Thomas Tolfvenstam

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.

Frequency of human parvovirus B19 infection in intrauterine fetal death

BACKGROUND Parvovirus B19 is known to cause fetal death in the second trimester, mainly in combination with hydrops fetalis. However, the frequency of parvovirus-B19-associated non-hydropic fetal loss in the late second and third trimester has not been thoroughly investigated. We aimed to investigate the frequency of parvovirus B19 infection in unselected cases of intrauterine fetal death and to assess the sensitivity of different diagnostic procedures. METHODS Of 14147 deliveries in three hospitals in the major Stockholm area of Sweden, all cases of intrauterine fetal death (>22 gestational weeks) that occurred between January, 1998, and May, 1999 (n=47), referred cases of miscarriage (<22 gestational weeks, n=37), and induced abortions (n=29), were included in the study. Placental and fetal tissues were examined by means of parvovirus-B19-specific PCR, histopathology, and immunohistochemistry. Placental tissues from 53 normal pregnancies at term were also examined. FINDINGS Significantly more cases of intrauterine fetal death were positive for parvovirus B19 DNA (seven [15%]) than were normal pregnancies at term (zero, p=0.049). Furthermore, parvovirus B19 DNA was found in two (5%) of the miscarriages but not in any of the cases of induced abortion. Only three of nine DNA-positive cases had parvovirus-B19-associated inclusions and stained positive for viral proteins. All but one of the DNA-positive cases of intrauterine fetal death were non-hydropic. INTERPRETATION The presence of parvovirus B19 DNA in cases of late second-trimester and third-trimester fetal death is common, and most are non-hydropic. The sensitivity of conventional diagnostic procedures for intrauterine fetal death could be greatly improved by addition of parvovirus B19 PCR.

Parvovirus B19 infection: association with third‐trimester intrauterine fetal death

Objective To identify the presence of parvovirus B19 infection as a possible cause of fetal loss in the third trimester.

Clinical Utility of PCR for Common Viruses in Acute Respiratory Illness

BACKGROUND: Acute respiratory illness (ARI) accounts for a large proportion of all visits to pediatric health facilities. Quantitative real-time polymerase chain reaction (qPCR) analyses allow sensitive detection of viral nucleic acids, but it is not clear to what extent specific viruses contribute to disease because many viruses have been detected in asymptomatic children. Better understanding of how to interpret viral findings is important to reduce unnecessary use of antibiotics. OBJECTIVE: To compare viral qPCR findings from children with ARI versus asymptomatic control subjects. METHODS: Nasopharyngeal aspirates were collected from children aged ≤5 years with ARI and from individually matched, asymptomatic, population-based control subjects during a noninfluenza season. Samples were analyzed by using qPCR for 16 viruses. RESULTS: Respiratory viruses were detected in 72.3% of the case patients (n = 151) and 35.4% of the control subjects (n = 74) (P = .001). Rhinovirus was the most common finding in both case patients and control subjects (47.9% and 21.5%, respectively), with a population-attributable proportion of 0.39 (95% confidence interval: 0.01 to 0.62). Metapneumovirus, parainfluenza viruses, and respiratory syncytial virus were highly overrepresented in case patients. Bocavirus was associated with ARI even after adjustment for coinfections with other viruses and was associated with severe disease. Enterovirus and coronavirus were equally common in case patients and control subjects. CONCLUSIONS: qPCR detection of respiratory syncytial virus, metapneumovirus, or parainfluenza viruses in children with ARI is likely to be causative of disease; detection of several other respiratory viruses must be interpreted with caution due to high detection rates in asymptomatic children.

Prolonged activation of virus-specific CD8+T cells after acute B19 infection.

Background Human parvovirus B19 (B19) is a ubiquitous and clinically significant pathogen, causing erythema infectiosum, arthropathy, transient aplastic crisis, and intrauterine fetal death. The phenotype of CD8+ T cells in acute B19 infection has not been studied previously. Methods and Findings The number and phenotype of B19-specific CD8+ T cell responses during and after acute adult infection was studied using HLA–peptide multimeric complexes. Surprisingly, these responses increased in magnitude over the first year post-infection despite resolution of clinical symptoms and control of viraemia, with T cell populations specific for individual epitopes comprising up to 4% of CD8+ T cells. B19-specific T cells developed and maintained an activated CD38+ phenotype, with strong expression of perforin and CD57 and downregulation of CD28 and CD27. These cells possessed strong effector function and intact proliferative capacity. Individuals tested many years after infection exhibited lower frequencies of B19-specific cytotoxic T lymphocytes, typically 0.05%–0.5% of CD8+ T cells, which were perforin, CD38, and CCR7 low. Conclusion This is the first example to our knowledge of an “acute” human viral infection inducing a persistent activated CD8+ T cell response. The likely explanation—analogous to that for cytomegalovirus infection—is that this persistent response is due to low-level antigen exposure. CD8+ T cells may contribute to the long-term control of this significant pathogen and should be considered during vaccine development.

Clinical and Laboratory Findings in Immunocompetent Patients with Persistent Parvovirus B19 DNA in Bone Marrow

The clinical relevance of parvovirus B19 DNA persistence in bone marrow was examined in 10 immunocompetent individuals undergoing examinations for unexplained fever, arthralgia or chronic leukopenia. Common causes of these symptoms had been ruled out and bone marrow aspiration was indicated at this stage of investigation. In addition to morphological analysis of the bone marrow, a test for B19 DNA was performed with 2 nested PCRs. Five of these 10 selected patients had detectable B19 DNA in their bone marrow, whereas no viraemia was observed. Additional bone marrow samples were collected at least 6 months after the first sample from the B19 DNA-positive patients, of whom 3 were found to be still positive. Indeed, 2 of the patients have been positive for more than 5 y of follow-up. Sera from all patients with persistent B19 DNA in bone marrow could neutralize the virus. One patient responded to treatment with immunoglobulin but later relapsed. No other cause of the symptoms was found, despite extensive investigations, and at least some of the prolonged disease manifestations may be due to parvovirus B19.

Seroprevalence of viral childhood infections in Eritrea.

BACKGROUND The seroprevalence of viral childhood infections in Africa has not been thoroughly investigated. The relatively recently discovered human parvovirus B19 (B19) and human herpesvirus 6 (HHV-6) have received particularly little attention. OBJECTIVE To investigate the seroprevalence of viral childhood infections in different Eritrean populations and to define groups at high risk for infection. STUDY DESIGN Five population groups in Eritrea have been examined to define the prevalence of specific antibodies to several childhood viruses. The study population of more than 400 persons consisted of children, pregnant women, female sex workers and members of a secluded tribe called Rashaida. RESULTS All groups showed a high prevalence of antibodies to measles and HHV-6 (> 85%). For rubella, the seroprevalence was very high in all adult groups (93-99%) except the Rashaida group (71%). The mumps prevalence was surprisingly low in the Rashaida group (29%) compared to 46-85% in the other adults. Late encounter of mumps and rubella was also observed among the Rashaidas. The pattern of antibodies to B19 showed a higher seroprevalence in all groups (56-91%) compared to what has been reported from the western world. CONCLUSION The findings represent what might be expected in an unvaccinated population. The exception was the Rashaidas, which had low seroprevalences and late encounter of mumps and rubella. This is of importance because it makes this tribe vulnerable to these infections, which are associated with complications when acquired in adult age. Also noteworthy is the high frequency of antibodies to HHV-6 and particularly B19 in all groups, indicative of an early encounter of both these viruses.

Respiratory viruses associated with community-acquired pneumonia in children: matched case–control study

Background Community-acquired pneumonia (CAP) is the leading cause of death in children worldwide and a substantial proportion of childhood CAP is caused by viruses. A better understanding of the role of virus infections in this condition is needed to improve clinical management and preventive measures. The aim of the study was therefore to assess the association between specific respiratory viruses and childhood CAP. Methods A case–control study was conducted during 3 years in Stockholm, Sweden. Cases were children aged ≤5 years with radiological CAP. Healthy controls were consecutively enrolled at child health units during routine visits and matched to cases on age and calendar time. Nasopharyngeal aspirates were obtained and analysed by real-time PCR for 15 viruses. Multivariate conditional logistic regression was used to account for coinfections with other viruses and baseline characteristics. Results A total of 121 cases, of which 93 cases met the WHO criteria for radiological pneumonia, and 240 controls were included in the study. Viruses were detected in 81% of the cases (n=98) and 56% of the controls (n=134). Influenza virus, metapneumovirus and respiratory syncytial virus were detected in 60% of cases and were significantly associated with CAP with ORs >10. There was no association with parainfluenza virus, human enterovirus or rhinovirus and coronavirus and bocavirus were negatively associated with CAP. Conclusions Our study indicates viral CAP is an underestimated disease and points out hMPV as a new important target for the prevention of childhood CAP.

Parvovirus B19 Infection in Children with Acute Lymphoblastic Leukemia is Associated with Cytopenia Resulting in Prolonged Interruptions of Chemotherapy

BACKGROUND Parvovirus B19 infection causes severe cytopenia and can mimic a leukemic relapse or therapy-induced cytopenia in patients with hematologic malignancies. We evaluated the complications of parvovirus B19 infection, including delays in the scheduled course of chemotherapy, in children with acute lymphoblastic leukemia (ALL). METHODS Consecutive bone marrow samples were collected from 117 children with ALL and were analyzed for parvovirus B19 DNA by polymerase chain reaction. Clinical and laboratory data were collected from the Nordic Childhood Leukemia Registry and from medical records. RESULTS Among the 117 children with ALL, 18 (15%) were found to be parvovirus B19 DNA positive. The infection was suspected on clinical grounds in only 1 of these 18 patients. Patients with viremia at diagnosis or during therapy for infection had lower viral loads (median viral load, 7 x 10(4) copies/mL) than did those who became viremic during maintenance therapy (median viral load, 2 x 10(8) copies/mL). The former group also had fewer clinical complications. Indeed, when parvovirus B19 DNA was present during the maintenance treatment, the number of complications (including cytopenia) increased, causing significantly longer periods without chemotherapy (median duration without chemotherapy, 59 days vs. 30 days; P < or = .05) and a higher number of blood transfusions (P = .018) in parvovirus B19 DNA-positive patients than in parvovirus B19 DNA-negative patients. CONCLUSIONS Children with ALL who were infected with parvovirus B19 became cytopenic, leading to reduced treatment intensity and to complications during treatment. Screening for parvovirus B19 DNA by quantitative polymerase chain reaction in pediatric patients with ALL and unexplained cytopenia is suggested.

Persistent B19 parvovirus infection in pediatric malignancies

BACKGROUND AND PROCEDURE The frequency and clinical importance of parvovirus B19 infection were studied in children investigated or treated for various malignancies and cytopenias. RESULTS B19 infection was thus demonstrated in six out of 53 unselected children with malignancies by bone marrow examination, using the B19, DNA-specific, polymerase chain reaction (PCR). Examinations using the PCR in serum samples were equally or less sensitive than in bone marrow samples. One of the children had a persistent B19 infection during maintenance therapy for acute lymphoblastic leukemia. She developed a prolonged and severe cytopenia, and the clinical signs included facial rash, chills, high undulating fever, and pharyngitis. She also seroconverted and became B19 IgM-antibody positive during the study period. CONCLUSIONS Parvovirus B19 infection was detected in 10% of the children and was either asymptomatic or was associated with severe and prolonged cytopenia. Bone marrow examinations are recommended for the detection of B19 DNA in immunosuppressed children.