Herd immunity to helminth infection and implications for parasite control

Despite much research on immunological responses to helminth parasites, knowledge of the dynamic interplay between levels of herd immunity in humans and the rates of exposure, establishment and mortality of parasites remains limited. We describe here a simple mathematical model for the population dynamics of helminth infections which mirrors the development of a degree of acquired immunity within populations which are genetically heterogeneous with respect to immunological responsiveness. We interpret observed patterns in the age-specific intensity of infection and attempt to understand the possible effects of control measures based on chemotherapy and vaccination. Mass chemotherapy can, in some circumstances, reduce the level of herd immunity such that average worm burdens in the adult age classes rise above their precontrol levels. When certain individuals or groups are predisposed to heavy infection, selective or targeted drug treatment can have significantly greater impact than mass or random application. Conversely, model predictions suggest that effective parasite control by vaccination (if and when vaccines become available) is difficult to achieve in communities that are genetically heterogeneous in their ability to mount protective responses to infection.     

Adhesion molecules and animal development

In recent years considerable progress has been made in the identification and characterization of molecules that mediate cell adhesion during animal development. This review attempts to pick out from the vast amount of information in this rapidly expanding field some of the key features of adhesion molecules, to present ideas about their role in development, and to indicate the directions in which the field is now moving.     

Fluorescing valvular nerves in the guinea-pig heart

Résumé Des plexus fluorescents de nerfs dans les valvules du cur du Cobaye sont décrits. Bien que du tissu musculaire et des nerfs cholinergiques fussent présents dans les valvules atrioventriculaires, les nerfs adrénergiques de la valvule pulmonaire ne se rapportaient qu'au tissu connectif fibreux. Puisque dans cette situation il n'y a pas d'emplacement effecteur évident ou que ces nerfs influencement des nerfs dont la présence n'est pas révélée par des techniques de cholinesterase ou qu'ils sont de caractère afférent.

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Acknowledgment. The author thanks Prof.G. A. G. Mitchell for his continued interest.     

Selection at the Adh locus inDrosophila melanogaster: Adult survivorship-mortality in response to ethanol

Summary Functionally significant biochemical properties of the naturally occurring electrophoretic variants at the Adh locus (ADH^fast and ADH^Slow) are correlated with the adult flies' ability to utilize and survive in an ethanol environment. The results are consistent with the idea that an environmentally dependent form of balancing selection is responsible, at least in part, for the maintenance of the polymorphism at this locus.Acknowledgment. This work was supported by NSF grant DEB 7815466 to J.M.