Rubella or German measles is caused by
Rubivirus, a
member of the Togavirus family of enveloped ss (+)RNA viruses. Other
togaviruses include Eastern Equine Encephalitis virus and Western
Equine Encephalitis virus.
German measles (rubella) is distinct from measles (rubeola). The
disease is similar to measles but milder, of shorter duration, and
involving fewer complications. It does not have the serious
complications of measles often seen in the very young. It was
considered as a relatively harmless disease until it was discovered
that women contracting rubella during the first trimester of pregnancy
gave birth to babies with congenital defects.
The only serious effects of rubella are on the unborn infant if the
disease occurs during the first trimester of pregnancy. The estimate of
structural abnormalities ranges from 12-83% of those children born to a
mother who had rubella at this time in pregnancy. Defects include
stillborn, cataracts, heart disease, deafness and microcephaly.
The pattern of multiplication and dissemination of the virus is similar
to measles. The disease is highly contagious, spread by nasal
secretions. Rash appears 14-25 days following infection. Unlike measles
the symptoms may be inapparent.
Infection confers permanent immunity, which is evidence for a single
immunological type of virus. The vaccine which is in use is derived
from the German measles virus (Rubivirus) after many subcultures in
tissue cultures. It produces a milder disease than the wild type
rubella virus.
The best prophylactic measure to prevent birth defects is exposure to
rubella or the vaccinating virus before reaching child-bearing
years. The vaccine cannot be administered to women who might be
pregnant since the vaccine virus can infect the fetus and might damage
it.
The rubella vaccine is available as a single antigen preparation,
combined with mumps vaccine, or combined with measles and mumps
vaccines (MMR). More than 95% of vaccinees 12 months of age or older
develop permanent immunity with a single vaccination.
