Rubella

Microbiology and Pathogenesis

The Virus and How It Spreads

• Viral structure: The rubella virus is a positive-sense, single-stranded RNA virus with a lipid envelope studded with E1 and E2 glycoprotein spikes. It belongs to the genus Rubivirus, family Matonaviridae (formerly Togaviridae).
• Entry and viremia: The virus spreads by respiratory droplets → multiplies in the nasopharyngeal lining and regional lymph nodes → causes viremia after 7–14 days. It then travels in the bloodstream to the skin, joints, and placenta.
• How the rash forms: The rash results from antigen–antibody immune complexes depositing in small dermal vessels, together with a lymphocytic infiltrate around the vessels.

How Rubella Causes Birth Defects (Teratogenesis) in Congenital Rubella Syndrome (CRS)

When a pregnant woman develops viremia in the first trimester, the rubella virus crosses the placenta and causes a systemic infection in the fetus:

• Mitotic arrest: The virus slows cell division in embryonic cells while the organs are forming.
• Vessel blockage and endothelial necrosis: The virus directly destroys the endothelial cells of small embryonic vessels, starving tissues of blood.
• Result: Arrested development or structural malformations of the eyes (cataracts), ears (sensorineural deafness), heart (patent ductus arteriosus), and brain (brain atrophy, developmental delay).

Clinical Features

Acquired Rubella in Children and Adults:

• Incubation period: 14–21 days (average 16–18 days).
• Prodrome: Low-grade fever (37.5–38.5°C), tiredness, headache, and mild conjunctivitis without light sensitivity.
• Characteristic tender lymphadenopathy: The posterior auricular, suboccipital, and posterior cervical nodes become swollen, soft, and very tender. This appears 24–48 hours before the rash and lasts 1–2 weeks.
• Enanthem: Forchheimer spots, tiny red petechiae on the soft palate, appear on the first day of the rash.
• Exanthem: A fine, pink maculopapular rash with spots 1–2 mm across. It starts on the face → spreads quickly to the trunk and limbs within 24 hours. The spots stay separate rather than merging and fade quickly in the same order they appeared, within 3 days (hence "3-day measles"), leaving no dark marks behind.

Congenital Rubella Syndrome (CRS): Occurs when the mother is infected with rubella during pregnancy.

• The classic Gregg triad:
  • Eyes: Bilateral cataracts, farsightedness, pigmentary retinopathy.
  • Ears: Sensorineural deafness, the most common complication.
  • Heart: Patent ductus arteriosus (PDA), pulmonary artery stenosis.
• "Blueberry muffin" rash: Firm, dark red-purple macules and papules scattered over the body, caused by extramedullary hematopoiesis in the baby's dermis.

Differential Diagnosis of Benign Maculopapular Rashes

How We Diagnose Rubella at Haute-Derma

Clinical and Exposure Assessment:

• Recognizing the triad: a fine pink 3-day rash + tender posterior auricular/occipital nodes + Forchheimer spots on the palate.
• Asking about contact with infected people and MMR vaccination history.

Serology to Confirm the Diagnosis:

• Rubella IgM antibody: Positive from day 3–5 after the rash appears and persists for 6–8 weeks.
• Rubella IgG antibody and avidity index:
  • A more than 4-fold rise in IgG between two samples taken 2 weeks apart confirms a recent infection.
  • Low avidity: Confirms an infection within the past 3 months (very important for assessing risk in pregnancy).

Molecular Diagnosis (RT-PCR) and Pregnancy Screening:

• Rubella RT-PCR: Detects viral RNA in throat swabs, urine, or blood.
• Prenatal diagnosis: If the mother is confirmed to have an acute infection, amniocentesis can be performed from week 16–18 of pregnancy to test the amniotic fluid for rubella virus by RT-PCR.

Management, Treatment, and Vaccination at Haute-Derma

Treating Acquired Rubella

• Rest and symptom relief:
  • Acetaminophen (paracetamol) 10–15 mg/kg per dose for fever and for lymph node and joint pain.
  • Plenty of fluids and good nutrition.
  • Calamine lotion or an oral H1 antihistamine if there is mild itching.
• Isolation: Patients should stay isolated for at least 7 days after the rash appears to avoid infecting pregnant women nearby.

Counseling and Care for Pregnant Women With Rubella

The risk of birth defects (CRS) depends directly on the stage of pregnancy when the mother is infected:

• Infection before 12 weeks: 80–90% risk of CRS → the doctor should provide in-depth counseling about the risk of severe defects and discuss whether to end the pregnancy.
• Infection at 13–16 weeks: About 15–20% risk of CRS (mainly sensorineural deafness).
• Infection after 20 weeks: The risk of CRS defects is close to zero, and ending the pregnancy is not indicated.

Prevention With the MMR (Measles–Mumps–Rubella) Vaccine

• Vaccine type: Live attenuated vaccine.
• Pre-pregnancy planning at Haute-Derma:
  • We recommend that every woman planning a pregnancy have a quantitative rubella IgG test.
  • If IgG is negative (not immune): one dose of MMR vaccine is required.
  • IMPORTANT: Because this is a live attenuated vaccine, women should use reliable contraception and avoid becoming pregnant for at least 1 month (30 days) after MMR vaccination.