Human parvovirus B19: relevance in internal medicine.

Infection by the human parvovirus B19 can lead to several clinical manifestations which are relevant in internal medicine. These include aplastic crisis in chronic haemolytic anaemias, exanthemathous disease and arthropathy, mainly in women, and chronic anaemia in the immunocompromised host. After initial replication, probably in the respiratory tract, the virus enters its target cells in the bone marrow, erythroid precursor cells, through its receptor, the blood group P antigen. Viral replication in these cells leads to an arrest in erythropoiesis, normally lasting approximately 1 week. In this stage, an aplastic crisis can be produced in all patients under 'erythropoietic stress'. The viraemia disappears as specific antibodies to the virus become detectable in serum, which may give rise to a rash or arthralgia, symptoms that are probably immune-mediated. In immunologically normal individuals the infection is cleared by the humoral immune system within several weeks, whereafter detectable specific IgG confers lifelong immunity to reinfection. In patients with absent or dysfunctional humoral immunity to this virus, however, persistent infection can occur, which results in chronic suppression of erythropoiesis with chronic anaemia. Passive immunization, by means of normal immunoglobulin preparations has been reported to be effective in treating this condition. Diagnosis of parvovirus infection is usually possible by the detection of specific antibodies of IgM class in cases of recent infection. In patients with aplastic crisis and patients with chronic anaemia diagnosis rests upon the detection of parvovirus B19 DNA in serum by polymerase chain reaction. Parvovirus B19 is a ubiquitous virus. By the age of 15, about 50% of individuals have serologic evidence of a past infection, which may present as the common childhood disease erythema infectiosum. At the age of 70, seroprevalence reaches 80 to 100%. A vaccine against this virus is currently being developed.