B19 parvovirus induced red cell aplasia complicating acute cold antibody mediated haemolytic anaemia

Human Parvoviruses

Parvovirus B19 (B19V) and human bocavirus 1 (HBoV1), members of the large Parvoviridae family, are human pathogens responsible for a variety of diseases. For B19V in particular, host features determine disease manifestations. These viruses are prevalent worldwide and are culturable in vitro, and serological and molecular assays are available but require careful interpretation of results. Additional human parvoviruses, including HBoV2 to -4, human parvovirus 4 (PARV4), and human bufavirus (BuV) are also reviewed. The full spectrum of parvovirus disease in humans has yet to be established. Candidate recombinant B19V vaccines have been developed but may not be commercially feasible. We review relevant features of the molecular and cellular biology of these viruses, and the human immune response that they elicit, which have allowed a deep understanding of pathophysiology.

A case of pure red cell aplasia complicated by Evans syndrome

A 33-year-old woman complaining of severe anemia was admitted to our hospital for polyclonal hyperglobulinemia. She was diagnosed with pure red cell aplasia (PRCA) associated with Evans syndrome. Initially, the presence of human parvovirus B19 (HPV B19) IgM appeared to indicate that the cause of PRCA was HPV B19 infection. Evans syndrome improved with steroid therapy, but PRCA was refractory. Cyclosporine was administered; consequently, the patient markedly recovered from PRCA and was discharged. PRCA complicated by Evans syndrome occurred during the course of polyclonal hyperglobulinemia. The most direct etiology for the onset of PRCA was unclear; however, immunological disorders such as polyclonal hyperglobulinemia, in addition to HPV B19 infection, may have been partly responsible for the etiology of PRCA.

B19 parvovirus

B19 parvovirus is pathogenic in man and causes a variety of clinical illnesses, among them several haematological diseases. Acute infection of a host with underlying haemolysis produces transient aplastic crisis; of the midtrimester fetus, hydrops fetalis; and of an immunocompromised patient, pure red cell aplasia. The target of B19 parvovirus infection is the human erythroid progenitor cell. Infection is cytotoxic due to expression of the viral nonstructural protein. The virus can be propagated in cultures of human bone marrow, blood, and fetal liver. Humoral immunity normally terminates infection, and commercially available immunoglobulin can be used to treat persistent infection. Recombinant capsids, produced in a baculovirus system, are suitable as a vaccine reagent.

Parvovirus B19-associated haemophagocytosis in Evans syndrome: aplastic crisis accompanied by severe thrombocytopenia

A 36-year-old man who had been treated for Evans syndrome (ES) developed an aplastic crisis caused by acute human parvovirus B19 (HPV) infection. Profound thrombocytopenia (8.0 x 10(9)/l) followed with a sudden increase in platelet-associated IgG (PAIgG) (1376.9 ng/10(7) plts). Bone marrow examination revealed a considerable number of haemophagocytic histiocytes without any disturbance of megakaryopoiesis. To our knowledge this is the first case of aplastic crisis with virus-associated haemophagocytosis in a patient with ES, which provides an interesting insight into the mechanisms for thrombocytopenia in HPV infection.

Viruses and the blood

Haematological syndromes attributed to viruses demonstrate geographical variations in incidence and great dependence on host factors. Severe haematological disease is the exception rather than the rule in dengue virus infection, and probably depends at least in part on the host immune response to the virus. The increased incidence of hepatitis-associated aplasia in east Asia may reflect distribution of an infectious agent, an environmental toxin, or genetic predisposition, but probably represents some combination of these factors. Agents with apparently universal distribution, such as parvovirus B19 and Epstein-Barr virus, are associated with bone marrow failure only in a very narrow range of hosts. These examples teach us that viral causes cannot automatically be excluded from the differential diagnosis of syndromes whose occurrence is rare or apparently sporadic. Further investigation of these syndromes should include more detailed characterization of host factors, particularly immunological characteristics, and possible infectious and toxic cofactors which are associated with morbidity.