Parvovirus B19 is the only member of the family Parvoviridae known to be pathogenic in humans. The virus is widespread, and manifestations of infection vary with the immunologic and hematologic status of the host. Infection with B19 occurs early in life and virus is transmitted by respiratory secretions and occasionally by blood products. Infection in adults is sometimes associated with an acute symmetric polyarthropathy that may mimic Rheumatoid arthritis.