Rubella

Rubella is caused by the rubella virus, a single-stranded RNA virus belonging to the family Matonaviridae and genus Rubivirus. It is the only member of its genus, and its closest relatives are viruses infecting mammals and bats¹. The virus is enveloped and has a positive-sense RNA genome of approximately 9,760 nucleotides. It encodes two glycoproteins, E1 and E2, which are targets for neutralizing antibodies.

Transmission occurs via respiratory droplets from infected individuals, with an incubation period of 12–23 days. The virus replicates in the nasopharynx and regional lymph nodes, then spreads via the bloodstream to cause viremia. Infected individuals are contagious from about one week before to one week after the rash appears. The virus is relatively fragile and does not survive long outside the host².

The hallmark of rubella is a maculopapular rash that begins on the face and spreads downward, often accompanied by low-grade fever, malaise, and lymphadenopathy, particularly of the suboccipital and postauricular nodes. In children, the rash may be the only sign, while adults may experience prodromal symptoms such as headache and conjunctivitis. Up to 50% of infections are subclinical³.

Diagnosis is typically confirmed by serology: detection of rubella-specific IgM antibodies or a four-fold rise in IgG titers between acute and convalescent sera. Reverse transcription-polymerase chain reaction (RT-PCR) can detect viral RNA from throat swabs, urine, or blood, and is useful for confirming congenital infection. Differential diagnosis includes measles, parvovirus B19 infection, and dengue fever⁴.

Congenital rubella syndrome (CRS) is the most serious consequence of rubella, occurring when a pregnant woman is infected, especially during the first trimester. The virus crosses the placenta and can cause fetal death, miscarriage, or a constellation of birth defects known as the classic triad: sensorineural hearing loss, cataracts, and cardiac anomalies (most commonly patent ductus arteriosus). Other manifestations include microcephaly, intellectual disability, and hepatosplenomegaly⁵.

The risk of CRS is as high as 90% if infection occurs before 11 weeks of gestation, declining to about 20% by 16 weeks. Infants with CRS may shed the virus for months, posing a risk to unvaccinated contacts. Long-term complications include diabetes mellitus and progressive rubella panencephalitis, a rare neurodegenerative disorder that can appear years later⁶.

Vaccination is the cornerstone of rubella prevention. The rubella vaccine is a live attenuated virus, typically administered as part of the measles-mumps-rubella (MMR) vaccine. Two doses are recommended, with the first at 12–15 months and the second at 4–6 years. The vaccine is highly effective, with over 97% of recipients developing protective antibodies after two doses⁷.

Global efforts have led to substantial declines in rubella incidence. The Americas were declared free of endemic rubella in 2015, and the WHO has set targets for elimination in other regions. However, gaps in vaccination coverage, particularly in low-income countries, continue to cause outbreaks and CRS cases. In 2020, an estimated 100,000 CRS cases occurred globally, highlighting the need for sustained immunization programs⁸.

Rubella was historically confused with measles and scarlet fever; it was not recognized as a distinct disease until the 19th century. The name "German measles" likely stems from its description by German physicians in the 1750s. The virus was first isolated in 1962 by two independent teams, Paul Parkman and colleagues and Thomas Weller and Franklin Neva, a breakthrough that enabled vaccine development¹.

An unusual aspect is the phenomenon of "rubella retinopathy," a pigmentary change in the retina that is often asymptomatic but can be a diagnostic clue in CRS. Additionally, rubella virus has been used in laboratory research as a model for studying viral teratogenesis, and it is one of the few viruses known to cause persistent infection in human cells, which may explain its ability to induce long-term complications⁶.

Congenital rubella syndrome (CRS)

A condition in infants caused by rubella infection during pregnancy, leading to birth defects such as deafness, cataracts, and heart defects.

MMR vaccine

A combined vaccine protecting against measles, mumps, and rubella.

Viremia

The presence of viruses in the bloodstream, allowing systemic spread.

Teratogenesis

The production of birth defects in a developing fetus.