Human parvovirus B19 (B19V) is a small, single-stranded, nonenveloped DNA virus in the family Parvoviridae, genus Erythrovirus.
Infection with B19V is common worldwide. Infection occurs mostly among school-aged children where the major manifestation is erythema infectiosum (also called fifth disease). Infection in adults can be entirely asymptomatic or may result in polyarthropathy syndrome and/or petechial, papular-purpuric gloves-and-socks syndrome. The prevalence of immunoglobulin G (IgG) antibodies directed against B19V ranges from 15% to 60% in children 6 to 19 years old. About 35% to 45% of women of childbearing age do not possess protective IgG antibodies against B19V and therefore are susceptible to primary infection. The incidence of acute B19V infection in pregnancy is 3.3% to 3.8%. Annual seroconversion rates in pregnant women in the United States range from 1% to 1.5%. The incubation period is between 4 and 14 days but can be as long as 21 days.
The pathogenesis of B19V infection is related to its tropism for erythroid progenitor cells. Infection and lysis of these cells make B19V a potent inhibitor of hematopoiesis. The cellular receptor for B19V is globoside or P-antigen, which is found on erythrocyte progenitor cells, synovium, placental tissue, fetal myocardium, and endothelial cells. The B19V-associated red blood cell aplasia is related to caspase–mediated apoptosis of erythrocyte precursors. Infection with B19V is usually acquired through respiratory droplets, but the virus can also be transmitted by blood or blood products and vertically from mother to fetus. In children and adults, viremia develops 2 days after exposure and reaches its peak at approximately 1 week. During the phase of viral replication and shedding, the patient is generally asymptomatic. When the typical rash (characterized by a “slapped cheek” appearance on the face and a “lace-like” erythematous rash on the trunk and extremities) or arthralgias develop, the patient is no longer infectious to others. Symptoms of the papular-purpuric gloves-and-socks syndrome can occur in association with viremia and before development of antibody response, and affected patients should be considered infectious. Symptoms during pregnancy are nonspecific and include a flulike syndrome with a low-grade fever, sore throat, generalized malaise, and headache. The fetus may become infected during the maternal viremic stage. Because of active erythropoiesis in the fetus with a shortened red cell life span, marked fetal anemia, high-output cardiac failure, and fetal hydrops may develop. Myocarditis, and less often fetal hepatic infection, may contribute to fetal cardiac failure. Teratogenicity from B19V has been described in case reports; also, one study found high prevalence of trisomy in pregnancy loss ascribable to B19V/erythrovirus infection. Despite that, B19V is considered nonteratogenic based on large epidemiologic studies.
The risk of acquiring B19V infection during pregnancy is highest in schoolteachers, daycare workers, and women who have school-aged children at home.