Parvovirus B19 infection of the fetus. Histology and in situ hybridization

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 review of blood diseases and cytopenias associated with human parvovirus B19 infection

Parvovirus B19 is a single-stranded DNA virus which preferentially targets the erythroblast resulting in red cell aplasia, which is temporary in immunocompetent persons. Since the discovery of B19 virus in 1975, a wide variety of blood diseases and cytopenias affecting several blood cell lineages have been documented during or following B19 infection. These include cytopenias affecting the erythroid, megakaryoblastoid, myeloid and lymphoid lineages, as well as a variety of bicytopenias, pancytopenia, bone marrow necrosis / fat embolism syndrome, myelodysplastic syndrome, leucoerythroblastopenia, and hemophagocytic lymphohistiocytosis. B19 infection may also complicate and precede the course of acute leukemia, the significance of which remains to be determined. This review describes the current state of knowledge of the abnormalities of individual blood cell lineages encountered during parvovirus B19 infection, over the almost 40 years since its discovery, and reveals some very interesting themes, which improve our understanding of the pathogenesis of B19 infection with particular reference to the bone marrow.

Risk of fetal hydrops and non-hydropic late intrauterine fetal death after gestational parvovirus B19 infection

BACKGROUND

Risk assessment of parvovirus B19 (B19)-associated fetal complications following gestational B19 infection remains controversial.

OBJECTIVES

To determine the risk of fetal hydrops or non-hydropic late intrauterine fetal death following acute maternal B19 infection at defined gestational weeks.

STUDY DESIGN

Observational cohort study of pregnant women with serologic evidence of acute B19 infection. If available, fetal or neonatal tissue samples from cases complicated by fetal loss or hydrops were investigated for the presence of B19 DNA by polymerase chain reaction (PCR) and/or in situ hybridization (ISH).

RESULTS

Of 236 women with known pregnancy outcome, 228 had a live birth and 8 a fetal loss. The observed rate of fetal hydrops for all pregnant women was 4.2% (10/236) (95% confidence interval [CI], 2.1-7.7) and 10.6% (10/94) (95% CI, 5.2-18.7) for those infected between 9 and 20 weeks gestation. Tissue samples from 8 hydrops cases were investigated by PCR or ISH and all were B19 DNA positive. Fetal death occurring during or after gestational week 22 was only observed in one case which was associated with B19-derived fetal hydrops.

CONCLUSIONS

Our findings demonstrate that although adverse fetal outcome is a rare complication of gestational B19 infection, a relevant risk of fetal hydrops exists particularly for women infected between 9 and 20 weeks' gestation. Cases of B19-derived non-hydropic late intrauterine fetal death were not observed in the present study.

Viral Infections of the Lung

The lungs are among the most vulnerable to microbial assault of all organs in the body. From a contemporary vantage, lower respiratory tract infections are the greatest cause of infection-related mortality in the United States, and rank seventh among all causes of deaths in the United States.2,3 From a global and historic perspective, the scope and scale of lower respiratory tract infection is greater than any other infectious syndrome, and viral pneumonias have proven to be some of the most lethal and dramatic of human diseases. The 1918–1919 influenza pandemic, perhaps the most devastating infectious disease pandemic in recorded history, resulted in an estimated 40 million deaths worldwide, including 700,000 deaths in the U.S.4 The global outbreak of severe acute respiratory syndrome (SARS) during 2003, although considerably smaller in scale, resulted in 8098 cases and 774 deaths5 and is a dramatic contemporary example of the ability of viral pneumonias to rapidly disseminate and cause severe disease in human populations.

Unusual bone marrow manifestations of parvovirus B19 infection in immunocompromised patients

Parvovirus B19 is responsible for a spectrum of disease in humans. The usual bone marrow findings in acute parvovirus infections are marked erythroid hypoplasia and occasional giant erythroblasts. Intranuclear inclusions in developing erythroid precursors are rarely described in children or adults with parvovirus infection, although abundant intranuclear inclusions are commonly observed in the placenta and other tissues in infected fetuses. In this study, 8 patients are reported in whom the first evidence of parvovirus infection was the recognition of numerous intranuclear inclusions in erythroid precursors on bone marrow biopsy sections. Six of the 8 patients had documented immunodeficiencies; 4 had acquired immune deficiency syndrome (AIDS), and 2 were on chemotherapy. Five of 7 patients were negative for immunoglobulin G (IgG) antiparvovirus antibodies, including all 4 with AIDS. Unlike the typical pattern in parvovirus infection, the bone marrow was hypercellular in most of the patients, and erythroid precursors were usually increased with the entire spectrum of normoblast maturation represented; abundant intranuclear inclusions were observed similar to the finding in fetuses. The inclusions were variably eosinophilic and compressed the chromatin against the nuclear membrane. In situ hybridization showed parvovirus B19 DNA in numerous erythroid precursors in all cases. The findings of erythroid maturation and abundant viral inclusions in these immunocompromised patients is consistent with the hypothesis that failure to produce effective IgG parvovirus neutralizing antibodies may lead to persistent infection through viral tolerance that allows erythroid development of infected cells past the pronormoblast stage. Identification of parvovirus inclusions in marrow biopsies and subsequent confirmation of infection by in situ hybridization can be important in the assessment of anemia in immunodeficient patients because serological studies for parvovirus B19 are frequently negative.

Parvovirus B19 infection induces apoptosis of erythroid cells in vitro and in vivo

OBJECTIVE

intrauterine parvovirus B19 infection is related to non-immune hydrops fetalis, the pathogenesis of which is based on the strict tropism of B19 for erythroid precursor cells and the massive destruction of the infected erythroid cells, although the mechanism of beta19-induced cytotoxicity has not been studied in detail. The purpose of this study is to provide empirical evidence that beta19 induces apoptosis of erythroid cells both in vitro and ill vivo.

METHODS

we analysed culture cells infected in vitro by B19 and tissues of nine cases of hydrops fetalis caused by B19 intrauterine infection by histological and biological methods.

RESULTS

cells infected iil vitro by B19 showed nuclear changes characteristic of apoptosis by light microscopic examination and DNA extracted from the infected cells was fragmented. Electron microscopic examination showed the nuclei of infected cells contained crescent-shaped clumps of heterochromatin with increased density and double staining with anti-B1 9 antibody and terminal deoxynucleotidyl transferase (TdT)-mediated deoxyuridine triphosphate-digoxigenin nick-end labeling (TUNEL) confirmed apoptosis of individual cells. Tissues of cases of hydrops fetalis caused by B19 contained erythroid cells with nuclear inclusions and characteristic nuclear changes of apoptosis by light microscopy. The double-staining confirmed apoptosis of erythroid cells in the tissues. Immunohistochemical analysis with antibodies against cellular factors involved in apoptosis showed that caspase3, p53 and p21 were positive in infected cells.

Parvovirus B19 infections in pregnancy

Parvovirus B19 is the viral agent that causes the childhood exanthum erythema infectiosum, or fifth disease. Approximately 50% of pregnant women are seropositive for this agent and thus immune to primary infection. However, acute infection may develop in seronegative pregnant women exposed to B19. Acute B19 infections during pregnancy have been associated with miscarriage and hydrops fetalis. This latter condition is amenable to fetal therapy via intrauterine transfusion.

Frequency of parvovirus B19 infection in nonimmune hydrops fetalis and utility of three diagnostic methods

The rate of parvovirus B19 (PV) infection in cases of "idiopathic" nonimmune hydrops fetalis (NIHF) is reported to be approximately 16% with polymerase chain reaction (PCR)-based methods. Antibodies for use in paraffin-embedded tissue have not been systematically compared with PCR or with the presence of inclusions at varying gestational ages. All autopsy cases of NIHF and those with effusions of multiple serous membranes examined between 1991 and 1996 (n = 29) were evaluated for the presence of PV DNA by PCR analysis of paraffin-embedded liver tissue. PCR-positive cases and "idiopathic" cases were examined for the presence of inclusions in routine histological sections and for PV protein using a monoclonal antibody (NovoCastra R92F6). Among the four clinically idiopathic cases, one (25%) was positive for PV using PCR. The three negative idiopathic cases had no inclusions and were negative for PV by PCR and immunohistochemistry (IHC); all were third-trimester gestations (28, 31, and 32 weeks). Identifiable risk factors for NIHF other than PV in the remaining 25 cases included cystic hygroma, seven (three 45,X; two 46,XX; two no growth); complex cardiac anomaly, six; infection, three (two CMV, one chlamydia); twin-twin transfusion, two; lymphangiectasia, two; diaphragmatic hernia, tracheal atresia, trisomy 21, congenital cystic adenomatoid malformation, one each. One of these nonidiopathic cases, a fetus with cystic hygroma and a 45,X karyotype, was positive for PV DNA only on the blot, consistent with a low titer; no inclusions were present, and IHC was negative in multiple organs in this instance. One of four (25%) cases of idiopathic NIHF cases contained PV DNA by PCR analysis; there were abundant inclusions in multiple organs, and IHC was strongly positive as well. Of 25 cases of nonidiopathic NIHF, one (4%) was also positive for PV DNA by PCR. PV protein was detected by IHC only in the presence of inclusions; IHC thus may be useful for highlighting sparse inclusions. No second-trimester case of NIHF was unexplained. Late (third-trimester) cases of "idiopathic" NIHF are likely to be negative by all methods, either because they are not attributable to PV infection or because PV protein and DNA are below detectable levels or are no longer present. Maternal serology for PV and TORCH agents may be the best method for investigating third-trimester losses to otherwise unexplained NIHF.

Novel cytomorphology of the giant proerythroblasts of parvovirus B19 infection

The morphology of the giant proerythroblasts (GPE) in air-dried and Wright-Giemsa-stained smears of bone marrow in 16 patients with pure red cell aplasia (PRCA) caused by parvovirus B19 infection is described. B19 infection was diagnosed by the presence of the virus or viral DNA and/or IgM antibodies. Twelve patients had chronic hemolytic anemia and aplastic crisis and 4 patients had AIDS with chronic PRCA. In patients with chronic hemolytic anemia and aplastic crisis, GPE were not detectable in bone marrow biopsies that showed any degree of recovery of erythropoiesis. The GPE morphology was quite variable. The early (basophilic) GPE measured 25 to 35 microm in diameter, had a narrow rim of intensely blue and often vacuolated cytoplasm with pseudopodia, round nuclei with compact uncondensed chromatin, and an indistinct and inclusion-like purple-colored tinctorial change. The "intermediate" and "late" GPE measured 25 to 45 microm in diameter and showed cytoplasmic swelling, gradual loss of cytoplasmic basophilia, and fraying of the cytoplasm with focal rupture; the nuclei showed an increase in volume, a highly uncondensed and coarse sieve-like chromatin, and 1 to 3 prominent, pale to moderate purple inclusion-like nucleoli or inclusions. Bare nuclei similar in size and chromatin pattern to those of the GPE were present in proximity to the GPE and may have arisen from the GPE by dissolution of the cytoplasm. The glassy intranuclear inclusions with central clearing, the so-called lantern cells described in formalin-fixed tissues of patients with B19 infection, were absent in all cases. These findings suggest that direct toxic cell injury rather than apoptosis may be involved in the pathogenesis of erythroid aplasia in B19 infection.

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.

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.

Detection of infection or infectious agents by use of cytologic and histologic stains

A wide variety of stains are useful for detection of different organisms or, for viruses, the cytopathologic changes they induce, in smears prepared directly from clinical specimens and in tissue sections. Other types of stains, such as hematoxylin and eosin, are used routinely to stain tissue sections and are most valuable for assessing the immunologic response of the host to the invading pathogen. In many cases, the pattern of inflammation provides important clues to diagnosis and helps to guide the selection of additional "special" stains used predominantly for diagnosis of infectious diseases. A stain may be nonspecific, allowing detection of a spectrum of organisms, as do the Papanicolaou stain and silver impregnation methods, or detection of only a limited group of organisms, as do the different acid-fast techniques. Some nonspecific stains, such as the Gram stain, are differential and provide valuable preliminary information concerning identification. Immunohistochemical stains, on the other hand, are specific for a particular organism, although in some cases cross-reactions with other organisms occur. Despite the wealth of information that can be gleaned from a stained smear or section of tissue, however, the specific etiology of an infection often cannot be determined on the basis of only the morphology of the organisms seen; culture data are essential and must be considered in the final diagnosis.

Detection of parvovirus B19 DNA in bone marrow cells by chemiluminescence in situ hybridization

A chemiluminescence in situ hybridization method was developed for the search of B19 parvovirus DNA in bone marrow cells, employing digoxigenin-labeled B19 DNA probes, immunoenzymatically detected with a highly sensitive 1,2-dioxetane phosphate as chemiluminescent substrate. The light emitted from the in situ-hybridized probe was analyzed and measured by a high-performance luminograph connected to an optical microscope and to a personal computer for the quantification of the photon fluxes from the single cells and for image analysis. The chemiluminescence in situ hybridization was applied to bone marrow cell smears of patients with aplastic crisis or hypoplastic anemia, who had been previously tested by in situ hybridization with colorimetric detection, dot blot hybridization, and nested PCR. The chemiluminescent assay provided an objective estimation of the data, proved specific, and showed an increased sensitivity in detecting B19 DNA compared with in situ hybridization with colorimetric detection.

Comparative evaluation of virological and serological methods in prenatal diagnosis of parvovirus B19 fetal hydrops

Human parvovirus B19 infection in pregnancy represents a potential hazard to the fetus since fetal loss or fetal hydrops can occur. The risk of fetal loss due to transplacental B19 transmission has been evaluated in several studies using different diagnostic methods on maternal and fetal specimens. We analyzed the diagnostic value of virological and serological techniques on maternal serum, fetal cord blood, and amniotic fluid specimens obtained at the time of clinical diagnosis of fetal hydrops in 18 cases of B19 fetal hydrops. B19 DNA was detected by nested PCR, dot blot hybridization, and in situ hybridization assay. Anti-B19 immunoglobulin M and G antibodies were detected by immunoassays using recombinant B19 antigens. Our data suggest that for maternal sera, virological and serological methods have a complementary role in diagnosis, while for fetal specimens the in situ detection of B19 DNA in fetal cord blood is the most sensitive diagnostic system.

Fetal pathology in intrauterine death due to parvovirus B19 infection

OBJECTIVES

To study the pathological features of fetuses dying because of parvovirus B19 infection, with particular reference to the presence of hydrops; to assess the usefulness of immunochemistry as a screening method for the detection of parvovirus infection at post-mortem examination.

DESIGN

Review of clinical, sonographic, serological and pathological data; immunohistochemical staining of post-mortem tissue.

SAMPLE

Cases of intrauterine fetal death occurring during the 18-month period January 1993 to June 1994 inclusive, referred for post-mortem examination to the Pathology Department, Royal Victoria Infirmary, Newcastle upon Tyne.

RESULTS

Eleven cases of fetal death due to parvovirus infection were identified. Seven fetuses were less than 18-week size. Three fetuses showed conspicuous hydropic change. One of the 11 cases was detected for the first time by retrospective immunochemical screening. Of cases originating from the Newcastle district, parvovirus infection was responsible for about 10% of all non-malformed fetal deaths occurring between 10 and 24 weeks of gestation referred for pathological examination.

CONCLUSIONS

During the period of study, parvovirus infection was a relatively common cause of mid-trimester fetal death. Many fetuses dying because of this infection are not noticeably hydropic, and the possibility of parvovirus infection should be considered in any case of intrauterine fetal death. Immunochemistry can be used to confirm the histopathological diagnosis, and may be of particular help where there is advanced autolysis; immunohistochemical screening may detect occasional cases not initially identified by examination of routinely stained tissue sections.

Identification of human parvovirus B19 infection in idiopathic nonimmune hydrops fetalis

OBJECTIVE

This retrospective study was designed to determine the incidence of B19 associated with idiopathic nonimmune hydrops fetalis by use of a sensitive molecular tool, the polymerase chain reaction assay.

STUDY DESIGN

Placental and fetal tissues from 57 cases of nonimmune hydrops fetalis were analyzed for B19 deoxyribonucleic acid. Thirty-four of these cases were classified as idiopathic. The remaining 23 cases had known, noninfectious-based causes.

RESULTS

Eighteen percent of all cases (6/34) of idiopathic nonimmune hydrops fetalis contained B19 deoxyribonucleic acid. In contrast, none of the 23 cases of known, noninfectious-based nonimmune hydrops fetalis examined contained any B19 deoxyribonucleic acid. Presence of the virus was confirmed in each of the six cases by either B19-specific deoxyribonucleic acid in situ hybridization or immunocytochemistry. However, histologic examination was unsuccessful at detecting characteristic viral-like inclusions in one third of the cases.

CONCLUSION

Eighteen percent of cases of idiopathic nonimmune hydrops fetalis contained B19 deoxyribonucleic acid. This significant finding demonstrates the usefulness of polymerase chain reaction to aid in the differential diagnosis of this disease.

Parvovirus B19 infection

Human parvovirus B19, discovered in 1974, is a single-stranded DNA virus which causes erythema infectiosum, arthralgia, aplastic crisis in patients with red cell defects, chronic anaemia in immunocompromised patients, and fetal hydrops. Seroprevalence in developed countries is 2-10% in children less than 5 years, 40-60% in adults more than 20 years, and 85% or more in those over 70 years. The virus may be transmitted by the respiratory route and by transfusion of infected blood and blood products. After an incubation period of six to eight days, viraemia occurs, during which reticulocyte numbers fall dramatically resulting in a temporary drop in haemoglobin of 1 g/dl in a normal person. Clearance of viraemia is dependent on development of specific antibody to the B19 structural proteins, VP1 and VP2. The red cell receptor for the virus is blood group P antigen. Diagnosis in immunocompetent persons depends on detection of specific IgM in serum. Diagnosis in immunocompromised persons depends on detection of B19 antigen or DNA in serum. There is no specific treatment for B19 infection; however, human normal immunoglobulin may be used as a source of specific antibody in chronically infected persons. A recombinant parvovirus B19 vaccine is under development.

Infectious causes of hydrops fetalis

A variety of infectious agents have been associated with nonimmune hydrops fetalis, most notably parvovirus B19, cytomegalovirus, herpes simplex virus, Toxoplasma gondii, and Treponema pallidum. These agents produce hydrops through effects on fetal bone marrow, myocardium, or vascular endothelium. Knowledge of the epidemiology and clinical characteristics of maternal and fetal infection can be used to select a diagnostic approach. Etiologic diagnosis will guide prognosis and the selection of specific chemotherapy.

Fetal parvovirus B19 infection and liver disease of antenatal onset in an infant with Ebstein's anomaly

Fetal parvovirus B19 infection has been reported in association with hydrops and fetal demise, myocarditis, and congenital anomalies, as well as with normal outcome of pregnancy. One infant with liver disease of fetal onset associated with parvovirus B19 infection has been described. We have seen another such infant, in whom marked siderosis of the liver suggested accelerated destruction of erythrocytes and portal tract fibrosis with proliferation of bile ducts suggested intrauterine infection. Viral cytopathic effects were not seen. Maternal serum obtained postpartum contained IgM class antibodies against parvovirus B19, and parvovirus B19 nucleic acid sequences were identified in the infant's liver by polymerase chain reaction studies. We propose that recognition of this combination of siderosis with fibrosis and bile duct proliferation will permit identification of cases of fetal parvovirus B19 infection.

Immunoelectron microscopic identification of human parvovirus B19

A mildly macerated, hydropic fetus was delivered spontaneously at 25 weeks gestation by a multigravidous black mother. At autopsy, gross and microscopic evidence suggested fetal anemia, and excessive extramedullary erythroblastosis was present generally. Erythroid precursor cells in the pulmonary capillary circulation contained eosinophilic nuclear inclusions consistent with human parvovirus B19 infection. Transmission electron microscopy on osmicated Epon lung sections showed lucent, granular chromatin corresponding to the inclusions. In rare foci only these sections contained paracrystalline arrays of 20-nm virions. In the same cells, similar virions were seen within the cytoplasm, both randomly distributed and in paracrystalline aggregates. Postembedding immunoelectron microscopy, done on formalin-fixed lung embedded in a hydrophilic resin, showed positive labelling over the nuclear inclusions, and also localized the viral capsid antigen to cytoplasmic virion aggregates. The nuclear aggregates suggest that the virus would reach the circulation after cell lysis whereas those in cytoplasm suggest that parvovirus also may be excreted from infected cells before they lyse.

Case report: detection of parvovirus B19 in a skin biopsy of a patient with erythema infectiosum

We report the findings on a skin biopsy taken from a child acutely infected with parvovirus B19 showing the typical exanthematous rash. By indirect immunofluorescence with a monoclonal antibody to B19, viral capsid proteins were detected in epidermal cells localized mainly in the stratum basale. Additionally, B19 DNA was detected in epidermal cells of the stratum basale by in situ hybridization using a Dig-labelled B19 DNA probe. The detection of viral capsid proteins and viral DNA suggests the presence of complete viral particles. It is therefore concluded that B19 plays a direct role in the formation of the exanthematous rash in erythema infection.

Identification of a novel simian parvovirus in cynomolgus monkeys with severe anemia. A paradigm of human B19 parvovirus infection

Although human B19 parvovirus infection has been clearly associated with a number of distinct syndromes (including severe anemia, abortion, and arthritis), detailed knowledge of its pathogenesis has been hindered by the lack of a suitable animal model. We have identified a novel simian parvovirus in cynomolgus monkeys with severe anemia. Sequencing of a 723-bp fragment of cloned viral DNA extracted from serum revealed that the simian parvovirus has 65% homology at the DNA level with the human B19 parvovirus but little homology with other known parvoviruses. Light microscopic examination of bone marrow from infected animals showed intranuclear inclusion bodies, and ultrastructural studies showed viral arrays characteristic of parvoviruses. Another striking feature was the presence of marked dyserythropoiesis in cells of the erythroid lineage, raising the possibility that B19 parvovirus infection may underlie related dyserythropoietic syndromes in human beings. Affected animals had concurrent infection with the immunosuppressive type D simian retrovirus, analogous to HIV patients who develop severe anemia because of infection with B19 parvovirus. The remarkable similarities between the simian and B19 parvoviruses suggest that experimentally infected cynomolgus monkeys may serve as a useful animal model of human B19 infection.

Detection of parvovirus B19 in fetal autopsies

In a 10-year retrospective study we examined the incidence of parvovirus B19 (B19)-related hydrops fetalis in fetal autopsies (n = 1,299) carried out between 1982 and 1991. Intrauterine death had occurred in 399 cases (30.7%); in 42 (10.5%) of these hydrops fetalis was diagnosed. Of these 42 hydropic fetuses, parvovirus B19 infection was identified in 6 (14.3%) cases by the presence of typical erythroblastic nuclear inclusions in hematoxylin-eosin stained tissue and the diagnosis was confirmed by in situ hybridization using a Digoxigenin-labelled B19 DNA probe. The study shows that the overall incidence of B19-associated intrauterine death associated with hydrops fetalis is low. However, B19 infection should be considered in all cases of hydrops fetalis.

Diagnosis and incidence of fetal parvovirus infection in an autopsy series: II. DNA amplification

This study evaluates the practical utility of the polymerase chain reaction (PCR) as a diagnostic method for intrauterine fetal parvovirus infection in cases of hydrops fetalis. Paraffin-embedded, formalin-fixed fetal tissues from cases of hydrops fetalis were assessed for parvovirus B19 by histology and PCR in conjunction with 32P hybridization. Of 673 fetal and neonatal autopsies performed at Women and Infants' Hospital for the years 1985 through 1990, 32 cases were determined to have hydrops fetalis, of which five were positive for parvovirus infection by both histology and the PCR. PCR was not used in seven (22%) of the 32 hydrops cases because 1 microgram of DNA was not available for study. Histology was as sensitive as PCR in detecting parvovirus B19 in fetal autopsy tissues from cases of hydrops fetalis, and could be used reliably in each case to diagnose parvovirus infection. In our hands, histology is as sensitive as PCR and less labor-intensive. We would reserve PCR for cases without inclusions and with a strong suspicion of parvovirus infection, or for fluids in which histological analysis is not available.

Diagnosis and incidence of fetal parvovirus infection in an autopsy series: I. Histology

This study was undertaken to obtain additional information about the incidence and characteristics of fetal parvovirus B19 infection in an unselected autopsy series, and to assess the distribution and quantitation of inclusions in various organs. Autopsy records from 673 fetal and neonatal autopsies performed at Women and Infants' Hospital during 1985 through 1990 were reviewed. Thirty-two cases of hydrops fetalis were identified, and, of these, 5 had parvovirus infection. This gives an incidence of fetal parvovirus infection resulting in hydrops fetalis of 0.7% among all autopsies, and a 16% incidence among cases of hydrops. Thirty-five percent of the cases of hydrops had malformations; a muscular ventricular septal defect was noted in one of the 5 cases of parvovirus infection. All 5 parvovirus cases had characteristic erythroid nuclear inclusions, and these inclusions were resistant to tissue degenerative changes. The most reliable tissue for histologic diagnosis was the liver, followed by heart and lung. Only 2 of 5 placentas had diagnostic inclusions, making examination of the placenta alone insufficient for ruling out fetal parvovirus infection.

Non-isotopic in situ hybridisation and immunophenotyping of infected cells in the investigation of human fetal parvovirus infection

AIMS

To compare the use of biotinylated and digoxigenin labelled probes for diagnosis of human fetal parvovirus B19 infection in formalin fixed, paraffin wax embedded tissues; and to assess the cellular distribution of the virus in positive cases.

METHODS

Sections of lung tissue from 23 cases of anatomically normal non-immune fetal hydrops presenting between 1984 and 1989, and from 13 control cases of hydrops due to chromosomal abnormality were probed for B19 DNA by in situ hybridisation using both biotinylated and digoxigenin labelled probes. The distribution of the virus was then investigated in all cases of fetal B19 infection confirmed in this laboratory to date (n = 11) by combining in situ hybridisation for viral DNA (using the digoxigenin system) with immunohistological labelling for a range of cellular antigens.

RESULTS

Five unequivocal cases of B19 infection were identified among the 23 fetuses with unexplained hydrops using both probe labels. When combined with data from previous studies of the period 1974-1983, the results indicate that B19 infection was responsible for 27% of cases of anatomically normal non-immune hydrops and 8% of all cases, of non-immune hydrops presenting to this hospital over 15 years. False positive signal was seen in an additional three cases, using biotinylated probes. Digoxigenin labelled probes gave greater specificity and permitted detailed investigation of tissues high in endogenous biotin. Though most cells containing B19 DNA colabelled as erythroid precursors, viral DNA was frequently detected within mononuclear-phagocytic cells. In three cases viral signal was also found within occasional myocardial cells labelled by antibody to desmin.

CONCLUSIONS

A relatively high proportion of cases of anatomically normal, non-immune hydrops are caused by B19 infection. Digoxigenin is a more reliable probe label than biotin for in situ hybridisation in archival fetal tissues. Double labelling for cellular antigens and viral nucleic acid is a powerful technique for investigating virus-host cell interactions, and provides evidence that cell types other than those of erythroid lineage may have a role in human fetal parvovirus infection.

Replication of parvovirus B19 in hematopoietic progenitor cells generated in vitro from normal human peripheral blood

Erythroid progenitor cells generated in vitro from peripheral human blood in the presence of interleukin-3 and erythropoietin were infected with human parvovirus B19. B19 virus DNA replication was highest 48 to 72 h after infection, and maximum levels of B19 virus proteins were detected in culture supernatants at 72 to 96 h after infection. B19 virus propagated in vitro was infectious. This cell culture system with peripheral blood cells facilitates studies in vitro of B19 virus replication.

Prevalence of antibodies to parvovirus B19 in selected groups of patients and healthy individuals

The prevalence of antibodies to parvovirus B19 in sera (n = 745) of various groups of patients and healthy individuals was determined by the enzyme immunoassay, using viral particles as antigen. Among healthy individuals, anti-B19 IgG prevalence was highest in nurses (65.4% (17/26)); in medical students it was 34.1% (47/138) and in pregnant females, 24.4% (48/197). 37.0% (44/119) of HIV-negative haemophiliac patients and 91.7% (33/36) of haemophilic patients with HIV infection were anti-B19 IgG-positive. 45.8% (55/120) of dialysis patients and 27.5% (30/109) of patients with asymptomatic HIV infection were positive for anti-B19 IgG. With the exception of HIV-infected haemophiliac patients, no specific "risk group" for B19 infection could be identified.

Diagnosis of human parvovirus B19 infections by polymerase chain reaction

The polymerase chain reaction (PCR) was used for detecting parvovirus B19 DNA in clinical specimens. A pair of oligonucleotide primers spanning the PstI-fragment of the B19 virus genome was used for PCR, and a PCR product of 727 bp was amplified. B19 virus DNA was detected in all sera (n = 26) of individuals in the incubation period and acute phase of infection. PCR was useful for detecting viral B19 DNA in amniotic fluid and fetal blood of hydropic fetuses, confirming fetal B19 virus infection.