Using Continuous-Time Spatial Capture-Recapture models to make inference about animal activity patterns.

Quantifying the distribution of daily activity is an important component of behavioral ecology. Historically, it has been difficult to obtain data on activity patterns, especially for elusive species. However, the development of affordable camera traps and their widespread usage has led to an explosion of available data from which activity patterns can be estimated.Continuous-time spatial capture-recapture (CT SCR) models drop the occasion structure seen in traditional spatial and nonspatial capture-recapture (CR) models and use the actual times of capture. In addition to estimating density, CT SCR models estimate expected encounters through time. Cyclic splines can be used to allow flexible shapes for modeling cyclic activity patterns, and the fact that SCR models also incorporate distance means that space-time interactions can be explored. This method is applied to a jaguar dataset.Jaguars in Belize are most active and range furthest in the evening and early morning and when they are located closer to the network of trails. There is some evidence that females have a less variable pattern than males. The comparison between sexes demonstrates how CT SCR can be used to explore hypotheses about animal behavior within a formal modeling framework.SCR models were developed primarily to estimate and model density, but the models can be used to explore processes that interact across space and time, especially when using the CT SCR framework that models the temporal dimension at a finer resolution.

The effect of features of the metabolic syndrome on atherosclerotic risk in relatively long-surviving patients with type 1 diabetes.

BACKGROUND: Increasing numbers of patients with type 1 diabetes (T1DM) are developing features of the metabolic syndrome. The additional effect of this on the development of atherosclerosis, as inferred by the carotid artery intima media thickness (IMT), has not previously been assessed. The aim of this study was to assess the effect of features of the metabolic syndrome on carotid artery IMT in a cohort of long-surviving patients with T1DM. METHODS: Long-surviving patients with T1DM attending the Centre for Diabetes and Endocrinology were assessed regarding their risk factor profile. All underwent measurement of carotid artery IMT. In all, 156 patients who had T1DM for more than 18 years had their carotid artery IMT measured. All had been attending the clinic for over 10 years, and past clinical and laboratory records were available. RESULTS: A total of 37 patients had metabolic syndrome according to the International Diabetes Federation (IDF) definition. Those with metabolic syndrome had a significantly increased carotid artery IMT (P = 0.003) compared to those without the syndrome. There was a significant relationship between the number of features of metabolic syndrome and increased atherosclerotic risk according to the carotid artery IMT (P = 0.01). A significant correlation was found between carotid artery IMT and both waist circumference (P < 0.001) and insulin resistance (P = 0.005). CONCLUSIONS: In long-surviving patients with T1DM, those that develop metabolic syndrome are more likely to have thicker carotid artery IMT, and, by inference, be at higher risk of atherosclerosis and possibly cardiovascular disease. A linear relationship was present between both waist circumference and insulin resistance and carotid artery IMT.

Nonlinear mixed effects modeling of gametocyte carriage in patients with uncomplicated malaria.

BACKGROUND: Gametocytes are the sexual form of the malaria parasite and the main agents of transmission. While there are several factors that influence host infectivity, the density of gametocytes appears to be the best single measure that is related to the human host's infectivity to mosquitoes. Despite the obviously important role that gametocytes play in the transmission of malaria and spread of anti-malarial resistance, it is common to estimate gametocyte carriage indirectly based on asexual parasite measurements. The objective of this research was to directly model observed gametocyte densities over time, during the primary infection. METHODS: Of 447 patients enrolled in sulphadoxine-pyrimethamine therapeutic efficacy studies in South Africa and Mozambique, a subset of 103 patients who had no gametocytes pre-treatment and who had at least three non-zero gametocyte densities over the 42-day follow up period were included in this analysis. RESULTS: A variety of different functions were examined. A modified version of the critical exponential function was selected for the final model given its robustness across different datasets and its flexibility in assuming a variety of different shapes. Age, site, initial asexual parasite density (logged to the base 10), and an empirical patient category were the co-variates that were found to improve the model. CONCLUSIONS: A population nonlinear modeling approach seems promising and produced a flexible function whose estimates were stable across various different datasets. Surprisingly, dihydrofolate reductase and dihydropteroate synthetase mutation prevalence did not enter the model. This is probably related to a lack of power (quintuple mutations n = 12), and informative censoring; treatment failures were withdrawn from the study and given rescue treatment, usually prior to completion of follow up.

Carotid artery intima-media complex thickening in patients with relatively long-surviving type 1 diabetes mellitus.

OBJECTIVE: The factors responsible for premature coronary atherosclerosis in patients with type 1 diabetes are ill defined. We therefore assessed carotid intima-media complex thickness (IMT) in relatively long-surviving patients with type 1 diabetes as a marker of atherosclerosis and correlated this with traditional risk factors. DESIGN: Cross-sectional study of 148 patients with relatively long-surviving (>18 years) type 1 diabetes (76 men and 72 women) attending the Centre for Diabetes and Endocrinology, Johannesburg. METHODS: The mean common carotid artery IMT and presence or absence of plaque was evaluated by high-resolution B-mode ultrasound. Their median age was 48 years and duration of diabetes 26 years (range 18-59 years). Traditional risk factors (age, duration of diabetes, glycemic control, hypertension, smoking and lipoprotein concentrations) were recorded. Three response variables were defined and modeled. Standard multiple regression was used for a continuous IMT variable, logistic regression for the presence/absence of plaque and ordinal logistic regression to model three categories of "risk." RESULTS: The median common carotid IMT was 0.62 mm (range 0.44-1.23 mm) with plaque detected in 28 cases. The multiple regression model found significant associations between IMT and current age (P=.001), duration of diabetes (P=.033), BMI (P=.008) and diagnosed hypertension (P=.046) with HDL showing a protective effect (P=.022). Current age (P=.001) and diagnosed hypertension (P=.004), smoking (P=.008) and retinopathy (P=.033) were significant in the logistic regression model. Current age was also significant in the ordinal logistic regression model (P<.001), as was total cholesterol/HDL ratio (P<.001) and mean HbA(1c) concentration (P=.073). CONCLUSIONS: The major factors influencing common carotid IMT in patients with relatively long-surviving type 1 diabetes are age, duration of diabetes, existing hypertension and HDL (protective) with a relatively minor role ascribed to relatively long-standing glycemic control.