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S Davis

Publications and source records attributed to S Davis.

At least 19 recordsLinked to original sources
PubMed2006

Plague metapopulation dynamics in a natural reservoir: the burrow system as the unit of study.

The ecology of plague (Yersinia pestis infection) in its ancient foci in Central Asia remains poorly understood. We present field data from two sites in Kazakhstan where the great gerbil (Rhombomys opimus) is the major natural host. Family groups inhabit and defend burrow systems spaced throughout the landscape, such that the host population may be considered a metapopulation, with each occupied burrow system a subpopulation. We examine plague transmission within and between family groups and its effect on survival. Transmission of plague occurred disproportionately within family groups although not all gerbils became infected once plague entered a burrow system. There were no spatial patterns to suggest that family groups in close proximity to infected burrow systems were more at risk of infection than those far away. At one site, infection increased the chances of burrow-system extinction. Overall, it is useful to consider the burrow system as the unit of study within a much larger metapopulation.

Animals↗
PubMed2006

Demographic and spatio-temporal variation in human plague at a persistent focus in Tanzania.

Human plague in the Western Usambara Mountains in Tanzania has been a public health problem since the first outbreak in 1980. The wildlife reservoir is unknown and eradication measures that have proved effective elsewhere in Tanzania appear to fail in this region. We use census data from 2002 and hospital records kept since 1986 to describe the temporal, spatial and demographic variation in human plague. A seasonal peak in cases occurs from December to February with the numbers of cases during this peak varying between 0 and 1150. Variation in incidence, calculated for each village as the mean number of cases per thousand inhabitants per year, indicates that human plague is concentrated around a group of three neighbouring, relatively isolated, high-altitude villages; Nywelo, Madala and Gologolo. However, there was no evidence that these villages were acting as a source of infection for the remainder of the focus. The likelihood of becoming infected with plague is highest between the ages of 5 and 19 and lowest for adult men. This was most clear in the ward encompassing the three high-incidence villages where the risk of plague among children aged 10-14 was 2.2 times higher than for adults aged 30-34, and among adults aged 30-34, the risk was 2.4 times higher for women than men.

Adolescent↗
PubMed2006

Using contrast sensitivity to estimate the cost-effectiveness of verteporfin in patients with predominantly classic age-related macular degeneration.

AIMS: To re-evaluate the cost-effectiveness of photodynamic therapy with verteporfin (Visudyne, Novartis AG, Switzerland) in patients with predominantly classic and classic choroidal neovascularization (CNV) owing to age-related macular degeneration (AMD), using new evidence on the impact of contrast sensitivity on health status. METHOD: A health economic model is used to synthesise the evidence on contrast sensitivity and treatment rates from the TAP Investigation with health state utilities and costs. Impairment of visual function is estimated using a Markov model to predict transitions between states of contrast sensitivity. Each state is associated with costs and a health state utility. Total expected costs and benefits for a cohort of patients over a defined number of cycles are calculated. The expected health state utility for each disease state was estimated using results from a study of 209 patients with AMD in Sheffield. The model includes the costs associated with treatment and monitoring in the verteporfin treatment arm and costs offset by delaying the deterioration of visual function. RESULTS: Beyond 3 years, the annual costs of the verteporfin arm are estimated to be less than the annual costs of the control arm, owing to the cost associated with higher blindness prevalence in the control arm. Over time, the results show that both the incremental utility and cost decreases. By 10 years, the estimated incremental cost-effectiveness is approximately pound20 996 per Quality-Adjusted Life Years. CONCLUSION: The results of this study suggest that the verteporfin therapy in the treatment for patients with predominantly classic and classic CNV owing to AMD is encouraging.

Aged↗
PubMed2006

Deletion of the Coffin-Lowry syndrome gene Rsk2 in mice is associated with impaired spatial learning and reduced control of exploratory behavior.

Coffin-Lowry Syndrome (CLS) is an X-linked syndromic form of mental retardation associated with skeletal abnormalities. It is caused by mutations of the Rsk2 gene, which encodes a growth factor regulated kinase. Gene deletion studies in mice have shown an essential role for the Rsk2 gene in osteoblast differentiation and function, establishing a causal link between Rsk2 deficiency and skeletal abnormalities of CLS. Although analyses in mice have revealed prominent expression of Rsk2 in brain structures that are essential for learning and memory, evidence at the behavioral level for an involvement of Rsk2 in cognitive function is still lacking. Here, we have examined Rsk2-deficient mice in two extensive batteries of behavioral tests, which were conducted independently in two laboratories in Zurich (Switzerland) and Orsay (France). Despite the known reduction of bone mass, all parameters of motor function were normal, confirming the suitability of Rsk2-deficient mice for behavioral testing. Rsk2-deficient mice showed a mild impairment of spatial working memory, delayed acquisition of a spatial reference memory task and long-term spatial memory deficits. In contrast, associative and recognition memory, as well as the habituation of exploratory activity were normal. Our studies also revealed mild signs of disinhibition in exploratory activity, as well as a difficulty to adapt to new test environments, which likely contributed to the learning impairments displayed by Rsk2-deficient mice. The observed behavioral changes are in line with observations made in other mouse models of human mental retardation and support a role of Rsk2 in cognitive functions.

Abnormalities, Multiple↗
PubMed2006

A model of Leptospirosis infection in an African rodent to determine risk to humans: seasonal fluctuations and the impact of rodent control.

Human leptospirosis (Leptospira spp. infection) is a worldwide public health problem that is of greatest concern for humid tropical and subtropical regions. The magnitude of the problem in these areas is larger because of the climatic and environmental conditions the bacterium face outside their hosts but also because of the frequency of contacts between people and sources of infection. Rodents are thought to play the most important role in the transmission of human leptospirosis. We here model the dynamics of infection in an African rodent (Mastomys natalensis) that is thought to be the principal source of infection in parts of Tanzania. Our model, representing the climatic conditions in central Tanzania, suggests a strong seasonality in the force of infection on humans with a peak in the abundance of infectious mice between January and April in agricultural environments. In urban areas the dynamics are predicted to be more stable and the period of high numbers of infectious animals runs from February to July. Our results indicate that removal of animals by trapping rather than reducing the suitability of the environment for rodents will have the greater impact on reducing human cases of leptospirosis.

Animals↗
PubMed2006

Factors affecting tibial plateau expansion in healthy women over 2.5 years: a longitudinal study.

OBJECTIVE: There is evidence for tibial bone area to increase in response to risk factors for knee osteoarthritis (OA) in healthy subjects and to increase over time in subjects with knee OA. We performed a cohort study to examine whether tibial plateau bone area changes over time in healthy subjects and identify factors influencing the change. DESIGN: Eighty-one healthy women (age range 50-76 years) underwent magnetic resonance imaging (MRI) on their dominant knee at baseline and approximately 2.5 years later. Tibial plateau bone area was measured at baseline and follow-up. Risk factors assessed at baseline were tested for their association with change in tibial plateau bone area over time using multiple linear regression. RESULTS: The mean tibial plateau bone area increased from 1733+/-209 to 1782+/-203 mm(2) for the medial, and from 1090+/-152 to 1109+/-152 mm(2) for the lateral over the study period, representing an annual average increase rate of 1.2% (95% CI 0.03%, 1.6%) and 0.8% (95% CI 0.7%, 1.8%), respectively. Baseline tibial plateau bone area was inversely associated with the increase rate of tibial plateau bone area. There was a trend for static knee alignment to be related to the increase rate of tibial plateau bone area. CONCLUSION: In healthy women, tibial plateau bone area increases over time. Baseline tibial plateau bone area is the main factor affecting the rate of increase, with biomechanical factors, such as static anatomical alignment, likely to affect the expansion of tibial plateau. Further work will be needed to determine the effect of subchondral bone change in the pathogenesis of knee OA.

Aged↗
PubMed2006

Lesions in the cerebellar fastigial nucleus have a small effect on the hyperpnea needed to meet the gas exchange requirements of submaximal exercise.

The purpose of this study was to test the hypothesis that an intact cerebellar fastigial nucleus (CFN) is necessary for the hyperpnea to meet the gas exchange needs of submaximal exercise. Bilateral stainless steel microtubules were implanted in the cerebellum inside (n = 12) or outside (n = 2) the CFN for injection (0.5 to 10 microl) of the neurotoxin ibotenic acid. All goats had difficulty maintaining normal posture and walking for up to 1 mo after the implantation of the microtubules and again for hours or days after the neurotoxin was injected. Postmortem histology indicated there were 55% fewer living neurons (P < 0.001, n = 9, 3,720 +/- 553 vs. 1,670 +/- 192) in the CFN of the experimental goats compared with a control group of goats. As is typical for goats before implantation of the microtubules, the decrease in arterial Pco(2) from rest during mild and moderate treadmill exercise was 2.0 +/- 0.39 and 3.5 +/- 0.45 Torr, respectively. Implantation of the microtubules did not significantly change this exercise hyperventilation. However, neurotoxic lesioning with 10 mul ibotenic acid significantly (P < 0.05) attenuated the decrease in arterial Pco(2) by 1.3 and 2.8 Torr at the first and second workload, respectively. The modest attenuation of the exercise hypocapnia at both workloads in CFN-lesioned goats suggests that the CFN is part of the control system that enables the ventilatory response to meet the gas exchange requirements of submaximal exercise.

Animals↗
PubMed2006

CO2/H+ chemoreceptors in the cerebellar fastigial nucleus do not uniformly affect breathing of awake goats.

Our objective in this study was to test the hypothesis that focal acidosis (FA) in the cerebellar fastigial nucleus (CFN) of awake goats arising from global brain acidosis induced by increasing inspired CO2 will increase breathing. FA was created by reverse microdialysis of mock cerebral spinal fluid, equilibrated with 6.4, 25, 50, or 80% CO2 through chronically implanted microtubules (cannula). Dialysis with 6.4% CO2 had no significant effects on any physiological parameters. However, microdialysis at higher levels of CO2 increased pulmonary ventilation (V(I)) in one group of studies and decreased V(I) in a second group and the difference between the groups was significant (t = 9.16, P < 0.001). In one group of studies (n = 8), FA with 50 and 80% CO2 significantly increased (P < 0.05) Vi by 16 and 12%, respectively, and significantly increased (P < 0.05) heart rate by 13 and 9%, respectively. In contrast, in another group of studies (n = 6), FA with 25 and 50% CO2 significantly decreased (P < 0.05) Vi by 7 and 10%, respectively. In this group oxygen consumption was decreased during dialysis with 80% CO2. On the basis of histology, we estimate that the increased and decreased responses were associated with FA primarily in the rCFN and cCFN, respectively. We conclude that there are CO2/H+-sensitive neurons in the CFN that do not uniformly affect breathing. In addition, the significant changes in heart rate and oxygen consumption during FA indicate that the CFN can also influence non-respiratory-related control systems.

Acidosis, Respiratory↗
PubMed2006

Implications of increased susceptibility to predation for managing the sylvatic cycle of Echinococcus multilocularis.

The ability to increase the chances that infectious prey are taken by predators is an observed feature of many parasites that rely on one or more predator-prey relationships to complete their life-cycle. In the sylvatic life-cycle of Echinococcus multilocularis - the causative agent of human alveolar echinococcosis-- foxes are the final host, with voles acting as intermediate hosts. Here we review the evidence that E. multilocularis causes increased susceptibility to predation and present a general mathematical model for the sylvatic life-cycle. The ability to increase susceptibility to predation in the intermediate host reduces the sensitivity of the parasite population to adverse conditions. For example, there is no critical density of foxes below which the parasite is expected to die out, even if the effect of the parasite on infected prey is very small. We suggest that increased susceptibility to predation is a plausible explanation for the observed resilience of E. multilocularis during and following field trials of praziquantel baiting.

Animals↗
PubMed2006

Airway hyperresponsiveness and body mass index: the Child Health and Environment Cohort Study in Hesse, Germany.

Increased body mass index has been linked to wheezing, a diagnosis of asthma, and morbidity. We investigated the association between body mass index (BMI), breastfeeding, and airway hyperresponsiveness (AHR) in 536 German schoolchildren. We analyzed consecutive surveys in 1994-1995 and 1997, conducted as part of the Child Health and Environment Cohort Study in Hesse, Germany. The questionnaire included questions adapted from the German version of the International Study of Asthma and Allergy in Childhood (ISAAC). A bronchial challenge test using 4.5% hypertonic saline was conducted during the 1997 survey. AHR was defined as a fall in forced expiratory volume in 1 sec (FEV(1)) of > or = 15%. Of 536 children who participated in the 1997 survey (median age, 10.3 years), 82 (15%) tested positive for AHR. In a multivariate analysis, there was no association between AHR determined at age 10 years and the highest quintile of BMI compared to the lowest quintile at age 4 years (odds ratio (OR), 1.4; 95% confidence interval (CI), 0.5-3.6), 7-8 years (OR, 0.6; 95% CI, 0.1-2.5), or 10 years (OR, 1.1; 95% CI, 0.2-4.3). Breastfeeding for 12 weeks or longer protected against AHR (OR, 0.4; 95% CI, 0.2-0.9). However, when children in the highest quintile of BMI at age 4 years had been breastfed for 8 weeks or less, the prevalence of AHR at age 10 years was significantly increased (27.7%, P = 0.01). In conclusion, our results demonstrate a protective effect of breastfeeding against AHR, and reinforce the need to encourage breastfeeding. Although there was no association between BMI and AHR, our finding of an interactive effect of high BMI and short breastfeeding on AHR suggests a complex etiological pathway that needs to be further explored.

Adolescent↗
PubMed2006

Cultured skin fibroblast cells derived from bluetongue virus-inoculated sheep and field-infected cattle are not a source of late and protracted recoverable virus.

A recent hypothesis to explain the recurrence of bluetongue disease after winter seasonal absences of the vector has suggested a role for persistent infection of sheep. This report presents combined independent work from two laboratories investigating the possible recovery of Bluetongue virus (BTV) over a protracted period after infection of both sheep and cattle. Prior to infection with either cell-culture-adapted or non-culture-adapted BTV, sheep were subjected to a preliminary exposure to Culicoides sp. insects, which reportedly facilitates recovery of virus from infected sheep several months post-infection (p.i.). A series of skin biopsies at different intervals p.i. was used to establish skin fibroblast (SF) cultures from which attempts were made to detect virus by isolation and by molecular and immunological methods. Also examined was the effect on virus recovery of additional exposure to Culicoides sp. prior to skin biopsy during the post-inoculation period. A herd of cattle sentinels for surveillance of natural BTV infection in northern Australia was monitored prospectively for seroconversion. Evidence of infection initiated attempted virus recovery by establishing SF cultures. It was found that in both cattle and sheep there was not a protracted period over which BTV could be recovered from SF cultures. The data do not support a general hypothesis that BTV persists in either sheep or cattle.

Animals↗
PubMed2006

Treating the acute stroke patient as an emergency: current practices and future opportunities.

Developments in acute stroke therapy have followed advances in the understanding of the evolving pathophysiology in both ischaemic stroke and intracerebral haemorrhage (ICH). In ischaemic stroke, rapid reperfusion of the ischaemic penumbra with thrombolysis within 3 h of symptom onset is of proven benefit, but few patients currently receive therapy, mainly due to the short-time window and lack of stroke expertise. In ICH, a recent study indicated that a haemostatic agent can limit ongoing bleeding and improve outcomes when administered within 4 h of stroke onset. These advances in acute stroke therapy underlie the concept that 'time is brain' and that urgent intervention can limit cerebral damage. Neuroprotective therapy could offer the prospect of a greater proportion of stroke patients receiving treatment, potentially before imaging and even in the ambulance setting. Virtually all stroke patients would benefit from receiving multidisciplinary care in acute stroke units.

Emergencies↗
PubMed2006

Value of low-dose 2 x 2 Gy palliative radiotherapy in advanced low-grade non-Hodgkin's lymphoma.

Low-dose radiotherapy over the last decade has been reported to provide effective palliation for patients with low-grade non-Hodgkin's lymphoma. In this retrospective case series of 10 patients, we report our early experience using low-dose radiotherapy (usually 2 x 2 Gy) for patients with advanced-stage follicular, mucosal associated lymphoid tissue, mantle cell and small lymphocytic lymphomas. Median follow up was 27 weeks. Response rates were high (complete response, 70%; partial response, 20%), the response durable and the toxicity was minimal (no toxicity greater than grade 1). Low-dose irradiation is an effective treatment option for patients with low-grade lymphomas with local symptoms.

Aged↗
PubMed2006

The impact of meaning in life and life goals on adherence to a tuberculosis medication regimen in South Africa.

SETTING: Out-patient tuberculosis (TB) clinics in Durban, South Africa. OBJECTIVE: Health care provider concerns about persons with active TB defaulting on medications led to a study of adherence among persons receiving anti-tuberculosis therapy and, specifically, the relationships between meaning in life, life goals, sense of coherence, social support, symptom presence and intensity, and adherence in individuals diagnosed with TB. DESIGN: A cross-sectional, descriptive design was used to gather self-reported data from TB-infected individuals who were enrolled in out-patient clinics. Data were collected from 159 Zulu and/or English-speaking persons who agreed to participate in the study. RESULTS: A significant relationship was found between higher life goals and adherence to TB treatment (P = 0.027). Analysis of variance revealed that higher meaning in life ratings were significantly associated with older age (P = 0.007). Having children and children living in the same household were significantly associated with low meaning in life ratings (P = 0.006 and P < or = 0.001, respectively), indicating that these individuals were more concerned about basic matters of home and sustenance. CONCLUSIONS: The results of this study indicate that meaning in life and life goals may be useful for identifying individuals who will require additional support in adhering to anti-tuberculosis treatment.

Adolescent↗
PubMed2005

Childhood leukaemia in Belarus, Russia, and Ukraine following the Chernobyl power station accident: results from an international collaborative population-based case-control study.

BACKGROUND: There is little evidence regarding the risk of leukaemia in children following exposure to radionuclides from the Chernobyl Nuclear Power Plant explosion on April 26, 1986. METHODS: This population-based case-control study investigated whether acute leukaemia is increased among children who were in utero or <6 years of age at the time of the Chernobyl accident. Confirmed cases of leukaemia diagnosed from April 26, 1986 through December 31, 2000 in contaminated regions of Belarus, Russia, and Ukraine were included. Two controls were matched to each case on sex, birth year, and residence. Accumulated absorbed radiation dose to the bone marrow was estimated for each subject. RESULTS: Median estimated radiation doses of participants were <10 mGy. A significant increase in leukaemia risk with increasing radiation dose to the bone marrow was found. This association was most evident in Ukraine, apparent (but not statistically significant) in Belarus, and not found in Russia. CONCLUSION: Taken at face value, these findings suggest that prolonged exposure to very low radiation doses may increase leukaemia risk as much as or even more than acute exposure. However the large and statistically significant dose-response might be accounted for, at least in part, by an overestimate of risk in Ukraine. Therefore, we conclude this study provides no convincing evidence of an increased risk of childhood leukaemia as a result of exposure to Chernobyl radiation, since it is unclear whether the results are due to a true radiation-related excess, a sampling-derived bias in Ukraine, or some combination thereof. However, the lack of significant dose-responses in Belarus and Russia also cannot convincingly rule out the possibility of an increase in leukaemia risk at low dose levels.

Age Distribution↗
PubMed2005

Testosterone for peri- and postmenopausal women.

BACKGROUND: : The value of adding testosterone to hormone therapy (HT) for the management of peri- and postmenopausal women is controversial and has not been systematically reviewed. OBJECTIVES: : To determine the benefits and risks of testosterone therapy for peri- and postmenopausal women taking hormone therapy. SEARCH STRATEGY: : We searched the Cochrane Menstrual Disorders and Subfertility Group Trials Register (1st November 2003), The Cochrane Library (Issue 2, 2003), MEDLINE (1966 to 1st November 2003), EMBASE (1980 to 1st November 2003), Biological Abstracts (1969 to 2002), PsycINFO (1972 to 1st November 2003), CINAHL (1982 to 1st November 2003), and reference lists of articles. We also contacted pharmaceutical companies and researchers in the field. SELECTION CRITERIA: : Studies that were randomized comparisons of testosterone plus hormone therapy versus hormone therapy alone in peri- or postmenopausal women. DATA COLLECTION AND ANALYSIS: : Two review authors assessed the quality of the trials and extracted data independently. Where it was necessary, the corresponding authors of eligible trials were contacted for additional information. For dichotomous outcomes Peto odds ratios and 95% confidence intervals were calculated. For continuous outcomes non-skewed data from valid scales were synthesized using a weighted mean difference or standardized mean difference. If statistical heterogeneity was found, a random-effects model was used and reasons for the heterogeneity were explored and discussed. MAIN RESULTS: : Twenty-three trials with 1957 participants were included in the review. The median study duration was 6 months (range 1.5 to 24 months). Most of the trials were of adequate quality with regard to randomization and concealment of allocation sequence. The major methodological limitations were attrition bias and lack of a washout period in the cross-over studies. The pooled estimate from the studies suggested that the addition of testosterone to HT regimens improved sexual function scores for postmenopausal women. A significant adverse effect was a decrease in high-density lipoprotein (HDL) cholesterol levels. The discontinuation rate was not significantly greater with testosterone therapy (Peto odds ratio 1.01, 95% confidence interval 0.76 to 1.33) than with HT alone. There was insufficient evidence of a treatment effect for perimenopausal women or for other outcomes. AUTHORS' CONCLUSIONS: : Only a limited number of studies could be pooled in the meta-analyses. This limited the power of the meta-analysis to provide conclusions about efficacy and safety. However, there is evidence that adding testosterone to HT has a beneficial effect on sexual function in postmenopausal women. There was a reduction in HDL cholesterol associated with the addition of testosterone to the HT regimens. The meta-analysis combined studies using different testosterone regimens. It is, therefore, difficult to estimate the effect of testosterone on sexual function in association with any individual hormone treatment regimen.

Androgens↗
PubMed2005

Dietary determinants of one-carbon metabolism and the risk of non-Hodgkin's lymphoma: NCI-SEER case-control study, 1998-2000.

The role of dietary one-carbon determinants remains largely unexplored for non-Hodgkin's lymphoma (NHL). In a population-based case-control study of non-African-American adult (aged 20-74 years) women and men from four US Surveillance, Epidemiology, and End Results study centers (Detroit, Michigan; Iowa; Los Angeles, California; and Seattle, Washington; 1998-2000), the authors examined folate; vitamins B2, B6, and B12; methionine; and a one-carbon antagonist, alcohol, in 425 incident NHL cases and 359 controls who completed a detailed food frequency questionnaire. Adjusted odds ratios and 95% confidence intervals were estimated by using unconditional logistic regression. Higher intake of one-carbon determinants from food was associated with a lower risk of NHL, but that for only vitamin B6 (highest vs. lowest quartile: odds ratio = 0.57, 95% confidence interval: 0.34, 0.95; p trend = 0.01) and methionine (odds ratio = 0.49, 95% confidence interval: 0.31, 0.76; p trend = 0.002) reached statistical significance. Folate from food was inversely associated with diffuse subtype (odds ratio = 0.47, 95% confidence interval: 0.23, 0.94; p trend = 0.03). The authors found no association between total (food plus supplement) vitamins and NHL. Nonusers of alcohol had an elevated NHL risk compared with users, and alcohol did not modify other nutrient-NHL associations. Findings suggest that one-carbon nutrients, particularly vitamin B6 and methionine, may be protective against NHL.

Adult↗