Modelling and spatial discrimination of small mammal assemblages: an example from western Sichuan (China).

We investigate the relationship between landscape heterogeneity and the spatial distribution of small mammals in two areas of Western Sichuan, China. Given a large diversity of species trapped within a large number of habitats, we first classified small mammal assemblages and then modelled the habitat of each in the space of quantitative environmental descriptors. Our original two step "classify then model" procedure is appropriate for the frequently encountered study scenario: trapping data collected in remote areas with sampling guided by expert field knowledge.In the classification step, we defined assemblages by grouping sites of similar species composition and relative densities using an expert-class-merging procedure which reduced redundancy in the habitat factor used within a multinomial logistic regression predicting species trapping probabilities. Assemblages were thus defined as mixtures of small mammal frequency distributions in discrete groups of sampled sites.In the modelling step, assemblages' habitats and environments of the two sampled areas were discriminated in the space of remotely sensed environmental descriptors. First, we compared the discrimination of assemblage/study areas by linear and non-linear forms of Discriminant Analysis (Linear Discriminant Analysis versus Mixture Discriminant Analysis) and of Multiple Regression (Generalized Linear Models versus Multiple Adaptive Regression Splines). The "best" predictive modelling technique was then used to quantify the contribution of each environmental variable in discriminations of assemblages and areas.Mixtures of Gaussians provided a more efficient model of assemblage coverage in environmental space than a single Gaussian cluster model. However, non-linearity in assemblage response to environmental gradients was consistently predicted with lower deviance and misclassification error by Multiple Adaptive Regression Splines. The two study areas were mainly discriminated along vegetation indices. However, although the Normalized Difference Vegetation Index (NDVI) could discriminate forested from non-forested habitats, its power to discriminate assemblages in Maerkang, where a greater diversity of forest habitat was observed, was seen to be limited, and in this case NDVI was outperformed by the Enhanced Vegetation Index (EVI). Our analyses highlight previously unobserved differences between the environments and small mammal communities of two fringe areas of the Tibetan plateau and suggests that a biogeograph-ical approach is required to elucidate ecological processes in small mammal communities and to reduce extrapolation uncertainty in distribution mapping.

Weather influences M. arvalis reproduction but not population dynamics in a 17-year time series.

Rodent outbreaks have plagued European agriculture for centuries, but continue to elude comprehensive explanation. Modelling and empirical work in some cyclic rodent systems suggests that changes in reproductive parameters are partly responsible for observed population dynamics. Using a 17-year time series of Microtus arvalis population abundance and demographic data, we explored the relationship between meteorological conditions (temperature and rainfall), female reproductive activity, and population growth rates in a non-cyclic population of this grassland vole species. We found strong but complex relationships between female reproduction and climate variables, with spring female reproduction depressed after cold winters. Population growth rates were, however, uncorrelated with either weather conditions (current and up to three months prior) or with female reproduction (number of foetuses per female and/or proportion of females reproductively active in the population). These results, coupled with age-structure data, suggest that mortality, via predation, disease, or a combination of the two, are responsible for the large multi-annual but non-cyclic population dynamics observed in this population of the common vole.

Safety of mefloquine in infants with acute falciparum malaria.

We evaluated retrospectively the safety of mefloquine (25 mg/kg) for the curative treatment of uncomplicated Plasmodium falciparum malaria in 26 infants weighing <15 kg and managed during a 5-year period. Side effects were recorded in 30.8% of patients and consisted chiefly of mild and transient gastrointestinal symptoms. Mefloquine was safe in infants weighing <15 kg in our experience.

Is the prevalence of Taenia taeniaeformis in Microtus arvalis dependent on population density?

Populations of common voles Microtus arvalis were studied as hosts of the tapeworm Taenia taeniaeformis during a 14-yr survey. They were monitored in spring, summer, and autumn in a pastoral ecosystem in eastern France. A total of 7,574 voles were sampled during 2 multiannual population fluctuations. A third fluctuation was sampled during the increase phase only. Overall prevalence was lowest in summer (0.6%), increased by 3 times in autumn (1.5%) and a further 5 times in spring (7.8%). Analysis of prevalence, based on 7,384 voles, by multiple logistic regression revealed that extrinsic factors such as season and intrinsic factors such as host age and host density have a combined effect. In the longer term, host age and host density were positively associated with prevalence in summer. Host density was strongly associated with autumn prevalence. There was no association between the fluctuation phase and prevalence. The study shows that a long timescale (here a multiannual survey) is necessary to demonstrate the positive effect of host density on the prevalence of this indirectly transmitted parasite. The demonstration of this relationship depends on the rodents being intermediate rather than definitive hosts.

Severe deficiency of the specific von Willebrand factor-cleaving protease (ADAMTS 13) activity in a subgroup of children with atypical hemolytic uremic syndrome.

OBJECTIVE: The von Willebrand factor-cleaving protease (VWF-cp) activity has been reported to be deficient in adults with thrombotic thrombocytopenic purpura (TTP) and generally normal in adults with hemolytic uremic syndrome (HUS). The goal of this study was to determine VWF-cp activity in children with typical postdiarrheal (d+) HUS or atypical non-postdiarrheal (d-) HUS. Study design We measured VWF-cp activity in the plasma of 64 children with either (d+) HUS (n = 41) or (d-) HUS (n = 23). RESULTS: In the acute phase of HUS, VWF-cp activity was normal (>50%) in 54 children and undetectable (<5%) in one (d+) HUS and in 6 (d-) HUS children. After a 3-month remission, the (d+) HUS patient recovered a 100% VWF-cp activity, and the 6 (d-) HUS patients kept an undetectable level. In these 6 (d-) HUS patients, the disease was characterized by a neonatal onset and several relapses (hemolytic anemia, thrombocytopenia, transient acute renal failure, cerebral ischemia), and sometimes the development of arterial hypertension or end stage renal failure. CONCLUSION: A subgroup of pediatric patients with atypical (d-) HUS, with hematologic symptoms starting at birth and a recurrent course progressively involving kidney and brain, is related to VWF-cp deficiency and actually corresponds to Upshaw-Schulman syndrome revisited as congenital TTP.