Evidence for nanocoulomb charges on spider ballooning silk.

We report on three launches of ballooning Erigone spiders observed in a 0.9m^{3} laboratory chamber, controlled under conditions where no significant air motion was possible. These launches were elicited by vertical, downward-oriented electric fields within the chamber, and the motions indicate clearly that negative electric charge on the ballooning silk, subject to the Coulomb force, produced the lift observed in each launch. We estimate the total charge required under plausible assumptions, and find that at least 1.15 nC is necessary in each case. The charge is likely to be nonuniformly distributed, favoring initial longitudinal mobility of electrons along the fresh silk during extrusion. These results demonstrate that spiders are able to utilize charge on their silk to attain electrostatic flight even in the absence of any aerodynamic lift.

Evidence for high levels of vertical transmission in Toxoplasma gondii.

Toxoplasma gondii is a highly ubiquitous and prevalent parasite. Despite the cat being the only definitive host, it is found in almost all geographical areas and warm blooded animals. Three routes of transmission are recognised: ingestion of oocysts shed by the cat, carnivory and congenital transmission. In natural populations, it is difficult to establish the relative importance of these routes. This paper reviews recent work in our laboratory which suggests that congenital transmission may be much more important than previously thought. Using PCR detection of the parasite, studies in sheep show that congenital transmission may occur in as many as 66% of pregnancies. Furthermore, in families of sheep on the same farm, exposed to the same sources of oocysts, significant divergent prevalences of Toxoplasma infection and abortion are found between different families. The data suggest that breeding from infected ewes increases the risk of subsequent abortion and infection in lambs. Congenital transmission rates in a natural population of mice were found to be 75%. Interestingly, congenital transmission rates in humans were measured at 19.8%. The results presented in these studies differ from those of other published studies and suggest that vertical transmission may be much more important than previously thought.

Evidence that primary infection of Charollais sheep with Toxoplasma gondii may not prevent foetal infection and abortion in subsequent lambings.

A study carried out on a sheep farm examined whether Toxoplasma gondii foetal infection and associated abortion occur in successive lambings. We identified 29 ewes that gave birth to lambs on at least 2 successive years over our study period, 2000-2003. Tissue samples from the progeny of these ewes were analysed by PCR to determine infection status with T. gondii. T. gondii-infected lambs were born in 31% of successive pregnancies. T. gondii-positive lambs were aborted in successive pregnancies in 21% of lambings during study period, 2000-2003. The frequency of successive abortions within this flock over the period 1992-2003 was 18%. If a lamb was congenitally infected there was a high risk (69%) that the successive lamb from that ewe would also be congenitally infected. Similarly, if a lamb was aborted there was a high risk (55%) of abortion in the next lamb produced. These data suggest that life-long immunity to T. gondii infections may not always be acquired following an initial infection and raises the question as to whether the mechanisms of T. gondii transmission prior to and during ovine pregnancies are fully understood.

Does vertical transmission contribute to the prevalence of toxoplasmosis?

Toxoplasma gondii is a ubiquitous parasite with a widespread distribution both in terms of geographical and host range. Although the definitive host is the cat, it is also a major health hazard to domestic animals and humans. Three routes of transmission are recognised (infection from the cat, carnivory and congenital transmission). We aimed to assess the relative importance of congenital transmission, using sheep as a model system, due to the lack of carnivory. We report, using PCR as a diagnostic tool, that congenital transmission occurs with high frequency (69%). If transmission from oocysts was important in sheep, we would expect sheep reared under the same environmental conditions (i.e. a single farm) to have a random distribution of Toxoplasma infection. Using breeding records in conjunction with PCR, some families were found to have high Toxoplasma prevalence and abortion while others were free of Toxoplasma infection and abortion (P < 0.01). This supports the notion that Toxoplasma may be transmitted vertically. In humans, we conducted a similar study and showed that Toxoplasma was transmitted from mother to baby in 19.8% of cases. Vertical transmission in Toxoplasma may be more important than previously thought and this knowledge should be considered in any eradication strategies.

The prevalence of Neospora caninum and co-infection with Toxoplasma gondii by PCR analysis in naturally occurring mammal populations.

Neospora caninum and Toxoplasma gondii are closely related intracellular protozoan parasites associated with bovine and ovine abortion respectively. Little is known about the extent of Neospora/Toxoplasma co-infection in naturally infected populations of animals. Using nested PCR techniques, based on primers from the Nc5 region of N. caninum and SAG1 for T. gondii, the prevalence of N. caninum and its co-infection with T. gondii were investigated in populations of Mus domesticus, Rattus norvegicus and aborted lambs (Ovis aries). A low frequency of infection with N. caninum was detected in the Mus domesticus (3%) and Rattus norvegicus (4.4%) populations. A relatively high frequency of infection with N. caninum was detected in the brains of aborted lambs (18.9%). There was no significant relationship between N. caninum and T. gondii co-infection. Investigation of the tissue distribution of Neospora, in aborted lambs, showed that Neospora could not be detected in tissues other than brain and this was in contrast to Toxoplasma where the parasite could be frequently detected in a range of tissues.

Significant familial differences in the frequency of abortion and Toxoplasma gondii infection within a flock of Charollais sheep.

A study was carried out to investigate the frequencies of abortion and congenital Toxoplasma gondii infection within 27 families (765 individuals) of a pedigree Charollais sheep flock maintained on a working farm in Worcestershire, UK, since 1992. Pedigree lambing records were analysed to establish the frequency of abortion for each family. The frequency of congenital infection was determined for each family by PCR analysis of tissue samples taken from newborn lambs. A total of 155 lambs were tested for congenital T. gondii infection, which were all born during the study period 2000-2003. Significant differences in the frequency of abortion between sheep families within this flock were observed with frequencies ranging between 0% and 48% (P < 0.01). Significantly different infection frequencies with T. gondii were also observed for different families and ranged between 0% and 100% (P<0.01). Although the actual cause of each abortion was not verified, a highly significant positive correlation was found to exist between the frequency of abortion and the frequency of T. gondii infection in the same families (P<0.01). The data presented here raise further questions regarding the significance of congenital transmission of T. gondii within sheep populations, the possible successive vertical transmission of T. gondii within families of sheep, and the potential role of inherited genetic susceptibility to abortion with respect to T. gondii infection. This work invites further study into the epidemiology of ovine toxoplasmosis and may have implications for sheep husbandry methods in the future.

High levels of congenital transmission of Toxoplasma gondii in longitudinal and cross-sectional studies on sheep farms provides evidence of vertical transmission in ovine hosts.

Recent research suggests that vertical transmission may play an important role in sustaining Toxoplasma gondii infection in some species. We report here that congenital transmission occurs at consistently high levels in pedigree Charollais and outbred sheep flocks sampled over a 3-year period. Overall rates of transmission per pregnancy determined by PCR based diagnosis, were consistent over time in a commercial sheep flock (69%) and in sympatric (60%) and allopatric (41%) populations of Charollais sheep. The result of this was that 53.7 % of lambs were acquiring an infection prior to birth: 46.4% of live lambs and 90.0% of dead lambs (in agreement with the association made between T. gondii and abortion). No significant differences were observed between lamb sexes. Although we cannot distinguish between congenital transmission occurring due to primary infection at pregnancy or reactivation of chronic infection during pregnancy, our observations of consistently high levels of congenital transmission over successive lambings favour the latter.

Can any ostrich fly?: some new data on belief bias in syllogistic reasoning.

According to one version of the mental models theory (Oakhill, J.V., Johnson-Laird, P.N., Garnham, A., 1989. Believability and syllogistic reasoning. Cognition 31, 117-140) beliefs exert their influence on reasoning in three ways. First they can affect the interpretation of the premises, for example by conversion. Second, they can curtail the search for alternative models of the premises, if an initial model supports a believable conclusion. Third, they can act as a filter on any conclusion that is eventually generated. This last influence is important in explaining the effects of belief bias in one-model syllogisms with no convertible premises, since such syllogisms, by definition, have no alternative models. However, the most natural interpretation of such a filter is that it filters out conclusions and leads to the response 'no valid conclusion'. The present study, which was conducted with groups of both British and Italian subjects, looked at the effect of prior knowledge on syllogistic reasoning, and showed that: (1) invalid conclusions for such one model syllogisms, either thematic or abstract, are typically not of the type 'no valid conclusion', but state invalid relations between the end terms; (2) belief-bias is completely suppressed when previous knowledge is incompatible with the premises, and therefore the premises themselves are always considered. The results are compatible with a version of the mental models theory in which a representation of prior knowledge precedes modelling of the premises, which are then incorporated into the representation of this knowledge. The relation between this theory and other accounts of belief bias in syllogistic reasoning, and the implications of these findings for reasoning more generally, are considered.

Comparative quinidine plasma profiles at steady state of two controlled-release products and quinidine sulfate in solution.

A study was conducted to compare, at steady state, the plasma quinidine level profiles of two commercial controlled-release products (quinidine sulfate controlled release and quinidine gluconate controlled release) with quinidine sulfate given in solution. Twenty-four healthy volunteers entered the study and 23 completed it. Quinidine formulations were given at 600 mg day-1 for 4 days in each of three periods in a randomized crossover study. In addition to frequent blood sampling on the fourth day of each period, samples were taken during the approach to steady state to confirm by minimum plasma concentrations (Cmin) that steady state had been attained. Quinidine concentrations were measured by using a high-performance liquid chromatographic assay specific for quinidine. The bioavailability of the two controlled-release products relative to quinidine sulfate in solution was adequate when dose correction to account for differences in quinidine base content was done. Without dose correction, the area under the plasma concentration-time curve (AUC) for the quinidine gluconate form was 85 per cent that of the solution: an amount equivalent to the relative actual amount of quinidine base in the quinidine gluconate dosage form. The maximum plasma concentration (Cmax), Cmin, peak-to-trough differences, and AUC from the quinidine sulfate extended-release form given 300 mg q12h were similar to the solution given 150 mg q6h. With dose correction, the quinidine gluconate controlled-release form given q12h had equivalent AUC but larger peak-to-trough differences than either the quinidine sulfate extended-release product given q12h or quinidine sulfate in solution given q6h.