Modelling the proportion of influenza infections within households during pandemic and non-pandemic years

Background

The key epidemiological difference between pandemic and seasonal influenza is that the population is largely susceptible during a pandemic, whereas, during non-pandemic seasons a level of immunity exists. The population-level efficacy of household-based mitigation strategies depends on the proportion of infections that occur within households. In general, mitigation measures such as isolation and quarantine are more effective at the population level if the proportion of household transmission is low.

Methods/Results

We calculated the proportion of infections within households during pandemic years compared with non-pandemic years using a deterministic model of household transmission in which all combinations of household size and individual infection states were enumerated explicitly. We found that the proportion of infections that occur within households was only partially influenced by the hazard h of infection within household relative to the hazard of infection outside the household, especially for small basic reproductive numbers. During pandemics, the number of within-household infections was lower than one might expect for a given because many of the susceptible individuals were infected from the community and the number of susceptible individuals within household was thus depleted rapidly. In addition, we found that for the value of at which 30% of infections occur within households during non-pandemic years, a similar 31% of infections occur within households during pandemic years.

Interpretation

We suggest that a trade off between the community force of infection and the number of susceptible individuals in a household explains an apparent invariance in the proportion of infections that occur in households in our model. During a pandemic, although there are more susceptible individuals in a household, the community force of infection is very high. However, during non-pandemic years, the force of infection is much lower but there are fewer susceptible individuals within the household.     

Endothelin‐1 Suppresses Long‐Chain Fatty Acid Uptake and Glucose Uptake Via Distinct Mechanisms in 3T3‐L1 Adipocytes

Endothelin‐1 (ET‐1) has been demonstrated to induce insulin resistance (IR) and lipolysis, raising the possibility that ET‐1 may also contribute to the elevated fatty acid levels in IR‐associated comorbidities. We attempted to evaluate whether ET‐1 also affects the long‐chain fatty acid (LCFA) utilization in 3T3‐L1 adipocytes. The effects of chronic ET‐1 exposure on basal and insulin‐stimulated LCFA uptake, and LCFA uptake kinetics were examined in 3T3‐L1 adipocytes. Chronic exposure to ET‐1 induced IR and suppressed basal and insulin‐stimulated LCFA uptake. Given that insulin acutely stimulates LCFA uptake, there was dramatically similar trend of dose‐response curves for ET‐1‐suppressed LCFA uptake, and also similar corresponding IC₅₀ values, between basal and insulin‐stimulated states, reflecting that ET‐1 predominantly suppresses basal LCFA uptake. Results of LCFA kinetics, western blots, and CD36 inhibition using sulfosuccinimidyl oleate (SSO) revealed that suppression of LCFA uptake by ET‐1 is associated with downregulation of CD36. ET type A receptor (ET_AR) antagonist BQ‐610 reversed the IR induction and the ET‐1‐suppressed LCFA uptake. Exogenous replenishment of phosphatidylinositol (PI) 4, 5‐bisphosphate (PIP₂) prevented IR induction, but not the suppression of LCFA uptake by ET‐1. Pharmacological inhibition of the activation of mitogen‐activated protein kinase (MAPK)/extracellular signal‐regulated kinase (ERK) completely blocked the ET‐1‐suppressed LCFA uptake. Serving as an inducer of IR, ET‐1 also chronically suppresses LCFA uptake via PIP₂‐independent and ERK‐dependent pathway. The interplay between impaired glucose disposal and diminished LCFA utilization, induced by ET‐1, could worsen the dysregulation of adipose metabolism and energy homeostasis in insulin‐resistant states.     

Phasevarion mediated epigenetic gene regulation in Helicobacter pylori

Many host-adapted bacterial pathogens contain DNA methyltransferases (mod genes) that are subject to phase-variable expression (high-frequency reversible ON/OFF switching of gene expression). In Haemophilus influenzae and pathogenic Neisseria, the random switching of the modA gene, associated with a phase-variable type III restriction modification (R-M) system, controls expression of a phase-variable regulon of genes (a "phasevarion"), via differential methylation of the genome in the modA ON and OFF states. Phase-variable type III R-M systems are also found in Helicobacter pylori, suggesting that phasevarions may also exist in this key human pathogen. Phylogenetic studies on the phase-variable type III modH gene revealed that there are 17 distinct alleles in H. pylori, which differ only in their DNA recognition domain. One of the most commonly found alleles was modH5 (16% of isolates). Microarray analysis comparing the wild-type P12modH5 ON strain to a P12ΔmodH5 mutant revealed that six genes were either up- or down-regulated, and some were virulence-associated. These included flaA, which encodes a flagella protein important in motility and hopG, an outer membrane protein essential for colonization and associated with gastric cancer. This study provides the first evidence of this epigenetic mechanism of gene expression in H. pylori. Characterisation of H. pylori modH phasevarions to define stable immunological targets will be essential for vaccine development and may also contribute to understanding H. pylori pathogenesis.     

Scoring schemes of palindrome clusters for more sensitive prediction of replication origins in herpesviruses

Many empirical studies show that there are unusual clusters of palindromes, closely spaced direct and inverted repeats around the replication origins of herpesviruses. In this paper, we introduce two new scoring schemes to quantify the spatial abundance of palindromes in a genomic sequence. Based on these scoring schemes, a computational method to predict the locations of replication origins is developed. When our predictions are compared with 39 known or annotated replication origins in 19 herpesviruses, close to 80% of the replication origins are located within 2% of the genome length. A list of predicted locations of replication origins in all the known herpesviruses with complete genome sequences is reported.     

The distribution and activity of tachykinin-related peptides in the blood-feeding bug, Rhodnius prolixus

The invertebrate tachykinin-related peptides (TRPs) with the conserved C-terminal sequence FX1GX2Ramide shows sequence similarity to the vertebrate tachykinins after which they are named, and are hypothesized to be ancestrally related. In this study a polyclonal antiserum generated against a locust tachykinin (LomTK I), was used to demonstrate the presence and describe the distribution of LomTK-like immnoreactivity in the CNS and gut of Rhodnius prolixus. Reverse phase high performance liquid chromatography (RP-HPLC) was used in combination with a sensitive radioimmunoassay (RIA) to demonstrate picomolar amounts of immunoreactive material in the CNS, and femptomolar amounts associated with the hindgut. Furthermore, the results from CNS extracts separated by RP-HPLC, suggest that at least two tachykinin isoforms exist in R. prolixus. A hindgut contraction assay was developed to quantify the myotropic effects of selected LomTKs on R. prolixus hindgut contraction. Both LomTK I and II caused an increase in the frequency of hindgut contractions with EC50 values of 3.6x10(-8)M and 3.8x10(-8)M for LomTK I and II, respectively.     

Prevalence of viable Toxoplasma gondii in beef, chicken, and pork from retail meat stores in the United States: risk assessment to consumers

The prevalence of viable Toxoplasma gondii was determined in 6,282 samples (2,094 each of beef, chicken, and pork) obtained from 698 retail meat stores from 28 major geographic areas of the United States. Each sample consisted of a minimum of 1 kg of meat purchased from the retail meat case. To detect viable T. gondii, meat samples were fed to T. gondii-free cats and feces of cats were examined for oocyst shedding. Initially, 100 g of meat from 6 individual samples of a given species were pooled (total, 600 g), fed to a cat over a period of 3 days, and feces were examined for oocysts for 14 days; the remaining meat samples were stored at 4 C for 14 days (until results of the initial cat fecal examination were known). When a cat fed pooled samples had shed oocysts, 6 individual meat samples from each pool were bioassayed for T. gondii in cats and mice. Toxoplasma gondii isolates were then genetically characterized using the SAG2 locus and 5 hypervariable microsatellite loci. In all, 7 cats fed pooled pork samples shed oocysts. Toxoplasma gondii oocysts were detected microscopically in the feces of 2 of the cats; 1 isolate was Type II and the second was Type III. Analyzed individually, T. gondii was detected by bioassay in 3 of the 12 associated samples with genetic data indicating T. gondii isolates present in 2. The remaining 5 pooled pork samples had so few oocysts that they were not initially detected by microscopic examination, but rather by mouse bioassay of cat feces. Two were Type I, 1 was Type II, and 2 were Type III. None of the cats fed chicken or beef samples shed oocysts. Overall, the prevalence of viable T. gondii in retail meat was very low. Nevertheless, consumers, especially pregnant women, should be aware that they can acquire T. gondii infection from ingestion of undercooked meat, and in particular, pork. Cooking meat to an internal temperature of 66 C kills T. gondii.     

Insulin-like growth factor-1 increases endothelin receptor A levels and action in cultured rat aortic smooth muscle cells

Insulin is known to cause an increase in endothelin-1 (ET-1) receptors in vascular smooth muscle cells (SMCs), but the effect of insulin-like growth factor 1 (IGF-1) on ET-1 receptor expression is not known. We therefore carried out the present study to determine the effect of IGF-1 on the binding of ET-1 to, and ET type A receptor (ETAR) expression and ET-1-induced 3H-thymidine incorporation in, vascular SMCs. In serum-free medium, IGF-1 treatment increased the binding of 125I-ET-1 to SMC cell surface ET receptors from a specific binding of 20.1%+/-3.1% per mg of protein in control cells to 45.1%+/-8.6% per mg of protein in cells treated with IGF-1 (10 nM). The effect of IGF-1 was dose-related, with a significant effect (1.4-fold) being seen at 1 nM. The minimal time for IGF-1 treatment to be effective was 30 min and the maximal effect was reached at 6 h. Immunoblotting analysis showed that ETAR expression in IGF-1-treated cells was increased by 1.7-fold compared to controls. Levels of ETAR mRNA measured by the RT-PCR method and Northern blotting were also increased by 2-fold in IGF-1-treated SMCs. These effects of IGF-1 were abolished by cycloheximide or genistein. Finally, ET-1-stimulated thymidine uptake and cell proliferation were enhanced by IGF-1 treatment, with a maximal increase of 3.2-fold compared to controls. In conclusion, in vascular SMCs, IGF-1 increases the expression of the ET-1 receptor in a dose- and time-related manner. This effect is associated with increased thymidine uptake and involves tyrosine kinase activation and new protein synthesis. These findings support the role of IGF-1 in the development of atherosclerotic, hypertensive, and diabetic vascular complications.     

Phospholipid transfer protein (PLTP) mRNA expression is stimulated by developing embryos in the oviduct

In mammal, fertilization and early preimplantation embryo development occurs in the oviduct. Evidence is accumulating that the oviductal epithelia secrete various biomolecules to the lumen during the secretory phase of the estrus cycle to enhance embryo development. This secretory activity of the oviduct is under the regulation of steroid hormones. Observations also suggested that the gametes and embryos modulate the physiology and gene-expressing pattern of the oviduct. However, the underlying molecular changes remain elusive. We hypothesize that the developing embryos interact with the surrounding environment and affect the gene expression patterns of the oviduct, thereby modulating the oviductal secretory activity conducive to the preimplantation embryo development. To test this hypothesis, suppression subtractive hybridization (SSH) was used to compare the gene expressions in mouse oviduct containing transferred in vitro cultured preimplantation embryos with that of oviduct containing oocytes during the preimplantation period. We reported here the identification and characterization of phospholipids transfer protein (PLTP), which is highly expressed in the embryo-containing oviduct and localized at the oviductal epithelium by in situ hybridization. PLTP contains signal peptide putative for secretory function. More importantly, PLTP mRNA increases in the oviductal epithelia of pregnant, but not pseudo-pregnant mice when assayed by real-time PCR. Taken together, our data suggested that PLTP may play important role(s) during in vivo preimplantation embryo development. This molecule would be a target to delineate the mechanisms and the roles of oviductal secretory proteins on early embryonic development.     

The effects of phenytoin and its metabolite 5-(4-hydroxyphenyl)-5-phenylhydantoin on cellular glucose transport

Glucose is the principal fuel for brain metabolism and its movement across the blood-brain barrier depends on Glut1. Impaired glucose transport to the brain may have deleterious consequences. For example, Glut1 deficiency syndrome (Glut1DS) is the result of heterozygous loss of function Glut1 mutation leading to energy failure of the brain and subsequently, epileptic encephalopathy. To preserve the integrity of the energy supply to the brain in patients with compromised glucose transport function, consumption of compounds with glucose transport inhibiting properties should be avoided. Phenytoin is a widely used anticonvulsant that affects carbohydrate metabolism. In this study, the hypothesis that phenytoin and its metabolite 5-(4-hydroxyphenyl)-5-phenylhydantoin (HPPH) affect cellular glucose transport was tested. With a focus on Glut1, the effects of phenytoin and HPPH on cellular glucose transport were studied. Glucose uptake assay measuring the zero-trans influx of radioactive-labeled glucose analogues showed that phenytoin and HPPH did not exert immediate effects on erythrocyte Glut1 activity or glucose transport in Hs68 control fibroblasts, Glut1DS primary fibroblasts isolated from two patients, or in rat primary astrocytes. Prolonged exposure to the two compounds could stimulate glucose transport by up to 30-60% over the control level (p <0.05) in Hs68 and Glut1DS fibroblasts as well as in rat astrocytes. The stimulation of glucose transport by HPPH was dose-dependent and accompanied by an up-regulation of GLUT1 mRNA expression (p <0.05). In conclusion, phenytoin and HPPH do not compromise cellular glucose transport. Prolonged exposure to these compounds can modify carbohydrate homeostasis by up-regulating glucose transport in both normal and Glut1DS conditions in vitro.