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Biomedical subjects

S Charles

Publications and source records attributed to S Charles.

At least 19 recordsLinked to original sources
PubMed2006

Evolution and invasion dynamics of multiple infections with Wolbachia investigated using matrix based models.

Endosymbiotic bacteria are often transmitted vertically from one host generation to the next via oocytes cytoplasm. The generally small number of colonizing bacteria in the oocytes leads to a bottleneck at each generation, resulting in genetic homogenization of the symbiotic population. Nevertheless, in many of the species infected by Wolbachia (maternally transmitted bacteria), individuals do sometimes simultaneously harbor several bacterial strains, owing to the fact that Wolbachia induces cytoplasmic incompatibility (CI) that maintains multiple infections. CI occurs in crosses in which the male is infected by at least one Wolbachia strain that the female lacks, and consequently it favors individuals with the greatest symbiotic diversity. CI results in death of offspring in diploid species. In haplodiploid individuals, unfertilized eggs hatch normally into males and fertilized ones, which would lead to females, either die (female mortality type: FM) or develop into males (male development type: MD). Until now, only one theoretical study, restricted to diploid species, has investigated the associations where multiple CI-inducing Wolbachia co-exist, and explored the conditions under which multiple infections can spread. The consequences of double infections on Wolbachia maintenance in host populations, and the selective pressures to which it is subjected have not yet been analysed. Here, we have re-written a model previously developed for single infection in matrix form, which allows easy extension to multiple infections and introduction of mutant strains. We show that (i) the CI type has a strong influence on invasiveness and maintenance of multiple infections; (ii) double infection lowers the invasion threshold of less competitive strains that hitch-hike with their companion strain; (iii) when multiple infections occur, as in single infections, the strains selected are those which maximize the production of infected offspring; and (iv) for the MD CI type, invasion of mutant strains can carry the whole infection to extinction.

Animals↗
PubMed2005

Imidacloprid/moxidectin topical solution for the prevention of heartworm disease and the treatment and control of flea and intestinal nematodes of cats.

Sixteen controlled laboratory studies, involving 420 kittens and cats, were conducted to evaluate the efficacy and safety of topically applied formulations of imidacloprid and moxidectin for the prevention of feline heartworm disease, treatment of flea infestations and treatment and control of intestinal nematodes. Unit-dose applicators and the dosing schedule used in these studies were designed to provide a minimum of 10mg imidacloprid and 1mg moxidectin/kg. Treatments were applied topically by parting the hair at the base of the skull and applying the solution on the skin. Imidacloprid treatment alone did not display activity against Dirofilaria immitis or intestinal nematodes and moxidectin treatment alone provided little or no activity against adult Ctenocephalides felis infestations. The formulation containing 10% imidacloprid and 1% moxidectin was 100% efficacious against the development of adult D. immitis infections when cats were treated 30 days after inoculation with third-stage larvae. A single treatment with this formulation also provided 88.4-100% control of adult C. felis for 35 days. Imidacloprid/moxidectin was 100% efficacious against adult Toxocara cati and 91.0-98.3% efficacious against immature adults and fourth-stage T. cati larvae. The formulation provided 98.8-100% efficacy against adult Ancylostoma and immature adults and third-stage A. tubaeforme larvae. Monthly topical application with 10% imidacloprid/1% moxidectin is convenient, efficacious and safe for the prevention of feline heartworm disease, treatment of flea infestation and for the treatment and control of intestinal nematode infections of cats.

Administration, Topical↗
PubMed2003

Do migratory or demographic disruptions rule the population impact of pollution in spatial networks?

Ecotoxicology supplies environmental quality criteria mainly based on the potential effects of contaminants on demographic rates of natural populations. Possible impacts through pollutant-induced disruptions of spatial behaviors are totally neglected. Should it be significant to take into account this "second way"? We developed the example of a hypothetical brown trout population living in a river network. We analyzed how behaviors of toxic avoidance or attraction during the spawning migration alter the impact of pollution. Attraction behaviors basically enhanced the bad effect of pollution. More interesting, avoidance behaviors can weakly lift the asymptotic population growth rate, while if there is density-dependent effects on recruitment, pollutant avoidance can actually lead to a substantial drop in equilibrium size. Our model allowed comparing the relative significance of migratory and demographic disruptions for explaining the population impacts of pollution; we thus stress on the need of increasing efforts to develop knowledge relative to toxicant-induced spatial behaviors and to integrate such effects in the definition of environmental quality criteria.

Animal Migration↗
PubMed2003

Successful mobilization of peripheral blood stem cells after addition of ancestim (stem cell factor) in patients who had failed a prior mobilization with filgrastim (granulocyte colony-stimulating factor) alone or with chemotherapy plus filgrastim.

This study assessed the ability of recombinant human stem cell factor (rHuSCF) to mobilize stem cells in 44 patients who had failed a prior mobilization (CD34(+) yield 0.5-1.9 x 10(6)/kg BW) with filgrastim-alone or chemotherapy-plus-filgrastim. The same mobilization regimen was used with the addition of rHuSCF. In the filgrastim-alone group (n=13), rHuSCF 20 microg/kg was started 3 days before filgrastim and continued for the duration of filgrastim. In the chemotherapy-plus-filgrastim group (n=31), rHuSCF 20 microg/kg/day plus filgrastim 5-10 microg/kg/day were administered concurrently. Leukaphereses were continued to a maximum of four procedures or a target of >or=3 x 10(6) CD34(+) cells/kg. In both groups, CD34(+) yield (x 10(6)/kg BW) of the study mobilization was higher than that of the prior mobilization (median: 2.42 vs 0.84 P=0.002 and 1.64 vs 0.99 P=<0.001, respectively). In all 54 and 45% of patients in the filgrastim-alone group and chemotherapy-plus-filgrastim group, respectively, reached the threshold yield of 2 x 10(6)/kg. The probability of a successful mobilization was the same in those with a CD34+ yield of 0.5-0.75 x 10(6)/kg BW in the prior mobilization as in those with 0.76-1.99 x 10(6)/kg BW. Downmodulation of c-kit expression and a lower percentage of Thy-1 positivity in the mobilized CD34(+) cells were noted in the successful mobilizers compared with those in the poor mobilizers. This study shows that rhuSCF is effective in approximately half the patients who had failed a prior mobilization and allows them to proceed to transplant. It also points to the likely role of the SCF/c-kit ligand pair in mobilization.

Adult↗
PubMed2002

Host patch selection induced by parasitism: basic reproduction ratio r(0) and optimal virulence.

The effects of parasites on the behavior of their hosts are well documented. For example, parasites may affect the habitat selection of the host individual. We used variables aggregation methods to investigate the way in which parasites affect the spatial pattern of susceptible hosts. We developed a simple epidemiological model, taking into account both the reproduction processes of hosts (density-dependent birth and death) and infection, considered separately on two different patches, and the migration of susceptible hosts between these two patches. We used the complete model of three equations to generate an aggregated model describing the dynamics of the combined susceptible and infected host populations. We obtained the basic reproduction ratio (R(0)) from the aggregated model, and then studied the effect of the migratory behavior of susceptible hosts on the ability of the parasite to invade the system. We also used the basic reproduction ratio to investigate the evolution of parasite virulence in relation to the migration decisions of susceptible hosts. We found that host investment in avoidance of the infected patch leads to an increase in optimal virulence if host investment is costly.

Animals↗
PubMed2002

Risk factors in HIV-associated diarrhoeal disease: the role of drinking water, medication and immune status.

In a cross-sectional survey of 226 HIV-infected men, we examined the occurrence of diarrhoea and its relationship to drinking water consumption patterns, risk behaviours, immune status and medication use. Diarrhoea was reported by 47% of the respondents. Neither drinking boiled nor filtered water was significantly associated with diarrhoea (OR = 0.5 [0.2, 1.6], 1.2 [0.6, 2.5] respectively), whereas those that drank bottled water were at risk for diarrhoea (OR = 3.0 [1.1, 7.8]). Overall, 47% always or often used at least one water treatment. Of the 37% who were very concerned about drinking water, 62% had diarrhoea, 70% always or often used at least one water treatment. An increase in CD4 count was protective only for those with a low risk of diarrhoea associated with medication (OR = 0.6 [0.5, 0.9]). A 30% attributable risk to diarrhoea was estimated for those with high medication risk compared to those with low medication risk. The significant association between concern with drinking water and diarrhoea as well as between concern with drinking water and water treatment suggests awareness that drinking water is a potential transmission pathway for diarrhoeal disease. At the same time we found that a significant portion of diarrhoea was associated with other sources not related to drinking water such as medication usage.

Adult↗
PubMed2002

Associations between water-treatment methods and diarrhoea in HIV-positive individuals.

This manuscript extends our previously published work (based on data from one clinic) on the association between three drinking water-treatment modalities (boiling, filtering, and bottling) and diarrhoeal disease in HIV-positive persons by incorporating data from two additional clinics collected in the following year. We conducted a cross-sectional survey of drinking water patterns, medication usage, and episodes of diarrhoea among HIV-positive persons attending clinics associated with the San Francisco Community Consortium. We present combined results from our previously published work in one clinic (n = 226) with data from these two additional clinics (n = 458). In this combined analysis we employed logistic regression and marginal structural modelling of the data. The relative risk of diarrhoea for 'always' vs. 'never' drinking boiled water was 0.68 (95% CI 0.45-1.04) and for 'always' vs. 'never' drinking bottled water was 1.22 (95 % CI 0.82-1.82). Drinking filtered water was unrelated to diarrhoea (1.03 (95% CI 0.78, 1.35) for 'always' vs. 'never' drinking filtered water]. Adjustment for confounding did not have any notable effect on the point estimates (0.61, 1.35 and 0.98 for boiled, bottled, and filtered water respectively, as defined above). The risk of diarrhoea was lower among those consuming boiled water but this finding was not statistically significant. Because of these findings, the importance of diarrhoea in immunocompromised individuals, and the limitations of cross-sectional data further prospective investigations of water consumption and diarrhoea among HIV-positive individuals are needed.

Adolescent↗
PubMed2001

A mathematical model describing the thermal virus inactivation.

A new mathematical model is proposed to describe the inactivation of viruses at different temperatures. This model takes into account the exponential decrease of the viral titer with time, the inactivation rate being an exponential function of the temperature. A one-step non-linear regression was used to fit oral poliovirus vaccine (OPV) experimental data. In one of the applications of the model, we illustrate the use of our model to compare the accelerated degradation test of OPV new formulations to standard OPV. Such a model is both simple and convenient to use. It should be a useful tool in optimizing formulations for live viral vaccines.

Drug Stability↗
PubMed2001

Absolute configuration of anabasine from Messor and Aphaenogaster ants.

A method has been developed to assign the absolute configuration and enantiomeric excess of anabasine based on small amounts of material (in the microgram range), by derivatization with (+)-menthylchloroformate followed by capillary GC analysis of the resulting carbamate(s). This method was applied to three samples of anabasine isolated from Messor and Aphaenogaster ants. In Messor sanctus, only (2'S)-anabasine was present, whereas in Aphaenogaster subterranea and A. miamiana (2'S)-anabasine was determined to have an ee of 78 and 24%, respectively.

Anabasine↗
PubMed2001

Nerve fiber bundle visual field defect resulting from a giant peripapillary cotton-wool spot.

Cotton-wool spots are the clinical manifestation of focal infarcts of the retinal nerve fiber layer. They rarely cause significant visual field loss. A large idiopathic cotton-wool spot in a 34-year-old healthy woman caused a nerve fiber bundle visual field defect and an afferent pupillary defect that remained after the cotton-wool spot had disappeared and the retina and optic nerve appeared normal.

Adult↗
PubMed2000

Emergence of individual behaviour at the population level. Effects of density-dependent migration on population dynamics.

The aim of this work is to study the effects of different individual behaviours on the overall growth of a spatially distributed population. The population can grow on two spatial patches, a source and a sink, that are connected by migrations. Two time scales are involved in the dynamics, a fast one corresponding to migrations and a slow one associated with the local growth on each patch. Different scenarios of density-dependent migration are proposed and their effects on the population growth are investigated. A general discussion on the use of aggregation methods for the study of integration of different ecological levels is proposed.

Animals↗
PubMed1999

Behavioral choices based on patch selection: a model using aggregation methods.

The aim of this work is to study the influence of patch selection on the dynamics of a system describing the interactions between two populations, generically called 'population N' and 'population P'. Our model may be applied to prey-predator systems as well as to certain host-parasite or parasitoid systems. A situation in which population P affects the spatial distribution of population N is considered. We deal with a heterogeneous environment composed of two spatial patches: population P lives only in patch 1, while individuals belonging to population N migrate between patch 1 and patch 2, which may be a refuge. Therefore they are divided into two patch sub-populations and can migrate according to different migration laws. We make the assumption that the patch change is fast, whereas the growth and interaction processes are slower. We take advantage of the two time scales to perform aggregation methods in order to obtain a global model describing the time evolution of the total populations, at a slow time scale. At first, a migration law which is independent on population P density is considered. In this case the global model is equivalent to the local one, and under certain conditions, population P always gets extinct. Then, the same model, but in which individuals belonging to population N leave patch 1 proportionally to population P density, is studied. This particular behavioral choice leads to a dynamically richer global system, which favors stability and population coexistence. Finally, we study a third example corresponding to the addition of an aggregative behavior of population N on patch 1. This leads to a more complicated situation in which, according to initial conditions, the global system is described by two different aggregated models. Under certain conditions on parameters a stable limit cycle occurs, leading to periodic variations of the total population densities, as well as of the local densities on the spatial patches.

Animals↗
PubMed1999

Trace elements in soils fertilized with poultry litter.

Poultry litter is used on agricultural land because of its high nutrient content. The litter contains trace elements. With land application of litter, these elements may accumulate in the soil or plants, may be transported as run-off to surface water, or may be leached into groundwater. The objective of this research was to measure the concentrations of trace elements in soils fertilized with poultry litter. Soil was collected from three agricultural farms in Wicomico County, MD. These farms had a long history of poultry litter application. A nitric acid extraction was performed on soil samples collected to a depth of 60 cm. The concentrations of As, Cd, Cu, Mn, Pb, and Zn were determined using atomic absorption spectrophotometry. Arsenic, Cd, Cu, and Mn concentrations were higher in the manured fields than in the control fields. Lead and Zn concentrations did not significantly change with the application of poultry litter.

Agriculture↗
PubMed1998

The labour market costs of community care.

This paper reports an empirical investigation into the influence of informal care responsibilities on the labour supply of women. The objective is to examine the argument that the UK policy of caring for the chronic sick 'in the community' involves a nontrivial opportunity cost in the form of the forgone labour supply of the informal carers upon which it relies. We find that informal carers who care for less than 20 h per week are, in fact, more likely to participate in the labour market, but tend to work for fewer hours per week than otherwise similar noncarers. Informal carers who care for 20 h or more a week are less likely to participate, but only slightly. However, when they do undertake formal employment, they tend to earn less per hour and work for fewer hours per week.

Adult↗
PubMed1997

Reappraisal of the effect of temperature on the growth kinetics of Aeromonas salmonicida.

The effect of temperature (1-34 degrees C) on the maximum specific growth rate of Aeromonas salmonicida could not be described by the classical growth models; for some strains, two optimal temperatures at 23 degrees C and 30 degrees C were observed, as well as an unexpected increase in the pseudolag time above 27 degrees C. This could be explained by the presence of two subsets, notably S-layer+ and S-layer- sub-populations. The A- cells had higher growth parameters (Topt and mu opt) than the A+ cells and were selected by subcultures above 30 degrees C. Yet the relative proportion of A+ cells did not explain all the variation of mu max versus temperature, and the growth kinetics of an Aer. salmonicida isolate remained unpredictable.

Aeromonas↗