Robin Sayers

A longitudinal study of environmental salmonella contamination in caged and free-range layer flocks

The environmental contamination by salmonella was examined over a 12-month period in 74 commercial layer flocks from eight farms in the UK, which previously had been identified as being contaminated with salmonella. Samples of faeces, dust, litter, egg belt spillage and wildlife vectors were taken, plus swabs of cages, feeders, drinkers, floors, egg belts and boots. Some sampling was performed in each month of the year. Numerous serovars were detected but Salmonella enterica serotype Enteritidis was the only persistent serotype found among single-age flocks. There was a significant correlation between qualitative environmental samples and semi-quantitative faeces samples. The level of environmental contamination increased significantly over time. There were significant temperature and seasonal effects upon contamination. Wildlife vectors proved to be sensitive samples for the detection of salmonella. The efficacy of cleaning and disinfection upon residual salmonella contamination, and upon subsequent flock contamination, was highly variable between and within premises. The variability between detected prevalences over time and between flocks indicates a need for regular, sensitive monitoring of flocks for salmonella to permit targeting of control measures aimed at eliminating contamination of the layer environment by salmonella. There is substantial scope for improvement of cleaning and disinfection procedures.

Three serial passages of bovine spongiform encephalopathy in sheep do not significantly affect discriminatory test results.

During the 1980s, bovine spongiform encephalopathy (BSE)-contaminated meat and bonemeal were probably fed to sheep, raising concerns that BSE may have been transmitted to sheep in the UK. The human disease, variant Creutzfeldt-Jakob disease, arose during the BSE epidemic, and oral exposure of humans to BSE-infected tissues has been implicated in its aetiology. The concern is that sheep BSE could provide another source of BSE exposure to humans via sheep products. Two immunological techniques, Western immunoblotting (WB) and immunohistochemistry (IHC), have been developed to distinguish scrapie from cases of experimental sheep BSE by the characteristics of their respective abnormal, disease-associated prion proteins (PrP(d)). This study compares the WB and IHC characteristics of PrP(d) from brains of primary, secondary and tertiary experimental ovine BSE cases with those of cattle BSE and natural sheep scrapie. Discrimination between experimental sheep BSE and scrapie remained possible by both methods, regardless of the route of challenge.

Performance of TB immunodiagnostic tests in Eurasian badgers (Meles meles) of different ages and the influence of duration of infection on serological sensitivity

BackgroundIn parts of Great Britain and Ireland, Eurasian badgers (Meles meles) constitute a reservoir of Mycobacterium bovis infection and a potential source of infection for cattle. In vitro diagnostic tests for live badgers are an important component of strategies to control TB in this species. Immunological tests have been developed for badgers, although little is known about the influence of the age of the animal on test performance. To address this, we evaluated the performance of three immunological tests for badgers with respect to the age of the animal: the Brock Test and BrockTB STAT-PAK® serological tests and the recently developed interferon-gamma enzyme immunoassay (IFNγ EIA). Data published elsewhere suggested that seropositivity was associated with more progressive forms of TB in the badger. To gain further evidence for this, we used longitudinal data from a well-studied population of badgers to test for an association between the sensitivity of the Brock Test and the duration of TB infection.ResultsSensitivity of the two serological tests was approximately 54% for both cubs and adults. Sensitivity of the IFNγ EIA was lower in cubs (57%) compared with adults (85%) when a common cut-off value was used to define test positivity. Taking data from the cubs alone, the IFNγ EIA cut-off value could be adjusted to increase the sensitivity to 71% with no loss in specificity. As a general observation, specificity of all tests was higher in cubs, although only significantly so in the case of the Brock Test. Using logistic regression analysis to adjust for age, sensitivity of the Brock Test was significantly lower at first culture positive event (58%), but increased to >80% as infection progressed.ConclusionThese data suggest that serodiagnosis could be a valuable tool for detecting a higher proportion of badgers with the greatest probability of transmitting infection. The age category of the badger appeared to exert little influence on the performance of the serological tests. Although data were only available for the IFNγ EIA in a small number of cubs, reduced sensitivity of the test in these individuals suggests a lower cut-off may be needed when testing younger animals.

Assessment of anti-Salmonella activity of boot dip samples

The introduction of pathogens from the external environment into poultry houses via the boots of farm workers and visitors presents a significant risk. The use of boot dips containing disinfectant to help prevent this from happening is common practice, but the effectiveness of these boot dips as a preventive measure can vary. The aim of this study was to assess the anti-Salmonella activity of boot dips that are being used on poultry farms. Boot dip samples were collected from commercial laying hen farms in the UK and tested within 24 hours of receipt at the laboratory to assess their anti-Salmonella activity. All boot dip samples were tested against a field strain of Salmonella enterica serovar Enteritidis using three test models: pure culture, paper disc surface matrix and yeast suspension model. Of the 112 boot dip samples tested 83.6% were effective against Salmonella in pure culture, 37.3% in paper disc surface matrix and 44.5% in yeast suspension model. Numerous factors may influence the efficacy of the disinfectants. Disinfectants used in the dips may not always be fully active against surface or organic matter contamination; they may be inaccurately measured or diluted to a concentration other than that specified or recommended; dips may not be changed regularly or may have been exposed to rain and other environmental elements. This study showed that boot dips in use on poultry farms are frequently ineffective.

Simple objective measurement of the cutaneous delayed-type hypersensitivity reaction to tuberculin using spectrophotometry.

Background/aims:  A number of subjective methods have been used to quantify the extent of the cutaneous delayed‐type hypersensitivity (DTH) reaction. However, because of their subjective nature, significant differences in measurements may be seen between individual observers or laboratories unless thorough training is given to each observer.

Assessment of the anti-Salmonella activity of commercial formulations of organic acid products

Organic acid products are widely used in the UK poultry industry as feed or water additives. Claims for Salmonella control are made for some of these products, but there are few studies comparing the anti-Salmonella effect of the various products in tests that reflect field application. The present studies examined the effects of 13 commercial blends (four water products and nine feed products) on Salmonella Enteritidis and Typhimurium strains. Initial screening, in nutrient broth, of all products with all strains revealed little variation between strains in respect of maximum inhibitory and bactericidal dilutions of each product. However, between the products there was wide and significant variation in the maximum inhibitory and bactericidal dilutions, spanning a 700-fold range in the case of bactericidal dilutions for feed-associated products. Further tests were performed, examining reductions in inoculated Salmonella numbers in various matrices (water, feed, soiled litter, crop and caecal contents) following the addition of the products at recommended inclusion rates. One product, incorporating formaldehyde in addition to organic acid, was consistently most active in all matrices, exceeding reductions associated with other products by 1 to 3 log units at most time points. Many products showed only modest anti-Salmonella activity, amounting to 0 or 1 log unit above negative controls at many time points, and the most active products were not the same in all matrices. Tap water appeared to enhance the ability of products to reduce Salmonella, in comparison with bottled mineral or river water.

A review of the official sampling of flocks of laying hens in the Salmonella National Control Programme in Great Britain

Abstract 1. In line with European legislation and the UK National Control Programme for Salmonella, poultry farms are sampled to establish their Salmonella status. Regular samples are collected by the farmer (operator), with annual routine (official) samples being collected by the competent authority to verify achievement of the Salmonella programme reduction target. 2. To confirm sampling was being carried out effectively, a questionnaire-based survey was conducted. The aim was to identify any complicating factors the samplers encountered and the decisions made in these circumstances. 3. There was good compliance with the official sampling visits, with few delays reported. However, farm-specific clothing/separate boots for non-caged houses were rarely provided by the operator, whereas boot dips and hand washing facilities were usually available. The collection of dust was often a problem for official samplers, operator boot swabs were not always moistened before sampling and both sampler groups did not always follow the recommended method for the collection of faeces from belts and scrapers. 4. Overall, there was a good application of the sampling protocol, although a few areas for improvement were identified.