Klaus Hedman

Persistence of human parvovirus B19 in human tissues.

Human parvovirus B19 infection causes various clinical symptoms, such as rash, arthropathy, anemias and fetal death, but it can also remain asymptomatic. The arthropathies and anemias can become chronic for several years, not infrequently resembling autoimmune syndromes. B19 replicates only in red blood cell precursors of bone marrow or fetal liver, resulting in high-titred short-lived viremia, but viral DNA is detectable also in cells of several other types. Recently B19 DNA has been found, by very sensitive amplification tests, in certain tissues not only of symptomatic but also of healthy individuals for several years or decades after B19 infection. The mere presence of B19 DNA in these tissues of a symptomatic patient (e.g. joints in chronic arthritis or skin in dermatomyositis) thereby does not prove that the present disease is caused by B19. The diagnosis has to be verified by other innovative means. How and why viral DNA persists in the tissues of healthy individuals is under investigation.

Etiological Diagnosis of Childhood Pneumonia by Use of Transthoracic Needle Aspiration and Modern Microbiological Methods

Childhood pneumonia is usually treated without determining its etiology. The causative organism can be isolated from specimens of blood, empyema fluid, or lung aspirate, but this is rarely done. The potential of transthoracic needle aspiration for identification of causative agents was tested with use of modern microbiological methods. Aspiration was performed for 34 children who had radiological signs compatible with community-acquired pneumonia and had alveolar consolidation. In addition to bacterial and viral cultures and viral antigen detection, nucleic acid detection for common respiratory pathogens was performed on aspirate specimens. Aspiration disclosed the etiology in 20 (59%) of 34 cases overall and in 18 (69%) of 26 patients from whom a representative specimen was obtained. Aspirations advantages are high microbiological yield and a relatively low risk of a clinically significant adverse event. Aspiration should be used if identification of the causative agent outweighs the modest risk of the procedure.

Serologically verified human bocavirus pneumonia in children.

Human bocavirus (HBoV) is a newly identified parvovirus frequently found in children suffering from acute respiratory and intestinal infections. The aim of the present study was to evaluate, by using a newly developed antibody assay, the role of HBoV in pediatric community‐acquired pneumonia (CAP) and the seropositivity rate to HBoV in a prospective study in North‐Italian children.

Real-Time Quantitative PCR Detection of Four Human Bocaviruses

ABSTRACT Human bocavirus (HBoV) was discovered in 2005 and is associated with respiratory tract symptoms in young children. Three additional members of the genus B ocavirus, HBoV2, -3, and -4, were discovered recently from fecal specimens, and early results indicate an association between HBoV2 and gastrointestinal disease. In this study, we present an undifferentiating multiplex real-time quantitative PCR assay for the detection of these novel viruses. Differentiation of the individual bocavirus species can be subsequently achieved with corresponding singleplex PCRs or by sequencing. Both multiplex and singleplex assays were consistently able to detect ≤10 copies of HBoV1 to -4 plasmid templates/reaction, with dynamic quantification ranges of 8 logs and 97% to 102% average reaction efficiencies. These new assays were used to screen stool samples from 250 Finnish patients (median age, 40 years) that had been sent for diagnosis of gastrointestinal infection. Four patients (1.6%; median age, 1.1 years) were reproducibly positive for HBoV2, and one patient (0.4%; 18 years of age) was reproducibly positive for HBoV3. The viral DNA loads varied from <103 to 109 copies/ml of stool extract. None of the stool samples harbored HBoV1 or HBoV4. The highly conserved sequence of the hydrolysis probe used in this assay may provide a flexible future platform for the quantification of additional, hitherto-unknown human bocaviruses that might later be discovered. Our results support earlier findings that HBoV2 is a relatively common pathogen in the stools of diarrheic young children, yet does not often occur in the stools of adults.

Seroepidemiology of the Newly Found Trichodysplasia Spinulosa–Associated Polyomavirus

Trichodysplasia spinulosa (TS)-associated polyomavirus (TSV) was recently (in 2010) discovered in TS lesions. To investigate the seroprevalence and primary exposure time of this virus, we set up a virus protein (VP1) viruslike particle (VLP)-based immunoglobulin G enzyme immunoassay. The seroprevalence of TSV was 5%, among children aged 1-4 years, rising to 48% at 6-10 years, and 70% among 149 adults. The TSV antibodies did not cross-react with corresponding Merkel cell polyomavirus VLPs, and their reactivity appeared conformational. TSV circulates widely in the human population and primary exposure is extensive in childhood, beginning at age 1-2 years.

T Helper Cell–Mediated In Vitro Responses of Recently and Remotely Infected Subjects to a Candidate Recombinant Vaccine for Human Parvovirus B19

T cell proliferation to human parvovirus B19 antigen was measured in 6 patients with recent B19 infection (1 with pneumonia and pleuritis), 1 patient with symptoms persisting >180 days after onset, 18 nonsymptomatic subjects with remote B19 immunity, and 12 B19-seronegative control subjects. Recombinantly expressed virus-like particles (VP1/2 capsids), a candidate B19 vaccine, were used as antigen. Virus-specific T helper cell proliferation was detectable in all the recently infected patients and in most (17/18) of the remotely infected subjects but not in the seronegative control subjects. The B19-specific T cell responses, in general, were most vigorous among the recently infected patients. However, such strong B19-specific proliferation was not confined within the acute phase, as 28% (5/18) of the remotely infected healthy individuals had B19-specific reactivity persisting at acute-phase levels, apparently for years or decades. These data indicate that B cells recognizing the VP1/2 capsids receive class II-restricted help from CD4(+) T lymphocytes.

Improved Diagnosis of Gestational Parvovirus B19 Infection at the Time of Nonimmune Fetal Hydrops

BACKGROUNDnIn the diagnosis of parvovirus B19 infection, the detection of virus-specific IgG in the absence of virus-specific IgM is considered to indicate past immunity.nnnMETHODSnWe determined the diagnostic value of a high-quality B19 IgM EIA, compared with that of a VP1 IgG avidity EIA, a VP2 IgG epitope-type specificity (ETS) EIA, and real-time polymerase chain reaction (PCR) in the diagnosis of maternal B19 infection during nonimmune fetal hydrops.nnnRESULTSnSerum samples from 101 pregnant women with confirmed B19-induced fetal hydrops were collected at the time of invasive prenatal diagnosis. The samples were investigated for B19 IgM, VP1 IgG avidity, and VP2 IgG ETS. With the B19 IgM EIA, 78 women (77.2 %) showed positive results, 15 (14.9%) showed negative results, and 8 (7.9 %) showed equivocal results. According to the combined B19 IgG avidity and IgG ETS EIA results, only 5 (5%) of 101 women were classified as having past immunity. Available serum samples (n = 24) that had nondiagnostic results in the antibody assays were further investigated by PCR. All were B19 DNA positive (mean load, 2.5 x 10(4) genome equivalents/mL; range, 2.5 x 10(3) - 7.8 x 10(6)).nnnCONCLUSIONSnAt the time of B19-induced hydrops, detection of B19 DNA in maternal blood had the best diagnostic sensitivity for identifying maternal B19 infection. However, given the long persistence of B19 DNAemia, supplementary measurement of VP1 IgG avidity and VP2 IgG ETS improves the precision of diagnosis and management of pregnant women affected by the B19 virus.

Lymphoproliferative disease after allogeneic stem cell transplantation—pre-emptive diagnosis by quantification of Epstein–Barr virus DNA in serum

BACKGROUNDnLymphoproliferative disease (PTLD) is a life-threatening complication of organ transplantation. In matched, allogeneic, non-T-cell-depleted stem-cell transplantations (SCT) the disease develops early but has been thought to be rare.nnnOBJECTIVESnWe determined by strict histopathological criteria the incidence of fatal Epstein-Barr-virus (EBV)-related PTLD in a large number of SCT, and assessed the diagnostic value of a real-time quantitative polymerase chain reaction (qPCR) for EBV-DNA in serum specimens.nnnSTUDY DESIGNnOf the 257 SCT performed in Helsinki during 1994-1999, 132 (51%) recipients were alive and 125 (49%) had succumbed by June 2001. The necropsies were analyzed for EBV-related PTLD as evidenced by disseminated lymphocytic infiltrates labeled histochemically for antigens and RNA (EBER 1 and 2) detectable by in situ technology. From a subset of the PTLD cases (N=12) and a series of corresponding stem-cell recipient controls (N=36), consecutive samples of serum (N=103 and 364, respectively) were studied by qPCR for EBV-DNA, and the clinical data were reviewed.nnnRESULTSnThe post-mortem analysis revealed 18 cases of PTLD (14% of the deceased), all of whom had received intensive immunosuppressive treatment including anti-thymocyte globulin for treatment or prophylaxis of graft versus host disease (GVHD). By using qPCR all the PTLD patients became EBV-DNA positive, in progressively rising copy numbers. EBV-DNA was first detectable 70 (median; range 24-154) days after SCT or 23 (4-86) days before death; i.e. earlier than the symptoms which appeared 15 (2-85) days before death. Among the SCT controls, EBV-DNA occurred sporadically (in only 3.9% sera).nnnCONCLUSIONSnqPCR for EBV-DNA in serum is a highly sensitive (100%) and specific (96%) diagnostic approach. Intensely immunosuppressed stem-cell recipients are at a great risk of developing PTLD, and should be carefully monitored for EBV-DNA, for pre-emptive treatment of this life-threatening disorder.

A new method for determination of varicella-zoster virus immunoglobulin G avidity in serum and cerebrospinal fluid

BackgroundAvidity determination of antigen-specific immunoglobulin G (IgG) antibodies is an established serological method to differentiate acute from past infections. In order to compare the avidity of varicella-zoster virus (VZV) IgG in pairs of serum and cerebrospinal fluid (CSF) samples, we developed a new technique of avidity testing, the results of which are not influenced by the concentration of specific IgG.MethodsThe modifications introduced for the new VZV IgG avidity method included the use of urea hydrogen peroxide as denaturing reagent, the adaptation of the assay parameters in order to increase the sensitivity for the detection of low-level VZV IgG in CSF, and the use of a new calculation method for avidity results. The calculation method is based on the observation that the relationship between the absorbance values of the enzyme immunoassays with and without denaturing washing step is linear. From this relationship, a virtual absorbance ratio can be calculated. To evaluate the new method, a panel of serum samples from patients with acute and past VZV infection was tested as well as pairs of serum and CSF.ResultsFor the serum panel, avidity determination with the modified assay gave results comparable to standard avidity methods. Based on the coefficient of variation, the new calculation method was superior to established methods of avidity calculation.ConclusionsThe new avidity method permits a meaningful comparison of VZV IgG avidity in serum and CSF and should be of general applicability for easy determination of avidity results, which are not affected by the concentration of specific IgG.

Cloning and sequencing of TT virus genotype 6 and expression of antigenic open reading frame 2 proteins.

The near-full-length genome of a TT virus (TTV) (HEL32), closely related to the previously uncharacterized genotype 6, was cloned and sequenced. The genomic organization of HEL32 was compared to 41 published near-full-length TTV sequences representing 17 genotypes. In the majority of genomes, the open reading frame (ORF) 2 region was divided into two separate ORFs, 2a and 2b. The ORF2a sequence was conserved among all genotypes, while the ORF2b region showed more variability. The two corresponding putative proteins of HEL32 were expressed in prokaryotes and their antigenic potential was studied. IgM and IgG antibodies to the respective ORF2-encoded proteins, fp2a and fp2b, and the presence of TTV DNA were studied in the sera of 89 constitutionally healthy adults. By immunoblot using the small TTV proteins as antigens, strong IgM and IgG reactivities were found in 9 and 10% of subjects, respectively. Follow-up studies for 12-15 years of three subjects showed either a persistent coexistence of IgM and TTV DNA or the appearance of viral DNA regardless of pre-existing antibodies. The low prevalence of IgG could be due to the weak immunogenicity of these probably non-structural proteins or to a genotype-specific antibody response. By nested PCR of the conserved ORF2a region, the prevalence of TTV DNA was 85%. TTV genotype 6 sequences were found by specific PCR in 3 of 35 (8.6%) subjects. The low prevalence of TTV IgG compared to the high TTV DNA prevalence, the coexistence of antibodies and viral DNA and the appearance of TTV DNA regardless of pre-existing antibodies suggest that the B-cell immunity against these minor TTV proteins would not be cross protective.