Oscar Norbeck

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.

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.

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.

Respiratory viruses, a common microbiological finding in neutropenic children with fever.

Abstract Background Febrile neutropenia is a common complication in children undergoing chemotherapy for malignancies. A microbial agent is only identified in 15–30% of the fever episodes and corresponds mostly to bacterial findings. Objective To investigate viral infections as possible etiologic agents in episodes of febrile neutropenia. Study design Nasopharyngeal aspirates (NPAs) from patients presenting with neutropenic fever at two pediatric oncology wards in Sweden and Australia were analyzed with a conventional virus-diagnostic approach and RT-PCR. Coupled blood samples were analyzed for the detection of CMV, EBV, adenovirus and erythrovirus. Bacterial blood culture was performed routinely. Results Conventional virus-diagnostic approach coupled to routinely performed bacterial analyzes revealed an infectious agent in 29% compared to 60% when using PCR. By adding PCR, a viral pathogen was detected in 46% of the NPAs and in 4% of the blood samples collected. In half of the patients with bacteremia, respiratory tract viruses were co-detected. Conclusion Respiratory viruses were frequently detected in NPAs suggesting a significant role of viral infections in children presenting with neutropenic fever. The meaning of these findings needs to be further evaluated but has the potential to individualize infection treatment and to reduce the extensive use of antibiotics in immunocompromised children with neutropenia.

Sustained CD8+ T-Cell Responses Induced after Acute Parvovirus B19 Infection in Humans

ABSTRACT Murine models have suggested that CD8+ T-cell responses peak early in acute viral infections and are not sustained, but no evidence for humans has been available. To address this, we longitudinally analyzed the CD8+ T-cell response to human parvovirus B19 in acutely infected individuals. We observed striking CD8+ T-cell responses, which were sustained or even increased over many months after the resolution of acute disease, indicating that CD8+ T cells may play a prominent role in the control of parvovirus B19 and other acute viral infections of humans, including potentially those generated by live vaccines.

Flocked nasal swab versus nasopharyngeal aspirate for detection of respiratory tract viruses in immunocompromised adults: a matched comparative study

BackgroundSeveral studies have compared nasal swabs to the more invasive nasopharyngeal aspirate (NPA) for detection of respiratory viruses. Mostly, the comparisons have been performed on immunocompetent children with upper respiratory tract symptoms. The results range from a relatively poor sensitivity for the swabs to an even higher sensitivity than for the NPA. We aimed to investigate the sensitivity of a flocked nasal swab (fNS) on immunocompromised adults with febrile neutropenia.MethodsDuring 16 months, adults with a hematological disorder presenting with febrile neutropenia were enrolled in the study. Paired samples of the fNS and NPA were collected in the outer part of the nasal cavity and the nasopharynx, respectively. The samples were analyzed regarding a panel of 15 respiratory viruses by means of quantitative polymerase chain reaction. Furthermore, as an indirect measure of cell yield by either method, the copy number of the human beta actin gene was also determined. Cohens kappa was calculated as a measure of agreement of the results obtained from either method. Wilcoxon signed-rank test was used for comparison of cell yield.ResultsA total of 98 paired samples from a total of 89 patients were collected. Twenty of the pairs had virus detected in at least one of the specimens; 11 in both, 7 in NPA only, and 2 in fNS only. For the fNS, the overall sensitivity for any virus and for rhinovirus only was 65% and 78%, respectively. NPA was significantly superior to the fNS in collecting epithelial cells.ConclusionWe found the overall sensitivity of 65% to be too low to replace NPA with this sampling technique in this patient category.

Detection of parvovirus B19, cytomegalovirus and enterovirus infections in cases of intrauterine fetal death

Abstract Aims: Maternal infections with parvovirus B19, cytomegalovirus (CMV) and enterovirus have been associated with intrauterine fetal death (IUFD), but the incidence of these infections is not clear. This prospective study was conducted to estimate this incidence. Methods: A prospective study of 38 months was conducted on cases of IUFD referred to Huddinge University Hospital, Stockholm, Sweden. Placental biopsies, fetal blood and amniotic fluid were collected from cases of IUFD (n=52). Placental biopsies from normal pregnancies at term (n=53) were used as controls. These tissues were examined for parvovirus B19 DNA, CMV DNA and enterovirus RNA using polymerase chain reaction (PCR). Maternal viral serology was measured in 46 cases and virus isolation for enterovirus in maternal stool samples was performed in 31 cases. Results: Viral nucleic acid was recovered in at least one tissue sample from six cases of fetal death (parvovirus B19 in two cases, CMV in three and enterovirus in one), while all placental biopsies from controls were found negative. Serological signs of primary maternal infection were found in two of the cases, and virus isolation for enterovirus was negative in all samples examined. Conclusion: Parvovirus B19, CMV and enterovirus may be considered as etiologic agents in cases of fetal death. PCR on placental and/or fetal tissue improves diagnostic accuracy for these infections.

Recombinant Parvovirus B19 Empty Capsids Inhibit Fetal Hematopoietic Colony Formation in vitro

Erythroid lineage cells are target cells for human parvovirus B19, and a natural infection often results in transient anemia. To determine whether recombinant B19 capsid proteins (VP1/VP2) also inhibit human hematopoietic progenitor growth, a model system was set up. The B19 capsids were inoculated into primary cultures of hematopoietic stem cells derived from human fetal liver, resulting in a 70–95% reduction of BFU-E (burst-forming unit erythroid cells) as compared with the medium control. A similar effect was seen in human hematopoietic stem cell cultures derived from cord blood and adult bone marrow. Preincubation of the B19 capsids with either a monoclonal antibody to the virus or with B19 IgG positive human sera reduced the inhibitory effect. Furthermore, the inhibitory effect could be reduced by preincubating the target cells with a monoclonal antibody to the cellular receptor for the virus, the P antigen. These findings thus show that the inhibition of colony formation of human hematopoietic stem cells can occur in the absence of parvovirus B19 nonstructural proteins. We speculate that B19 capsid could provide a possible strategy to downregulate indigenous hematopoiesis in fetal stem cell transplantations.

Decreased functional T lymphocyte-mediated cytokine responses in patients with chemotherapy-induced neutropenia.

The degree of immunosuppression in patients with haematological malignancies treated with chemotherapy is routinely measured as number of circulating cells (preferable neutrophils) in peripheral blood. A parallel decline in the number of T cells is expected, but a possible alteration in their functionality has been less well explored. The ability of T cells to secrete more than one cytokine simultaneously is known to indicate protective immunity. The aim of this study was to determine whether the function of circulating T cells is altered in patients with chemotherapy‐induced neutropenia.

No evidence of presence of parvovirus 4 in a Swedish cohort of severely immunocompromised children and adults.

The recently discovered human parvovirus 4 (PARV4) has been associated with seropositivity for human immunodeficiency virus, hepatitis B virus and hepatitis C virus. High prevalence is seen especially in intravenous drug users. The virus has been detected in blood products and persons who have been repeatedly transfused have shown to be a risk-group. Furthermore, reports from different parts of the world suggesting a prevalence ranging from zero to one third of the healthy population and the virus is thought to cause a latent or persistent infection. We investigated the presence of PARV4 DNA and parvovirus B19 (B19) DNA in serum from 231 severely immunocompromised cancer patients that have been exposed for blood products. Compared to B19, which was found in 3.9% of the patients, we found no evidence of PARV4. Our results may indicate a very low prevalence of the virus in Sweden, and it would be useful to measure the real PARV4 exposure of the healthy population as well as individuals with known risk factors by serology.