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.

    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.

    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.

  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.)

    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.

    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.

see reference #18