http://www.stanford.edu/group/virus/parvo/2000/B19.html
Human Parvovirus B19
Common appearance of "slapped cheek" disease, a.k.a. fifth disease.
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General Information
The B19 parvovirus, a member of the genus, Erythrovirus, is the
cause of
a range of clinical syndromes, the most common of which is erythema
infectiosum, or "fifth disease." This manifestation of B19 is a mild
condition seen in children and adults, and about 50% of adults are
seropositive after adolescence. Other clinical syndromes caused by B19
include Arthritis (especially in young women), Aplastic crisis in
chronic
hemolytic anemia, Chronic anemia in immunodeficiency syndromes, and
Hydrops
foetalis in newborn infants.
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Epidemiology
Parvovirus B19 is a very common, ubiquitous disease that tends to
produce spring epidemics in children 4-10 years of age. It is easily
transmitted through respiratory secretions and close contact, and
transmission is common in daycare centers and schools. The virus is
transmitted from person to person during the incubation period,
before a
clinical rash actually appears. By the time the rash actually does
appear,
the infected individual is no longer capable of infecting others.
Over 50%
of adults are seropositive and immune to B19.
Transplacental transmission is also possible, but unlikely. If
fetal
infection does occur, it is usually harmless. In less than 5% of all
cases,
however, primary maternal infections can lead to Hydrops foetalis,
and in
rare cases, fetal death. Transmission through blood transfusion is
also
possible.
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Incubation
B19 can present as a biphasic illness, with the first symptoms of
malaise occurring 8-11 days after infection and the rash appearing
between
days 17-24.
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Pathogenesis
Viremia reaches its peak one week after infection, at which point
the
virus is shed from the throat. Right after viremia ends, levels of
specific
IgM antibodies peak. Parvovirus B19 is selective for erythrocyte
progenitors, infecting them and inhibiting their development into
mature
erythrocytes.
The schematic representation below shows the progression of the
virologic,
hematologic and clinical events in parvovirus B19 infection:
From A.J. Zuckerman, et al., "Principles and Practice of Clinical
Virology,"
2nd Ed. Wiley, Chicheste, 1990.)
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Symptomology and Outcome
In the case of fifth disease, or erythema infectiosum, a "slapped-
cheek"
rash appears on the face of the child, giving him/her a flushed look.
The
rash also involves the limbs and trunk, where it takes on a lacy
appearance.
Adults may also experience joint swelling and pain that usually
resolves
fairly rapidly, but may remain for weeks. The regular rash usually
resolves
in about a week, and the individual gains immunity to future
infection.
In the case of Transient Aplastic Crisis, the patient experiences
lethargy, pallor and weakness that are all characteristic of severe
anemia.
This condition occurs as a complication in individuals with various
forms of
chronolytic anemia. Recovery usually occurs within a week, but the
condition
may be life threatening and blood transfusions may be required to
prevent
death.
Chronic anemia may be another complication of B19 infection and
has been
observed in immunodeficient patients.
Hydrops foetalis is a rare condition that is presumed to result
from
severe anemia and congestive heart failure in the fetus of PVB19
infected
mothers.
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Prevention and Management
There is no vaccine available against B19 and usually no
treatment is
necessary. Aplastic crisis and hemolytic anemia require supportive
care and
blood transfusion. Intravenous administration of immunoglobulin is
beneficial in the treatment of severe persistent anemia in
immunocompromised
individuals.
Washing hands frequently is probably the best method for
prevention.
