Recurrence quantification analysis of resting state EEG signals in autism spectrum disorder - a systematic methodological exploration of technical and demographic confounders in the search for biomarkers

BACKGROUND

Autism spectrum disorder (ASD) is a neurodevelopmental disorder with a worldwide prevalence of 1-2%. In low-resource environments, in particular, early identification and diagnosis is a significant challenge. Therefore, there is a great demand for 'language-free, culturally fair' low-cost screening tools for ASD that do not require highly trained professionals. Electroencephalography (EEG) has seen growing interest as an investigational tool for biomarker development in ASD and neurodevelopmental disorders. One of the key challenges is the identification of appropriate multivariate, next-generation analytical methodologies that can characterise the complex, nonlinear dynamics of neural networks in the brain, mindful of technical and demographic confounders that may influence biomarker findings. The aim of this study was to evaluate the robustness of recurrence quantification analysis (RQA) as a potential biomarker for ASD using a systematic methodological exploration of a range of potential technical and demographic confounders.

METHODS

RQA feature extraction was performed on continuous 5-second segments of resting state EEG (rsEEG) data and linear and nonlinear classifiers were tested. Data analysis progressed from a full sample of 16 ASD and 46 typically developing (TD) individuals (age 0-18 years, 4802 EEG segments), to a subsample of 16 ASD and 19 TD children (age 0-6 years, 1874 segments), to an age-matched sample of 7 ASD and 7 TD children (age 2-6 years, 666 segments) to prevent sample bias and to avoid misinterpretation of the classification results attributable to technical and demographic confounders. A clinical scenario of diagnosing an unseen subject was simulated using a leave-one-subject-out classification approach.

RESULTS

In the age-matched sample, leave-one-subject-out classification with a nonlinear support vector machine classifier showed 92.9% accuracy, 100% sensitivity and 85.7% specificity in differentiating ASD from TD. Age, sex, intellectual ability and the number of training and test segments per group were identified as possible demographic and technical confounders. Consistent repeatability, i.e. the correct identification of all segments per subject, was found to be a challenge.

CONCLUSIONS

RQA of rsEEG was an accurate classifier of ASD in an age-matched sample, suggesting the potential of this approach for global screening in ASD. However, this study also showed experimentally how a range of technical challenges and demographic confounders can skew results, and highlights the importance of probing for these in future studies. We recommend validation of this methodology in a large and well-matched sample of infants and children, preferably in a low- and middle-income setting.

Bleeding and infection with external ventricular drainage: a systematic review in comparison with adjudicated adverse events in the ongoing Clot Lysis Evaluating Accelerated Resolution of Intraventricular Hemorrhage Phase III (CLEAR-III IHV) trial

BACKGROUND

Retrospective series report varied rates of bleeding and infection with external ventricular drainage (EVD). There have been no prospective studies of these risks with systematic surveillance, threshold definitions, or independent adjudication.

OBJECTIVE

To analyze the rate of complications in the ongoing Clot Lysis: Evaluating Accelerated Resolution of Intraventricular Hemorrhage Phase III (CLEAR III) trial, providing a comparison with a systematic review of complications of EVD in the literature.

METHODS

Patients were prospectively enrolled in the CLEAR III trial after placement of an EVD for obstructive intraventricular hemorrhage and randomized to receive recombinant tissue-type plasminogen activator or placebo. We counted any detected new hemorrhage (catheter tract hemorrhage or any other distant hemorrhage) on computed tomography scan within 30 days from the randomization. Meta-analysis of published series of EVD placement was compiled with STATA software.

RESULTS

Growing or unstable hemorrhage was reported as a cause of exclusion from the trial in 74 of 5707 cases (1.3%) screened for CLEAR III. The first 250 patients enrolled have completed adjudication of adverse events. Forty-two subjects (16.8%) experienced ≥1 new bleeds or expansions, and 6 of 250 subjects (2.4%) suffered symptomatic hemorrhages. Eleven cases (4.4%) had culture-proven bacterial meningitis or ventriculitis.

CONCLUSION

Risks of bleeding and infection in the ongoing CLEAR III trial are comparable to those previously reported in EVD case series. In the present study, rates of new bleeds and bacterial meningitis/ventriculitis are very low despite multiple daily injections, blood in the ventricles, the use of thrombolysis in half the cases, and generalization to >60 trial sites.

Abstract 94: Mortality Review For The First 400 Patients Enrolled In The Clot Lysis: Evaluation Of Accelerated Resolution Of Intraventricular Hemorrhage Trial (CLEAR III)

Objective: CLEAR III is a Phase III, 500-subject, multicenter, double-blind, randomized study comparing extraventricular drainage (EVD) plus intraventricular recombinant tissue plasminogen activator (rtPA) vs. EVD plus placebo for treatment of intraventricular hemorrhage (IVH) in patients with intracerebral hemorrhage (ICH) volume <30cc. We compared proximate causes of death in the acute and post-hospitalization phase of the first 400 subjects enrolled.

Methods: We reviewed serious adverse event (SAE) reports for 106 events that resulted in death within 1 year follow-up. We recorded clinical and volumetric data including ICH and IVH volumes on diagnostic, stability, and end-of-treatment (EOT) computed tomography (CT) scans. EOT was defined as the CT at 72 hours post administration of last dose of test article.

Results: Of the first 400 subjects enrolled, 27% (106) died, 12% (47) within 30 days of symptom onset. Median [iqr] time to death was 41.5 [71] days. Mean age (±SEM) was 64.0(±1.0) years. Proximate cause of death was neurologic in 52.8% (56), followed by respiratory (14.1%; 15), cardiac (10.4%; 11), multi-organ failure (5.7%; 6), infection (3.8%; 4) and unknown (11.3%; 12). Withdrawal of care (WOC) occurred in 46.2% (49); the majority of deaths were neurologic. Median time to death depended on proximate cause (p=0.0005): Neurologic deaths occurred at 25.5 [36] days vs. 67 [102] days for non-neurologic deaths (p=0.0002). WOC led to death 22 [53] days after ICH and cardiac arrest at 27 [25] days. Patients with no WOC and non-neurologic death died at 76 [106.5] days after ICH. After adjusting for diagnostic IVH volume, age and WOC, factors independently associated with early (≤30d) vs. later (>30-365d) death were male gender (p=0.01), lower admission Glasgow coma scale (p=0.02), no pneumonia (p=0.02) and higher EOT IVH volume (trend p=0.06).

Conclusion: The CLEAR III mortality rate for the first 400 subjects enrolled remains below literature estimates for severe IVH and is below the pre-specified recruitment suspension threshold of 40%. Approximately half of known causes of death are directly due to neurologic events and occur significantly earlier than non-neurologic causes. Reduction in IVH volume may lower early mortality risk.

Biosorption of heavy metals from aqueous solutions with tobacco dust

A typical lignocellulosic agricultural residue, namely tobacco dust, was investigated for its heavy metal binding efficiency. The tobacco dust exhibited a strong capacity for heavy metals, such as Pb(II), Cu(II), Cd(II), Zn(II) and Ni(II), with respective equilibrium loadings of 39.6, 36.0, 29.6, 25.1 and 24.5mg of metal per g of sorbent. Moreover, the heavy metals loaded onto the biosorbent could be released easily with a dilute HCl solution. Zeta potential and surface acidity measurements showed that the tobacco dust was negatively charged over a wide pH range (pH>2), with a strong surface acidity and a high OH(-) adsorption capacity. Changes in the surface morphology of the tobacco dust as visualized by atomic force microscopy suggested that the sorption of heavy metal ions on the tobacco could be associated with changes in the surface properties of the dust particles. These surface changes appeared to have resulted from a loss of some of the structures on the surface of the particles, owing to leaching in the acid metal ion solution. However, Fourier transform infrared spectroscopy (FTIR) showed no substantial change in the chemical structure of the tobacco dust subjected to biosorption. The heavy metal uptake by the tobacco dust may be interpreted as metal-H ion exchange or metal ion surface complexation adsorption or both.

New methodology for hazardous waste classification using fuzzy set theory Part II. Intelligent decision support system

In part 1 of this paper, factors that influence hazards and eco/toxicity in composite hazardous wastes were described. In part 2, a computer-aided decision support tool based on fuzzy set theory is proposed to support the classification of composite wastes. Given the chemical properties, the nature of microorganisms that may be present, the behaviour of chemicals in humans and ecosystems, and the quantities of wastes, the computer-aided tool automatically classifies the waste as benign, partially hazardous, hazardous or highly hazardous. The functionality of the computer-aided decision tool is demonstrated through nine worked examples and the results are discussed in detail.

New methodology for hazardous waste classification using fuzzy set theory Part I. Knowledge acquisition

In the literature on hazardous waste classification, the criteria used are mostly based on physical properties, such as quantity (weight), form (solids, liquid, aqueous or gaseous), the type of processes generating them, or a set of predefined lists. Such classification criteria are inherently inadequate to account for the influence of toxic and hazard characteristics of the constituent chemicals in the wastes, as well as their exposure potency in multimedia environments, terrestrial mammals and other biota. Second, none of these algorithms in the literature has explicitly presented waste classification by examining the contribution of individual constituent components of the composite wastes. In this two-part paper, we propose a new automated algorithm for waste classification that takes into account physicochemical and toxicity effects of the constituent chemicals to humans and ecosystems, in addition, to the exposure potency and waste quantity. In part I, available data on the physicochemical and toxicity properties of individual chemicals in humans and ecosystems, their exposure potency in environmental systems and the effect of waste quantity are described, because they fundamentally contribute to the final waste ranking. Knowledge acquisition in this study was accomplished through the extensive review of published and specialized literature to establish facts necessary for the development of fuzzy rule-bases. Owing to the uncertainty and imprecision of various forms of data (both quantitative and qualitative) essential for waste classification, and the complexity resulting from knowledge incompleteness, the use of fuzzy set theory for the aggregation and computation of waste classification ranking index is proposed. A computer-aided intelligent decision tool is described in part II of this paper and the functionality of the fuzzy waste classification algorithm is illustrated through nine worked examples.

An aggregate fuzzy hazardous index for composite wastes

In this paper, a fuzzy waste index for evaluating the hazard posed by composite wastes generated from industrial processes is proposed. Within this methodology, a fuzzy index as a measure of hazardousness of a given composite waste is derived from the crisp inputs of its component's flammability, corrosivity, toxicity and reactivity attributes based on the National Fire Protection Association (NFPA) hazard rankings. The novelty of this work lies in establishing an integrated fuzzy hazardous waste index (FHWI) which provides a single-value representing the hazard ranking of a composite waste. This is contrary to current techniques which do not provide a final aggregated hazard index. The efficacy of the new proposed approach is illustrated through several worked examples. The results demonstrate that the fuzzy algorithm can be useful in aiding policy and decision-makers in conducting comprehensive initial evaluation of the status of waste hazardous status without the need for costly laboratory experiments. As such, the approach offers a robust and transparent decision-making methodology.

Embedding of multidimensional time-dependent observations

A method is proposed to reconstruct dynamic attractors by embedding of multivariate observations of dynamic nonlinear processes. The Takens embedding theory is combined with independent component analysis to transform the embedding into a vector space of linearly independent vectors (phase variables). The method is successfully tested against prediction of the unembedded state vector in two case studies of simulated chaotic processes.

A null mutation in HLA-G is not associated with preeclampsia or intrauterine growth retardation

Modulation of the expression of genes of the major histocompatibility complex (MHC) in tissues at the maternal-fetal interface almost certainly plays a role in successful development of the semi-allogeneic fetus. While expression of the classical class I genes (HLA-A, B, C) is low to non-existent at this site, the non-classical molecule, HLA-G, is expressed uniquely in fetal cells at the maternal-fetal interface. The recent demonstration that homozygotes for a deletion mutation in exon 3 (1597DeltaC) of HLA-G do not express the full-length HLA-G1 isoforms indicates a potential reduction in expression of this isoform in heterozygotes. If the full-length isoform of HLA-G (i.e. HLA-G1) contributes to proper invasion of maternal spiral arteries by extravillous cytotrophoblast, then 1597DeltaC heterozygotes could be at increased risk for disorders of trophoblast invasion. Two populations, infants with intrauterine growth retardation (IUGR) and infants of preeclamptic (PE) mothers, were genotyped for the 1597DeltaC polymorphism. The frequency of 1597DeltaC in these samples was not significantly different from healthy controls, suggesting that heterozygotes for this deletion mutation are not at significantly increased risk for PE or IUGR (P = 0.727 and 0.803, respectively).

Apoptosis and regeneration of hepatocytes during recovery from transient hepadnavirus infections

It is well known that hepatitis B virus infections can be transient or chronic, but the basis for this dichotomy is not known. To gain insight into the mechanism responsible for the clearance of hepadnavirus infections, we have performed a molecular and histologic analysis of liver tissues obtained from transiently infected woodchucks during the critical phase of the recovery period. We found as expected that clearance from transient infections occurred subsequent to the appearance of CD4(+) and CD8(+) T cells and the production of interferon gamma and tumor necrosis factor alpha in the infected liver. These events were accompanied by a significant increase in apoptosis and regeneration of hepatocytes. Surprisingly, however, accumulation of virus-free hepatocytes was delayed for several weeks following this initial influx of lymphocytes. In addition, we observed that chronically infected animals can exhibit levels of T-cell accumulation, cytokine expression, and apoptosis that are comparable with those observed during the initial phase of transient infections. Our results are most consistent with a model for recovery predicting replacement of infected hepatocytes with regenerated cells, which by unknown mechanisms remain protected from reinfection in animals that can be cured.

Aberrant expression of a cytokeratin in a subset of hepatocytes during chronic WHV infection

Chronic infection of woodchucks with woodchuck hepatitis virus (WHV) invariably leads, within 2-4 years, to the appearance of hepatocellular carcinoma (HCC). HCC is preceded by an extended period of chronic liver damage, probably resulting from the immune response to viral antigens. It may be that infection itself also induces changes in the hepatocyte population. To begin to identify some of the changes in the liver prior to the appearance of HCC, monoclonal antibodies (MAbs) were generated from mice immunized with hepatocytes from a woodchuck chronically infected with WHV or with a tumor lysate. Immunofluorescence microscopy was used to select MAbs that reacted with host markers whose patterns of expression would distinguish chronically infected from uninfected liver or from liver tumors. One of these MAbs (2F2) reacted strongly with a subset of hepatocytes in chronically infected liver; a similar staining pattern was not detected in uninfected or transiently infected liver. Evidence is presented that this strong staining reaction reflects the overexpression or accumulation of the hepatocyte-specific intermediate filament protein, cytokeratin K18, a protein previously implicated in cryptogenic cirrhosis of the liver in humans (Ku, N. O. , Wright, T. L., Terrault, N. A., Gish, R., and Omary, M. B. J. Clin. Invest. 99: 19-23, 1997). Double immunofluorescent staining with antibodies to K18 and M-envelope protein of WHV suggested that strong reactivity to K18 was limited to cells expressing high levels of one or both of the large viral-envelope proteins, M and L; however, high expression of these viral proteins was not always associated with a strong K18 staining reaction.

HLA-G1 protein expression is not essential for fetal survival

HLA-G is a nonclassical, class I HLA gene that is primarily expressed by fetal cells at the maternal-fetal interface and is thought to play a key role in the induction of tolerance in pregnancy. This paper reports the identification of a single base pair deletion at position 1597 (1597delC) in exon 3 (encoding the alpha2-domain) of HLA-G on 20 of 272 (7.4 per cent) African American chromosomes, three of 102 (2.9 per cent) Hispanic chromosomes, and none of 134 Caucasian chromosomes. This relatively common frameshift mutation results in amino acid substitutions in all of the residues in the second half of exon 3 including the conserved cysteine at codon 164. An adult individual was identified who was homozygous for this 'null' allele, and a first trimester placenta that was homozygous for 1597delC had no detectable HLA-G1 protein. These data indicate that expression of HLA-G1 protein is not essential for fetal survival.

Natural killer cells recognize common antigenic motifs shared by H-2Dd, H-2Ld and possibly H-2Dr molecules expressed on bone marrow cells

Murine natural killer (NK) cells can mediate specific rejection of bone marrow cell (BMC) allografts. Whereas positive recognition of allogeneic MHC antigens forms the basis for T cell alloreactivity, it has been postulated that NK cells are reactive against targets that do not express certain self-encoded MHC class I antigens. Here, we study the immunogenicity of BMC grafts from two class I transgenic mice, D8 (B6 mice with an H-2Dd transgene) and C3H.Ld (C3H mice with an H-2Ld transgene). D8 BMC grafts are acutely rejected by B6 but not D8 recipients. This suggests that antigenic motifs associated with the H-2Dd molecule are recognized. B6 mice depleted of their CD3+ but not NK1.1+ cells can still reject D8 BMC grafts. These data suggest that NK1.1+/CD3- cells recognize the H-2Dd derived antigenic motifs. Similarly, C3H.Ld BMC grafts are rejected by B6 x C3H F1 but not B6 x C3H.Ld F1 recipients. Thus, antigenic motifs associated with the H-2Ld molecule can also be recognized. Furthermore, expression of either H-2Dd or H-2Ld by the recipients renders them unable to reject D8 or C3H.Ld BMC grafts. Therefore, H-2Dd and H-2Ld molecules appear to express common antigenic motifs recognized by NK cells. Additional studies with B6.R4 (KbIbSbDr), an intra-H-2 recombinant mouse, indicated that a third class I molecule, possibly H-2Dr, also shared the common antigenic motifs with both H-2Dd and H-2Ld molecules. Thus, positive recognition of class I antigens by NK cells can occur. However, expression of some of these antigenic motifs appear to be negatively controlled by certain H-2r genes as suggested by rejection of D8 and B6.R4 BMC grafts by D8 x B10.RIII F1 and B6.R4 x B10.RIII F1 hybrids respectively.

Proteolytic processing of ovalbumin and beta-galactosidase by the proteasome to a yield antigenic peptides

The identification of genes in the class II region of the MHC that are homologous to genes encoding subunits of the proteasome has led to intense interest in the possible role of this enzyme in the proteolytic processing of polypeptide Ags. We have tested the ability of the 20S proteasome to produce peptides that can be presented by class I molecules as targets for killing by OVA-specific and beta-galactosidase-specific CTL clones. Samples of intact OVA and beta-galactosidase were subjected to digestion in vitro by 20S proteasome purified from bovine red cells and the resulting peptide mixtures were fractionated by reverse-phase HPLC. The fractions were tested for their ability to sensitize appropriate mouse target cells for lysis by specific CTL clones. In both cases, components that under all chromatographic conditions eluted with retention times indistinguishable from synthetic peptides representing known epitopes of the naturally processed proteins were found to be able to sensitize the target cells. Moreover, in the case of OVA, the presence of the expected target peptides was demonstrated directly by amino acid sequence and mass spectrometric analysis. The results demonstrate that the pure 20S proteasome is capable of generating antigenic peptides from two proteins for presentation by class I molecules without the participation of additional components of the protein degradation system. This finding is consistent with the hypothesis of proteasome involvement in Ag processing in vivo.

Proteolytic processing of ovalbumin and beta-galactosidase by the proteasome to a yield antigenic peptides

The identification of genes in the class II region of the MHC that are homologous to genes encoding subunits of the proteasome has led to intense interest in the possible role of this enzyme in the proteolytic processing of polypeptide Ags. We have tested the ability of the 20S proteasome to produce peptides that can be presented by class I molecules as targets for killing by OVA-specific and beta-galactosidase-specific CTL clones. Samples of intact OVA and beta-galactosidase were subjected to digestion in vitro by 20S proteasome purified from bovine red cells and the resulting peptide mixtures were fractionated by reverse-phase HPLC. The fractions were tested for their ability to sensitize appropriate mouse target cells for lysis by specific CTL clones. In both cases, components that under all chromatographic conditions eluted with retention times indistinguishable from synthetic peptides representing known epitopes of the naturally processed proteins were found to be able to sensitize the target cells. Moreover, in the case of OVA, the presence of the expected target peptides was demonstrated directly by amino acid sequence and mass spectrometric analysis. The results demonstrate that the pure 20S proteasome is capable of generating antigenic peptides from two proteins for presentation by class I molecules without the participation of additional components of the protein degradation system. This finding is consistent with the hypothesis of proteasome involvement in Ag processing in vivo.

Ham-2 corrects the class I antigen-processing defect in RMA-S cells

The murine major histocompatibility complex (MHC) contains two genes (Ham-1 and Ham-2) that encode members of a super-family of ATP-dependent transport proteins. These genes are believed to mediate the transport of peptide antigen from the cytoplasm into the lumen of the endoplasmic reticulum for binding by MHC class I molecules. Evidence for such a function has come from the rescue of class I surface expression by a cloned copy of the human homologue of Ham-1, PSF-1, in a human cell line that is defective in antigen processing. A mutant murine cell line, RMA-S, has an identical antigen-processing-defective phenotype. Here we show that expression of a cloned copy of the Ham-2 gene in RMA-S cells results in recovery of the ability to process and present class I-restricted antigens to cytotoxic T lymphocytes, and in partial recovery of class I surface expression. Processing defects for classical (H-2 K and D) and non-classical (Qa1 and HMT) class I molecules are corrected by Ham-2. These data indicate that both MHC-linked transporter genes are probably required for class I antigen processing, and that the functional transporter in this pathway may consist of a Ham-1/Ham-2 heterodimer.

Evidence that less-than-full-length pol gene products are functional in hepadnavirus DNA synthesis

Duck hepatitis B virus mutants containing frameshift or stop codon mutations in a portion of the viral pol gene separating the terminal protein and reverse transcriptase domains had a leaky phenotype and, depending on the location and type of mutation, synthesized up to 10% as much viral DNA as did the wild type. This region of the pol gene had previously been reported to be refractory to missense mutations; in fact, the leakiness of most of our mutants appeared attributable to translational suppression, which would also be expected to introduce amino acid changes. However, at least one mutant (pH1093 + 2), which was ca. 10% as active as the wild type, appeared to use a novel pathway to express the viral pol gene. Our analyses indicated that pH1093 + 2 synthesized the viral reverse transcriptase as a fusion protein with the amino-terminal portion of the pre-S envelope protein. Thus, in this case, the products of the terminal-protein and reverse transcriptase domains of the pol gene would function as separate protein species, though perhaps noncovalently joined in a dimeric structure during assembly of DNA replication complexes. Evidence was also obtained that was consistent with the idea that the wild-type pol gene may, at least in certain instances, be expressed as functional, subgenic polypeptides.

The OVEIA assay, a simultaneous measurement of oestrone and pregnanediol glucuronides, for studying the treatment of infertility patients

A new simple assay developed for establishing the limits of the fertile period was evaluated in infertility patients. This assay is a colorimetric method for measuring the oestrone glucuronide/pregnanediol glucuronide ratio. Steroid levels were assayed simultaneously and an index of their ratio was obtained in this dual analyte assay (DAA). Twenty subfertile women, receiving clomiphene citrate for ovulation induction, were monitored for the DAA index using early morning urine samples. Ten of these women were also monitored in a pretreatment cycle. A further 10 patients on an in-vitro fertilization (IVF) programme were assessed with the same assay. DAA ratios were found to correlated with follicular phase serum oestradiol levels. Peak DAA ratios dropped dramatically when significant rises in urinary luteinizing hormone concentrations occurred prior to ovulation. An association between high DAA ratios and adequate luteal phase activity was also established. In addition, the total volume of the three largest ovarian follicles, as measured by ultrasound, in IVF patients was found to correlate with DAA measurements.

Replication of human hepatitis delta virus in primary cultures of woodchuck hepatocytes

We obtained two lines of evidence that monolayer cultures of primary woodchuck hepatocytes support replication of the genome of human hepatitis delta virus (HDV). (i) From a Northern (RNA blot) analysis of the HDV-related RNA in infected cultures, both genomic and antigenomic 1.7-kilobase RNA species were detected at 11 days after infection. The ratio of genomic RNA to antigenomic RNA was 2:1 to 10:1, comparable to that previously reported in studies of experimentally infected chimpanzees and woodchucks. (ii) Replication in culture was also demonstrated by in situ hybridization with a strand-specific probe. Such studies showed that only a small fraction of the cultured cells supported replication and that in such cells the relative and absolute levels of the HDV RNAs were comparable to those in liver cells infected in vivo. Furthermore, as with the in vivo studies, the HDV RNAs were predominantly localized to the nucleus. In summary, we demonstrated that cultured cells supported both the early events of HDV adsorption and penetration and the intermediate events of genome replication.

Experimental transmission of duck hepatitis B virus

Susceptibility to experimental infection with duck hepatitis B virus (DHBV) was explored, with the objective of defining procedures that were both rapid and reproducible. For the purpose of these experiments, a small flock of DHBV-free breeders was established as a source of susceptible eggs and ducklings, since ca. 10% of the ducks (all ages) from commercial flocks were DHBV infected. Intravenous inoculation of DHBV into 15-day duck embryos from the DHBV-free flock produced a persistent infection, with a high-titer viremia, in at least 80% of the injected animals. The tissue tropism of DHBV in these experimentally infected animals was similar to that associated with natural, congenital infections from viremic ducks to their progeny. Virus antigen was found not only in hepatocytes and bile duct epithelium of liver, but also in cells associated with exocrine and endocrine pancreas, and in proximal convoluted tubular epithelium of kidney. Infection of embryonic liver was rapid, as evidenced by active synthesis of DHBV-DNA by reverse-transcription of RNA by 24 hr postinjection. During this latter analysis, formation of supercoiled viral DNA appeared to precede the reverse-transcription phase of viral DNA synthesis, suggesting that this species may be important in initiation of infection.

Asymmetric replication of duck hepatitis B virus DNA in liver cells: Free minus-strand DNA

In order to study the replication of the DNA genome of duck hepatitis B virus, an avian virus related to human hepatitis B virus, we have characterized viral DNAs present in the livers of viremic ducks by agarose gel electrophoresis and the Southern blot procedure. In addition to relaxed circular DNA similar to virion DNA, livers contained a heterogeneous population of rapidly migrating species. The conformation of the rapidly migrating species was markedly sensitive to salt, suggesting that these species were largely single stranded. The largest major rapidly migrating species was shown to have an electrophoretic mobility that was insensitive to preheating of the DNA to 100 degrees C and was similar to that of denatured virus DNA 3 kilobases long, suggesting that this DNA was a single-stranded copy of the entire virus genome. Hybridization with strand-specific probes demonstrated that this 3-kilobase species, as well as more rapidly migrating DNAs, were predominantly minus strands.