Infectiousness of pigs infected by the Porcine Reproductive and Respiratory Syndrome virus (PRRSV) is time-dependent

The time-dependent transmission rate of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) and the correlation between infectiousness, virological parameters and antibody responses of the infected pigs were studied in experimental conditions. Seven successive transmission trials involving a total of 77 specific pathogen-free piglets were carried out from 7 to 63 days post-inoculation (dpi). A semi-quantitative real time RT-PCR was developed to assess the evolution of the viral genome load in blood and nasal swabs from inoculated and contact pigs, with time. Virus genome in blood was detectable in inoculated pigs from 7 to 77 dpi, whereas viral genome shedding was detectable from nasal swabs from 2 to 48 dpi. The infectiousness of inoculated pigs, assessed from the frequency of occurrence of infected pigs in susceptible groups in each contact trial, increased from 7 to 14 dpi and then decreased slowly until 42 dpi (3, 7, 2, 1 and 0 pigs infected at 7, 14, 21, 28 and 42 dpi, respectively). These data were used to model the time-dependent infectiousness by a lognormal-like function with a latency period of 1 day and led to an estimated basic reproduction ratio, R₀ of 2.6 [1.8, 3.3]. The evolution of infectiousness was mainly correlated with the time-course of viral genome load in the blood whereas the decrease of infectiousness was strongly related to the increase in total antibodies.     

Antagonistic effect of indigenous skin bacteria of brook charr (Salvelinus fontinalis) against Flavobacterium columnare and F. psychrophilum

Industrial fish production exposes fish to potentially stressful conditions, which in turn may induce infections by opportunistic pathogens. Probiotics appear to be a promising way to prevent opportunistic infections in aquaculture. In this study, we tested the inhibitory potential of endogenous bacterial communities found in the mucus of brook charr (Salvelinus fontinalis) against two major pathogens Flavobacterium columnare and Flavobacterium psychrophilum. Nine bacterial strains were isolated from brook charr skin mucus and tested for potential antagonistic activity. Results from both agar diffusion assays and broth co-culture assays showed the presence of antagonism. We identified seven bacterial strains, collected from unstressed fish, which exerted strong antagonism against F. psychrophilum and/or F. columnare. These strains were mixed and used to treat columnaris disease in an in vivo experiment in which four distinct fish families were tested. This treatment resulted in a decrease of mortality (54-86%) across fish families indicating that candidates from the host microbiota are potentially suitable for probiotic development. This would allow for the efficient (ability to adhere and colonize the host mucus) and durable management (antagonistic effect against pathogens which would be harmless for the host and safe for its environment) of opportunistic diseases in aquaculture.     

Dietary traces of neonicotinoid pesticides as a cause of population declines in honey bees: an evaluation by Hill's epidemiological criteria

BACKGROUND: Honey bees are important pollinators of both crops and wild plants. Pesticide regimes that threaten their sustainability should therefore be assessed. As an example, evidence that the agricultural use of neonicotinoid pesticides is a cause of the recently observed declines in honey bees is examined. The aim is to define exacting demographic conditions for a detrimental factor to precipitate a population decline, and Hill's epidemiological ‘causality criteria’ are employed as a structured process for making an expert judgement about the proposition that trace dietary neonicotinoids in nectar and pollen cause population declines in honey bees. RESULTS: In spite of the absence of decisive experimental results, the analysis shows that, while the proposition is a substantially justified conjecture in the context of current knowledge, it is also substantially contraindicated by a wide variety of circumstantial epidemiological evidence. CONCLUSION: It is concluded that dietary neonicotinoids cannot be implicated in honey bee declines, but this position is provisional because important gaps remain in current knowledge. Avenues for further investigations to resolve this longstanding uncertainty are therefore identified. Copyright © 2012 Society of Chemical Industry     

Surgical endodontics in dogs: a review

Surgical endodontic therapy (apical surgery) is a treatment alternative aimed at removing periapical inflammatory tissue followed by apical resection and retro-filling of the root canal. These procedures are performed through a trans-osseous approach. Terminology pertinent to this article include: apical (periapical) curettage--a surgical procedure to remove diseased tissue from the alveolar bone in the apical region of a pulpless tooth; apical cyst--a cyst in bone at the apex of a pulpless tooth. It is believed that such cysts arise after the death of the pulp from noxious physical, chemical, or bacterial stimulation of epithelial rests of Malassez; apicoectomy (apical resection) amputation of the apical portion of the root and removal of soft tissue in the bone; epithelial rests of Malassez--cords, strands, or clusters of ectodermal cells in the periodontal ligament (or sometimes alveolar bone) derived from remnants of Hertwigs epithelial root sheath. These cells frequently begin proliferating when inflammation occurs in the periodontal ligament and are believed to be responsible for the genesis of the epithelial lining of apical cysts.     

Risk factors associated with fecal Salmonella shedding among hospitalized horses with signs of gastrointestinal tract disease

OBJECTIVE: To estimate prevalence of and identify risk factors for fecal Salmonella shedding among hospitalized horses with signs of gastrointestinal tract disease. DESIGN: Cross-sectional study. ANIMALS: 465 hospitalized horses with gastrointestinal tract disease. PROCEDURE: Horses were classified as positive or negative for fecal Salmonella shedding during hospitalization by means of standard aerobic bacteriologic methods. The relationship between investigated exposure factors and fecal Salmonella shedding was examined by means of logistic regression. RESULTS: The overall prevalence of fecal Salmonella shedding was 13%. Salmonella serotype Newport was the most commonly isolated serotype (12/60 [20%]), followed by Anatum (8/60 [13%]), Java (13%), and Saint-paul (13%). Foals with gastrointestinal tract disease were 3.27 times as likely to be shedding Salmonella organisms as were adult horses with gastrointestinal tract disease. Adult horses that had been treated with antimicrobial drugs prior to hospitalization were 3.09 times as likely to be shedding Salmonella organisms as were adult horses that had not been treated with antimicrobial drugs prior to hospitalization. Adult horses that underwent abdominal surgery were 2.09 times as likely to be shedding Salmonella organisms as were adult horses that did not undergo abdominal surgery. CONCLUSIONS AND CLINICAL RELEVANCE: Results suggest that a history of exposure to antimicrobial drugs prior to hospitalization and abdominal surgery during hospitalization were associated with Salmonella shedding in adult horses with gastrointestinal tract disease. Foals with gastrointestinal tract disease were more likely to shed Salmonella organisms than were adult horses with gastrointestinal tract disease.     

Familial aortic aneurysm in Leonberg dogs

A thoracic aortic aneurysm was diagnosed in a 6-month-old male Leonberg dog by use of radiography, transthoracic and transesophageal echocardiography, and magnetic resonance imaging. The aneurysm was associated with a twisted ascending aorta and dilatation of several other thoracic arteries (pulmonary trunk, brachiocephalic trunk, and left subclavian artery). Histologic examination of the aorta revealed cystic medial necrosis, with disruption of the elastic network, collagen fibers, and the muscle glycoprotein fibrillin-1. The dam and sire of the dog and 8 littermates were examined by use of transthoracic echocardiography. The sire and 1 male littermate also had an aneurysm of the ascending aorta. To the authors' knowledge, this is the first report of familial aortic aneurysm in dogs.     

Genetic isolation by distance and landscape connectivity in the American marten (Martes americana)

Empirical studies of landscape connectivity are limited by the difficulty of directly measuring animal movement. ‘Indirect’ approaches involving genetic analyses provide a complementary tool to ‘direct’ methods such as capture–recapture or radio-tracking. Here the effect of landscape on dispersal was investigated in a forest-dwelling species, the American marten (Martes americana) using the genetic model of isolation by distance (IBD). This model assumes isotropic dispersal in a homogeneous environment and is characterized by increasing genetic differentiation among individuals separated by increasing geographic distances. The effect of landscape features on this genetic pattern was used to test for a departure from spatially homogeneous dispersal. This study was conducted on two populations in homogeneous vs. heterogeneous habitat in a harvested boreal forest in Ontario (Canada). A pattern of IBD was evidenced in the homogeneous landscape whereas no such pattern was found in the near-by harvested forest. To test whether landscape structure may be accountable for this difference, we used effective distances that take into account the effect of landscape features on marten movement instead of Euclidean distances in the model of isolation by distance. Effective distances computed using least-cost modeling were better correlated to genetic distances in both landscapes, thereby showing that the interaction between landscape features and dispersal in Martes americana may be detected through individual-based analyses of spatial genetic structure. However, the simplifying assumptions of genetic models and the low proportions in genetic differentiation explained by these models may limit their utility in quantifying the effect of landscape structure.     

Textural Ordination Based on Fourier Spectral Decomposition: A Method to Analyze and Compare Landscape Patterns

We propose an approach to texture characterization and comparison that directly uses the information of digital images of the earth surface without requesting a prior distinction of structural ‘patches’. Digital images are partitioned into square ‘windows’ that define the scale of the analysis and which are submitted to the two-dimensional Fourier transform for extraction of a simplified textural characterization (in terms of coarseness) via the computation of a ‘radial’ power spectrum. Spectra computed from many images of the same size are systematically compared by means of a principal component analysis (PCA), which provides an ordination along a limited number of coarseness vs. fineness gradients. As an illustration, we applied this approach to digitized panchromatic air photos depicting various types of land cover in a semiarid landscape of northern Cameroon. We performed ‘textural ordinations’ at several scales by using square windows with sides ranging from 120 m to 1 km. At all scales, we found two coarseness gradients (PCA axes) based on the relative importance in the spectrum of large (> 50 km⁻¹), intermediate (30–50 km⁻¹), small (10–25 km⁻¹) and very small (<10 km⁻¹) spatial frequencies. Textural ordination based on Fourier spectra provides a powerful and consistent framework to identifying prominent scales of landscape patterns and to compare scaling properties across landscapes.