A. J. C. Cook

Survey of the prevalence of Salmonella species on commercial laying farms in the United Kingdom.

A survey of salmonella infection on 454 commercial layer flock holdings in the uk was carried out between October 2004 and September 2005. Fifty-four (11·7 per cent, 95 per cent confidence interval 9·3 to 14·0 per cent) were salmonella positive. The most common serovar identified was Salmonella Enteritidis at a prevalence of 5·8 per cent, and 70 per cent of these isolates were phage types 4, 6, 7 and 35. Salmonella Typhimurium was the second most prevalent serovar, found in 1·8 per cent of the farms. Of the three other serovars given top priority by the eu because of their public health significance, Salmonella Virchow and Salmonella Infantis were each isolated from one holding, but Salmonella Hadar was not isolated from any of the holdings. Analysis of antimicrobial resistance patterns revealed that over 76 per cent of the isolates were sensitive to all of the 16 drugs tested, and all the isolates were sensitive to ciprofloxacin, gentamicin, ceftazidime, apramycin, amikacin, amoxicillin/clavulanic acid, neomycin and cefotaxime.

Investigation of risk factors for Salmonella on commercial egg-laying farms in Great Britain, 2004–2005

In 2004/05, all European Union member states were required to carry out standardised prevalence surveys to establish the baseline prevalence of Salmonella in commercial laying flocks. As part of the survey in Great Britain, additional data were collected from 380 of the enrolled laying hen holdings to investigate risk factors for Salmonella at farm level. Stratified, simple random sampling was used to select holdings from which dust and boot swab samples were collected and tested for Salmonella using a modification of ISO 6579:2002. Using a multivariable logistic model weighted to account for the survey design, several factors significantly associated with Salmonella and Salmonella Enteritidis status were identified. Larger holdings (≥30,000 birds) were found to be at higher risk of Salmonella (odds ratio [OR] 4.79, P=0.025), while vaccination (OR 0.28, P=0.013), providing foot dips with brushes (OR 0.27, P=0.042), washing and disinfecting the house at depopulation (OR 0.19, P=0.003), having a clean car park away from house (OR 0.14, P=0.001), using an independent (OR 0.19, P=0.007) or other non-company (OR 0.40, P=0.049) source of feed, being over 1 km from the nearest neighbouring farm (OR 0.45, P=0.021) and the presence of cats and dogs on the farm (OR 0.26, P=0.002) or on contiguous farms (OR 0.44, P=0.030) reduced the risk of any Salmonella serovars being present. Factors found to be associated specifically with an increased risk of S Enteritidis infection included holding size (OR 14.88, P=0.001) and frequent sightings of rats (OR 8.17, P<0.001) or mice (OR 5.78, P=0.006). Non-caged systems (OR 0.14, P=0.002), vaccination (OR 0.08, P=0.001), the use of a non-company feed source (OR 0.11, P=0.003), running the site as all-in/all-out (OR 0.06, P<0.001) and the presence of cats and dogs on the farm (OR 0.14, P=0.002) were associated with a reduced risk.

Risk factors for Campylobacter colonisation during rearing of broiler flocks in Great Britain

We investigated the associations between Campylobacter colonisation and management practices and farm characteristics in 603 housed broiler batches originating from 137 farms in Great Britain. All study batches were the initial batch slaughtered from the selected house on enrolled farms. Between 1 and 15 batches were sampled from each farm throughout the study. A total of 34.2% of the batches was Campylobacter positive and multivariable multilevel logistic regression revealed that the risk of Campylobacter colonisation was highest in July (OR=3.4, CI95%:1.8; 6.4), August (OR=3.4, CI95%:1.9; 6.2) and September (OR=3.7, CI95%:1.9; 7.1). Cattle on or adjacent to the farm increased the risk (OR=1.7, CI95%:1.1; 2.7), whereas chlorinated drinking water reduced it (OR=0.5, CI95%:0.2; 0.9). If the first removed batch from the previous flock in the house had been Campylobacter positive, the first batch of the following flock was also more likely to be colonised (OR=3.2, CI95%:2.1; 4.9). This association was more likely due to a persistent risk practice or source of Campylobacter on the farm than a direct carry-over from previous flock.

Towards a standardised surveillance for Trichinella in the European Union.

Each year, more than 167 million pigs in the European Union (EU) are tested for Trichinella spp. under the current meat hygiene regulations. This imposes large economic costs on countries, yet the vast majority of these pigs test negative and the public health risk in many countries is therefore considered very low. This work reviewed the current Trichinella status across the EU as well as the national level of monitoring and reporting. It also reviewed which animal species were affected by Trichinella and in which species it should be surveyed. This information was used to design a cost-effective surveillance programme that enables a standardised monitoring approach within the EU. The proposed surveillance programme relies on identifying sub-populations of animals with a distinct risk. Low-risk pigs are finisher pigs that originate from so-called controlled housing. All other pigs are considered high-risk pigs. Controlled housing is identified by the application of a specific list of management and husbandry practices. We suggest that member states (MS) be categorised into three classes based on the confidence that Trichinella can be considered absent, in the specified sub-population of pigs above a specified design prevalence which we set to 1 per million pigs. A simple and transparent method is proposed to estimate this confidence, based on the sensitivity of the surveillance system, taking into account the sensitivity of testing and the design prevalence. The probability of detecting a positive case, if present, must be high (>95 or >99%) to ensure that there is a low or negligible risk of transmission to humans through the food chain. In MS where the probability of a positive pig is demonstrated to be negligible, testing of fattening pigs from a sub-population consisting of pigs from controlled housing can be considered unnecessary. Furthermore, reduced testing of finishers from the sub-population consisting of pigs from non-controlled housing might even be considered, if conducted in conjunction with a proportionate sampling scheme and a risk-based wildlife surveillance programme where applicable. The proposed surveillance programme specifies the required number of samples to be taken and found negative, in a MS. A MS with no data or positive findings will initially be allocated to class 1, in which all pigs should be tested. When a MS is able to demonstrate a 95% or 99% confidence that Trichinella is absent, the MS will be allocated to class 2 or 3, in which the testing requirement is lower than in class 1.

Longitudinal survey of the occurrence of Salmonella in pigs and the environment of nucleus breeder and multiplier pig herds in England

Eight pig breeding units previously associated with Salmonella Typhimurium were visited during a period of up to seven years. Samples from voided faeces, surfaces, fomites and wildlife were cultured. Certain serovars (Derby, Stanley, Give, Bredeney, Mbandaka and Manhattan) were isolated repeatedly on certain units, while others (Agona, Ajiobo, Heidelberg, Meleagridis, Muenchen, Montevideo, Rissen and Senftenberg) were detected only once or intermittently. Serovars Kedougou, Newport and Typhimurium were isolated consistently on some units but only intermittently on others. There was an association between the Salmonella serovar in pens and in the immediate environment of the pens. Pens holding breeding stock destined for production herds were frequently positive for Salmonella. Herds under common ownership showed similar serovar combinations. Serovars from wildlife were typical of the associated premises. Cleaning and disinfection was frequently ineffective. On one unit, a low level of Salmonella was attributed to a small herd size, good cleaning and disinfection, and good rodent control. Breeding herds are therefore susceptible to endemic infections with multiple Salmonella serovars, and cleaning, disinfection and vector control may be inadequate in many cases. The prevalence of S Typhimurium was greater in youngstock, which may have important implications for public health.

Survey of the prevalence of Salmonella on commercial broiler farms in the United Kingdom, 2005/06

Between October 2005 and September 2006, all European Union member states were required to carry out standardised surveys of the prevalence of Salmonella in broiler flock holdings to establish baseline data from which to derive national targets for disease reduction. In the uk 382 holdings were sampled, 41 of which were positive for Salmonella, giving an estimated weighted prevalence of 10·7 per cent (95 per cent confidence interval [ci] 8·1 to 13·1 per cent). The serotype most frequently isolated was Salmonella Ohio, with a weighted prevalence of 2·2 per cent (95 per cent ci 1·2 to 3·7 per cent), followed by Salmonella Kedougou at 1·7 per cent (95 per cent ci 0·9 to 3·2 per cent). There were no isolates of Salmonella Enteritidis and only a single isolation of Salmonella Typhimurium (0·2 per cent, 95 per cent ci 0·0 to 1·6 per cent). Of the three other serotypes given top priority by the eu owing to their public health significance, Salmonella Virchow was isolated from one holding, but Salmonella Hadar and Salmonella Infantis were not detected on any of the holdings.

Use of laboratory data to reduce the time taken to detect new diseases: VIDA to FarmFile.

The analysis of laboratory data can provide information about the health of livestock populations; in Great Britain the Veterinary Investigation Diagnosis Analysis (vida) system has provided such data since 1975. However vida covers only known diagnoses, with limited epidemiological characterisation. The unexpected outbreak of bse showed that it was necessary to improve surveillance to detect new diseases, and a necessary update of the vida database for the millennium date change provided the opportunity. The information required to enhance the value of laboratory data was identified, a new form and database, ‘FarmFile’, were designed to record it, and they began to be used in 1999. The detection of new diseases depends on making comparisons with the expected or ‘usual’ levels of unexplained disease. The data are analysed quarterly to assess any changes in the levels of unexplained disease in different species, categorised in terms of clinical sign or body system, by comparison with previous years. No new diseases have been detected either through FarmFile or more traditional means since the new analyses started in earnest in 2004, but they have indicated that an unexplained event was not a new disease of concern, and developments continue to improve the systems sensitivity and specificity.

Producing Salmonella-free pigs: a review focusing on interventions at weaning

Salmonella infection in pig production is typically endemic and largely asymptomatic. It is a cause of substantial concern among food safety bodies, prompting voluntary and legislative responses aimed at monitoring and reducing the number of Salmonella-infected animals entering the human food chain. Elimination of the problem at an early stage of production is highly desirable, and to this end the present review examines published evidence on the carriage of Salmonella by piglets before and after weaning, as well as evidence on the dynamics of Salmonella infection in the weaner and grower stages of pig production, the effects of maternal immunity, and risk factors for Salmonella excretion after weaning. Various interventions to reduce or eliminate Salmonella infection in young pigs have been tried, such as vaccination, competitive exclusion, treatments in feed and water, antibiotic administration, disinfection of animals, and segregated weaning to clean accommodation. The evidence on the effectiveness of these is considered, and the last is examined in some detail, as it appears currently to offer the best chance of eliminating Salmonella from growing stock.

Descriptive and social network analysis of pig transport data recorded by quality assured pig farms in the UK.

The aim of this study was to examine farm-to-farm pig movement connections, and the usage of hauliers and abattoirs, for farms in the United Kingdom (UK), to determine the interconnectivity of the pig farm network and the implications this may have for the transmission and control of Salmonella, which was chosen as an example of an important endemic disease. Data were collected from three Quality Assurance Schemes on the use of abattoirs and livestock hauliers by commercial pig farms, and the supply of pigs to and from farms. The observed dataset had considerable variability in the number of direct (farm-to-farm) and indirect (via hauliers or abattoirs) connections between each farm over a 12-month period. The use of multiple hauliers and abattoirs by many farms resulted in considerable interconnectivity between farms due to these indirect routes. The network displayed a higher level of clustering, and short network distances between farms, than that shown by equivalent randomly generated datasets, indicating that infectious diseases might transmit quickly amongst farms but within certain clusters of farms, thus limiting the total number of farms affected. This structure and the occurrence of multiple indirect routes between many pairs of farms (via pig movements to other interconnected farms or from hauliers used by both farms), may indicate that targeting surveillance and controls on those farms with high network centrality characteristics (degree, betweenness) alone would not prove effective. Encouraging all farms within the network to reduce the number of connections might be a useful way of reducing Salmonella prevalence as it would reduce the effect of high prevalence on other farms within the network. The analysis also highlighted differences in the connections between geographical regions that were used to discuss the comparatively low Salmonella prevalence in Scotland detected by previous studies. Farms identified as belonging to large companies, as categorised by our analysis, were shown to mostly have movement connections within that company. However, small company farms had connections to farms belonging to large companies or other small companies, demonstrating that they may play an important role in creating links between large companies. The majority of farms in both Scotland and North-East and Eastern England belonged to large companies, and this finding is discussed in relation to how this may help explain the lower Salmonella seroprevalence in these areas. The study provides a first description of the characteristics of the UK pig movement network and the analysis has indicated a number of findings that might have implications for disease transmission and targeting surveillance and control.

Review of diagnostic laboratory submissions of adult cattle ‘found dead’ in England and Wales in 2004

A total of 253 submissions from adult cattle ‘found dead’ in England and Wales were referred to the Veterinary Laboratories Agency in 2004. Carcases accounted for 54 per cent of the submissions and were of more diagnostic value than other types of sample. Whether the animals were beef or dairy, their distance from the laboratory and the number of deaths in the incident affected the likelihood of samples being submitted. The probability of reaching a diagnosis was influenced by the type of sample, the level of testing and the interval from sampling to receipt in the laboratory. Systemic disease was the most frequent cause of death in both dairy and beef cattle with hypomagnesaemia being the most frequent diagnosis (52 per cent) in beef cattle. In dairy cattle, 34 per cent of the diagnoses were for sporadic events, including haemorrhage and torsions of the digestive and reproductive tracts.