Parvovirus B19 belongs to a genus that infects both animals and humans. These are small DNA viruses without an outer envelope. Replication appears to take place in erythroid precursors of the bone marrow. The two most common diseases produced are erythema infectiosum (“fifth disease”), a condition somewhat resembling rubella, but with a rash that has a somewhat different body distribution; and transient aplastic crises. Both are more frequent in children. In both conditions, the incubation period is about 5-15 days, but may be as long as 20 days. In both conditions there may be a viral-type prodrome with fever, malaise, and other symptoms. Most patients with aplastic crises due to B19 already have some type of hemolytic anemia (such as sickle cell disease), either congenital or acquired. Immunocompromised patients (such as those with HIV-1 infection) can also have aplastic crises. It is thought that B19 infection is responsible for 90% of aplastic crises in patients with these conditions.

IgM antibody becomes detectable in the second week after infection and IgG antibody during the third week. IgM antibody decreases to nondetectable levels at roughly 6 months but can persist longer. The most commonly used tests are EIA for IgM antibody and nucleic acid (DNA) probe methods for viral antigen in serum or body fluids during acute illness. These tests would usually have to be obtained at large reference laboratories or university centers.