Human parvovirus (HPV) B19 was first discovered in 1975 by Cossart and colleagues while screening healthy blood bank donors’ sera. HPV B19 is a small (20–25 nm), single-stranded, nonenveloped DNA virus of the family Parvoviridae, genus Erythrovirus. It is the infectious agent of a number of clinical syndromes (eg, erythema infectiosum) and can cause intrauterine infection of the fetus as well.
PATHOGENESIS AND EPIDEMIOLOGY
Parvovirus infections occur worldwide as sporadic cases or within clustered outbreaks. In temperate climates, cases occur generally in late winter or spring. Parvovirus infections are most commonly recognized during childhood, and approximately 70% occur in children between 5 and 15 years of age. Infection continues at a lower rate throughout adult life, and antibody seroprevalence rates in young adults and elderly are estimated to be 50% and 90%, respectively. Women of child-bearing age in the United States have seroconversion rates of approximately 1.5%.
Parvovirus B19 is readily transmitted from person to person via respiratory droplets, fomites, and close person-to-person contact. Secondary attack rates are approximately 50% within households and variable in school outbreaks. The virus is also transmitted vertically, from mother to child, and hematogenously by blood and blood products, including albumin and plasma. Rarely, nosocomial transmission has been described.
The incubation period from acquisition of the virus to onset of initial symptom is between 4 and 14 days but can be as long as 3 weeks. Patients are most contagious in the few days preceding the rash, but those with aplastic anemia are considered contagious before the onset of symptoms and for at least 1 week after symptoms.
Viral replication occurs in human erythroid progenitor cells of the bone marrow and blood, leading to cytotoxicity and inhibition of erythropoiesis. Erythroid specificity is due to the virus’s cellular receptor, globoside, or blood group P antigen. The antigen is also present on fetal myocardial cells, which may explain the direct myocardial effects seen in fetal infection. Individuals who genetically lack the P antigen are resistant to parvovirus B19 infection.
Parvovirus B19 classically causes erythema infectiosum (EI), or fifth disease, a common childhood exanthem. EI begins as a mild nonspecific prodromal illness that includes fever, malaise, headache, myalgia, nausea, and rhinorrhea typically beginning 5 to 7 days after initial infection and coinciding with the onset of viremia. This is followed by the classic “slapped cheek” or erythematous macular exanthem on the cheeks, which may be accompanied by circumoral pallor or fine desquamation (Fig. 314-1A). One to 4 days following the facial rash, a lacy or reticulated exanthem often develops on the trunk and extremities (Fig. 314-1B). The rash is pruritic in approximately 50% of patients. Classic EI is more common in children than adults. EI is believed to be immunologically ...