Outbreak of aplastic crises in sickle cell anaemia associated with parvovirus-like agent

Biological and immunological relations among human parvovirus B19 genotypes 1 to 3

The human parvovirus B19 is now divided into three genotypes: type 1 (prototype), type 2 (A6- and LaLi-like), and type 3 (V9-like). In overall DNA sequence, the three virus types differ by approximately 10%. The most striking DNA dissimilarity, of >20%, is observed within the p6 promoter region. Because of the scarcity of data on the biological activities and pathogenetic potentials of virus types 2 and 3, we examined the functional characteristics of these virus types. We found the activities of the three p6 promoters to be of equal strength and to be most active in B19-permissive cells. Virus type 2 capsid protein VP2, alone or together with VP1, was expressed with the baculovirus system and was shown to assemble into icosahedral parvovirus-like particles, which were reactive in the hemagglutination assay. Furthermore, sera containing DNA of any of the three B19 types were shown to hemagglutinate. The infectivities of these sera were examined in two B19-permissive cell lines. Reverse transcription-PCR revealed synthesis of spliced B19 mRNAs, and immunofluorescence verified the production of NS and VP proteins in the infected cells. All three genotypes showed similar functional characteristics in all experiments performed, showing that the three virus types indeed belong to the same species, i.e., human parvovirus B19. Additionally, the antibody activity in sera from B19 type 1- or type 2-infected subjects (long-term immunity) was examined with homo- and heterologous virus-like particles. Cross-reactivity of 100% was observed, indicating that the two B19 genotypes comprise a single serotype.

Conformational changes in the VP1-unique region of native human parvovirus B19 lead to exposure of internal sequences that play a role in virus neutralization and infectivity

The unique region of the capsid protein VP1 (VP1u) of human parvovirus B19 (B19) elicits a dominant immune response and has a phospholipase A(2) (PLA(2)) activity, which is necessary for the infection. In contrast to the rest of the parvoviruses, the VP1u of B19 is thought to occupy an external position in the virion, making this region a promising candidate for vaccine development. By using a monoclonal antibody against the most-N-terminal portion of VP1u, we revealed that this region rich in neutralizing epitopes is not accessible in native capsids. However, exposure of capsids to increasing temperatures or low pH led to its progressive accessibility without particle disassembly. Although unable to bind free virus or to block virus attachment to the cell, the anti-VP1u antibody was neutralizing, suggesting that the exposure of the epitope and the subsequent virus neutralization occur only after receptor attachment. The measurement of the VP1u-associated PLA(2) activity of B19 capsids revealed that this region is also internal but becomes exposed in heat- and in low-pH-treated particles. In sharp contrast to native virions, the VP1u of baculovirus-derived B19 capsids was readily accessible in the absence of any treatment. These results indicate that stretches of VP1u of native B19 capsids harboring neutralizing epitopes and essential functional motifs are not external to the capsid. However, a conformational change renders these regions accessible and triggers the PLA(2) potential of the virus. The results also emphasize major differences in the VP1u conformation between natural and recombinant particles.

Clinical aspects of parvovirus B19 infection

Parvovirus B19 is a significant human pathogen that causes a wide spectrum of clinical complications ranging from mild, self-limiting erythema infectiosum in immunocompetent children to lethal cytopenias in immunocompromised patients and intrauterine foetal death in primary infected pregnant women. The infection may also be persistent and can mimic or trigger autoimmune inflammatory disorders. Another important clinical aspect to consider is the risk of infection through B19-contaminated blood products. Recent advances in diagnosis and pathogenesis, new insights in the cellular immune response and newly discovered genotypes of human parvoviruses form a platform for the development of modern therapeutic and prophylactic alternatives.

Molecular and functional analyses of a human parvovirus B19 infectious clone demonstrates essential roles for NS1, VP1, and the 11-kilodalton protein in virus replication and infectivity

In an attempt to experimentally define the roles of viral proteins encoded by the B19 genome in the viral life cycle, we utilized the B19 infectious clone constructed in our previous study to create two groups of B19 mutant genomes: (i) null mutants, in which either a translational initiation codon for each of these viral genes was substituted by a translational termination codon or a termination codon was inserted into the open reading frame by a frameshift; and (ii) a deletion mutant, in which half of the hairpin sequence was deleted at both the 5' and the 3' termini. The impact of these mutations on viral infectivity, DNA replication, capsid protein production, and distribution was systematically examined. Null mutants of the NS and VP1 proteins or deletion of the terminal hairpin sequence completely abolished the viral infectivity, whereas blocking expression of the 7.5-kDa protein or the putative protein X had no effect on infectivity in vitro. Blocking expression of the proline-rich 11-kDa protein significantly reduced B19 viral infectivity, and protein studies suggested that the expression of the 11-kDa protein was critical for VP2 capsid production and trafficking in infected cells. These findings suggest a previously unrecognized role for the 11-kDa protein, and together the results enhance our understanding of the key features of the B19 viral genome and proteins.

Erythrovirus B19 infection in acquired immunodeficiency syndrome: screening by histopathology, immunohistochemistry, and in situ hybridization

Erythrovirus B19 infects erythrocytic progenitors, transiently interrupting erythropoiesis. In AIDS patients it causes chronic anemia amenable to treatment. We looked for evidences of B19 infection in stored bone marrow material from patients with acquired immunodeficiency syndrome. Histological sections were made from stored paraffin blocks from 33 autopsies (39 blocks) and 35 biopsies (45 blocks, 30 patients) performed from 1988 to 2002. They were examined after hematoxylin-eosin (HE) staining, immunohistochemical (IHC), and in situ hybridization. HE revealed intra-nuclear inclusion bodies ("lantern cells") suggesting B19 infection in 19 sections corresponding to 19 of 63 patients examined with this test. Seven of 78 sections subjected to immunohistochemistry were positive, corresponding to 7 of 58 patients examined with this test. Fourteen sections corresponding to 13 of the 20 HE and/or IHC positive patients were subjected to in situ hybridization, with six positives results. Among the 13 patients subjected to the three techniques, only one gave unequivocal positive results in all and was considered a true positive. The frequency of B19 infection (1/63 patients) in the material examined can be deemed low.

Parvovirus B19 infection after transplantation: a review of 98 cases

BACKGROUND

Infections with parvovirus B19 (PVB19) can cause significant morbidity in transplant recipients.

METHODS

To characterize the epidemiology and clinical spectrum of posttransplant PVB19 infection, we reviewed all cases at our institution during a 16-year period, summarized the data from 91 cases published in the medical literature, and performed longitudinal molecular surveillance for PVB19 DNAemia among 47 solid organ and hematopoietic stem cell transplant recipients.

RESULTS

The median time to onset of PVB19 disease was 7 weeks after transplantation. Anemia, leukopenia, and thrombocytopenia were present in 98.8%, 37.5%, and 21.0% of patients, respectively. Hepatitis, myocarditis, and pneumonitis were also reported in association with PVB19 disease. Allograft tissue loss or dysfunction was observed at the time of PVB19 disease in 10% of cases. At the onset of disease, PVB19 IgM serological test results were negative in 29% of cases. Almost all patients (96%) with anti-PVB19 IgM had a positive PVB19 polymerase chain reaction assay result. Intravenous immunoglobulin was the most commonly used treatment modality. Three of 98 patients died of myocarditis and cardiogenic shock associated with PVB19 disease. Molecular surveillance throughout the first year after transplantation did not reveal PVB19 DNAemia in 47 anemic solid organ and hematopoietic stem cell transplant patients.

CONCLUSIONS

PVB19 is a rare but clinically significant infection that manifests as refractory anemia during the posttransplantation period. The use of polymerase chain reaction for diagnosis is particularly helpful in immunosuppressed transplant patients who may fail to mount antibodies against PVB19 during active infection.

A cluster of parvovirus B19 infections in renal transplant recipients: a prospective case series and review of the literature

Up to 9% of renal transplant recipients have severe multifactorial erythropoietin-resistant anemia. Human parvovirus B19 (PVB19) infection can cause severe anemia and is likely underreported. Sparse information on epidemiology and management in this population exists. To address these issues, after our first index case, we modified our clinical practice to prospectively screen patients with persistent hemoglobin (Hb) <10 mg/dL for PVB19 infection after excluding common causes of anemia including erythropoietin resistance. Potentially infected patients were further evaluated by serology, qualitative polymerase chain reaction (quPCR) and bone marrow biopsy (BMB) for cytomegalovirus, Epstein-Barr virus, PVB19 and other etiologies. Over 3 months, 212 kidney recipients visited outpatient clinics. Of 52 recipients with anemia, 8 had an Hb <10 mg/dL with erythropoietin resistance and were screened for PVB19 infection. Three cases had PVB19 infection by quPCR and often-inconclusive serology/BMB results. Cases had immunosuppression reduced and received IVIG (0.5 gm/kg x 4 doses) with recovery from anemia, viral clearance in two cases and one recurrence. PVB19-mediated anemia occurred in up to three out of eight (38%) screened kidney recipients with Hb <10 mg/dL resistant to erythrypoietin. We recommend prospective risk stratification for this population, high indices of suspicion using at least qualitative techniques for diagnosis and treatment goal for viral eradication.

Infectious disease in pediatric out-of-home child care

Provision of some form of child care outside of the home is certainly not a new phenomenon. In the past, most out-of-home care was provided by a relative, a friend, or someone who had a specific relationship with the family of the child. The frequency of utilization of child care centers for out-of-home care and the different formats of out-of-home care services has increased within recent decades and will vary by geographic location. Also, there is an increased utilization of temporary child care such as "mother's day out" or baby-sitting services provided at churches, grocery stores, and other places. Child care centers represent special risks for transmission of infectious agents because young children exhibit high susceptibility to many community-acquired viruses and bacteria; they lack developmental understanding required for good hygiene; and they frequently receive antibiotics (appropriately and inappropriately). Infections acquired in child care centers can significantly impact the health of the children who acquire the infection and also result in significant economic impacts on the child's family, particularly if 1 or more of the parents has to lose time from work. In the United States, it is estimated that families who have children in child care lose 13 days of work per year for all types of infections. Interventions that have proven valuable for reducing infections within child care centers include the following: (1) formal written policies for infection control within the child care center, (2) formal education of child care center staff concerning infection control practices (needs to be repeated; preferably on a recurring basis), (3) good hand hygiene by both staff and children, (4) appropriate cleaning of contaminated surfaces, (5) separation of food preparation and diaper changing, (6) exclusion of certain ill children, (7) cohorting ill children when exclusion is not possible, (8) ensuring adequate age-appropriate immunization of child care attendees and staff, and (9) optimal ratios of children to staff.

A case of hemoglobin SC disease with cold agglutinin-induced hemolysis

Children with sickle cell disease commonly require red blood cell (RBC) transfusion. We report the first case of hemoglobin (Hb) SC disease with development of severe anemia induced by cold agglutinin hemolysis after Mycoplasma infection. Complete blood count (CBC) showed falsely decreased RBC count and hematocrit and falsely elevated MCV and MCHC. Peripheral blood smear showed RBC clumping at room temperature; this disappeared after warming to 37 degrees C. Anti C3b-C3d was present on red cells, and indirect antiglobulin test revealed a circulating cold agglutinin. Furthermore, anti-Mycoplasma pneumoniae IgM antibody was detected in serum. Careful evaluation of CBCs and peripheral blood smears is required in cases of worsening anemia among sickle cell patients and consideration should be given to cold hemagglutinin disease as an etiology.

Parvovirus B19 infections

Abstract Parvovirus B19 infections cause a wide range of clinical findings, including erythema infectiosum, "glove-and-socks" syndrome, arthropathies, red cell aplasia, and intrauterine infections. The condition can be diagnosed serologically. The prognosis is excellent in healthy, immunocompetent individuals.

Advances in the biology, diagnosis and host-pathogen interactions of parvovirus B19

Increased recognition of parvovirus B19 (B19), an erythrovirus, as a significant human pathogen that causes fetal loss and severe disease in immunocompromised patients has resulted in intensive efforts to understand the pathogenesis of B19-related disease, to improve diagnostic strategy that is deployed to detect B19 infection and blood-product contamination and, finally, to elucidate the nature of the cellular immune response that is elicited by the virus in diverse patient cohorts. It is becoming clear that at least three related erythrovirus strains (B19, A6/K71 and V9) are circulating in the general population and that viral entry into target cells is mediated by an expanding range of cellular receptors, including P antigen and beta-integrins. Persistent infection by B19 is emerging as a contributory factor in autoimmune disease, a hypothesis that is constrained by the detection of B19 in the skin of apparently healthy individuals. B19 infection during pregnancy may account for thousands of incidences of fetal loss per annum in Europe, North America and beyond, yet there is currently only minimal screening of pregnant women to assess serological status, and thereby risk of infection, upon becoming pregnant. Whilst major advances in diagnosis of B19 infection have taken place, including standardization of serological and DNA-based detection methodologies, blood donations that are targeted at high-risk groups are only beginning to be screened for B19 IgG and DNA as a means of minimizing exposure of at-risk patients to the virus. It is now firmly established that a Th1-mediated cellular immune response is mounted in immunocompetent individuals, a finding that should contribute to the development of an effective vaccine to prevent B19 infection in selected high-risk groups, including sickle-cell anaemics.

Clinical presentation of parvovirus B19 infection in children with aplastic crisis

The records of 22 children with parvovirus B19-induced aplastic crisis were reviewed. The group consisted of 16 children with sickle cell hemoglobinopathies and 6 with hereditary spherocytosis. Children presented to the hospital 0.5 to 8 days (mean, 2.4 days) after the onset of symptoms. The children with sickle-cell disease presented earlier (mean, 1.4 days) than did children with hereditary spherocytosis (mean, 5 days; P = 0.02. Fever was the most common symptom, occurring in 73% of children. Rash did not occur in either group. Reticulocyte counts began to rise 1 week after onset of illness associated with a rise in parvovirus B19-specific IgG antibody. These data suggest that parvovirus B19 infection in children with sickle-cell hemoglobinopathies and heredity spherocytosis differs from infection in normal children.

Epidemiology of human parvovirus B19 in children with sickle cell disease

Human parvovirus (HPV) B19 causes significant morbidity and mortality in children with sickle cell disease (SCD), but little data are published about the epidemiology of HPV B19 infection and its associated complications in this patient population. In this study, prevalence and incidence rates of HPV B19 were determined in 633 patients with SCD followed at The Children's Hospital of Philadelphia between November 1996 and December 2001. Thirty percent (30%) were HPV B19 immunoglobulin G (IgG) positive at first testing, and the 70% without evidence of past HPV B19 infection were tested annually. One hundred ten patients developed evidence of HPV B19 infection for an incidence rate of 11.3 per 100 patient years. Sixty-eight episodes of HPV B19-induced transient red cell aplasia occurred with the following clinical events: fever (89.7%), pain (61.8%), acute splenic sequestration (19.1%), and acute chest syndrome (11.8%). Pain, fever, and acute splenic sequestration were more frequent events with acute HPV B19 infections compared with acute events in uninfected patients. The results of this epidemiologic study, the largest and most comprehensive to date, justify the development of HPV B19 prevention strategies to diminish the frequent and often severe complications associated with HPV B19 infections in patients with SCD.

Subclinical parvovirus B19 infection in children with sickle cell anemia

PURPOSE

To investigate the prevalence and clinical consequences of previous parvovirus B19 exposure in a large cohort of pediatric patients with sickle cell anemia (SCA).

METHODS

Prospective serologic testing for previous parvovirus B19 exposure was performed in steady-state pediatric patients with SCA, either prior to starting hydroxyurea therapy or in preparation for transition to the adult service. A retrospective chart review was performed to ascertain whether patients had a documented history of a transient aplastic crisis.

RESULTS

The prevalence of serologic evidence of previous parvovirus infection increased with age. The overall prevalence in 102 children with SCA was 53%, ranging from 44% between 5 and 9 years of age to 71% between 17 and 21 years of age. Only 27% of patients had a previous clinically recognized transient aplastic crisis.

CONCLUSIONS

By the teenage years, most pediatric patients with SCA have serologic evidence of previous parvovirus B19 exposure. However, subclinical parvovirus infection appears to be common in children with SCA, since most patients have no documented previous transient aplastic crisis.

Neurological manifestations of human parvovirus B19 infection

Since its discovery, human parvovirus B19 has been linked with a broad spectrum of clinical syndromes. An aetiological role for the virus has been confirmed in erythema infectiosum, transient aplastic crisis, persistent infection manifesting as pure red cell aplasia in immunocompromised persons, non-immune hydrops fetalis and arthritis. Less commonly recognised, but receiving increasing attention recently, are the neurological manifestations, a variety of which have been described in patients with either clinically diagnosed or laboratory confirmed B19 infection. The purpose of this review is to summarise present knowledge of B19, its known and potential pathogenic mechanisms and its association with human diseases, particularly those with neurological manifestations. The outcome of the review supports an aetiological role of the virus in neurological disease. However, the pathogenesis remains unknown and elucidating this is a priority.

Human parvovirus B19

Parvovirus B19 (B19) was discovered in 1974 and is the only member of the family Parvoviridae known to be pathogenic in humans. Despite the inability to propagate the virus in cell cultures, much has been learned about the pathophysiology of this virus, including the identification of the cellular receptor (P antigen), and the control of the virus by the immune system. B19 is widespread, and manifestations of infection vary with the immunologic and hematologic status of the host. In healthy immunocompetent individuals B19 is the cause of erythema infectiosum and, particularly in adults, acute symmetric polyarthropathy. Due to the tropism of B19 to erythroid progenitor cells, infection in individuals with an underlying hemolytic disorder causes transient aplastic crisis. In the immunocompromised host persistent B19 infection is manifested as pure red cell aplasia and chronic anemia. Likewise, the immature immune response of the fetus may render it susceptible to infection, leading to fetal death in utero, hydrops fetalis, or development of congenital anemia. B19 has also been suggested as the causative agent in a variety of clinical syndromes, but given the common nature, causality is often difficult to infer. Diagnosis is primarily based on detection of specific antibodies by enzyme-linked immunosorbent assay or detection of viral DNA by dot blot hybridization or PCR. Treatment of persistent infection with immunoglobulin reduces the viral load and results in a marked resolution of anemia. Vaccine phase I trials show promising results.

Haematological response to parvovirus B19 infection in homozygous sickle-cell disease

Infection with human parvovirus B19 is known to cause aplastic crises in patients with homozygous sickle-cell disease. We studied the haematological consequences of parvovirus B19 infection in 280 such patients who had been followed up from birth in Jamaica. Evidence of seroconversion was routinely sought with a baculovirus-based, enzyme immunoassay in serum samples taken during aplastic crises and in all stored annual serum samples. 70% of patients had seroconverted by age 20 years; of 177 infections, haematological change was typical of aplastic crises in 118 (67%), minor in 16 (9%), and not discernible in 43 (24%). This assay increased the detection of unsuspected seroconversion-an observation important in planning a strategy for parvovirus B19 immunisation.

Evidence for persistence of parvovirus B19 DNA in livers of adults

Recent studies have suggested a pathogenic role of human parvovirus B19 (B19) in the development of acute fulminant liver failure in children. The hypothesis was based on the detection of B19 DNA in 8 of 10 explanted livers of children requiring liver transplantation. In the present study, explanted livers from 43 adults selected at random undergoing orthotopic liver transplantation for various reasons were examined. Pre-transplant sera were available from 40 patients of whom 35 (88%) were anti-B19 IgG-seropositive. All but one serum were negative for anti-B19 IgM antibody. By polymerase chain reaction, B19 DNA was detected in the livers of 15/35 (43%) anti-B19 IgG-positive patients, in 2/3 livers of patients with unknown anti-B19 antibody status, and in the initial transplant of an anti-B19 IgG-positive patient who underwent liver retransplantation, and whose own liver was negative for B19 DNA. In a second study group, liver and bone marrow samples from 23 autopsied adults selected at random were tested. Serum specimens were available from 22 individuals, of whom 17 (77%) were anti-B19 IgG-seropositive. All sera were negative for anti-B19 IgM antibody. B19 DNA was detected in the livers of 4/17 (24%) anti-B19 IgG-positive individuals, three of whom had also B19 DNA in their bone marrow. This is the first report demonstrating that B19 DNA is frequently present in livers of anti-B19 seropositive adults suggesting persistence of B19 in the liver. Further studies are needed to address whether B19 is an innocent bystander in the liver or whether the presence of B19 in liver is of biological and clinical significance.

Cerebrovascular complications and parvovirus infection in homozygous sickle cell disease

Human parvovirus B19 infection causes most clinically defined aplastic crises in homozygous sickle cell (SS) disease. With transfusion support, the outcome is generally benign; however, cerebrovascular complications in close temporal association with B19-induced aplastic crises have been described. We carried out a retrospective review, between 1978 and 1999, of 346 aplastic crises in patients with SS disease attending the Sickle Cell Clinic of the University Hospital of the West Indies, Kingston, Jamaica. Six cerebrovascular episodes, 5 with hemiplegia, occurred within 2 days of aplastic crises; and 4, all with features of encephalitis, occurred within 2 to 5 weeks. Hemiplegia in 2 children resolved completely, one is improving, and one persists 20 years later; one patient died from recurrent strokes. Of the 4 children whose events occurred later, all had seizure disorders and 2 had transient cortical blindness. The crude risk of cerebrovascular episodes in the 5-week interval after B19 infection was calculated as 58 times greater than expected, which is suggestive of a causal association.

RBC transfusion in sickle cell anemia (HbSS): experience from the Jamaican Cohort Study

BACKGROUND

RBC transfusion is widely advocated in the management of sickle cell anemia (SCA), but it carries potentially serious risks, especially in the setting of chronic transfusion. The Jamaican Sickle Cell Clinic is conservative in its use of transfusion, and this experience is presented to allow comparison with other centers in defining the role for transfusion in SCA.

STUDY DESIGN AND METHODS

Reported here is a retrospective, descriptive study of all RBC transfusions given to 311 subjects with SCA who were followed in a cohort study from birth and are, at this writing, 16.3 to 24.7 years old.

RESULTS

There were 520 transfusion episodes in 197 (63.3%) of the 311 subjects; 1 transfusion in 80 (41%) of those who received transfusion(s), 2 transfusions in 54 (27%), 3 transfusions in 21 (11%), 4 in 17 (9%), 5 in 9 (5%), and 6 or more in 16 (8%). Single transfusions were usual for acute anemia of aplastic crises or acute splenic sequestration, and multiple transfusions (up to 21 episodes) were usual in the prophylaxis of recurrent stroke. Indications were aplastic crisis (102), acute chest syndrome (90), acute splenic sequestration (75), stroke (62), septicemia (46), hypoplasia (40), hypersplenism (34), surgery (31), gastroenteritis (10), and miscellaneous (30).

CONCLUSION

Despite conservative transfusion use, 70.6 percent of patients had received at least one transfusion by 20 years of age in the Jamaican Sickle Cell Clinic:

Haematological consequences of parvovirus B19 infection

Parvovirus B19, a member of the Erythrovirus genus, is the only member of the Parvoviridae family known to be pathogenic in humans. Erythroviruses are so named because of their tropism and selective replication in erythroid progenitor cells. Haematological consequences of B19 infection arise due to a direct cytotoxic effect on erythroid progenitors in bone marrow with interruption of erythrocyte production. In addition, the physiology of host haematopoiesis and competence of the immune response each determines clinical manifestations of B19 infection: in individuals with underlying haemolytic disorders, B19 infection causes transient aplastic crisis; in immunocompromised patients, persistent B19 infection may develop that manifests as pure red cell aplasia and chronic anaemia; B19 infection in utero may result in fetal death, hydrops fetalis, or congenital anaemia. Diagnosis is based on examination of bone marrow and B19 virological studies. Treatment of persistent infection with immunoglobulin leads to a prompt resolution of the anaemia.

Quantitative direct probe method for the detection of parvovirus B19

Parvovirus B19 infection is associated with anemia and spontaneous abortions. While many qualitative assays are available, a few molecular-based quantitative methods have been described. This study reports the development and optimization of a quantitative direct-probe method for the detection of Parvovirus B19 DNA. Different concentrations of RNA probes were used to identify the optimal conditions for hybridizing to the target DNA. Detection of DNA was linear between concentrations of 2 ng/ml to 200 pg/ml. Because this method requires no enzymatic amplification, it is not susceptible to amplifier contamination or enzymatic inhibitors, and it can be applied to serum samples or paraffin-embedded tissue.

Infection of the erythroid cell line, KU812Ep6 with human parvovirus B19 and its application to titration of B19 infectivity

A human parvovirus B19 (B19) infectivity assay was developed using the erythroid cell line, KU812Ep6. KU812Ep6 was cloned for high efficiency infection with B19 in vitro, in the presence of erythropoietin by a limiting dilution method from the parent cell line, KU812. B19 was effectively propagated in KU812Ep6 and was detected for B19 antigens, VP1 and VP2. The titers of B19 positive sera measured with KU812Ep6 cells were in the range of 10(6) to 10(8) TCID50 ml. This KU812Ep6 infectivity assay had a 10(3)-10(4.5) higher sensitivity than the colony forming unit-erythroid (CFU-e) injury assay. It was calculated that one TCID50 needed 10(3) B19 genome copies, judging from the infectivity assay and semi-quantitative PCR. The KU812Ep6 infectivity assay was also used to determine infectivity of B19 in vitro, and to evaluate inactivation, as well as clearance of the virus. The inactivation of B19 by heating was carried out and infectivity declined from 10(4) TCID50 ml to < 10 TCID50 ml (lower limit of detection) at 60 degrees C for 3 h or at 70 degrees C for 30 min, but only decreased to 10(2.5) TCID50 ml at 50 degrees C for 8 h.

Human parvovirus B19 infection: its relationship with systemic lupus erythematosus

OBJECTIVES

The clinical presentation and outcome of four cases of human parvovirus-B19 (HPV-B19) infection, initially diagnosed as systemic lupus erythematosus (SLE), were reviewed and compared with similar cases previously reported in the literature. The relationship between HPV-B19 infection and SLE is discussed.

METHODS

The medical records of four patients with documented HPV-B19 infection, initially diagnosed as SLE, were reviewed and studied in detail. A Medline search from 1985 to 1997 was performed to identify other cases reported in the literature in which a relationship between HPV-B19 and SLE had been identified in both adults and children.

RESULTS

In all of our cases, the clinical findings (fever, rash, arthritis and malaise) and hematologic data (leukopenia, thrombocytopenia, anemia, presence of autoantibodies, hypocomplementemia, etc.) had initially suggested a diagnosis of juvenile SLE. Subsequently, evidence of HPV-B19 infection at the time of clinical presentation was ascertained. In three of these cases, the disease course was self-limiting with complete clinical remission and normalization of hematologic abnormalities within 18 months; one case, however, had persistent disease activity and repeated exacerbations.

CONCLUSIONS

The occurrence of HPV-B19 infection has been documented in patients with SLE, in particular in relation to disease onset. Similarities in clinical and immunological features of viral infections and SLE at presentation may hinder the differential diagnosis between these two conditions. The family history, a self-limiting disease course and certain disease specific clinical aspects may help the pediatrician formulate an accurate diagnosis. In our patients, HPV-B19 infection may have mimicked the onset of SLE in three cases, but triggered the disease in one.

Generation of neutralizing human monoclonal antibodies against parvovirus B19 proteins

Infections caused by human parvovirus B19 are known to be controlled mainly by neutralizing antibodies. To analyze the immune reaction against parvovirus B19 proteins, four cell lines secreting human immunoglobulin G monoclonal antibodies (MAbs) were generated from two healthy donors and one human immunodeficiency virus type 1-seropositive individual with high serum titers against parvovirus. One MAb is specific for nonstructural protein NS1 (MAb 1424), two MAbs are specific for the unique region of minor capsid protein VP1 (MAbs 1418-1 and 1418-16), and one MAb is directed to major capsid protein VP2 (MAb 860-55D). Two MAbs, 1418-1 and 1418-16, which were generated from the same individual have identity in the cDNA sequences encoding the variable domains, with the exception of four base pairs resulting in only one amino acid change in the light chain. The NS1- and VP1-specific MAbs interact with linear epitopes, whereas the recognized epitope in VP2 is conformational. The MAbs specific for the structural proteins display strong virus-neutralizing activity. The VP1- and VP2-specific MAbs have the capacity to neutralize 50% of infectious parvovirus B19 in vitro at 0.08 and 0.73 microgram/ml, respectively, demonstrating the importance of such antibodies in the clearance of B19 viremia. The NS1-specific MAb mediated weak neutralizing activity and required 47.7 micrograms/ml for 50% neutralization. The human MAbs with potent neutralizing activity could be used for immunotherapy of chronically B19 virus-infected individuals and acutely infected pregnant women. Furthermore, the knowledge gained regarding epitopes which induce strongly neutralizing antibodies may be important for vaccine development.

Human parvovirus B19 in rheumatoid arthritis

Viral arthritis occurs transiently in most cases, because the infection is self limiting. The arthropathy associated with human parvovirus B19, however, often lasts for more than 2 years and their clinical symptoms may resemble with those of rheumatoid arthritis. Data have been accumulating for the link of B19 infection with chronic polyarthropathy or rheumatoid arthritis (RA), and we discuss the possible mechanism for the role of B19 in the etiopathology of RA.

Human parvovirus B19 infection in organ transplant recipients

We report a 61-yr-old kidney transplant recipient with human Parvovirus B19 (HPV B19) infection presenting as a severe pancytopenia 1 month after transplantation. Bone marrow aspiration revealed severe erythroid hypoplasia with giant and dystrophic proerythroblasts. Bone marrow cells were positive for HPV B19 DNA detected by polymerase chain reaction (PCR). Pancytopenia resolved shortly after administration of intravenous immunoglobulins. Nineteen cases of HPV B19 infection in organ transplant recipients have been so far reported in the literature. Immunocompromised patients should be considered at risk from developing symptomatic HPV B19 infections. In such patients, specific anti-HPV B19 IgM and IgG antibodies may be absent or transient and therefore their negativity cannot rule out the diagnosis of HPV B19 infestation. Bone marrow smear morphological findings may suggest the diagnosis but testing for viral DNA by PCR is mandatory. Patients may spontaneously recover. However, since specific anti-viral therapy is not currently available, intravenous immunoglobulin administration appears to be the more efficacious treatment.

Sickle cell-like crisis and bone marrow necrosis associated with parvovirus B19 infection and heterozygosity for haemoglobins S and E

In the literature, heterozygosity for haemoglobins S and E is known as a clinically benign condition. Nevertheless, we present a case of double heterozygosity manifesting as an infarctive sickle cell-like crisis with acute chest syndrome and reversible bone marrow necrosis. Importantly, these complications were associated with serologically documented parvovirus B19 infection. Reviewing the literature, this case emphasizes a specific role of parvovirus B19 as a precipitating cause. Furthermore, it demonstrates how important the consideration of haemoglobin disorders can be even outside of the historically known areas.

Pattern of parvovirus B 19 infection during different trimesters of pregnancy in Kuwait

OBJECTIVE

Aims of this study were to determine the IgG and IgM seropositivity to parvovirus B19 during the three trimesters of pregnancy.

METHODS

Initially, a total of 1,047 pregnant women were included in a prospective study. Blood samples were obtained from 343, 406 and 298 cases in the first, second and third trimesters, respectively. To study the incidence of seroconversion, a second sample of blood was obtained 2-4 weeks later from the first 100 cases, who were IgG and IgM negative in the first trimester.

RESULTS

The seroprevalence of parvovirus B19 IgG and IgM was 53.3% and 2.2%, respectively. The incidence of seroconversion was 16.5%. The rate of fetal loss was 15.4% in patients with acute infection, all of which occurred in the first two trimesters.

CONCLUSIONS

The percentage of IgG positive cases is significantly higher in first and second trimesters compared to the third trimester. The seroconversion rate was 16.5%.

Recombinant human parvovirus B19 vectors: erythroid cell-specific delivery and expression of transduced genes

A novel packaging strategy combining the salient features of two human parvoviruses, namely the pathogenic parvovirus B19 and the nonpathogenic adeno-associated virus type 2 (AAV), was developed to achieve erythroid cell-specific delivery as well as expression of the transduced gene. The development of such a chimeric vector system was accomplished by packaging heterologous DNA sequences cloned within the inverted terminal repeats of AAV and subsequently packaging the DNA inside the capsid structure of B19 virus. Recombinant B19 virus particles were assembled, as evidenced by electron microscopy as well as DNA slot blot analyses. The hybrid vector failed to transduce nonerythroid human cells, such as 293 cells, as expected. However, MB-02 cells, a human megakaryocytic leukemia cell line which can be infected by B19 virus following erythroid differentiation with erythropoietin (N. C. Munshi, S. Z. Zhou, M. J. Woody, D. A. Morgan, and A. Srivastava, J. Virol. 67:562-566, 1993) but lacks the putative receptor for AAV (S. Ponnazhagan, X.-S. Wang, M. J. Woody, F. Luo, L. Y. Kang, M. L. Nallari, N. C. Munshi, S. Z. Zhou, and A. Srivastava, J. Gen. Virol. 77:1111-1122, 1996), were readily transduced by this vector. The hybrid vector was also found to specifically target the erythroid population in primary human bone marrow cells as well as more immature hematopoietic progenitor cells following erythroid differentiation, as evidenced by selective expression of the transduced gene in these target cells. Preincubation with anticapsid antibodies against B19 virus, but not anticapsid antibodies against AAV, inhibited transduction of primary human erythroid cells. The efficiency of transduction of primary human erythroid cells by the recombinant B19 virus vector was significantly higher than that by the recombinant AAV vector. Further development of the AAV-B19 virus hybrid vector system should prove beneficial in gene therapy protocols aimed at the correction of inherited and acquired human diseases affecting cells of erythroid lineage.

Rheumatic manifestations of parvovirus B19 infection

Human parvovirus B19 is an emerging DNA virus. B19 infection is common and widespread. Major manifestations of B19 infection are transient aplastic crisis, erythema infectiosum, hydrops fetalis, acute and chronic rheumatoid-like arthropathy, and, in the immunocompromised host, chronic or recurrent bone marrow suppression. A number of less common manifestations of B19 infection include various rash illnesses, neuropathies, and acute fulminant liver failure. Of rheumatologic interest, B19 infection must be differentiated from early presentation of more classic erosive rheumatoid arthritis and, in some cases, systemic lupus erythematosus. It is unlikely that B19 plays a role in classic erosive rheumatoid arthritis, but understanding pathogenesis of B19 arthropathy may provide insights into the mechanisms by which rheumatoid arthritis develops. Evidence for persistence of B19 infection suggests that human parvovirus B19 infection may serve as a model for the study of virus-host interactions and the role of viruses in the pathogenesis of rheumatic diseases.

Experimental infection of cynomolgus monkeys with simian parvovirus

Simian parvovirus is a recently discovered parvovirus that was first isolated from cynomolgus monkeys. It is similar to human B19 parvovirus in terms of virus genome, tropism for erythroid cells, and characteristic pathology in natural infections. Cynomolgus monkeys were infected with simian parvovirus to investigate their potential usefulness as an animal model of human B19 parvovirus. Six adult female cynomolgus monkeys were inoculated with purified simian parvovirus by the intravenous or intranasal route and monitored for evidence of clinical abnormalities; this included the preparation of complete hematological profiles. Viremia and simian parvovirus-specific antibody were determined in infected monkeys by dot blot and Western blot assays, respectively. Bone marrow was examined at necropsy 6, 10, or 15 days postinfection. All of the monkeys developed a smoldering, low-grade viremia that peaked approximately 10 to 12 days after inoculation. Peak viremia coincided with the appearance of specific antibody and was followed by sudden clearance of the virus and complete, but transient, absence of reticulocytes from the peripheral blood. Clinical signs were mild and involved mainly anorexia and slight weight loss. Infection was associated with a mild decrease in hemoglobin, hematocrit, and erythrocyte numbers. Bone marrow showed marked destruction of erythroid cells coincident with peak viremia. Our findings indicate that infection of healthy monkeys by simian parvovirus is self-limited and mild, with transient cessation of erythropoiesis. Our study has reproduced Koch's postulates and further shown that simian parvovirus infection of monkeys is almost identical to human B19 parvovirus infection of humans. Accordingly, this animal model may prove valuable in the study of the pathogenesis of B19 virus infection.

Infection by parvovirus B 19 during pregnancy: a review

Fetal infection by Parvovirus B 19 is a common cause of fetal anemia and nonimmune hydrops fetalis and may result in fetal death. Recent improvements in diagnosing parvovirus infections by sensitive molecular biology techniques now allow for a new insight into its pathogenic rule, immunology, and the varied clinical manifestations. The estimated overall risk of fetal loss after maternal exposure is about 6.5 percent, which is much less than previously thought. Inasmuch as complete spontaneous reversal of fetal hydrops has been commonly described, controversy exists regarding the management of the fetus with clinical signs of infection by Parvovirus B 19. According to the experience that has accumulated, it seems that only cases with severe fetal anemia or signs of fetal compromise should be managed by intrauterine transfusion. This procedure, however, is not without risk. Although an association between fetal viral infection and structural abnormalities has been described, it has not been proved yet. However, infection by Parvovirus B 19 has been recently proposed as a causative factor for congenital red blood cell aplasia.

New aspects of exanthematous diseases of childhood

The childhood exanthems include a spectrum of common and uncommon disorders caused by a variety of pathogens. In this article, timely issues relating to immunization for measles and varicella are discussed. Recently reported exanthematous illnesses, including papular-purpuric gloves and socks syndrome, unilateral laterothoracic exanthem, and eruptive pseudo-angiomatosis, are described. The current research and debate about bacterial toxins as the cause of Kawasaki syndrome are presented.

Detection of adeno-associated virus type 2 sequences in the human genital tract

Adeno-associated virus (AAV) is a defective parvovirus with unknown pathogenicity. It requires helper functions for its normal replication in human tissue and therefore is not readily isolated from clinical specimens. We have used the PCR method to examine the following clinical samples for the presence of AAV sequences: (i) 15 nasopharyngeal aspirates from symptomatic patients, (ii) 7 swab or fluid specimens from vesicles of patients suspected of having varicella-zoster virus infections, (iii) 21 human papilloma virus-positive genital biopsy specimens, (iv) 61 genital swab specimens from women suspected of having herpes simplex virus (HSV) infection examined either directly or following propagation in tissue culture, (v) 62 samples of first-trimester aborted material, including 38 samples from spontaneous abortions and 24 samples from induced abortions, (vi) 11 samples of chorionic villi taken from women undergoing genetic prenatal diagnosis, and (vii) three lots of cultured human embryonic cells. AAV sequences were detected only in samples taken from the genital tracts of women suspected of having HSV infection and not in any of the other types of samples. Samples from 11 patients were positive for AAV: for 4 patients the original swab sample was positive, for 4 patients the cultured swab sample was positive, and for 3 patients both the original swab samples and the cultures were positive. Five of the 11 patients were infected with HSV. Our study demonstrates the presence of AAV in the female genital tract. However, in contrast to a previous report (E. Tobiasch, M. Rabreau, K. Geletneky, S. Larue-Charlus, F. Severin, N. Becker, and J. R. Schlehofer, J. Med. Virol. 44:215-222, 1994), we did not find solid evidence of its replication in maternal or embryonal tissues from the first trimester of pregnancy. The questions of a potential pathogenic etiology of AAV and the interaction with HSV remain open.

Treating anemia

Transfusion therapy is frequently used in the treatment of sickle cell disease and its complications, but its efficacy has not been well proven. Red cell transfusions are well established for the acute treatment of cerebrovascular accidents and for the prevention of their recurrence. Acute chest syndrome with respiratory insufficiency is also an established indication for transfusion, especially in children. The use of red cell transfusions, especially chronic transfusions, in the treatment of sickle cell disease should be initiated only after serious consideration of the clinical setting and possible adverse effects. Both risks and benefits should be discussed with the patient, and that discussion should be documented.