MEASLES
Measles, in spite of available vaccination, remains a heavy
public health burden worldwide especially in developing countries with 30-40
million cases occuring annually. In 2002, there were an estimated 610 000
deaths due to measles worldwide, 540 000 of them in children under the age of
five, representing 30-40% of the burden of vaccine-preventable diseases in
childhood. Measles may be ultimately responsible for more child deaths than any
other single agent because of complications from pneumonia, diarrhoea and
malnutrition. Measles is also the major cause of preventable blindness in the
world, affecting the same disadvantaged populations.
Of the deaths attributable to measles, 98% occur in
developing countries, where vitamin A deficiency is common. Case-fatality rates
in these countries are usually estimated to be in the range 1-5% but may reach
10-30% in some situations. Specific goals for reduction in measles mortality
and morbidity were set by the World Heath Assembly in 1989 and the Word Summit for
Children in 1990, as major steps towards the eventual eradication of the
disease.
Mode of transmission
Measles is transmitted primarily from person-to-person by
large respiratory droplets, but can also be spread by the airborne route as
aerosolized droplet nuclei.
Clinical description
Measles is most infectious during the prodrome. First there
is localized infection of the respiratory epithelium of the nasopharynx and
possibly the conjunctivae, with spread to regional lymphatics. Primary viremia
occurs 2 to 3 days following exposure, and an intense secondary viremia occurs
3 to 4 days later. The secondary viremia leads to infection of and further
replication in the skin, conjunctivae, respiratory tract and other distant
organs. The amount of virus in blood and infected tissues peaks 11 to 14 days
after exposure and then falls off rapidly over the next 2 to 3 days.
These events correspond with an incubation period between
exposure and the onset of symptoms of 10 to 12 days. The prodomal period then
begins, with fever, malaise, conjunctivitis, coryza, and tracheobronchitis.
Koplik spots appear on the buccal mucosa 1 to 2 days before
rash onset and may be noted for an additional 1 to 2 days after rash onset. The
rash is an erythematous maculopapular eruption that usually appears 14 days
after exposure and spreads from the head to the extremities over a 3 to 4 day
period. Over the next 3 to 4 days, the rash fades; in severe cases desquamation
may occur. Other constitutional signs and symptoms, such as anorexia, diarrhea
and generalized lymphadenopathy may also be present.
Complications of Measles
In industrialized countries, the most commonly
cited complications associated with measles infection are otitis media (7% to
9%), pneumonia (1% to 6%), postinfection encephalitis (l/1000 to l/2000 cases),
subacute sclerosing panencephalitis (SSPE) (l/100 000 cases) and death (l/10
000 cases). The risk of serious complications and death is
increased in young children and adults. SSPE is a rare
degenerative central nervous system disease caused by a persistent infection
with a defective measles-like virus, which develops approximately 7 years after
measles infection. Patients develop progressive personality changes, myoclonic
seizures, and motor disability, leading to coma and death. SSPE is more common
in males than females.
In developing countries, case-fatality rates (CFR) are
similar to those found in developed countries in the 1800s. Community studies
have shown CFRs varying from 3% to 15%. CFRs vary depending on the age at
infection, intensity of exposure, nutritional status, and availability of
treatment.
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