B19

B19, or human parvovirus B19, is a small, non-enveloped DNA virus of the Parvoviridae family. It is the type species of the genus Erythroparvovirus and infects humans. The virus is responsible for erythema infectiosum (fifth disease) in children and can cause a range of clinical manifestations in adults and people with certain medical conditions. The genome is a linear single-stranded DNA of about 5.6 kilobases.

Transmission occurs primarily via respiratory droplets, but can also occur through vertical transmission from mother to fetus or, less commonly, via blood products. Seroprevalence increases with age, and outbreaks are common in settings with close person-to-person contact, such as schools.

Pathogenesis involves infection of erythroid progenitor cells in the bone marrow through the P antigen (globoside) receptor, leading to a temporary suppression of erythropoiesis. This can be clinically silent in healthy individuals but may cause complications in those with high red blood cell turnover or weakened immune systems.

Clinical features vary by age and immune status. In children, infection often causes a characteristic erythematous “slapped-cheek” rash followed by a lacy reticular rash on the trunk and limbs, possibly with mild fever or malaise. Adults frequently experience arthralgia or arthritis. In people with chronic hemolytic anemia, infection can trigger an aplastic crisis. In pregnancy, fetal infection carries a risk of fetal anemia and hydrops fetalis, requiring close monitoring.

Diagnosis relies on serology for parvovirus B19 IgM and IgG antibodies and/or detection of viral DNA by PCR. There is no specific antiviral therapy or widely available vaccine; management is generally supportive, with transfusions in severe anemia and fetal monitoring in pregnancy.