagnosis of recent infection. Low avidity indicates recent infection whereas high avidity suggest past infection or infection that occurred before several weeks.
Re-infection It is difficult to identify patient with re-infections as they would be asymptomatic. However some may transmit infection to the unborn babies. Patients with re-infection will have Rubella IgG with high avidity and occasionally they have detectable Rubella IgM. The best way of diagnosing re-infection is achieved by isolating the virus from respiratory secretions or urine.
Rubella
Rubella IgM Rubella IgG Rubella IgG avidity Acute/ recent + + Weak Past infection/ immunisation _ + Strong
Definite diagnosis in unborn baby Virus isolation or PCR on amniotic fluids, tissues or foetal blood are used to detect the virus. The virus can be isolated from saliva, urine, amniotic fluid and tissues. The viral genome can be detected from these specimens.
Diagnosing Rubella infection in neonates Rubella IgM is useful to diagnose congenital infection in the newborn. IgM will remain detectable for more than 12 months. Care should be taken on newborn who have detectable level of IgG as it could be originally from the mother. IgG can cross the placenta. It is not possible to establish Rubella as a cause of mental developmental delay or cataract after the child is immunized with MMR
Screening tests Routine screening is done for all pregnant women in many countries. Serum (clotted blood ) for Rubella IgG should be send to microbiology laboratory. Susceptible women should be vaccinated for Rubella after delivery.
Treatment
It causes mild illness. Some patients with arthritis may require symptomatic treatment. Antipyretics and bed rest.
Obstetric care Abortion may be offered to pregnant women who have primary infection or evidence of re-infection with Rubella in the first 20 weeks of pregnancy.
Prevention
There is an effective vaccine. It is a live vaccine and it should not be given to pregnant women. The vaccine is recommended to all susceptible individuals over the age of 12 months. A pregnant women exposed to Rubella virus may be given Human Normal Immunoglobulin (HNIG) to prevent congenital infection. However some expert do not recognise its efficacy and considering potential problems associated with administering immunoglobulin, they do not advocate its use.
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Date this page is updated: 04/03/2007 23:13:30 www. virologynotebook.co.uk
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