Infectious animal disease and its control

The control of infectious diseases in the main food-producing animals is considered and the main factors involved in the epizootiology of disease are presented. The properties of infectious agents and their natural history together with factors that influence the spread and development of disease are summarized. The factors in intensive animal husbandry that affect the occurrence of infectious disease and its control are considered. These include population density, population movement, management, hygiene and genetic constitution of the host. They encourage the appearance of new diseases, changes in the character of established diseases and the development of pathogenicity in infectious agents that were previously of no importance. Intensive animal husbandry has also increased the importance of multifactorial disease, which includes diseases that require more than one infectious agent or one or more infectious agents plus other factors for their cause. The methods of control of infectious disease currently available are described and the success and difficulties of their control on a global, national and local (farm or enterprise) basis are considered. Examples of diseases of global importance where national and world programmes of control and eradication have been of varying success are described. Examples of diseases that are enzootic throughout the world and the procedures used for their control are also described. The technological opportunities for the improvement of the control of infectious disease in the future are discussed. It is considered that developments in molecular biology and immunology will provide improvements in diagnostic tools and will revolutionize the development of animal resistance to disease and the production and use of vaccines.     

Comparative genomic assessment of Multi-Locus Sequence Typing: rapid accumulation of genomic heterogeneity among clonal isolates of <Emphasis Type="Italic">Campylobacter jejuni</Emphasis>

Background  

Multi-Locus Sequence Typing (MLST) has emerged as a leading molecular typing method owing to its high ability to discriminate among bacterial isolates, the relative ease with which data acquisition and analysis can be standardized, and the high portability of the resulting sequence data. While MLST has been successfully applied to the study of the population structure for a number of different bacterial species, it has also provided compelling evidence for high rates of recombination in some species. We have analyzed a set of Campylobacter jejuni strains using MLST and Comparative Genomic Hybridization (CGH) on a full-genome microarray in order to determine whether recombination and high levels of genomic mosaicism adversely affect the inference of strain relationships based on the analysis of a restricted number of genetic loci.     

A versatile transgenic allele for mouse overexpression studies

For the analysis of gene function in vivo, gene overexpression in the mouse provides an alternative to loss-of-function knock-out approaches and can help reveal phenotypes where compensatory mechanisms are at play. Furthermore, when multiple lines overexpressing a gene-of-interest at varying levels are studied, the consequences of differences in gene dosage can be explored. Despite these advantages, inherent shortcomings in the methodologies used for the generation of gain-of-function transgenic mouse models have limited their application to functional gene analysis, and the necessity for multiple lines comes at a significant animal and financial cost. The targeting of transgenic overexpression constructs at single copy into neutral genomic loci is the preferred method for the generation of such models, which avoids the unpredictable outcomes associated with conventional random integration. However, despite the increased reliability that targeted transgenic methodologies provide, only one expression level results, as defined by the promoter used. Here, we report a new versatile overexpression allele, the promoter-switch allele, which couples PhiC31 integrase-targeted transgenesis with Flp recombinase promoter switching and Cre recombinase activation. These recombination switches allow the conversion of different overexpression alleles, combining the advantages of transgenic targeting with tunable transgene expression. With this approach, phenotype severity can be correlated with transgene expression in a single mouse model, providing a cost-effective solution amenable to systematic gain-of-function studies.

     

Cell-wall lysing enzymes and products of cell-wall digestion elicit ethylene in citrus

Ethylene production was induced in Valencia oranges [ Citrus sinensis (L.) Osbcck] by injection of the fungal enzyme mixture Pectolyase ( Aspergillus japonicus ) which contains pectolytic enzymes into the peel. The mixture also stimulated production of 1-aminocyclopropane-1-carboxylic acid (ACC). Cycloheximide partially inhibited the Pectolyase-induced ethylene response. Pectin fragments, resulting from partial acid hydrolysis or Pectolyase digestion, caused an increase in ethylene production when injected into the peel of intact orange fruits. Pectic fragments produced by fungal enzymes are known to be elicitors of phytoalexins and in this study are shown to elicit ethylene in citurs.     

Observations on the fine structure of the baroreceptors and adrenergic innervation of the guinea-pig carotid sinus

We examined the fine structure of the baroreceptors and the adrenergic innervation of the guinea-pig carotid sinus. The tunica adventitia contained many nerve bundles whose perineuria enclosed unmyelinated nerve fibers, alone or together with myelinated nerve fibers. Baroreceptors, which lay close to elastic and collagen fibers in the adventitia and media, were surrounded by “terminal” cells with ultrastructural features characteristic of Schwann cells and contained inclusions of various types. Morphologic features of the baroreceptors included densely packed mitochondria, osmiophilic lamellated and homogeneous bodies, clear and granular vesicles, lamellar systems, glycogen granules, neurofilaments, neurotubuli, and vacuolated mitochondria. In animals that had been treated with 6-hydroxydopamine, occasional electrondense endings (or fibers) were observed in the adventitial layer. The baroreceptors in the guinea-pig carotid sinus appear to have most of the morphologic features reported for other species.     

Identification of chloroplast genome loci suitable for high‐resolution phylogeographic studies of Colocasia esculenta (L.) Schott (Araceae) and closely related taxa

Recently, we reported the chloroplast genome‐wide association of oligonucleotide repeats, indels and nucleotide substitutions in aroid chloroplast genomes. We hypothesized that the distribution of oligonucleotide repeat sequences in a single representative genome can be used to identify mutational hotspots and loci suitable for population genetic, phylogenetic and phylogeographic studies. Using information on the location of oligonucleotide repeats in the chloroplast genome of taro (Colocasia esculenta), we designed 30 primer pairs to amplify and sequence polymorphic loci. The primers have been tested in a range of intra‐specific to intergeneric comparisons, including ten taro samples (Colocasia esculenta) from diverse geographical locations, four other Colocasia species (C. affinis, C. fallax, C. formosana, C. gigantea) and three other aroid genera (represented by Remusatia vivipara, Alocasia brisbanensis and Amorphophallus konjac). Multiple sequence alignments for the intra‐specific comparison revealed nucleotide substitutions (point mutations) at all 30 loci and microsatellite polymorphisms at 14 loci. The primer pairs reported here reveal levels of genetic variation suitable for high‐resolution phylogeographic and evolutionary studies of taro and other closely related aroids. Our results confirm that information on repeat distribution can be used to identify loci suitable for such studies, and we expect that this approach can be used in other plant groups.