Sensitivity testing of trypanosome detection by PCR from whole blood samples using manual and automated DNA extraction methods.

Automated extraction of DNA for testing of laboratory samples is an attractive alternative to labour-intensive manual methods when higher throughput is required. However, it is important to maintain the maximum detection sensitivity possible to reduce the occurrence of type II errors (false negatives; failure to detect the target when it is present), especially in the biomedical field, where PCR is used for diagnosis. We used blood infected with known concentrations of Trypanosoma copemani to test the impact of analysis techniques on trypanosome detection sensitivity by PCR. We compared combinations of a manual and an automated DNA extraction method and two different PCR primer sets to investigate the impact of each on detection levels. Both extraction techniques and specificity of primer sets had a significant impact on detection sensitivity. Samples extracted using the same DNA extraction technique performed substantially differently for each of the separate primer sets. Type I errors (false positives; detection of the target when it is not present), produced by contaminants, were avoided with both extraction methods. This study highlights the importance of testing laboratory techniques with known samples to optimise accuracy of test results.

Social networks and the spread of Salmonella in a sleepy lizard population.

Although theoretical models consider social networks as pathways for disease transmission, strong empirical support, particularly for indirectly transmitted parasites, is lacking for many wildlife populations. We found multiple genetic strains of the enteric bacterium Salmonella enterica within a population of Australian sleepy lizards (Tiliqua rugosa), and we found that pairs of lizards that shared bacterial genotypes were more strongly connected in the social network than were pairs of lizards that did not. In contrast, there was no significant association between spatial proximity of lizard pairs and shared bacterial genotypes. These results provide strong correlative evidence that these bacteria are transmitted from host to host around the social network, rather than that adjacent lizards are picking up the same bacterial genotype from some common source.

Seasonal and spatial dynamics of ectoparasite infestation of a threatened reptile, the tuatara (Sphenodon punctatus).

The conservation of threatened vertebrate species and their threatened parasites requires an understanding of the factors influencing their distribution and dynamics. This is particularly important for species maintained in conservation reserves at high densities, where increased contact among hosts could lead to increased rates of parasitism. The tuatara (Sphenodon punctatus) (Reptilia: Sphenodontia) is a threatened reptile that persists at high densities in forests (approximately 2700 tuatara/ha) and lower densities in pastures and shrubland (< 200 tuatara/ha) on Stephens Island, New Zealand. We investigated the lifecycles and seasonal dynamics of infestation of two ectoparasites (the tuatara tick, Amblyomma sphenodonti, and trombiculid mites, Neotrombicula sp.) in a mark-recapture study in three forest study plots from November 2004 to March 2007, and compared infestation levels among habitat types in March 2006. Tick loads were lowest over summer and peaked from late autumn (May) until early spring (September). Mating and engorgement of female ticks was highest over spring, and larval tick loads subsequently increased in early autumn (March). Nymphal tick loads increased in September, and adult tick loads increased in May. Our findings suggest the tuatara tick has a 2- or 3-year lifecycle. Mite loads were highest over summer and autumn, and peaked in March. Prevalences (proportion of hosts infected) and densities (estimated number of parasites per hectare) of ticks were similar among habitats, but tick loads (parasites per host) were higher in pastures than in forests and shrub. The prevalence and density of mites was higher in forests than in pasture or shrub, but mite loads were similar among habitats. We suggest that a higher density of tuatara in forests may reduce the ectoparasite loads of individuals through a dilution effect. Understanding host-parasite dynamics will help in the conservation management of both the host and its parasites.

Properties of rat kidney glutaminase enzymes and their role in renal ammoniagenesis.

Rat kidney contains two distinct glutaminase activities; the mitochondrial phosphate-dependent glutaminase and a second glutaminase activity associated with the brush border membrane which is maleate-activated and phosphate-independent. It has recently been shown that the phosphate-independent glutaminase is a partial reaction of gamma-glutamyl transpeptidase and that maleate activates this enzyme by blocking transpeptidation. The gamma-glutamyl transpeptidase in other rat tissues is also affected by maleate. This enzyme has at least a 100-fold greater affinity for glutathione or for glutathione derivatives than for glutamine, suggesting that under physiological conditions glutathione is the preferred substrate. With either type of substrate, maleate affects the Vmax of the reaction but not the Km. These findings suggest that this enzyme probably contributes very little to renal ammoniagenesis. In contrast, the phosphate-dependent glutaminase, whose activity increases 20 to 30-fold in the proximal convoluted tubule cells in response to metabolic acidosis, probably contributes significantly to renal ammoniagenesis. We have purified the rat kidney phosphate-dependent glutaminase and compared the phosphate activation and the phosphate-induced dimerization of the Tris form of this enzyme. There is an excellent correlation between increased activity and extent of dimerization as phosphate concentration is increased. The molecular weights of the Tris form are 1600000 and 316000 in the absence and presence of -1 M NaPO4, respectively. At saturating concentration of phosphate, increasing concentrations of chloride ion similarly reverse both activation and dimerization. These observations suggest that only the dimer form of the Tris enzyme is active.