Surveillance and control of asymptomatic carriers of drug‐resistant bacteria

Drug‐resistant bacterial infections constitute a major threat to global public health. Several key bacteria that are becoming increasingly resistant are among those that are ubiquitously carried by human beings and usually cause no symptoms (i.e. individuals are asymptomatic carriers) until and/or unless a precipitating event leads to symptomatic infection (and thus disease). Carriers of drug‐resistant bacteria can also transmit resistant pathogens to others, thus putting the latter at risk of resistant infections. Accumulating evidence suggests that such transmission occurs not only in hospital settings but also in the general community, although considerably more data are needed to assess the extent of this problem. Asymptomatic carriage of drug‐resistant bacteria raises important ethical questions regarding the appropriate public health response, including the degree to which it would be justified to impose burdens on asymptomatic carriers (and others) in order to prevent transmission. In this paper, we (i) summarize current evidence regarding the carriage of key drug‐resistant bacteria, noting important knowledge gaps; and (ii) explore the particular implications of existing public health ethics frameworks for policy‐making regarding asymptomatic carriers. Inter alia, we argue that the relative burdens imposed by public health measures on healthy carriers (as opposed to sick individuals) warrant careful consideration and should be proportionate to the expected public health benefits in terms of risks averted. We conclude that more surveillance and research regarding community transmission will be needed in order to clarify relevant risks and design proportionate policies, although extensive community surveillance itself would also require careful ethical consideration.     

Ecdysteroid production during caste differentiation in larvae of the ant, Plagiolepis pygmaea

ABSTRACT. Variations in ecdysteroids were measured by radio-immunoassay in worker-biased and queen-biased larvae of the ant Plagiolepis pygmaea Latr. (Hymenoptera, Formicidae) during late larval development, i.e. from the end of winter diapause up to the prepupal period. At the end of diapause, larvae are bipotential and, depending on culture conditions, can become either queens or workers. Ecdysteroid profiles revealed that there are striking differences between the two castes: worker larvae showed high titres during their development, queen larvae had low titres over the same period.     

Oocyte growth.

The main elements of reproduction are exposed with emphasis on its preparation during the larval stage. The system oocyte-nurse cells-follicular cells is described and the principal features of egg morphogenesis are indicated. Two types of problems are concentrated on : 1) sequential determination of growth and evolution of the follicle in the ovarian tube, 2) morphological and biochemical aspects of chorion formation. Variation in the functioning of the oocyte's morphogenetic system is explored with discussion of the role of larval alimentation, temperature, hormonal environment and genetic factors.     

Layers of contingency shroud pervasive ecological divergence in a local radiation of land snails

The predictability of evolution depends on the roles that selection and historical contingency play in determining its outcomes, but the relative importance of these evolutionary mechanisms has attracted considerable debate. One view is that historical events have such a profound impact on the genetic structure of populations that patterns of phenotypic evolution are essentially unpredictable. The opposing view is that selection is so powerful that evolutionary change is primarily deterministic, and thus highly predictable. By controlling for the effects of phylogeny, geographic location and habitat, this study examined the relative roles of contingency and determinism in a local radiation of land snails, genus Rhagada, in a continental archipelago. Informed by previous studies on a single island, which revealed a strong association between low‐spired shells and rocky habitats, 28 population pairs were sampled in directly adjoining rocky and spinifex plain habitats. When considered in their respective pairs, the effect of habitat was remarkably consistent, with lower‐spired shells observed in the rocky habitat in 24 of the comparisons. However, when analyzed outside the context of those pairs, the association was obscured by broad variation in shell shape within habitat types and among lineages. These results reveal the complex nature of a morphological radiation; while the pattern of ecological divergence is highly predictable at the scale that selection acts, deterministic evolution is largely obscured by phylogenetic and population history.