The impact of accuracy and precision of analytical test methods on the determination of withdrawal periods.

Treatment of food-producing animals with veterinary medicinal products (VMPs) can result in residues in foodstuffs (e.g. eggs, meat, milk, or honey) representing a potential consumer health risk. To ensure consumer safety, worldwide regulatory concepts for setting safe limits for residues of VMPs e.g. as tolerances (US) or maximum residue limits (MRLs, EU) are used. Based on these limits so-called withdrawal periods (WP) are determined. A WP represents the minimum period of time required between the last administration of the VMP and the marketing of foodstuff. Usually, WPs are estimated using regression analysis based on residue studies. With high statistical confidence (usually 95% in the EU and 99% in the US) the residues in almost all treated animals (usually 95%) have to be below MRL when edible produce is harvested. Here, uncertainties from both sampling and biological variability are taken into account but uncertainties of measurement associated with the analytical test methods are not systematically considered. This paper describes a simulation experiment to investigate the extent to which relevant sources of measurement uncertainty (accuracy and precision) can impact the length of WPs. A set of real residue depletion data was artificially 'contaminated' with measurement uncertainty related to permitted ranges for accuracy and precision. The results show that both accuracy and precision had a noticeable effect on the overall WP. Due consideration of sources of measurement uncertainty may improve the robustness, quality and reliability of calculations upon which regulatory decisions on consumer safety of residues are based.

Multiple host feeding in Glossina palpalis gambiensis and Glossina tachinoides in southeast Mali.

Changes in agricultural practices and the resulting extinction of wildlife have led to the reduction or disappearance of savannah tsetse species. Riparian tsetse such as Glossina palpalis gambiensis Vanderplank 1949 and Glossina tachinoides Westwood 1850 (Diptera: Glossinidae) continue to persist in peridomestic sites, transmitting trypanosomiasis. At present, little is known about interspecies differences in feeding behaviour in these two species in southeast Mali, or of the phenomenon of multiple bloodmeals. To study these topics, 279 samples of G. p. gambiensis and G. tachinoides containing host DNA, caught in the Sikasso region between November 2008 and April 2009, were analysed by applying host species-specific primers and sequencing. Human accounted for > 66% of G. p. gambiensis bloodmeals, whereas G. tachinoides contained in equal parts DNA of human, cattle or both, showing a significantly higher proportion of multiple host use. Further, the trypanosome infection rate was found to be three-fold higher in G. tachinoides. Logistic regression analysis revealed double-feeding and infection to be independent of one another, but showed infection to be correlated with engorgement in G. p. gambiensis and female sex in G. tachinoides. Enhanced host-seeking activities paired with the high trypanosome infection rate found in G. tachinoides would indicate that this species has a higher vectorial capacity than G. p. gambiensis.

Night-to-night variation of the oxygen desaturation index in sleep apnoea syndrome.

The current study investigated the night-to-night variability and diagnostic accuracy of the oxygen desaturation index (ODI), as measured by ambulatory monitoring, in the diagnosis of mild and moderate obstructive sleep apnoea-hypopnoea syndrome. To assess the variability of the ODI, 35 patients were monitored at home during 7 consecutive nights by means of a portable recording device, the MESAM-IV. The ODI variability factor and the influence of age, body mass index (BMI), alcohol, and body position were assessed. Furthermore, the diagnostic accuracy of the MESAM-IV was measured by comparison with polysomnographical outcomes in 18 patients. During home recording, the median ODI was 10.9 (interquartile range: 5.8-16.1) across the patients. Although the reliability of the ODI was adequate, the probability of placing the patient in the wrong severity category (ODI < or =15 or ODI >15) when only one single recording was taken is 14.4%. ODI variability was not significantly influenced by age, BMI, time spent in a supine position, or mild dosages of alcohol. A good correlation was found between the apnoea-hypopnoea index and the ODI. In conclusion, the findings suggest that the diagnostic accuracy of the MESAM-IV is strong, since the oxygen desaturation index is correlated with the apnoea-hypopnoea index. In most obstructive sleep apnoea-hypopnoea syndrome patients, oxygen desaturation index variability is rather small, and screening could be reliably based on single 1-night recordings.

Correlations among amino acid sites in bHLH protein domains: an information theoretic analysis.

An information theoretic approach is used to examine the magnitude and origin of associations among amino acid sites in the basic helix-loop-helix (bHLH) family of transcription factors. Entropy and mutual information values are used to summarize the variability and covariability of amino acids comprising the bHLH domain for 242 sequences. When these quantitative measures are integrated with crystal structure data and summarized using helical wheels, they provide important insights into the evolution of three-dimensional structure in these proteins. We show that amino acid sites in the bHLH domain known to pack against each other have very low entropy values, indicating little residue diversity at these contact sites. Noncontact sites, on the other hand, exhibit significantly larger entropy values, as well as statistically significant levels of mutual information or association among sites. High levels of mutual information indicate significant amounts of intercorrelation among amino acid residues at these various sites. Using computer simulations based on a parametric bootstrap procedure, we are able to partition the observed covariation among various amino acid sites into that arising from phylogenetic (common ancestry) and stochastic causes and those resulting from structural and functional constraints. These results show that a significant amount of the observed covariation among amino acid sites is due to structural/functional constraints, over and above the covariation arising from phylogenetic constraints. These quantitative analyses provide a highly integrated evolutionary picture of the multidimensional dynamics of sequence diversity and protein structure.

Positional dependence, cliques, and predictive motifs in the bHLH protein domain.

Quantitative analyses were carried out on a large number of proteins that contain the highly conserved basic helix-loop-helix domain. Measures derived from information theory were used to examine the extent of conservation at amino acid sites within the bHLH domain as well as the extent of mutual information among sites within the domain. Using the Boltzmann entropy measure, we described the extent of amino acid conservation throughout the bHLH domain. We used position association (pa) statistics that reflect the joint probability of occurrence of events to estimate the "mutual information content" among distinct amino acid sites. Further, we used pa statistics to estimate the extent of association in amino acid composition at each site in the domain and between amino acid composition and variables reflecting clade and group membership, loop length, and the presence of a leucine zipper. The pa values were also used to describe groups of amino acid sites called "cliques" that were highly associated with each other. Finally, a predictive motif was constructed that accurately identifies bHLH domain-containing proteins that belong to Groups A and B.

Molecular marker based taxonomy and phylogeny of Guinea yam (Dioscorea rotundata - D. cayenensis).

Four different molecular techniques were used to assess relationships among 21 accessions of Guinea yam (Dioscorea rotundata and Dioscorea cayenensis) and 21 accessions belonging to seven putative progenitor species. Random amplified polymorphic DNA (RAPD) and microsatellite-primed PCR (MP-PCR) analysis yielded 246 informative characters that were transformed into a matrix of pairwise distances and analyzed by neighbor joining or split decomposition. Both methods gave congruent results. Well-separated groups were formed that corresponded to their species designation. Dioscorea rotundata and D. cayenensis accessions were clearly separated from each other, supporting the concept that both are distinct species. Two morphological intermediates grouped together with D. rotundata. All investigated species fell into two main clusters, one comprising D. rotundata, D. cayenensis, Dioscorea abyssinica, Dioscorea liebrechtsiana, and Dioscorea praehensilis, the other comprising Dioscorea smilacifolia, Dioscorea minutiflora, Dioscorea burkilliana, and Dioscorea togoensis. The same grouping was also obtained by comparative sequence analysis of chloroplast DNA, which supports earlier studies of nuclear rDNA variation and chloroplast restriction fragment length polymorphisms. We also analyzed the same set of Dioscorea samples with the recently developed random amplified microsatellite polymorphism (RAMPO) technique. A series of diagnostic RAMPO bands was identified that clearly distinguished between D. rotundata and D. cayenensis. Some of these bands could also be traced back to the putative progenitors of both species. The evolutionary origin of Guinea yam is discussed in light of the present results.