Serologic study of human parvovirus B19 infection in pregnancy in Japan

The risk of maternal parvovirus B19 infection during pregnancy on fetal loss and fetal hydrops: A systematic review and meta-analysis

BACKGROUND

Human parvovirus B19 (B19) is widespread infection in humans, yet the impact on adverse pregnancy outcomes is controversial.

OBJECTIVE

to evaluate the impact of B19 infection during pregnancy on adverse pregnancy outcome, and investigated the incidence of fetal loss and fetal hydrops after maternal B19 infection during pregnancy.

STUDY DESIGN

A systematic literature search was performed using Embase, Medline, PubMed, Web of science, and the Cochrane Library database for relevant publications up to 10^th August 2018. Cohort studies and case-control studies were included in analyses.

RESULTS

In total, 36 eligible studies were included. Of these, 18 studies reported the risk of maternal B19 infection during pregnancy on fetal loss and 20 studies reported the incidence of fetal loss or fetal hydrops after maternal B19 infection. Collectively, the results indicated that maternal B19 infection increased the risk of fetal loss, spontaneous abortion, and stillbirth with ORs of 2.68 (95% CI: 2.02-3.55), 2.42 (95% CI: 1.76-3.33), and 3.53 (95% CI: 1.91-6.54), respectively, when compared with uninfected pregnant women. In addition, the incidence of fetal loss and fetal hydrops in B19 infected pregnant women was 7.6% (95% CI: 5.5-9.5) and 9.3% (95% CI: 5.6-13.0), respectively.

CONCLUSIONS

maternal parvovirus B19 infection during pregnancy increased the risk of fetal loss, spontaneous abortion, and stillbirth. A high incidence of fetal loss and fetal hydrops was observed in pregnant women with parvovirus B19 infection.

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.

Time-Series Analysis Comparing the Prevalence of Antibodies against Nine Viral Species Found in Umbilical Cord Blood in Japan

In this study, we investigated the prevalence of antibodies against 9 viral species found in umbilical cord blood from 561 neonates in 2013. Serum IgG antibodies against the following viruses were measured: herpes simplex virus (HSV), varicella-zoster virus (VZV), Epstein-Barr virus (EBV), cytomegalovirus (CMV), human herpesvirus 6 (HHV-6), measles virus (MV), rubella virus (RV), mumps virus (MuV), and human parvovirus B19 (HPV B19). A survey questionnaire regarding past medical history and maternal immunization status for the vaccine-preventable diseases of varicella, measles, rubella, and mumps was simultaneously administered. The results were compared with previous data collected in 2001-2002 from 378 umbilical cord blood samples. Viral seroprevalence data were: HSV, 54%; VZV, 96%; EBV, 96%; CMV, 67%; HHV-6, 100%; MV, 95%; RV, 94%; MuV, 64%; and HPV B19, 55%. The seroprevalence of CMV, MV, and MuV were significantly lower in 2013 than in 2001-2002 (CMV, 76%; MV, 98%; MuV, 93%). Compared with the 2001-2002 data, the mean IgG antibody values of the 4 vaccine-preventable diseases were significantly lower, and vaccination coverage for those diseases among mothers was significantly higher. Thus, attention should be paid to antibody levels in women of childbearing age in the future.

Estimating the risk of parvovirus B19 infection in blood donors and pregnant women in Japan

BACKGROUND

Seroepidemiological study of parvovirus B19 has not taken place for some 20 years in Japan. To estimate the risk of parvovirus B19 infection in Japan among blood donors and pregnant women in this century, a seroepidemiological survey and statistical modeling of the force of infection were conducted.

METHODOLOGY/PRINCIPAL FINDINGS

The time- and age-specific seroprevalence data were suggestive of strong age-dependency in the risk of infection. Employing a piecewise constant model, the highest forces of infection of 0.05 and 0.12 per year were observed among those aged 0-4 and 5-9 years, respectively, while estimates among older individuals were less than 0.01 per year. Analyzing the antigen detection data among blood donors, the age-specific proportion positive was highest among those aged 30-39 years, agreeing with the presence of dip in seroprevalence in this age-group. Among pregnant women, up to 107 fetal deaths and 21 hydrops fetalis were estimated to have occurred annually across Japan.

CONCLUSIONS

Seroepidemiological profiles of PVB19 infection in Japan was characterized with particular emphasis on the risk of infection in blood donors and the burden of infection among pregnant women. When a vaccine becomes available in the future, a similar seroepidemiological study is expected to play a key role in planning the appropriate immunization policy.

Intrauterine infection with parvovirus B19 and CMV: implications in early and late gestation fetal demise

In utero viral infections have been associated with an adverse pregnancy outcome and may have a causative role in the unexplained fetal death file. Parvovirus B19 and cytomegalovirus are among the most common pathogens implicated in fetal loss cases. Parvovirus B19 has been reported to account for cases of spontaneous abortions, intrauterine fetal death and nonimmune hydrops fetalis, whereas cytomegalovirus accounts for nonimmune hydrops fetalis, intrauterine growth retardation and congenital anomalies. This review aims to summarize the current literature in an attempt to underline the need for routine screening, close follow-up and prevention. A better understanding of the pathogenetic mechanisms of viral infections during the crucial time of organogenesis, along with early detection, may contribute to the reduction in stillbirth rate.

Diagnosis, management and possibilities to prevent parvovirus B19 infection in pregnancy

Human parvovirus B19 (B19V) infection in pregnancy can cause severe fetal anemia and nonimmune hydrops fetalis, which may be associated with spontaneous abortion and fetal death. Approximately 30–40% of women of child-bearing age are not immune to B19V infection. The risk to fetal life is particularly high if maternal infection occurs during the first 20 weeks of gestation. In this article we intend to give an overview on the molecular biology, epidemiology and management of B19V infection during pregnancy. These data will be combined with an assessment of the clinical situation of the infected fetus and the possibilities for avoiding and/or preventing B19V infection in pregnant women. Currently B19V infection is the causative agent of one of the most frequently occurring infectious complications in pregnancy that endangers fetal life, and so the necessity to develop a preventive vaccine is discussed.

False-negative serology in patients with acute parvovirus B19 infection

BACKGROUND

Acute parvovirus B19 (B19V) infection is characterized by high-level viremia. Antibodies against the capsid proteins VP1 and VP2 may complex with B19V-particles thereby becoming undetectable in diagnostic tests.

OBJECTIVES

We intended to obtain data on the frequency of false-negative serology in acute B19V-infection.

STUDY DESIGN

129 plasma or serum samples of healthy blood donors and of patients with suspected B19V-infection were analyzed for B19V-DNA by qPCR and VP1/VP2-specific IgG and IgM by ELISA. Eleven of these samples were derived from four pregnant women with previous contact to B19V-infected individuals. Using acidic conditions virus/antibody-complexes were disrupted and detected by WesternLine and ELISA.

RESULTS

83/118 samples were derived from acutely infected individuals displaying viremia (10(3)-10(12)geq/mL). In 24/83 viremic samples (28.9%) VP1/VP2-specific IgM and IgG were undetectable in ELISA, but could be demonstrated to be complexed with B19V-particles. Each 7/83 (8.4%) was IgM-positive/IgG-negative and IgM-negative/IgG-positive, in 45/83 samples (54.2%) IgG and IgM could be detected. 35 samples did not contain B19V-DNA; five of these were from seronegative persons. Analyzing consecutive sera derived from four pregnant women, B19V-DNA was demonstrated in 10/11 samples, B19V-specific IgG- and IgM-antibodies were detectable in 10/11 and 4/11 samples, respectively. In 2/4 women seroconversion was observed, but IgM was not detected in 50% of the samples. B19V-specific IgG but not IgM was detectable in 2/4 women.

CONCLUSION

Acute B19V-infection cannot be diagnosed by exclusive analysis of B19V-specific antibodies. Only the combination of assays for detection of B19V-DNA and antibodies enables correct serodiagnosis.

Parvovirus B19 infection in human pregnancy

Human parvovirus B19 infection is widespread. Approximately 30-50% of pregnant women are nonimmune, and vertical transmission is common following maternal infection in pregnancy. Fetal infection may be associated with a normal outcome, but fetal death may also occur without ultrasound evidence of infectious sequelae. B19 infection should be considered in any case of nonimmune hydrops. Diagnosis is mainly through serology and polymerase chain reaction. Surveillance requires sequential ultrasound and Doppler screening for signs of fetal anaemia, heart failure and hydrops. Immunoglobulins, antiviral and vaccination are not yet available, but intrauterine transfusion in selected cases can be life saving.

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.

Maternal human parvovirus B19 infection and the risk of fetal death and low birthweight: a case-control study within 35 940 pregnant women

OBJECTIVES

To assess the association between maternal parvovirus B19 infection and fetal death, birthweight and length of gestation.

DESIGN

Case-control study.

SETTING

Population based.

POPULATION

Cases were all 281 women with fetal death within a cohort of 35 940 pregnant woxmen in Norway. The control group consisted of a random sample of 957 women with a live born child.

METHOD

Information on pregnancy outcome was obtained from the Medical Birth Registry of Norway. First trimester serum samples were tested for antibodies against parvovirus B19 (IgM and IgG). In seronegative women, further serum was analysed to detect seroconversion during pregnancy.

MAIN OUTCOME MEASURES

Fetal death, length of gestation and birthweight.

RESULTS

Two of 281 (0.7%) of the women who experienced fetal death and nine of 957 (0.9%) of the controls had presence of IgM antibodies, crude odds ratio 0.8; 95% CI (0.2-3.5). In initially, seronegative women, 3.1% (2/65) with fetal death and 2.6% (8/307) with a live birth seroconverted, crude odds ratio 1.2; 95% CI (0.2-5.7). Presence of maternal parvovirus-specific IgG or IgM antibodies in the first trimester, or seroconversion during pregnancy were not associated with lower birthweight or reduced length of gestation in live born children, but was associated with low birthweight in stillborn offspring.

CONCLUSION

Maternal parvovirus B19 infection was not associated with fetal death in our study. Very few cases of fetal death may be attributed to maternal parvovirus B19 infection.

Fetal anaemia as a cause of fetal injury: diagnosis and management

PURPOSE OF REVIEW

This review provides up-to-date information on the diagnosis and management of fetal anaemia.

RECENT FINDINGS

Exciting advances in the field of red blood cell isoimmunization are phasing out the need for invasive procedures. Rhesus blood group genotyping using fetal DNA in maternal plasma has been introduced into clinical practice with remarkable success. The role of middle cerebral artery peak systolic velocity in screening for fetal anaemia has been confirmed in various causes of fetal anaemia. A recent review of a successful Iran national screening programme for thalassaemia provided a timely and valuable educational opportunity. The value of intrauterine transfusion as a treatment for fetal anaemia was demonstrated by both high success rate and low procedure-related pregnancy loss rate.

SUMMARY

Fetal anaemia is one of the severe fetal conditions that affect the worldwide population. Rhesus isoimmunization remains an important health issue despite the recommendation for anti-D immunoglobulin prophylaxis and injection after sensitizing events. Noninvasive ultrasound diagnostic methods have replaced traditional invasive procedures in the assessment of fetus at risk of anaemia due to various causes, including red blood cell isoimmunization, parvovirus B19 infection and thalassaemia. The increased availability of intrauterine transfusion will help to improve the prognosis of these anaemic fetuses.

Seroprevalence of parvovirus B19 in the German population

Acute parvovirus B19 infection is a risk for pregnant women. After vertical transmission the infected fetus may develop hydrops fetalis. Since B19 infection occurs mainly during childhood, children represent a main source for virus transmission. In order to determine whether certain groups in the German population show increased risks for B19 infection we analysed the seroprevalence using 6583 sera collected from adults in former Eastern and Western Germany during the German National Health Survey and 649 sera from healthy Thuringian children and adolescents. In adults the overall seroprevalence was 72.1%, rising from 20.4% in children (1-3 years) and 66.9% in adolescents (18-19 years) to 79.1% in the elderly (65-69 years). Significant differences were observed between females (73.3%) and males (70.9%) and between inhabitants of small (74.8%) and big cities (69.0%) but not between people of the former Eastern (72.8%) and Western states (72.0%) of Germany. For women during childbearing age (18-49 years) highest values were observed in those living together with two or more children (81.6%) and in women with occupational contact with children aged <6 years (88.9%). In contrast seroprevalence was significantly lower in age-matched female singles (64.8%) and in women with occupational contact with children aged >6 years and adolescents (63.8%).

[Parvovirus B-19 infections in pregnant women in day care facilities: health economic analysis of prohibition to employ seronegative women]

German protective legislation during pregnancy and maternity prohibit employing pregnant women if occupational activities endanger the health of either the mother-to-be or the fetus. This applies for parvovirus B19 seronegative women caring for children <6 years. Here we present a cost-effectiveness analysis from the view of the society for the prohibition to employ B19-seronegative women in day care. Prohibition of employment starting at the first day of pregnancy may prevent 1.4 cases of fetal death (mortality) and 1.7 cases of hydrops fetalis (morbidity) per year resulting in costs of 30 million <euro> (22 million <euro>/live birth). The incidence of B19 infection, the elevated occupational risk and the fetal death rate were varied in sensitivity analyses. This resulted in 0.2-3.1 fetal deaths prevented per year and costs between 10 million <euro> and 150 million <euro> per live birth. Indeed, the protective effect is assumed to be even lower since 30% of fetal deaths occur after infection during the first 8 weeks of pregnancy. During that time prohibition of employment is often unrealistic since the majority of women are not aware of pregnancy. In conclusion a small number of fetal lives can be saved by prohibiting employment in contrast to the extremely high costs. The regulations for maternal protection should be revised.

Parvovirus-B19-associated complications in renal transplant recipients

Parvovirus B19 is a common human pathogen, causing erythema infectiosum in children, hydrops fetalis in pregnant women, and transient aplastic crisis in patients with chronic hemolytic anemia. Immunosuppressed patients can fail to mount an effective immune response to B19, resulting in prolonged or persistent viremia. Renal transplant recipients can develop symptomatic B19 infections as a result of primary infection acquired via the usual respiratory route or via the transplanted organ, or because of reactivation of latent or persistent viral infection. The most common manifestations of B19 infection in immunosuppressed patients are pure red cell aplasia and other cytopenias. Thus, this diagnosis should be considered in transplant recipients with unexplained anemia and reticulocytopenia or pancytopenia. Collapsing glomerulopathy and thrombotic microangiopathy have been reported in association with B19 infection in renal transplant recipients, but a causal relationship has not been definitively established. Prompt diagnosis of B19 infection in the renal transplant recipient requires a high index of suspicion and careful selection of diagnostic tests, which include serologies and polymerase chain reaction. Most patients benefit from intravenous immunoglobulin therapy and/or alteration or reduction of immunosuppressive therapy. Conservative therapy might be sufficient in some cases.

Prevalence of antibody to human parvovirus B19 in pre-school age/young adult individuals in Shiraz, Iran

The present study was conducted to determine the prevalence of antibody against the human parvovirus B19 among 5-25 year old individuals in Shiraz, southern Iran. Serum samples from 908 individuals (505 female and 403 male) were studied. The patients were categorized into seven age groups. The IgG anti-parvovirus B19 was determined by the commercial ELISA kit. Anti-parvovirus B19 IgG was found in 70.09% of the females and 60.04% of the males in this study. In general, 65.63% of the study population had IgG against parvovirus B19. Results from this study have show that the prevalence of parvovirus infection is found to be higher in females than males and in the majority of cases, infection with parvovirus occurs in the pre-school age period. These findings may differ from what is found other countries.

Prevalência de anticorpos IgG antiparvovírus B19 em gestantes durante o atendimento pré-natal e casos de hidropisia fetal não imune atribuídos ao parvovírus B19, na Cidade do Rio de Janeiro

Com o objetivo de medir a prevalência de anticorpos IgG contra o parvovírus B19 em gestantes com até 24 semanas de idade gestacional e detectar a ocorrência de casos de hidropisia fetal não-imune atribuídos a esse vírus, coletamos 249 amostras de soro em uma maternidade de referência na cidade do Rio de Janeiro, entre junho de 2003 e março de 2005. As gestantes foram acompanhadas até o termo da gestação, sendo detectados 17 casos de hidropisia fetal. Quatro casos foram atribuídos ao parvovírus B19 e dois destes ocorreram em gestantes residentes na zona oeste da cidade, em fevereiro de 2005. Resultados positivos para anticorpos IgG antiparvovírus B19 foram encontrados em 172 (71,6%) gestantes (IC 95% 65,5-77,7%), sendo esta prevalência de anticorpos comparável à encontrada em outras cidades brasileiras. A única variável associada com aquisição prévia de anticorpos IgG foi número de gestações anteriores maior que um(p= 0,02, IC 95% 0,36-0,94).

Serologic and molecular detection of human Parvovirus B19 infection

Following its identification by Yvonne Cossart in 1975, human Parvovirus B19 has been recognized as the causative agent of a wide range of diseases. In childhood, the most common disease is a typical exanthema called "fifth disease". In adults, viral infection may be responsible for fetal loss and for aplastic anaemia in immuno-compromised patients. Because persistent viral infection may induce an autoimmune response, Parvovirus B19 is emerging as an environmental factor linked to the pathogenesis of autoimmunity. As a result of its expanding disease spectrum, Parvovirus B19 is the subject of intense efforts to clarify the pathogenesis of virus-related disorders as well as improve diagnostic laboratory testing including standardization of serological and nucleic acid-based detection assays. Enzymatic immunoassays based on conformational antigens have proven to be the most important tools for accurate diagnosis in the majority of cases. In other selected clinical cases, the detection of Parvovirus B19 infection can be complemented by PCR and, more recently, by the real-time PCR.

Clinical Manifestations and Outcomes of Parvovirus B19 Infection during Pregnancy in Japan

Parvovirus B19 is a small DNA virus. Infection with parvovirus B19 during pregnancy may cause serious complications in the fetus, including hydrops fetalis and fetal death. The purpose of the present study is to clarify the clinical manifestations and outcomes of parvovirus B19 infection during pregnancy. This prospective study enrolled 478 women with suspected B19 infections during pregnancy between 1999 and 2004. One hundred cases (21%) of B19 infection were detected in 478 pregnant women who had been exposed to B19. Serological infection was confirmed by measurement of B19-specific IgM and IgG in sera. Forty-nine cases reported maternal clinical symptoms and 51 cases were asymptomatic. Facial rash was the most common symptom, with 51% (25/49) of the symptomatic patients complaining of either a facial, body or limb rash. The most common infectious source was children living in the home. Overall, the incidence of adverse fetal effects (including hydrops fetalis and fetal death) related to intrauterine B19 infection was 7% (7/100), and all seven cases were exposed to B19 infection before 20 weeks of gestation. Although half of the cases with parvovirus B19 infections during pregnancy were asymptomatic, patients with adverse fetal effects tended to be symptomatic including rash and fever. These clinical data may supply useful information to produce clinical guidelines for managing B19 infection during pregnancy.

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.

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.

Parvovirus B19 infection in pregnancy: quantitative viral DNA analysis using a kinetic fluorescence detection system (TaqMan PCR)

Human parvovirus B19 infections are common in the general population, and infection during pregnancy may cause hydrops fetalis and fetal death. To initiate adequate treatment, accurate laboratory diagnosis is essential. The most sensitive tests are nested PCR systems, but these assays provide semiquantitative results at best. A parvovirus B19 DNA assay was developed based on the real time TaqMan PCR. This method was calibrated on the basis of serial plasmid dilutions and tested with an international parvovirus B19 standard. The assay was capable of quantifying parvovirus B19 DNA from one to about 5 x 10(7) genome equivalents per reaction (corresponding to 100 to 5 x 10(9) genome equivalents per ml serum). Samples from 51 pregnant women with suspected acute parvovirus B19 infection were tested, and positive PCR results were obtained in at least one of the materials investigated in 41 cases. The median viral DNA load in maternal blood samples was 1.3 x 10(4) copies/ml (range 7.2 x 10(2)-2.6 x 10(7)). Maternal virus DNA concentration was not associated with the presence of maternal symptoms and/or fetal complications. As the stage of infection was not known in the majority of cases, our data do not exclude an association between peak levels of parvovirus B19 DNA and the development of complications. Maternal sera and corresponding fetal material were available for concurrent testing from 15 DNA-positive cases: in most fetal samples, viral DNA concentrations were several orders of magnitude higher (up to 2.1 x 10(12) copies/ml) compared to the corresponding maternal blood samples.

An epidemic of parvovirus B19 in a population of 3,596 pregnant women: a study of sociodemographic and medical risk factors

OBJECTIVES

To estimate the incidence of human parvovirus B19 among pregnant women before and during an epidemic, to elucidate possible sociodemographic and medical risk factors during pregnancy and to estimate the association between parvovirus B19 infection and negative pregnancy outcome.

DESIGN

Prospective study among pregnant women followed from their first antenatal visit before 24 full weeks of gestation until delivery.

SETTING

Department of Obstetrics and Gynaecology, Odense University Hospital, Denmark, November 1992 to February 1994.

METHODS

3,596 pregnant women were invited to participate. The women were examined at first antenatal visit in the period from November 1992 to February 1994 and at delivery. The last delivery was in August 1994 and samples were thus collected before and during a large parvovirus B19 epidemic in Denmark January to September 1994. A blood sample for parvovirus B19 serology was taken at enrollment and from the umbilical cord at delivery. Three questionnaires were completed during 2nd and 3rd trimesters and a registration form at delivery. In total, 3,174 (87.6%) were enrolled and 79.5% completed the study.

RESULTS

The prevalence of B19 IgG seropositivity at the first antenatal visit before 24 full weeks of gestation was 66% . The cumulative prevalence proportion of acute parvovirus B19 infection during pregnancy among IgG negative women was found to be 10.3% (IgM seropositivity and/or IgG seroconversion). The IgG seroconversion incidence increased significantly from 1.0% to 13.5% among 932 seronegative pregnant women before and during the epidemic, respectively (P < 0.001). Independent risk factors related to increased risk of B19 infection during pregnancy, adjusted for other sociodemographic and medical factors, were: children at home (adjusted OR 2.1, 95% CI 1.3-3.2); serious medical disease (adjusted OR 3.0, 95% CI 1.0-8.5); and a stressful job (adjusted OR 1.8, 95% CI 1.0-3.3). Parvovirus B 19 IgM seropositivity was associated with events of late spontaneous abortions and stillbirths (crude OR 9.9; 95% CI 3.3-29.4).

CONCLUSION

Before and during an epidemic of acute B19 infection incidences were measured among pregnant women to be 1.0% and 13.5%, respectively. Three factors, significantly increasing the risk of acute B19, were identified as: having children at home; suffering from serious medical diseases; and having a stressful job. IgM positivity for parvovirus B19 was associated with negative outcome of pregnancy.

Pathogenesis of nonimmune hydrops fetalis caused by intrauterine B19 infection

Intrauterine human parvovirus B19 infection is related to non-immune hydrops fetalis and fetal death. First, we performed epidemiological studies to determine the critical period during which maternal infection led to hydrops fetalis. The studies showed that the hepatic period of hematopoietic activity was correlated with the critical period of maternal infection, which suggested that B19 might have affinity for erythroid lineage cells at the stage of hematopoiesis. We next established an in vitro infection experimental system of B19 using erythroid lineage cells derived from fetal liver cells. We demonstrated that the erythroid lineage cells proved to be appropriate targets for B19 virus and that B19 infection could induce apoptosis of infected cells. The massive destruction of erythroid lineage cells through apoptosis seems to cause severe anemia and to result in heart failure of the fetus. To analyze the cytotoxic mechanism in more detail, we established a stringent regulatory expression system of the NS1 protein encoded by the B19 genome and indicated that the apoptosis induced by B19 was directly caused by the NS1 protein. Experiments using mutations engineered in the ATP-binding domain of NS1 indicated that this domain played a critical role for the apoptosis induction. The present studies may contribute to a better understanding of the pathogenesis of hydrops fetalis associated with B19 infection during pregnancy.