Bioprosthetic valve thrombosis and degeneration following transcatheter aortic valve implantation (TAVI).

Bioprosthetic valve thrombosis (BPVT) is a recognised complication of prosthetic aortic valves and can be found in up to 13% of patients after transcatheter implantation. The mechanism of BPVT is not well known, abnormal flow conditions in the new and native sinuses and lack of functional endothelialisation are suspected causes. BPVT may result in valve dysfunction, possibly related to degeneration, and recurrence of patient symptoms, or remain subclinical. BPVT is best diagnosed at multiphase gated computed tomography (CT) angiography as the presence of reduced leaflet motion (RELM) and hypoattenuating aortic leaflet thickening (HALT). Although CT is used to exclude BPVT in symptomatic patients and those with increased valve gradients, the value of screening and prophylactic anticoagulation is debatable.

Factors associated with maternal death from direct pregnancy complications: a UK national case-control study.

OBJECTIVE: To investigate the factors associated with maternal death from direct pregnancy complications in the UK. DESIGN: Unmatched case-control analysis. SETTING: All hospitals caring for pregnant women in the UK. POPULATION: A total of 135 women who died (cases) between 2009 and 2012 from eclampsia, pulmonary embolism, severe sepsis, amniotic fluid embolism, and peripartum haemorrhage, using data from the Confidential Enquiry into Maternal Death, and another 1661 women who survived severe complications (controls) caused by these conditions (2005-2013), using data from the UK Obstetric Surveillance System. METHODS: Multivariable regression analyses were undertaken to identify the factors that were associated with maternal deaths and to estimate the additive odds associated with the presence of one or more of these factors. MAIN OUTCOME MEASURES: Odds ratios associated with maternal death and population-attributable fractions, with 95% confidence intervals. Incremental risk of death associated with the factors using a 'risk factors' score. RESULTS: Six factors were independently associated with maternal death: inadequate use of antenatal care (adjusted odds ratio, aOR 15.87, 95% CI 6.73-37.41); substance misuse (aOR 10.16, 95% CI 1.81-57.04); medical comorbidities (aOR 4.82, 95% CI 3.14-7.40); previous pregnancy problems (aOR 2.21, 95% CI 1.34-3.62); hypertensive disorders of pregnancy (aOR 2.44, 95% CI 1.31-4.52); and Indian ethnicity (aOR 2.70, 95% CI 1.14-6.43). Of the increased risk associated with maternal death, 70% (95% CI 66-73%) could be attributed to these factors. Odds associated with maternal death increased by three and a half times per unit increase in the 'risk factor' score (aOR 3.59, 95% CI 2.83-4.56). CONCLUSIONS: This study shows that medical comorbidities are importantly associated with direct (obstetric) deaths. Further studies are required to understand whether specific aspects of care could be improved to reduce maternal deaths among women with medical comorbidities in the UK.

The management and outcomes of placenta accreta, increta, and percreta in the UK: a population-based descriptive study.

OBJECTIVE: To describe the management and outcomes of placenta accreta, increta, and percreta in the UK. DESIGN: A population-based descriptive study using the UK Obstetric Surveillance System (UKOSS). SETTING: All 221 UK hospitals with obstetrician-led maternity units. POPULATION: All women diagnosed with placenta accreta, increta, and percreta in the UK between May 2010 and April 2011. METHODS: Prospective case identification through the monthly mailing of UKOSS. MAIN OUTCOME MEASURES: Median estimated blood loss, transfusion requirements. RESULTS: A cohort of 134 women were identified with placenta accreta, increta, or percreta: 50% (66/133) were suspected to have this condition antenatally. In women with a final diagnosis of placenta increta or percreta, antenatal diagnosis was associated with reduced levels of haemorrhage (median estimated blood loss 2750 versus 6100 ml, P = 0.008) and a reduced need for blood transfusion (59 versus 94%, P = 0.014), possibly because antenatally diagnosed women were more likely to have preventative therapies for haemorrhage (74 versus 52%, P = 0.007), and were less likely to have an attempt made to remove their placenta (59 versus 93%, P < 0.001). Making no attempt to remove any of the placenta, in an attempt to conserve the uterus or prior to hysterectomy, was associated with reduced levels of haemorrhage (median estimated blood loss 1750 versus 3700 ml, P = 0.001) and a reduced need for blood transfusion (57 versus 86%, P < 0.001). CONCLUSIONS: Women with placenta accreta, increta, or percreta who have no attempt to remove any of their placenta, with the aim of conserving their uterus, or prior to hysterectomy, have reduced levels of haemorrhage and a reduced need for blood transfusion, supporting the recommendation of this practice.

Bidirectional scatter measurements of a guided-mode resonant filter photonic crystal structure.

This work investigates the Bidirectional Scatter Distribution Function (BSDF) at incident angles other than normal and at 544-nm wavelength of a Guided Mode Resonance Filter (GMRF) Photonic Crystal (PC) structure designed for normally incident light at 532 nm. Strong out-coupling of PC diffraction orders into both the transmitted and reflected hemispheres was observed specifically at a 25.7° incidence angle, which we attribute to this incident angle/wavelength pair being a good match to the ( ± 1, 0) PC grating mode. BSDF measurements at incident angles of 15° and 35° also displayed some out-coupled diffraction, though much lower in magnitude, and are also attributed to being a weaker match to the ( ± 1, 0) PC grating mode. Three-dimensional finite-difference time-domain Maxwell's equation simulations demonstrate that since this GMRF was designed for complete destructive interference of the transmitted light upon normal incidence, stronger out-coupling of the diffraction is expected for modal solutions as the angle of incidence increases.

British HIV Association and Children's HIV Association position statement on infant feeding in the UK 2011.

To prevent the transmission of HIV infection during the postpartum period, the British HIV Association and Children's HIV Association (BHIVA/CHIVA) continue to recommend the complete avoidance of breast feeding for infants born to HIV-infected mothers, regardless of maternal disease status, viral load or treatment.

Avoidance of stimulation improves engraftment of cultured and retrovirally transduced hematopoietic cells in primates.

Recent reports suggest that cells in active cell cycle have an engraftment defect compared with quiescent cells. We used nonhuman primates to investigate this finding, which has direct implications for clinical transplantation and gene therapy applications. Transfer of rhesus CD34(+) cells to culture in stem cell factor (SCF) on the CH-296 fibronectin fragment (FN) after 4 days of culture in stimulatory cytokines maintained cell viability but decreased cycling. Using retroviral marking with two different gene transfer vectors, we compared the engraftment potential of cytokine-stimulated cells versus those transferred to nonstimulatory conditions (SCF on FN alone) before reinfusion. In vivo competitive repopulation studies showed that the level of marking originating from the cells continued in culture for 2 days with SCF on FN following a 4-day stimulatory transduction was significantly higher than the level of marking coming from cells transduced for 4 days and reinfused without the 2-day culture under nonstimulatory conditions. We observed stable in vivo overall gene marking levels of up to 29%. This approach may allow more efficient engraftment of transduced or ex vivo expanded cells by avoiding active cell cycling at the time of reinfusion.

Recombinant DNA-produced alpha 1-antitrypsin administered by aerosol augments lower respiratory tract antineutrophil elastase defenses in individuals with alpha 1-antitrypsin deficiency.

Alpha 1-Antitrypsin (alpha 1AT) deficiency is characterized by insufficient amounts of alpha 1AT to protect the lower respiratory tract from neutrophil elastase, resulting in emphysema. Yeast-produced recombinant alpha 1AT (rAAT) has normal antielastase function but is associated with high renal clearance, thus obviating chronic intravenous administration. As an alternative, we evaluated aerosol administration of rAAT to alpha 1AT-deficient individuals. After aerosol administration of single doses of 10-200 mg of rAAT, epithelial lining fluid (ELF) alpha 1AT antineutrophil elastase defenses were augmented in proportion to the dose of rAAT administered. ELF alpha 1AT levels and antineutrophil elastase capacity 4 h after 200 mg rAAT aerosol were increased 40-fold over preaerosol levels, and were fivefold increased over baseline at 24 h after aerosol administration. rAAT was detectable in serum after aerosol, indicating that the lower respiratory tract epithelium may be permeable to rAAT, and that aerosolized rAAT is capable of gaining access to lung interstitium. No adverse clinical effects were noted. These observations demonstrate that aerosol administration of rAAT is safe and results in significant augmentation of lung antineutrophil elastase defenses, suggesting this method is a feasible approach to therapy. Because this approach is clinically unproven, further studies will be necessary to establish the long-term clinical efficacy of aerosol therapy in alpha 1AT deficiency.

Generalized diffusion equation for anisotropic anomalous diffusion.

Motivated by studies of comblike structures, we present a generalization of the classical diffusion equation to model anisotropic, anomalous diffusion. We assume that the diffusive flux is given by a diffusion tensor acting on the gradient of the probability density, where each component of the diffusion tensor can have its own scaling law. We also assume scaling laws that have an explicit power-law dependence on space and time. Solutions of the proposed generalized diffusion equation are consistent with previously derived asymptotic results for the probability density on comblike structures.

Why is there a modifying effect of gestational age on risk factors for cerebral palsy?

OBJECTIVE: To investigate risk factors for cerebral palsy in relation to gestational age. DESIGN: Three case-control studies within a geographically defined cohort. SETTING: The former Oxfordshire Health Authority. PARTICIPANTS: A total of 235 singleton children with cerebral palsy not of postnatal origin, born between 1984 and 1993, identified from the Oxford Register of Early Childhood Impairment; 646 controls matched for gestation in three bands: or=37 weeks. RESULTS: Markers of intrapartum hypoxia and infection were associated with an increased risk of cerebral palsy in term and preterm infants. The odds ratio (OR) for hypoxia was 12.2 (95% confidence interval 1.2 to 119) at or=37 weeks. Corresponding ORs for neonatal sepsis were 3.1 (1.8 to 5.4) and 10.6 (2.1 to 51.9). In contrast, pre-eclampsia carried an increased risk of cerebral palsy at >or=37 weeks (OR 5.1 (2.2 to 12.0)) but a decreased risk at

Expression of interferon-gamma by stromal cells inhibits murine long-term repopulating hematopoietic stem cell activity.

Several lines of evidence suggest that overexpression of interferon gamma (IFN-gamma) in the marrow microenvironment may play a role in the pathogenesis of marrow suppression in aplastic anemia. We previously showed that overexpression of IFN-gamma by marrow stromal cells inhibits human long-term culture initiating cell activity assayed in vitro to a much greater degree than the addition of soluble IFN-gamma. The effect of IFN-gamma on true repopulating stem cells assayed in vivo has not been studied previously. We compared the effect of co-culture of murine marrow cells in the presence of stromal cells transduced with a retroviral vector expressing murine IFN-gamma vs stromal cells transduced with a control neo vector. Using a murine congenic competitive repopulation assay, there was significantly less long-term repopulating stem cell activity remaining after culture on mIFN-gamma-expressing stroma as compared to control stroma. We also investigated the effect of directly transducing murine bone marrow cells with the mIFN-gamma or control vector. Marrow cells transduced with either vector were transplanted into W/Wv recipient mice. The percentage of vector-containing cells in the mIFN-gamma mice was significantly lower than in the control mice, suggesting that mIFN-gamma-transduced primitive cells may not have survived culture, or that mIFN-gamma directly decreases gene transfer into repopulating cells. Despite no significant differences in white or red blood cells in the mice transplanted with the mIFN-gamma-transduced cells, the number of bone marrow colony-forming unit-C 16 weeks after transplantation was significantly lower in the IFN-gamma group. These data indicate that ectopic or overexpression of mIFN-gamma, especially by marrow microenvironmental elements, may have a marked effect on primitive hematopoiesis as assayed in vivo.

The effects of SCF/G-CSF prestimulation on radiation sensitivity and engraftment in nonmyeloablated murine hosts.

OBJECTIVE: Previous studies have shown improved engraftment in a murine model when granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF) were administered for 5 days prior to irradiation, with significant levels of engraftment in the growth factor-preconditioned group even at very low radiation doses. We sought to explore the mechanisms behind this effect. METHODS: The radiation sensitivity of mice with or without 5 days of prestimulation with G-CSF (200 microg/kg/d) and SCF (50 microg/kg/d) was compared. To further evaluate whether growth factor prestimulation enhances engraftment by mobilization of hematopoietic progenitors into peripheral blood, thus creating less endogenous competition within the marrow compartment, female mice were pretreated with 5 days of G-CSF/SCF or control diluent. Engraftment of 40 x 10(6) peripheral blood stem cells (PBSCs) harvested from G-CSF/SCF-mobilized male mice was compared in the two recipient groups. RESULTS: There was no difference in survival between the pretreated and control mice at the radiation doses tested. Additionally, there was no significant difference in the recovery of blood counts, bone marrow cellularity, colony-forming unit (CFU) content, or stem cell numbers assessed 4 months later in a competitive repopulation model. Engraftment levels of male cells did not differ between G-CSF/SCF-pretreated and control recipients, and could be detected in 30% of recipients at 20-24 weeks (4/12 in each group) at overall levels of 0.1-1%. CONCLUSIONS: The enhanced engraftment in cytokine pretreated recipients is unlikely to be due to increased endogenous stem-cell killing or to the creation of endogenous marrow "space" by egress of endogenous stem cells after cytokine prestimulation.

No discrepancy between in vivo gene marking efficiency assessed in peripheral blood populations compared with bone marrow progenitors or CD34+ cells.

Reports of 1- to 2-log higher gene transfer levels in purified CD34+ cells or marrow CFU compared with levels in mature circulating blood cells after transplantation of retrovirally transduced primitive human hematopoietic cells have resulted in concern that transduced progenitors do not contribute proportionally to ongoing hematopoiesis (Kohn et al., 1995; Brenner, 1996). To study the issue in a relevant large animal, we analyzed samples of mature blood cells, marrow CD34-enriched cells and marrow CD34-depleted cells, and marrow CFU from a cohort of 11 rhesus transplanted with retrovirally transduced cells and followed for up to 5.5 years. They were transplanted with CD34-enriched bone marrow (BM) or G-CSF/SCF-mobilized peripheral blood (PB) cells transduced with vectors containing either neo, human glucocerebrosidase, or murine adenosine deaminase genes. There were no significant differences between the levels of vector sequences found in BM CD34+ cells, BM CD34- cells, PB granulocytes, or PB mononuclear cells (MNCs) in any animal. In four animals transplanted with SCF/G-CSF-primed BM cells and analyzed 3-6 months posttransplantation, the percentage of CFU containing the neo vector appeared to be 1 log higher than the representation of marked cells in the PB of these animals, but this discrepancy did not persist at time points greater than 6 months posttransplantation. The level of CFU marking was no higher than PB granulocyte or MNC marking at any time points in the other animals. Low levels of mature gene-modified cells probably reflect poor transduction of repopulating stem cells, not a block in differentiation or specific immune rejection of mature cells. This study represents the longest follow-up of primates transplanted with transduced hematopoietic cells, and it is encouraging that the levels of vector-containing cells appear stable for up to 5 years.

In vivo persistence of retrovirally transduced murine long-term repopulating cells is not limited by expression of foreign gene products in the fully or minimally myeloablated setting.

Many nonmalignant hematologic disorders could potentially be treated by genetic correction of as few as 5-10% of target lineage cells. However, immune system clearance of cells expressing gene products perceived as foreign could be limiting. There is evidence that tolerance to foreign proteins can result when myeloablative conditioning is used, but this limits the overall applicability of such techniques. Therefore, we sought to evaluate the engraftment of hematopoietic stem cells carrying a foreign transgene after low-dose irradiation by comparing in vivo survival of murine long-term repopulating cells (LTRC) transduced with either a retroviral vector expressing the bacterial neomycin phosphotransferase gene (neo) or a vector containing neo gene sequences but modified to prevent protein expression (nonexpression). First, marrow cells from congenic donors were transduced with either vector and transplanted into recipients treated with standard dose irradiation of 800 rads. High-level engraftment and gene marking resulted, without differences in the marking levels or pattern of persistence of the cells between cells transduced with either vector. Low-dose irradiation at 100 rads was tested using higher cell doses. Marking levels as high as 10% overall were obtained, again with no differences between mice receiving cells transduced with the neo versus the nonexpression vectors. To investigate a potentially more immunogenic protein, marrow cells were transduced with a vector containing the green fluorescent protein (GFP) gene, and their persistence was studied in recipient mice receiving 100 rads. Stable GFP expression in 5-10% of circulating cells was observed long term. We conclude that even with very low dose conditioning, engraftment by genetically modified LTRC cells at clinically significant levels can be achieved without evidence for clearance of cells known to be expressing immunogenic proteins.

Analysis of origin and optimization of expansion and transduction of circulating peripheral blood endothelial progenitor cells in the rhesus macaque model.

Adult marrow-derived cells have been shown to contribute to various nonhematologic tissues and, conversely, primitive cells isolated from nonhematopoietic tissues have been shown to reconstitute hematopoiesis. Circulating endothelial progenitor cells (EPCs) have been reported to be at least partially donor derived after allogeneic bone marrow transplantation, and shown to contribute to neovascularization in murine ischemia models. However, it is unknown whether these EPCs are actually clonally derived from the same population of stem and progenitor cells that reconstitute hematopoiesis, or from another cell population found in the marrow or mobilized blood that is transferred during transplantation. To approach this question, we characterized circulating EPCs and also endothelial cells from large vessels harvested at autopsy from rhesus macaques previously transplanted with retrovirally transduced autologous CD34-enriched peripheral blood stem cells (PBSCs). Endothelial cells were grown in culture for 21-28 days and were characterized as CD31(+) CD14(-) via flow cytometry, as acLDL(+) UEA-1(+) via immunohistochemistry, and as Flk-1(+) by reverse transcriptase-polymerase chain reaction (RT-PCR). Animals had stable vector marking in hematopoietic lineages of 2-15%. Neither cultured circulating EPCs collected in steady state (n = 3), nor endothelial cells grown from large vessels (n = 2), had detectable retroviral marking. EPCs were CD34(+) and could be mobilized into the circulation with granulocyte colony-stimulating factor. Under ex vivo culture conditions, in which CD34(+) cells were optimized to transduce hematopoietic progenitor and stem cells, there was a marked depletion of EPCs. Transduction of EPCs was much more efficient under conditions supporting endothelial cell growth. Further elucidation of the origin and in vivo behavior of EPCs may be possible, using optimized transduction conditions and a vascular injury model.

The effects of nutritional supplementation on the diets of low-income families at risk of malnutrition.

Protein-energy malnutrition in synergism with infection is a major problem for most developing countries, and inadequate food consumption is a critical factor in its development. Food supplementation programs can improve nutrient consumption but may also have unintended consequences. Changes in consumption of foods as well as nutrients need to be identified and evaluated. The effects of a food supplementation program on family diet patterns and protein-energy intake were investigated using data from nutritionally at risk families in Bogota, Colombia. Because food supplements are income transfers they need to substitute for purchases of similar food items. However, the results of our investigation reveal that food supplementation based on familiar foods that are part of the usual family diet are consumed in substantial quantities and result in net nutrient consumption increases. The food supplementation program increases consumption of preferred food items and introduces greater diversity into the family diet. These effects are enhanced when combined with a home education program.

Nutritional supplementation: effects on child stunting because of diarrhea.

Research has shown that the positive effect of nutritional supplementation on child growth in malnourished populations is small relative to the large negative effect of diarrheal disease. To test the hypothesis that the effects of supplementation and diarrhea are synergistic in that supplementation modifies the negative effect of diarrhea on linear growth, length and diarrheal morbidity were compared at 36 mo of age for two cohorts of Colombian children: supplemented from birth and unsupplemented. Among unsupplemented children diarrhea was negatively associated with length. Among supplemented children diarrhea had no effect on length and differed from that of unsupplemented children. Thus, supplementation completely offset the negative effect of diarrheal disease on length. Targeting supplementation programs to the critical period of high diarrheal prevalence among infants and young children should increase the effectiveness of such programs in preventing growth retardation associated with diarrhea.

PIP: To test the hypothesis that supplementation modifies the negative effect of diarrhea on linear growth, body length and diarrheal morbidity were compared at 36 months of age for 2 cohorts of Columbian children: those receiving supplements from birth and those not receiving supplements. The sample was a subset from a longitudinal study that took place in Bogota, Columbia, between 1973 and 1980 and consisted of 456 families randomly assigned to 6 experimental groups. There were 148 children in the unsupplemented group. The 140 children from the supplemented group received supplements from the 6th month of pregnancy until they were 36 months old. The supplementary feeding included 30 g of protein daily, and 7.5 mg or 15 mg of ferrous sulphate daily as well as vitamin A every 6 months. Supplemented children had a mean 16 episodes of diarrhea, compared with a mean of 18 episodes of the unsupplemented cohort, and they spent a total of 73 days ill, compared with 83 days ill for unsupplemented children. Linear regression analysis showed that the slopes for unsupplemented children were significantly different from 0 (p 0.001). Each day with diarrhea was associated with a reduction of about 0.03 cm in attained length at age 36 months. In contrast, for supplemented children diarrhea had no effect on attained length at age 36 months. 2-way analysis of variance showed that the difference between supplemented and unsupplemented children in attained length in the lowest quartile of diarrhea was small, but the difference in the highest quartile was almost 5 cm. Cumulative growth patterns of children in the high quartile of diarrheal disease revealed that the difference between unsupplemented children was a median of 13 cm, thus supplementation made up nearly 40% of the deficit, compared with the reference standard (5 cm/13 cm). Targeting supplementation programs to the critical period of high diarrheal prevalence among infants and young children should help prevent growth retardation associated with diarrhea.

Cytomegalovirus urinary excretion and long term outcome in children with congenital cytomegalovirus infection. Congenital CMV Longitudinal Study Group.

BACKGROUND: Cytomegalovirus (CMV) is the most frequent cause of congenital infection, and both symptomatic and asymptomatic infants may have long term sequelae. Children with congenital CMV infection are chronically infected and excrete CMV in the urine for prolonged periods. However, the effect of prolonged viral replication on the long term outcome of these children is unknown. OBJECTIVE: To determine whether duration of CMV excretion is associated with outcome at 6 years of life in symptomatic and asymptomatic congenitally infected children. METHODS: Longitudinal cohort study. Children congenitally infected with CMV were identified at birth and followed prospectively in a study of long term effects of congenital CMV infection. The relationship between duration of CMV urinary excretion and growth, neurodevelopment and presence and progression of sensorineural hearing loss (SNHL) at 6 years of age was determined. RESULTS: There was no significant difference in the duration of viral urinary excretion between children born with asymptomatic (median, 4.55 years) and symptomatic (median, 2.97 years) congenital CMV infection (P = 0.11). Furthermore there was no association between long term growth or cognitive outcome and duration of viral excretion. However, a significantly greater proportion of children who excreted CMV for <4 years had SNHL and progressive SNHL compared with children with CMV excretion >4 years (P = 0.019, P = 0.009, respectively). CONCLUSIONS: Children congenitally infected with CMV are chronically infected for years, but the duration of CMV urinary excretion is not associated with abnormalities of growth, or neurodevelopmental deficits. However, SNHL and progressive SNHL were associated with a shorter duration of CMV excretion.

Augmentation of lung antineutrophil elastase capacity with recombinant human alpha-1-antitrypsin.

To evaluate the potential use of recombinant DNA-produced alpha-1-antitrypsin (alpha-1-AT) to augment the lung antineutrophil elastase defenses in alpha-1-AT deficiency, we compared the kinetics of intravenously administered recombinant produced alpha-1-AT (r alpha-1-AT) and purified normal human plasma alpha-1-AT (p alpha-1-AT) in the blood and lung of rhesus monkeys. The r alpha-1-AT was produced in yeast transformed with an expressing plasmid containing a full-length human alpha-1-AT complementary deoxyribonucleic acid and purified to greater than 99% homogeneity. The r alpha-1-AT has a molecular weight of 45,000, no carbohydrates, and is identical in sequence to normal plasma alpha-1-AT except for an additional N-terminal acetylmethionine. Despite its lack of carbohydrates, the r alpha-1-AT inhibited human neutrophil elastase with an association rate constant similar to that of p alpha-1-AT. Rhesus monkeys were infused intravenously with 120 mg/kg of r alpha-1-AT (n = 13) or p alpha-1-AT (n = 12) and the serum, urine, and lung epithelial lining fluid (ELF) concentrations of these molecules quantified at various intervals.(ABSTRACT TRUNCATED AT 250 WORDS)

Measuring infectious bursal disease virus RNA in blood by multiplex real-time quantitative RT-PCR.

A quantitative reverse transcription polymerase chain reaction (RT-PCR) protocol for assessing infectious bursal disease virus (IBDV) RNA levels in blood was developed using the ABI PRISM 7700 Sequence Detection System coupled with TaqMan chemistry. To control for variations in sampling and processing between samples 28S rRNA was co-amplified in a multiplex reaction and used to quantify total RNA. Relative quantification and standardisation was achieved using a log10 dilution series of RNA extracted from IBDV stock. A linear relationship was observed between input RNA and cycle threshold values (C(T)) over 5 log10 dilutions for the IBDV-specific product and 6 log10 dilutions for the 28S rRNA-specific product. As a test of the assay it was used to determine whether differences in susceptibility to IBDV observed between inbred lines of chickens could be detected at the level of viral load in the blood. Viral RNA levels peaked 2 days post-infection when there was significantly less viral RNA in the blood of resistant line 6(1) chickens compared with the more susceptible Brown Leghorns (P = 0.01). These results demonstrate that the course of IBDV infection can be monitored by quantifying IBDV RNA extracted from blood of infected chickens using TaqMan technology.