Human parvovirus B19: historical and clinical review

Human parvovirus B19 has been associated with disease only for the past few years. First isolated from sera obtained for studies on hepatitis B in 1975, it was not until 1981 that infection with this small, single-stranded DNA virus was related to aplastic crisis associated with hemolytic anemia. A nonspecific viral prodrome, the occurrence in family members, and epidemics of aplastic crisis suggested the infectious etiology. Human parvovirus infection has since been associated with arthritis, erythema infectiosum (fifth disease), fetal death, and hydrops fetalis. Through the use of recently developed serologic tests, epidemics of erythema infectiosum and parvoviral infection have been related not only to aplastic crisis but also to intrauterine infection and hydrops; DNA hybridization studies have allowed the detection of viral DNA in serum and tissue extracts. Studies have been hampered by the lack of an ability to culture the virus, but this is now possible utilizing bone marrow culture and erythropoietin. This article is a historical and clinical review of human parvovirus infection and disease and considers potential questions regarding their consequences.     

The role of parvovirus B19 in aplastic crisis and erythema infectiosum (fifth disease)

In 1984, simultaneous outbreaks of aplastic crisis and erythema infectiosum occurred in northeastern Ohio. Sera were analyzed from 26 patients with aplastic crisis: 24 had IgM specific for parvovirus B19, five had B19-like particles by electron microscopy, and 13 had DNA from B19; no sera from 33 controls had evidence of recent infection with B19 (P less than .0001). DNA from B19 was also detected in specimens of throat gargle and urine from two patients with aplastic crisis. Sera from 36 of 51 children with erythema infectiosum had B19-specific IgM, compared with serum from one of 42 susceptible controls (P less than .0001). DNA from B19 was detected in sera from only two of 51 patients who had erythema infectiosum. The secondary attack rates among susceptible contacts decreased with age (overall total, 49.6%). Differential rates of asymptomatic infection were observed among black (68.8%) and white (20.0%) household members (P = .003). These were the first identified simultaneous outbreaks of aplastic crisis and erythema infectiosum. Their occurrence provided an opportunity to study the epidemiology and spectrum of B19 infection with geographically and temporally matched comparison groups; our results support the hypothesis that infection with parvovirus causes these two clinical entities.     

Persistent B19 parvovirus infection in patients infected with human immunodeficiency virus type 1 (HIV-1): a treatable cause of anemia in AIDS

OBJECTIVE: To determine the role of B19 parvovirus in red cell aplasia of patients infected with human immunodeficiency virus type 1 (HIV-1). DESIGN: Uncontrolled clinical trial, with assay of serum, peripheral blood cells, and bone marrow for virus using DNA hybridization and immunocytochemistry techniques; these assays were then correlated with clinical findings, results of immunoassays for antivirus antibodies, and with immunoglobulin (Ig) therapy. SETTING: Government medical referral center, and university and private hospitals. PATIENTS: Seven patients with pure red cell aplasia and serologic evidence of infection with HIV-1. MEASUREMENTS AND MAIN RESULTS: All patients had giant pronormoblasts in the bone marrow (present in transient aplastic crisis caused by acute B19 parvovirus infection). High concentrations of B19 parvovirus were demonstrated in sera, in several cases in samples separated by weeks or months. Viral DNA and capsid protein were present in the bone marrow of three patients studied, and active viral replication was detected by southern analysis. There was no antivirus IgG in capture immunoassay and no or very low levels of antivirus IgM. The patients did not have symptoms of fifth disease, the illness caused by this virus in immunologically normal persons. Six patients were treated with a regimen of intravenous commercial immunoglobulin. In all cases, this therapy resulted in rapid reduction in serum virus concentrations and full recovery of erythropoiesis. Relapses in two cases were predicted by DNA hybridization studies, and these cases were successfully retreated. CONCLUSIONS: The B19 parvovirus is a remediable cause of severe chronic anemia in HIV-infected patients. Recognition of and therapy for parvovirus in this population will avoid erythrocyte transfusion and should prevent transmission of the virus to other persons, including immunosuppressed persons and women of child-bearing age.     

Productive infection by B19 parvovirus of human erythroid bone marrow cells in vitro

B19 parvovirus, the cause of fifth disease and transient aplastic crisis, has been successfully propagated in suspension cultures of human erythroid bone marrow cells obtained from patients with sickle cell disease and stimulated by erythropoietin. B19 inoculation in vitro resulted in a marked decline in identifiable erythroid cells over seven to nine days of incubation. Characteristic giant early erythroid cells were seen on Wright's-Giemsa stain of infected cultures. By in situ hybridization, 30% to 40% of erythroblasts were infected at 48 hours; a similar proportion of cells showed B19 capsid protein by immunofluorescence. B19 DNA was present in erythroblasts but not in the leukocyte fraction of bone marrow. B19 replication, as determined by Southern analysis, and B19 encapsidation, as determined by sensitivity of isolated cell fractions to DNase I, were restricted to the nuclei. B19 DNA was detectable in the nuclei from infected cultures beginning at 18 hours and in the supernatant at 32 hours; B19 genome copy number was estimated at about 25,000 to 30,000/infected cell at 48 hours. Recovery of virus depended on the multiplicity of infection (moi); at low moi, approximately 200x input virus was recovered from total cultures and 50x from the culture supernatants. Virus released into the supernatant was as infectious or more infectious than virus obtained from sera of infected patients. Human erythroid bone marrow culture represents a safe in vitro system for the elucidation of the cellular and molecular biology of the pathogenic B19 parvovirus.     

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.     

Parvovirus B19 infection in children with a variety of hematological disorders

This study was carried out to detect Parvovirus B19 (PB19) DNA together with its antibodies in the sera of children with a range of hematological disorders to clarify the contribution of this infection to changes observed in hematological picture in those populations. This study included 85 pediatric patients with different hematological disorders. Twenty healthy subjects with matched age and sex were included as controls. Patients were classified into four groups; group I included 25 patients with hemolytic anemia in aplastic crisis, group II included 20 patients with hemolytic anemia without aplastic crisis, group III included 20 acute leukemia patients under chemotherapy, group IV included 20 patients with recently diagnosed acute leukemia. Virological study for PB19 included determination of specific IgG & IgM together with viral DNA by polymerase chain reaction (PCR). In all groups of patients with positive markers for PB19, there were statistically significant differences in the mean Hb concentration and RBC count (P < 0.001 for each), presence of neutropenia (P = 0.003) and lymphocytosis (P < 0.001) compared to controls. There was statistically significant difference in the prevalence of PB19 IgM, IgG and PCR among studied groups compared to control group. In group I and group II IgG had the highest positive rate (56 and 35%, respectively). In group III IgG also had a high positive rate (45%). However, in group IV IgM had the highest positive rate (50%) followed by PCR (45%) then IgG (40%). In conclusion, PB19 infection is detected in high rates among children with hematological disorders. PB19 must be suspected and screened for when there is anemia in those patients associated with neutropenia and lymphocytosis. In patients with acute leukaemia under chemotherapy who have unexpected anemia, neutropenia and lymphocytosis Parvovirus infection should be considered before a change of chemotherapy protocol. Screening of blood for PB19 may be helpful in understanding the epidemiology of infection with this virus. The direct detection of DNA by PCR in sera needs to be coupled with serology for a more reliable diagnosis of PB19 infections in these children.     

Parvovirus-induced aplastic crisis in a child with hereditary spherocytosis: studies on the mechanisms of hemopoietic suppression

A 4 4/12-year-old girl with hereditary spherocytosis (HS) who presented with an aplastic crisis during a human parvovirus (HPV) B19 infection is reported. IgM and IgG antibodies to the HPVB19 and HPV19 DNA were detected. Each of Leu 7+, Leu 11+ and HLA-DR+ cells increased. OKT4/OKT8 ratio decreased to 0.71. In order to investigate the mechanism of aplastic crisis, we used an in vitro culture technique for erythroid and granulocyte-macrophage progenitor cells (BFU-E, CFU-E and CFU-C). The patient's HPV19 DNA-containing aplastic phase serum inhibited the formation of BFU-E, CFU-E and CFU-C. After removal of the adherent cells from the aplastic phase bone marrow, the numbers of BFU-E significantly increased. These results suggest that aplastic crisis of the patient with HS was caused by HPVB19, and that monocytes-macrophages and NK cells played an important role in the pathogenesis of aplastic crisis.     

Susceptibility of human erythropoietic cells to B19 parvovirus in vitro increases with differentiation

B19 human parvovirus is the etiologic agent of transient aplastic crisis. To better understand B19 virus-induced hematopoietic suppression, we studied the host cell range of the virus using in vitro bone marrow cultures. First, B19 virus replication was examined in the presence of various purified cytokines using DNA dot blot analysis. Replication was detected only in erythropoietin-containing cultures. The other cytokines (granulocyte/macrophage colony-stimulating factor [GM-CSF], G-CSF, M-CSF, interleukin-1 [IL-1], IL-2, IL-3, and IL-6) did not support virus replication, indicating the restriction of B19 virus replication to the erythroid cell lineage. Second, hematopoietic progenitor cells were serially assayed in B19-infected and uninfected bone marrow cultures. At initiation, B19 virus infection caused marked and moderate reduction in colony-forming unit erythroid (CFU-E) and burst-forming unit erythroid (BFU-E) numbers, respectively, without affecting CFU-Mix and CFU-GM numbers. Interestingly, the recovery of the erythroid progenitor numbers was observed at a late stage of cultures despite the sustained reduction in erythroblasts. The cells in the bursts derived from such reappearing BFU-E did not contain the virus genome. Although infectious virus was detected in the culture supernatants, the cultured CFU-E harvested at day 5 was relatively resistant to B19 virus infection compared with the CFU-E in fresh bone marrow. These findings suggest that pluripotent stem cells escaped B19 virus infection and restored the erythroid progenitor cells later in infected cultures. We conclude that the target cells of B19 virus are in the erythroid lineage from BFU-E to erythroblasts, with susceptibility to the virus increasing along with differentiation. Furthermore, the suppression of erythropoiesis and the subsequent recovery of the erythroid progenitor numbers in B19-infected liquid cultures may be analogous in part to the clinical features of B19 virus-induced transient aplastic crisis.     

Parvovirus B19 infection in children with a variety of hematological disorders

This study was carried out to detect Parvovirus B19 (PB19) DNA together with its antibodies in the sera of children with a range of hematological disorders to clarify the contribution of this infection to changes observed in hematological picture in those populations. This study included 85 pediatric patients with different hematological disorders. Twenty healthy subjects with matched age and sex were included as controls. Patients were classified into four groups; group I included 25 patients with hemolytic anemia in aplastic crisis, group II included 20 patients with hemolytic anemia without aplastic crisis, group III included 20 acute leukemia patients under chemotherapy, group IV included 20 patients with recently diagnosed acute leukemia. Virological study for PB19 included determination of specific IgG & IgM together with viral DNA by polymerase chain reaction (PCR).

In all groups of patients with positive markers for PB19, there were statistically significant differences in the mean Hb concentration and RBC count (P < 0.001 for each), presence of neutropenia (P = 0.003) and lymphocytosis (P < 0.001) compared to controls. There was statistically significant difference in the prevalence of PB19 IgM, IgG and PCR among studied groups compared to control group. In group I and group II IgG had the highest positive rate (56 and 35%, respectively). In group III IgG also had a high positive rate (45%). However, in group IV IgM had the highest positive rate (50%) followed by PCR (45%) then IgG (40%).

In conclusion, PB19 infection is detected in high rates among children with hematological disorders. PB19 must be suspected and screened for when there is anemia in those patients associated with neutropenia and lymphocytosis. In patients with acute leukaemia under chemotherapy who have unexpected anemia, neutropenia and lymphocytosis Parvovirus infection should be considered before a change of chemotherapy protocol. Screening of blood for PB19 may be helpful in understanding the epidemiology of infection with this virus. The direct detection of DNA by PCR in sera needs to be coupled with serology for a more reliable diagnosis of PB19 infections in these children.     

B19 virus--a pathogenic human parvovirus

B19 virus is the first human virus to be shown to be a member of the parvovirus genus. This review is concerned with the diseases associated with B19 virus, their nature, pathogenesis and diagnosis. The virus was discovered by chance in blood donors but has been shown to be a common infection of childhood. Infection may be asymptomatic or associated with mild, non-specific symptoms. The most common specific clinical manifestation is an erythematous rash illness which often has the classical features of erythema infectiosum. Often, however, it is described simply as rubelliform and only laboratory tests can distinguish B19 and rubella virus infections. Joint involvement is the most common complication of B19 virus infection occurring especially in adult females. It often involves the joints of the hands and wrists, clears rapidly in most patients but may persist for months or years in a few. B19 virus is also the principle cause of the transient aplastic crisis which complicates chronic haemolytic anaemia. This has been demonstrated repeatedly in sickle cell anaemia and hereditary spherocytosis and in individual cases of other haemolytic anaemias. The pathogenesis of the aplastic crisis is related to the ability of B19 virus to infect and damage early erythroid progenitor cells. Volunteer studies in normal individuals have demonstrated that this is a regular event occurring about a week after infection via the respiratory tract. Rash illness and joint involvement occur 7 to 10 days later and are presumably immune mediated. Diagnosis of B19 virus infection can be achieved by detection of the viraemia (aplastic crisis) or by detection of virus specific IgM antibody (all diseases).(ABSTRACT TRUNCATED AT 250 WORDS)     

Study of chronic hemolytic anaemia patients in Rio de Janeiro: prevalence of anti-human parvovirus B19 IgG antibodies and the development aplastic crises

The prevalence of anti-human parvovirus B19 IgG antibodies was determined in sera from 165 chronic hemolytic anemia patients, receiving medical care at Instituto Estadual de Hematologia (IEHE), Rio de Janeiro, during the year of 1994. This sample represents around 10% of the chronic hemolytic anemia patients attending at IEHE. Most of these patients (140) have sickle cell disease. Anti-B19 IgG antibodies were detected in 32.1% of patients. No statistically significant difference (p > 0.05) was seen between IgG antibody prevalence in male (27.8%) and female (35.5%) patients. Anti-B19 IgG antibodies were more frequent in older (37.6%) than younger (28.2%) than 20 years old patients, although this difference had no statistical significance (p > 0.05). Anti-B19 IgG antibody prevalence showed that 67.9% of patients enrolled in the study were susceptible to B19 acute infection. With the aim to detect acute B19 infection, patients follow up continued until February 1996. During this period four patients presented transient aplastic crisis due to human parvovirus B19 as confirmed by the detection of specific IgM antibodies. All four patients were younger than 20 years old, and 3 were younger than 10 years old. Three of them were sickle cell disease patients. Three of the four acute B19 infection occurred during 1994 springtime.     

Polymerase chain reaction with double primer pairs for detection of human parvovirus B19 induced aplastic crises in family outbreaks.

Parvovirus B19 DNA can be detected by polymerase chain reaction with double primer pairs (nested PCR). Recent infection was documented by a retrospective serological study using Parvoscan-B19 enzyme linked immunosorbent assay (EIA) for detection of B19 human parvovirus IgM and IgG antibodies in serum or plasma specimens. In 3 families B19 outbreaks caused aplastic crises necessitating blood transfusion in 5 children and 1 adult with hereditary sphaerocytosis. Four members from 2 of the families had clinically overt haemolytic anaemia prior to the event. Two members in another family presented with an aplastic crisis disclosing the underlying chronic haemolytic disease. All 7 patients were identified as PCR positive in serum samples taken 3-14 days after the onset of symptoms. Comparison with dot blot hybridization revealed detectable DNA in only 2/3 PCR positive patients. Thus, nested PCR is more sensitive than the dot blot hybridization method and is therefore a suitable complement to the antibody assay for identifying recent B19 infection.     

Severe aplastic anemia associated with human parvovirus B19 infection in a patient without underlying disease

 Human parvovirus B19 (B19 virus) infection is known to induce aplastic crisis in patients with hemolytic anemia. In healthy subjects, B19 infection may sometimes cause mild pancytopenia, but these changes are transient and recovery is spontaneous. We report the first case of aplastic anemia in a previously healthy boy without any underlying diseases, following asymptomatic infection with the B19 virus. Laboratory examination initially showed thrombocytopenia, mild leukopenia in the peripheral blood, and severe hypoplastic bone marrow. Since pancytopenia developed and worsened progressively, immunosuppressive therapy was given, resulting in a complete remission. Despite the lack of an infectious prodrome, serological and histological analysis revealed an underlying infection with the B19 virus. Thus, B19 virus infection must be considered one of the causes of aplastic anemia in patients without underlying hemolytic anemia and an apparent episode of the viral infection. Received: August 28, 1998 / Accepted: November 18, 1998     

Acute Parvovirus B19 Infection Leading to Severe Aplastic Anemia in a Previously Healthy Adult Female

Human Parvovirus B19 has been linked to a variety of diseases. One of the most common complications is transient aplastic crisis in patients with chronic hemolytic anemia. Very few case reports have implicated this virus as a putative etiology behind hepatitis and severe aplastic anemia in immuno competent individuals. We report a case of severe aplastic anemia in a previously healthy adult female due to acute parvovirus B19 infection. Laboratory examination showed pancytopenia in peripheral blood and severe hypoplastic bone marrow on biopsy. Serological analysis (ELISA) revealed acute Parvovirus B19 infection. In the face of unavailable HLA matched bone marrow donor, immuno-supressive therapy was contemplated, but could not be given because of financial constraints. Pancytopenia persists till date, 4 months after the diagnosis, with the patient requiring repeated packed red cell and irradiated platelet transfusions. Thus, acute infection with this virus must be considered a cause of acquired aplastic anemia even in individuals without underlying disease.     

Aplastic crisis due to human parvovirus B19 infection in hereditary hemolytic anaemia.

Specific anti-B19 IgM was demonstrated in sera from three children showing transient aplastic crisis. A two years-old boy living in Rio de Janeiro suffering from sickle-cell anaemia showed the crisis during August, 1990. Two siblings living in Santa Maria, RS, developed aplastic crisis during May, 1991, when they were also diagnosed for hereditary spherocytosis. For a third child from this same family, who first developed aplastic crisis no IgM anti-B19 was detected in her sera.     

Frequent infection with a viral pathogen,parvovirus B19, in rheumatic diseases of childhood

OBJECTIVE: To find further evidence of the association of parvovirus B19 infection with juvenile rheumatic diseases, and to get new insights into the immunopathogenesis of these diseases. METHODS: Paired serum and synovial fluid samples from 74 children with rheumatic disease were analyzed with respect to their content of viral DNA and antibodies directed against the B19 viral proteins VP1, VP2, and NS1. Control sera from 124 children with noninflammatory bone diseases or growth retardation were also analyzed. The sequence of the viral DNA, amplified by polymerase chain reaction (PCR), was determined. IgG-complexed virus was isolated from sera and synovial fluid by adsorption to protein A beads. The amount of free virus versus immunocomplexed virus particles was determined by quantification of the viral genomes by quantitative PCR. RESULTS: Twenty-six of the 74 patients (35%) had detectable amounts of parvovirus B19 DNA in the serum (n = 22 [30%]) and/or the synovial fluid (n = 16 [22%]), whereas only 9 of the 124 control sera (7%) were positive for the viral DNA (P < 0.0001). Forty-six patients (62%) had serum IgG against the structural proteins, indicating past infection with B19. NS1-specific antibodies were detected in sera from 29 patients (39%) and 27 controls (22%) (P < 0.001). In addition, 3 patients (4%) showed VP2-specific IgM. In 15 patients, viral DNA could be repeatedly detected in followup samples of serum and synovial fluid. Sequencing revealed low-degree nucleotide variations that are in the range of genotype 1 of parvovirus B19. Immunocomplexed virus was present in varying amounts, both in the sera and in the synovial fluid samples. CONCLUSION: Parvovirus B19 is frequently found in serum or synovial fluid of children with rheumatism. The rate of persistent B19 infection in these patients is significantly higher than in age-matched controls.     

Seroepidemiology of infection with Toxoplasma gondii in healthy blood donors of Durango, Mexico

Background

Human parvovirus B19 is the etiologic agent of erythema infectiosum in children. It is also associated with other clinical manifestations in different target groups. Patients with chronic hemolytic anemia are at high risk of developing acute erythroblastopenia following infection by the virus. They usually become highly viremic and pose an increased risk of virus transmission. Close monitoring of such high risk groups is required for epidemiologic surveillance and disease prevention activities. Here we report a molecular epidemiological study on B19 virus infection in Tunisian patients with chronic hemolytic anemia.

Methods

This study was conducted on 92 young chronic hemolytic anemia patients who attended the same ward at the National Bone Marrow Transplantation Center of Tunis and 46 controls from a different hospital. Screening for IgM and IgG anti-B19 antibodies was performed using commercially available enzyme immunoassays and B19 DNA was detected by nested PCR in the overlapping VP1/VP2 region. DNA was sequenced using dideoxy-terminator cycle sequencing technology.

Results

Anti-parvovirus B19 IgG antibodies were detected in 26 of 46 sickle-cell anemia patients, 18 of 46 β-thalassemia and 7 of 46 controls. Anti-parvovirus B19 IgM antibodies were detected only in 4 of the sickle-cell anemia patients: two siblings and two unrelated who presented with acute erythroblastopenia at the time of blood collection for this study and had no history of past transfusion. B19 DNA was detected only in sera of these four patients and the corresponding 288 bp nested DNA amplicons were sequenced. The sequences obtained were all identical and phylogenetic analysis showed that they belonged to a new B19 virus strain of Genotype1.

Conclusion

A new parvovirus B19 strain of genotype1 was detected in four Tunisian patients with sickle-cell anemia. Virus transmission appeared to be nosocomial and resulted in acute erythroblastopenia in the four patients. The possibility of independent transmission of this B19 variant to the patients is unlikely in light of the present epidemiological data. However this possibility cannot be ruled out because of the low genetic variability of the virus.     

Antibodies against monocytes and endothelial cells in the sera of patients with atherosclerotic peripheral arterial disease

We looked for antibodies against endothelial cells, monocytes, fibroblasts, lymphocytes and Epstein-Barr virus transformed lymphocytes in the sera of 28 elderly and 18 middle-aged patients with atherosclerotic peripheral arterial disease and 13 controls. Inclusion criteria were symptomatic peripheral arterial disease with intermittent claudication and ankle/radial Doppler pressure ratio less than 0.7 in the patient group and greater than 1 in the controls. The sera were tested using a standard cytotoxic technique against a cell panel of monocytes, T and B lymphocytes from 5 donors, and against endothelial cells, fibroblasts and Epstein-Barr virus transformed lymphocytes from one umbilical cord vein and blood. The sera of 30 of 46 (65.2%) patients showed toxicity against monocytes from at least one member of the cell panel and 12 of 19 sera tested (63%) reacted with endothelial cells. Only one of the control sera was positive against monocytes and none reacted with endothelial cells. None of the sera of either patients or controls contained cytotoxic antibodies against T and B lymphocytes, Epstein-Barr virus transformed lymphocytes or fibroblasts. The selective cytotoxicity suggests that the antibodies detected are not against HLA-antigens (which are expressed by normal lymphocytes and Epstein-Barr virus lymphocytes). Our results suggest that immune phenomena occur in atherosclerosis.     

Self-assembled B19 parvovirus capsids, produced in a baculovirus system, are antigenically and immunogenically similar to native virions.

B19 parvovirus is pathogenic in humans, causing fifth disease, transient aplastic crisis, some cases of hydrops fetalis, and acquired pure red cell aplasia. Efforts to develop serologic assays and vaccine development have been hampered by the virus's extreme tropism for human bone marrow and the absence of a convenient culture system. We constructed recombinants containing either the major (VP2) or minor (VP1) structural proteins of B19 in a baculovirus-based plasmid, from which the polyhedrin gene had been deleted; these recombinant plasmids were used to generate recombinant infectious baculovirus. Subsequent infection of insect cells in vitro resulted in high-level expression of either B19VP1 or VP2. Parvovirus capsids were obtained by self-assembly in cell cultures coinfected with either VP1- and VP2-containing baculoviruses or, surprisingly, VP2-containing baculoviruses alone. Empty B19 capsids composed of VP1 and VP2 could replace serum virus as a source of antigen in a conventional immunoassay for detection of either IgG or IgM antiparvovirus antibodies in human serum. Immunization of rabbits with capsids composed of VP1 and VP2 resulted in production of antisera that recognized serum parvovirus on immunoblot and neutralized parvovirus infectivity for human erythroid progenitor cells. Baculovirus-derived parvovirus antigen can substitute for scarce viral antigen in immunoassays and should be suitable as a human vaccine.