Contents:
Introduction
Disease
Vaccines
Issues
Additional
Links
Measles is the leading cause of vaccine preventable
deaths in children worldwide. This continues to be the case today,
despite major advances in measles control in the western hemisphere (see
picture). In 1996 approximately 1.67 million measles associated deaths
were prevented through vaccination programs, while 44 million cases and
1 million deaths still occurred. (1)
Measles Incidence Rate Per 100,000, 1998 Measles Vaccine Coverage Rates, 1998
|
|
Key:
Key:
White: incidence rate of zero
per 100,000
White: coverage > 80%
Pink: incidence rate of 1 to
10 per 100,000
Turquoise: Vaccine coverage 50-80%
Red: incidence rate of 10 to
100 per 10,000
Green: Vaccine coverage < 50%
Dark Red: incidence rate of
over 100 per 100,000 Grey:
No data available
Grey: No Data available
Virus
The measles virus is a single stranded, negative
sense RNA virus. Two proteins, the fusion protein and hemagglutinin
protein, are responsible for fusion of the virus and host cell membranes,
allowing viral penetration and hemolysis. Virons bind to the human
receptor CD46 and enter the cell through fusion with the membrane, subsequently
releasing the nucleocapsid into the cytoplasm. After a period of
24 hours, viral replication takes place and infectious viral particles
bud from the cell membrane.(2)
Clinical Presentation
Ten to twelve days after airborne or droplet
exposure to the measles virus, the first symptoms occur. The initial
symptoms are similar to that seen in any upper respiratory infection: fever,
malaise, conjunctivitis, coryza, and tracheobronchitis. In the next
four days fever intensifies, and koplik spots and enanthema appear.
The characteristic rash usually appears in the first 14 days and spreads
from the head to the trunk and extremities.(2)
Child with measles: http://www.immunize.org/images/ca.d/ipcd1861/img0014.htm
Immunity
Measles causes both activation and suppression
of the immune system. The cytokines released during measles infection
suggest activation of CD8+ T cells, which play an important role in viral
clearance. In addition type 2 CD4+ T cells provide antibody
production. Clearance and recovery from infection are associated
with production of serum secretory antibodies as well as establishment
of cellular immunity.(2)
Epidemiology
In the absence of a vaccination program, measles
is a highly contagious, seasonal disease. Passed from person to person
by large respiratory droplets or aerosolized droplet nuclei, nearly every
person is affected by adolescence. Peak transmission usually occurs
in young children.
In developing countries, before the introduction of widespread measles vaccination, the average age of infection was lower then observed in developed countries. This may be due to increased susceptibility because of poor nutrition and rapid loss of maternal antibody. It might also be a result of increased risk of exposure to the virus through earlier contact to the community at large. In contrast, children in industrialized countries were not usually exposed to measles before they entered school or daycare. In developing countries malnutrition, particularly Vitamin A deficiency decreases cellular and possibly humoral immunity and increases the risk of severe disease.(3)
For more information, view this additional
link:
http://www.cdc.gov/epo/mmwr/preview/mmwrhtml/00049427.htm
Treatments
Treatments for measles include interferon,
thymic humoral factor, thymostimulin, levaminsole, ribavirin, and immune
globulin. In developing countries, administering high doses of vitamin
A to children hospitalized with measles has effectively decreased overall
mortality and morbidity. Vitamin A is recommended for children with acute
measles by the World Health Organization.(4)
Vaccines
One measles strain, Edmonston, was used to
create many of the attenuated viral vaccines, which have been developed
worldwide. It was licensed in the United States in 1963 along with another
vaccine, which was attenuated from the Edmonston Strain by a similar process.
Later, two different attenuated viral vaccines were developed, the Moraten
vaccine is now the only vaccine used in the United States, while the Schwarz
vaccine is the predominant product in many other nations. The immune
response is similiar to that after natural infection, the primary difference
being that the immune response is a few days shorter after vaccination.(4)
For more information, view this link:
http://www.who.org/vaccines-diseases/research/virus1.htm
