Use of Akaike information criteria for model selection and inference. An application to assess prevention of gastrointestinal parasitism and respiratory mortality of Guinean goats in Kolda,Senegal

A field experiment was carried out in Kolda (southern Senegal) from July 1986 to July 1988. Its goals were to: (1) describe the patterns of mortality of female Guinean goats by age, season and year; (2) assess preventive measures against respiratory diseases and gastrointestinal parasitism in reducing mortality; and (3) estimate the overall impact of these measures on survival to 1 year of age. Preventive measures for respiratory disease included vaccination against peste des petits ruminants (PPR) and pneumonic pasteurellosis (Pasteurella multocida types A and D). Control of gastrointestinal parasites was by deworming does with morantel (7.5 mg kg⁻¹, three times during the rainy season). The effects of vaccines and deworming were tested in a randomised factorial field experiment with villages being the experimental units. A total of 19 villages, 113 goat herds and 1458 goats were included in the study.

Generalised linear models of survival for five cohorts of goats (defined by five different birth seasons) used a binomial assumption for the response distribution and a complementary log–log link. Explanatory variables included age, season, year, vaccination, deworming and their interactions. A complex a priori model was built on the basis of previous epidemiological knowledge; a purposively selected set of simpler models was compared to this full model by the Akaike information criterion (AIC) and derived statistics. Inference on 1-year survival and treatment effects accounted for model-selection uncertainty. It was carried out with a bootstrap procedure and used information from the whole set of selected models.

Large variations in mortality by year and season were observed but no regular seasonal pattern was apparent. Mortality probabilities of kids in dewormed groups decreased quickly after birth, but remained elevated up to 9 months of age in the non-dewormed groups. Deworming lowered the risk of mortality. Vaccination alone was not protective (except during an observed outbreak of PPR).     

Molecular characerization of the interaction between the fungal pathogen Cladosporium fulvum and tomato

The fungus Cladosprium fulvum is a biotrophic leaf pathogen of tomato. The fungus develops in the intercellular space without forming specialized feeding structures and does not affect the leaf tissue. The outcome of the C. fulvum-tomato interaction can be described by the gene-for-gene model. Failure of infection is expressed by a hypersensitive response. Two fungal proteins, ECP1 and ECP2, have been isolated and their corresponding genes have been cloned. In a compatible interaction including many physiological races ECP1 and ECP2 are highly produced and a role in pathogenicity is suggestive. The ecp1 gene shows some homology with tumor necrosis factor receptors (TNFRs) while the ecp2 gene shows no homology with sequences known in data bases. However, disruption of one of the two genes showed no reduced pathogenicity of the fungus. Two race-specific elicitors, AVR4 and AVR9, have been isolated and their corresponding genes have been cloned. The avirulence genes Avr4 and Avr9 are only present in C. fulvum avirulent on Cf-4 and Cf-9 cultivars, respectively. The expression of these two genes is, like the expression of the ecp genes, highly induced when the fungus grows in planta. Disruption of the Avr9 gene in wild type avirulent races leads to virulence on tomato genotypes carrying the complementary resistance gene Cf-9. A single base-pair change in the avirulence gene Avr4 leads to virulence on tomato genotypes carrying the Cf-4 resistance gene. Isolation, characterization and possible function of ECP1, ECP2, AVR4, and AVR9 will be discussed.     

Tuberculosis and brucellosis prevalence survey on dairy cattle in Mbarara milk basin (Uganda)

We determined the prevalence of tuberculosis and brucellosis reactors in the dairy herds in the Mbarara district of Uganda in 2002. This is one of the most important dairy-production areas of the country and includes both pastoral and agro-pastoral zones. A total of 340 (of 11,995) randomly selected herds were tested for tuberculosis, using the intradermal tuberculosis-skin test and 315 (of 10,562) herds tested for brucellosis using the serum Rose Bengal test.

The herd prevalence for tuberculosis reactors was 74.1% (95% confidence intervals 69, 78), the individual-animal prevalence was of 6.0% (5.6, 6.5) and within-herd range was 1–50% (up to 100% if suspicious reactors were included).

The herd prevalence for brucellosis was 55.6% (50, 61.2) individual-animal prevalence 15.8% (14.8, 16.7) and within-herd range 1–90%.

The reactor prevalence increased with the age of the animals for both tuberculosis and brucellosis.

Tuberculosis reactor prevalences were higher in animals from the agro-pastoral zone. However, the individual-animal and herd prevalences of brucellosis seroprevalences were higher in the pastoral zone.     

Within-herd spread of contagious bovine pleuropneumonia in Ethiopian highlands

Contagious bovine pleuropneumonia (CBPP) is a major threat for cattle health and production in Africa. This disease is caused by the small-colony type of Mycoplasma mycoides subspecies mycoides (MmmSC). Transmission occurs from direct and repeated contacts between sick and healthy animals. Veterinary services recently reported a resurgence of CBPP in the province of West Wellega, in the Ethiopian highlands. A research program was set up to estimate the epidemiological parameters of the within-herd infection spread. A follow-up survey was implemented in 71 sampled herds of the Boji district (West Wellega province). Fifteen herds were classified as newly infected and used in a serological- and clinical-incidence study. The overall 16-month cumulative sero-incidence risk was 34%. Clinical cases were recorded for 39% of the seropositive cattle; case-fatality risk was 13%. There was no evidence of benefit on infection spread of CBPP-control measures used locally by farmers (isolation or antibiotic treatments of sick animals). This might be related to a lack of power in the statistical analyses or to a quality problem for the medications used (and more generally, for health-care delivery in the Boji district).     

Organics captured from comet 81P/Wild 2 by the Stardust spacecraft

Organics found in comet 81P/Wild 2 samples show a heterogeneous and unequilibrated distribution in abundance and composition. Some organics are similar, but not identical, to those in interplanetary dust particles and carbonaceous meteorites. A class of aromatic-poor organic material is also present. The organics are rich in oxygen and nitrogen compared with meteoritic organics. Aromatic compounds are present, but the samples tend to be relatively poorer in aromatics than are meteorites and interplanetary dust particles. The presence of deuterium and nitrogen-15 excesses suggest that some organics have an interstellar/protostellar heritage. Although the variable extent of modification of these materials by impact capture is not yet fully constrained, a diverse suite of organic compounds is present and identifiable within the returned samples.     

Topography of the northern hemisphere of Mercury from MESSENGER laser altimetry

Laser altimetry by the MESSENGER spacecraft has yielded a topographic model of the northern hemisphere of Mercury. The dynamic range of elevations is considerably smaller than those of Mars or the Moon. The most prominent feature is an extensive lowland at high northern latitudes that hosts the volcanic northern plains. Within this lowland is a broad topographic rise that experienced uplift after plains emplacement. The interior of the 1500-km-diameter Caloris impact basin has been modified so that part of the basin floor now stands higher than the rim. The elevated portion of the floor of Caloris appears to be part of a quasi-linear rise that extends for approximately half the planetary circumference at mid-latitudes. Collectively, these features imply that long-wavelength changes to Mercury's topography occurred after the earliest phases of the planet's geological history.     

Dynamics of microcrack propagation in hardwood during heat treatment investigated by synchrotron-based X-ray tomographic microscopy

The process of crack propagation in wood during pyrolysis is strongly linked to heterogeneities in its hierarchical porous structure. Fundamental understanding of this process is necessary for the analysis of the behavior of wood structural elements during fire exposure. Synchrotron-based X-ray tomographic microscopy combined with a recently developed laser-based furnace at the TOMCAT beamline of the Swiss Light Source provides a unique opportunity to study the heat-induced propagation of microcracks in hardwood in situ with high spatial and temporal resolutions. In this study, attention was focused on the 3D microstructure of beech and the interconnectivity between morphology and cracking patterns. It is shown that thermal cracks initiate mainly along the ray cells in hardwood and in the junction of seasonal growth layers. There is a clear indication of increased total porosity of the wood due to charring.     

Towards a better understanding of Rift Valley fever epidemiology in the south-west of the Indian Ocean

Rift Valley fever virus (Phlebovirus, Bunyaviridae) is an arbovirus causing intermittent epizootics and sporadic epidemics primarily in East Africa. Infection causes severe and often fatal illness in young sheep, goats and cattle. Domestic animals and humans can be contaminated by close contact with infectious tissues or through mosquito infectious bites. Rift Valley fever virus was historically restricted to sub-Saharan countries. The probability of Rift Valley fever emerging in virgin areas is likely to be increasing. Its geographical range has extended over the past years. As a recent example, autochthonous cases of Rift Valley fever were recorded in 2007–2008 in Mayotte in the Indian Ocean. It has been proposed that a single infected animal that enters a naive country is sufficient to initiate a major outbreak before Rift Valley fever virus would ever be detected. Unless vaccines are available and widely used to limit its expansion, Rift Valley fever will continue to be a critical issue for human and animal health in the region of the Indian Ocean.     

Evaluation of 12-month interval methods for estimating animal-times at risk in a traditional African livestock farming system

Demographic parameters are useful for assessing productivity and dynamics of tropical livestock populations. Common parameters are the annual instantaneous hazard rates, which can be estimated by m/T (where m represents the number of the considered demographic events occurred during the year and T the cumulated animal-time at risk). Different approaches are encountered in the literature for computing T from on-farm survey data. One crude approach (“the 12-month interval approach”) only uses estimations of herds’ sizes at beginning and end of the year and aggregated counts of demographic events over the year. I evaluated the potential biases in using four 12-month interval methods (M1–M4) to estimate T. Biases were evaluated by comparing the 12-month estimates to gold-standard values of T. Data came from long-term herd monitoring on cattle and small ruminants in extensive agro-pastoral systems. Animal-times at risks were correctly estimated in average by methods M1, M2 and M4 (average relative biases <=6% in absolute values), except for adult-male small ruminants. For young animals, M2 and M4 showed equivalent biases. M2 is simple to implement and has the advantage of being applicable for any age-group, although M4 is only applicable for young animals. M3 was highly biased and I do not recommend it. Although accurate in average, 12-month interval methods showed highly variable biases. This variability results from interactions between the dates delimiting the 12-month interval and the distributions of the demographic events over time. This phenomenon is particularly important for the adult-male small ruminants. Based on the bias variability observed in the study, the user of 12-month interval methods has to remember that they only provide approximate results and that they cannot completely replace the gold-standard approaches.     

The Influence of a Particle Separation Technology on the Generation of Airborne Particles from Different Roughages and Bedding Materials Used for Horses

Four different types of bedding materials (wheat straw, wood shavings, hemp shives, flax shives) and two roughages (hay, haylage) were treated using an air-driven particle separation technology. The airborne particle and mold generation of both treated and untreated samples were then analyzed under standardized laboratory conditions. In addition, samples of all the treated materials were stored for 8 weeks either in a pressed or incoherent form and then analyzed again for their ability to generate airborne particles. The airborne particle concentrations were detected online with the gravimetrically measuring analyzer tapered element oscillating microbalance (TEOM) 1400a that was equipped successively with different inlets to measure the particle fractions PM₂₀, PM₁₀, PM_2.5, and PM_1.0 (PM = Particulate matter). The particle separation resulted in a reduction in the airborne particle (PM₂₀) generation in all materials: hay 49.16 to 22.79 mg/m³ (53.6%), haylage 28.57 to 25.04 mg/m³ (12.3%), wood shavings 141.68 to 15.04 mg/m³ (89.4%), wheat straw 143.08 to 22.97 mg/m³ (83.9%), flax 135.11 to 53.31 mg/m³ (60.5%), and hemp 63.67 to 17.64 mg/m³ (72.3%). The 8-week storage of the treated materials as compressed materials led to a renewed significant increase in the airborne particle (PM₁₀) concentration in the haylage (+29.9%), wheat straw (+104.0%), wood shavings (+40.4%), and hemp shives (+30.7%). Storage of the incoherent materials caused a significant increase in these particles only in the wheat straw (+44.2%). The separation treatment reduced the mold production by 92.4% in the wood shavings, 88.0% in the wheat straw, and 85.8% in the hay.