Survival and transmission of Salmonella enterica serovar typhimurium in an outdoor organic pig farming environment

Investigation of Salmonella, hepatitis E virus (HEV) and viral indicators of fecal contamination in four Italian pig slaughterhouses, 2021-2022

In the pork production chain, the control at slaughterhouse aims to ensure safe food thanks to proper hygienic conditions during all steps of the slaughtering. Salmonella is one of the main foodborne pathogens in the EU causing a great number of human cases, and pigs also contribute to its spreading. Pig is the main reservoir of the zoonotic hepatitis E virus (HEV) that can be present in liver, bile, feces and even rarely in blood and muscle. The aim of this study was to assess the presence of both Salmonella and HEV in several points of the slaughtering chain, including pig trucks. Other viruses hosted in the gut flora of pigs and shed in feces were also assayed (porcine adenovirus PAdV, rotavirus, norovirus, and mammalian orthoreovirus MRV). Torque teno sus virus (TTSuV) present in both feces, liver and blood was also considered. Four Italian pig abattoirs were sampled in 12 critical points, 5 of which were the outer surface of carcasses before processing. HEV and rotavirus (RVA) were not detected. Norovirus was detected once. Salmonella was detected in two of the 4 abattoirs: in the two lairage pens, in the site of evisceration and on one carcass, indicating the presence of Salmonella if carcass is improper handled. The sampling sites positive for Salmonella were also positive for PAdV. MRV was detected in 10 swabs, from only two abattoirs, mainly in outer surface of carcasses. TTSuV was also detected in all abattoirs. Our study has revealed a diverse group of viruses, each serving as indicator of either fecal (NoV, RVA, PAdV, MRV) or blood contamination (TTSuV). TTSuV could be relevant as blood contamination indicators, crucial for viruses with a viremic stage, such as HEV. The simultaneous presence of PAdV with Salmonella is relevant, suggesting PAdV as a promising indicator for fecal contamination for both bacterial and viruses. In conclusion, even in the absence of HEV, the widespread presence of Salmonella at various points in the chain, underscores the need for vigilant monitoring and mitigation strategies which could be achieved by testing not only bacteria indicators as expected by current regulation, but also some viruses (PAdV, TTSuV, MRV) which could represent other sources of fecal contamination.

Salmonellosis: An Overview of Epidemiology, Pathogenesis, and Innovative Approaches to Mitigate the Antimicrobial Resistant Infections

Salmonella is a major foodborne pathogen and a leading cause of gastroenteritis in humans and animals. Salmonella is highly pathogenic and encompasses more than 2600 characterized serovars. The transmission of Salmonella to humans occurs through the farm-to-fork continuum and is commonly linked to the consumption of animal-derived food products. Among these sources, poultry and poultry products are primary contributors, followed by beef, pork, fish, and non-animal-derived food such as fruits and vegetables. While antibiotics constitute the primary treatment for salmonellosis, the emergence of antibiotic resistance and the rise of multidrug-resistant (MDR) Salmonella strains have highlighted the urgency of developing antibiotic alternatives. Effective infection management necessitates a comprehensive understanding of the pathogen's epidemiology and transmission dynamics. Therefore, this comprehensive review focuses on the epidemiology, sources of infection, risk factors, transmission dynamics, and the host range of Salmonella serotypes. This review also investigates the disease characteristics observed in both humans and animals, antibiotic resistance, pathogenesis, and potential strategies for treatment and control of salmonellosis, emphasizing the most recent antibiotic-alternative approaches for infection control.

Veterinary bacteriology in Denmark from the 1880s to 2022

This paper gives an account of the history of veterinary bacteriology including clinical veterinary bacteriology as well as the area of veterinary public health in Denmark from the 1880s to 2022. We describe key persons, including B. Bang, C.O. Jensen, K.A. Jensen and others who made important contributions to the development of these areas of microbiological expertise, and we discuss how challenges ranging from bovine tuberculosis to bacterial antimicrobial resistance have been met. Further, we describe progress in research on important bacterial pathogens both with regard to animal clinical aspects and zoonotic food-related aspects. Finally, we describe current issues in relation to One Health and research organization.

Salmonella Infection in Pigs: Disease, Prevalence, and a Link between Swine and Human Health

Salmonella is one of the most spread foodborne pathogens worldwide, and Salmonella infections in humans still represent a global health burden. The main source of Salmonella infections in humans is represented by contaminated animal-derived foodstuffs, with pork products being one of the most important players. Salmonella infection in swine is critical not only because it is one of the main causes of economic losses in the pork industry, but also because pigs can be infected by several Salmonella serovars, potentially contaminating the pig meat production chain and thus posing a significant threat to public health globally. As of now, in Europe and in the United States, swine-related Salmonella serovars, e.g., Salmonella Typhimurium and its monophasic variant Salmonella enterica subsp. enterica 1,4,[5],12:i:-, are also frequently associated with human salmonellosis cases. Moreover, multiple outbreaks have been reported in the last few decades which were triggered by the consumption of Salmonella-contaminated pig meat. Throughout the years, changes and evolution across the pork industry may have acted as triggers for new issues and obstacles hindering Salmonella control along the food chain. Gathered evidence reinforces the importance of coordinating control measures and harmonizing monitoring programs for the efficient control of Salmonella in swine. This is necessary in order to manage outbreaks of clinical disease in pigs and also to protect pork consumers by controlling Salmonella subclinical carriage and shedding. This review provides an update on Salmonella infection in pigs, with insights on Salmonella ecology, focusing mainly on Salmonella Choleraesuis, S. Typhimurium, and S. 1,4,[5],12:i:-, and their correlation to human salmonellosis cases. An update on surveillance methods for epidemiological purposes of Salmonella infection in pigs and humans, in a "One Health" approach, will also be reported.

Evaluation of Disinfectant Efficacy against Biofilm-Residing Wild-Type Salmonella from the Porcine Industry

Salmonella enterica is a causative pathogen of Salmonellosis, a zoonosis causing global disease and financial losses every year. Pigs may be carriers of Salmonella and contribute to the spread to humans and food products. Salmonella may persist as biofilms. Biofilms are bacterial aggregates embedded in a self-produced matrix and are known to withstand disinfectants. We studied the effect of glutaraldehyde and peracetic acid, two active substances frequently used in disinfectant formulations in the pig industry, on representative biofilm-residing wild-type Salmonella collected from pig housings in the United Kingdom (UK). We screened biofilm production of strains using the microtiter plate (MTP) assay and Congo Red Coomassie Blue (CRCB) agar method. Previously published stainless-steel coupon (SSCA), polyvinylchloride coupon (PCA), and glass bead (GBA) assays were used for disinfection studies. The mean reduction in the tested wild-type strains met the criterion of ≥4 log₁₀ CFU at a disinfectant concentration of 0.05% with SSCA and GBA, and 0.005% with PCA for peracetic acid, along with 0.5% for glutaraldehyde with all three assays on the mean. At these concentrations, both tested disinfectants are suitable for disinfection of pig housings against Salmonella. When evaluating the efficacy of disinfectants, biofilms should be included, as higher disinfectant concentrations are necessary compared to planktonic bacteria.

Temporal Study of Salmonella enterica Serovars Isolated from Environmental Samples from Ontario Poultry Breeder Flocks between 2009 and 2018

This study's goal was to determine the prevalence, temporal trends, seasonal patterns, and temporal clustering of Salmonella enterica isolated from environmental samples from Ontario's poultry breeding flocks between 2009 and 2018. Clusters of common serovars and those of human health concern were identified using a scan statistic. The period prevalence of S. enterica was 25.3% in broiler breeders, 6.4% in layer breeders, and 28.6% in turkey breeders. An overall decreasing trend in S. enterica prevalence was identified in broiler breeders (from 27.8% in 2009 to 22.1% in 2018) and layer breeders (from 15.4% to 4.9%), while an increasing trend was identified in turkey breeders (from 12.0% to 24.5%). The most common serovars varied by commodity. Among broiler breeders, S. enterica serovars Kentucky (42.4% of 682 submissions), Heidelberg (19.2%), and Typhimurium (5.4%) were the most common. Salmonella enterica serovars Thompson (20.0% of 195 submissions) and Infantis (16.4%) were most common among layer breeders, and S. enterica serovars Schwarzengrund (23.6% of 1368 submissions), Senftenberg (12.9%), and Heidelberg and Uganda (9.6% each) were most common among turkey breeders. Salmonella enterica ser. Enteritidis prevalence was highest in submissions from broiler breeders (3.7% of 682 broiler breeder submissions). Temporal clusters of S. enterica serovars were identified for all poultry commodities. Seasonal effects varied by commodity, with most peaks occurring in the fall. Our study provides information on the prevalence and temporality of S. enterica serovars within Ontario's poultry breeder flocks that might guide prevention and control programs at the breeder level.

Multidrug-resistant Salmonella spp. in fecal samples of pigs with suspected salmonellosis in Antioquia, Colombia, 2019-2021

Objectives

To determine the proportion of Salmonella enterica in fecal samples of live pigs with suspected salmonellosis analyzed at the diagnostic unit of the University of Antioquia, Colombia between 2019 and 2021, and examine the serotypes and antimicrobial resistance patterns.

Methods

This was a laboratory-based cross-sectional study of routine data on fecal samples received from pig farms in all nine subregions of Antioquia state, Colombia. Salmonella spp. detection at the university is done using enrichment, selective culture, and polymerase chain reaction. Serotypes were identified using the Kauffmann-White scheme and isolates were tested for antimicrobial susceptibility using broth microdilution.

Results

Of 653 samples tested, 149 (23%) were positive for S. enterica. Nine serotypes were identified. The most common were Salmonella Typhimurium (56%) and its monophasic variant (35%). Resistance to ampicillin (70%) was most frequently observed, followed by ciprofloxacin (55%), and sulfamethoxazole-trimethoprim (52%). No isolates were resistant to amikacin and gentamicin. Multidrug resistance (resistance to ≥ 3 classes of antibiotics) was observed in 61 (44%) isolates. Multidrug resistance was highest in S. Typhimurium (57%) compared with the other serotypes. Serotype was associated with multidrug resistance (p = 0.01), but age of the pig and sub-region were not.

Conclusions

The proportion of Salmonella spp. and the associated high levels of multidrug resistance are of concern and may indicate irrational use of antimicrobials and poor management practices in pig production systems in the region. Strengthened surveillance is needed to monitor and improve farm management practices and the use of antimicrobials in farms in Colombia.

Temporal Study of Salmonella enterica Serovars Isolated from Fluff Samples from Ontario Poultry Hatcheries between 2009 and 2018

The objectives of this study were to determine the prevalence, temporal trends, seasonal patterns, and temporal clustering of Salmonella enterica isolated from fluff samples from poultry hatcheries in Ontario between 2009 and 2018. A scan statistic was used to identify clusters of common serovars and those of human health concern. A multi-level logistic regression model was used to identify factors (poultry commodity, year, season) associated with S. enterica presence. The period prevalence of S. enterica was 7.5% in broiler hatcheries, 1.6% in layer hatcheries, 7.6% in turkey hatcheries, 29.7% in waterfowl hatcheries, and 13.8% in game-bird hatcheries. An overall increasing trend in S. enterica prevalence was identified in waterfowl and game-bird hatcheries, while a decreasing trend was identified in broiler and turkey hatcheries. Overall, the most common S. enterica serovars were Kentucky, Enteritidis, Heidelberg, and Senftenberg. Salmonella enterica ser. Enteritidis was the most common serovar in waterfowl hatcheries. Temporal clusters were identified for all poultry commodities. Seasonal effects varied by commodity, with the highest odds of S. enterica occurring in the summer and fall. Our study offers information on the prevalence and temporality of S. enterica serovars that might guide prevention and control programs at the hatchery level.

PREVALENCE AND ANTIMICROBIAL RESISTANCE PATTERNS OF SALMONELLA SPP. IN TWO FREE-RANGING POPULATIONS OF EASTERN BOX TURTLES (TERRAPENE CAROLINA CAROLINA)

Salmonellosis is an important zoonotic infection, and exposure to pet reptiles has been implicated in several human outbreaks. Although several studies report a low prevalence of salmonellae in free-ranging chelonians, they may serve as a reservoir. In spring and summer of 2013 and 2019, free-ranging eastern box turtles (Terrapene carolina carolina) from populations in Illinois (rural) and Tennessee (urban) were collected through canine and visual search. Cloacal swab samples were collected from each turtle, selectively enriched with tetrathionate broth, then plated on selective and differential media to isolate Salmonella spp. Genus was confirmed via MALDI-TOF MS and antibiotic sensitivities were performed. Isolates were serotyped by the National Veterinary Services Laboratory. Of the 341 turtles sampled, Salmonella spp. were detected in nine individuals (2.64%; 95% CI: 1.2-5.0%). The isolates included five different serovars: Anatum (n = 2), Newport (n = 2), Thompson (n = 1), Bareilly (n = 2), and Hartford (n = 2). Salmonella spp. were detected from six animals in 2013 (3.19%, 95% CI: 1.2-6.8%) and three in 2019 (1.96%, 95% CI: 0.4-5.6%). There was no significant difference in prevalence between state, (P = 0.115), Illinois locations (P = 0.224), season (P = 0.525), year (P = 0.297), sex (P = 0.435), or age class (P = 0.549). The health of Salmonella-positive and -negative turtles was not significantly different, as assessed through hematology and plasma biochemistry (P > 0.05), indicating asymptomatic carrier status. The low prevalence detected in this study likely concludes that free-ranging eastern box turtles play a minimal role in the spread of salmonellae. However, the identified serotypes are potentially human- and animal-pathogenic. Documenting the prevalence of Salmonella serotypes in animal indicators furthers our understanding of their spread between humans, animal agriculture, and the environment.

Salmonella Typhimurium environmental reduction in a farrow-to-finish pig herd using a live attenuated Salmonella Typhimurium vaccine

Background

Salmonella Typhimurium is an important zoonotic pathogen in pigs, that can cause clinical disease. Many sow herds and finishing herds are infected with Salmonella, and therefore pose a threat for the contamination of pork and pork products and ultimately consumers.

Case presentation

This case study describes a farrow-to-finish pig herd, producing its own replacement gilts, which had experienced clinical outbreaks of salmonellosis since 2002. Outbreaks were characterised by profuse diarrhoea, dead pigs and high antimicrobial use (colistin sulphate). The aim of this study was to see whether using vaccination of sows and piglets with Salmoporc®, a live attenuated Salmonella Typhimurium vaccine, in combination with standard hygienic precautions, it was possible to reduce Salmonella Typhimurium to below the bacteriological detection limit. Monitoring of the presence of Salmonella was done using a total of 20 pooled faecal, sock and dust samples per herd visit in the period from September 2016 to October 2020. Within the first 10 months after the start of vaccination in August 2016, there was a rapid reduction in clinical symptoms, antimicrobial usage and the number of Salmonella-positive samples. During the winters of 2017/2018 and 2018/2019 the number of positive samples increased again, however with minimal need to use antimicrobials to treat the affected animals. In July 2019, only two samples from a corridor were positive. In September and November 2019 and in October 2020 all three samplings were completely negative for S. Typhimurium.

Conclusions

This case, together with other longitudinal studies, can be seen as a proof of the principle that long term vaccination with a live attenuated S. Typhimurium vaccine can reduce the level of S. Typhimurium in the herd environment to very low levels within a farrow-to-finish herd initially suffering from clinical salmonellosis. Also, clinical symptoms indicating salmonellosis were no longer observed and antimicrobials to treat clinically diseased pigs were no longer needed.

Transmission modelling of environmentally persistent zoonotic diseases: a systematic review

Transmission of many infectious diseases depends on interactions between humans, animals, and the environment. Incorporating these complex processes in transmission dynamic models can help inform policy and disease control interventions. We identified 20 diseases involving environmentally persistent pathogens (ie, pathogens that survive for more than 48 h in the environment and can cause subsequent human infections), of which indirect transmission can occur from animals to humans via the environment. Using a systematic approach, we critically appraised dynamic transmission models for environmentally persistent zoonotic diseases to quantify traits of models across diseases. 210 transmission modelling studies were identified and most studies considered diseases of domestic animals or high-income settings, or both. We found that less than half of studies validated their models to real-world data, and environmental data on pathogen persistence was rarely incorporated. Model structures varied, with few studies considering the animal-human-environment interface of transmission in the context of a One Health framework. This Review highlights the need for more data-driven modelling of these diseases and a holistic One Health approach to model these pathogens to inform disease prevention and control strategies.

Prevalence of Salmonella in Free-Range Pigs: Risk Factors and Intestinal Microbiota Composition

Extensive pig systems are gaining importance as quality production systems and as the standard for sustainable rural development and animal welfare. However, the effects of natural foods on Salmonella epidemiology remain unknown. Herein, we assessed the presence of Salmonella and the composition of the gut microbiota in pigs from both Salmonella-free and high Salmonella prevalence farms. In addition, risk factors associated with the presence of Salmonella were investigated. The pathogen was found in 32.2% of animals and 83.3% of farms, showing large differences in prevalence between farms. Most isolates were serovars Typhimurium monophasic (79.3%) and Bovismorbificans (10.3%), and exhibited a multi-drug resistance profile (58.6%). Risk factor analysis identified feed composition, type/variety of vegetation available, and silos' cleaning/disinfection as the main factors associated with Salmonella prevalence. Clear differences in the intestinal microbiota were found between Salmonella-positive and Salmonella-negative populations, showing the former with increasing Proteobacteria and decreasing Bacteroides populations. Butyrate and propionate producers including Clostridium, Turicibacter, Bacteroidaceae_uc, and Lactobacillus were more abundant in the Salmonella-negative group, whereas acetate producers like Sporobacter, Escherichia or Enterobacter were more abundant in the Salmonella-positive group. Overall, our results suggest that the presence of Salmonella in free-range pigs is directly related to the natural vegetation accessible, determining the composition of the intestinal microbiota.

Salmonella Typhimurium Level in Mealworms (Tenebrio molitor) After Exposure to Contaminated Substrate

Findings of viable Salmonella spp., which are important foodborne pathogens, are seemingly not reported in mealworms (Tenebrio molitor) for feed and food. Still, the bacterial load of mealworms is naturally high and includes members of the Enterobacteriaceae family to which Salmonella belong. This indicates that Salmonella may be able to thrive in mealworms if introduced into the production. Therefore, this study aimed to assess the quantitative level of Salmonella enterica serovar Typhimurium (ST) in mealworms over a 14-day course after exposure to substrate contaminated with ST levels from 1.7 to 7.4 log CFU/g at start (i.e., day 0). The level of ST found in larvae was below the quantitative detection level (1 or 2 log CFU/g) on day 1 in larvae exposed to contamination levels of 1.7, 3.4, and 3.6 log CFU/g opposed to contamination levels of 5.4, 5.6, and 7.4 log CFU/g, respectively. The maximum level of ST detected in individual 1-g larvae samples was 5.8 log CFU/g, but the level varied among the triplicate samples from each sampling, and the highest average value was 5.3 ± 0.3. Beyond day 7, only larvae exposed to the contamination level of 7.4 log CFU/g were >1.0 log CFU/g in the triplicate samples. However, qualitative testing (10 g) showed the presence of ST in larvae until the end of the experiment on day 14 except for the lowest contamination level of 1.7 log CFU/g. Parallel testing of surface disinfected larvae indicated that some larvae may be ST-positive due to Salmonella residing on the surface only. Still, any detection of Salmonella is of concern from a food safety perspective. In substrate with contamination levels below 3.6 log CFU/g, the level of ST was below the quantitative detection limit within a few days. Still, ST was detected until the end of experiment on day 14 except for the lowest contamination level of 1.7 log CFU/g. This study indicates the importance of avoiding introduction of Salmonella into the production, e.g., via contaminated substrate in order to avoid Salmonella-positive larvae as they remained positive for at least 14 days (except at the lowest contamination level).

Exploring Perspectives on Antimicrobial Use in Livestock: A Mixed-Methods Study of UK Pig Farmers

Increasing levels of antimicrobial resistance in human and veterinary medicine have raised concerns over the irresponsible use of antimicrobials. The role of administering antimicrobials in food producing animals most frequently falls to the farmer, therefore it is essential that their use of antimicrobials is both optimal and responsible. This study sought in-depth information on the drivers behind antimicrobial use behaviors and farmer attitudes to responsible use using a mixed-methodological approach. Initially, in-depth semi-structured interviews were conducted with a purposively selected sample of farmers (n = 22). A thematic analysis approach was taken to identify key themes from these qualitative data. The generalizability and variation of these themes was then tested on a larger randomly selected sample of pig farmers through a questionnaire study (n = 261). The influences behind antimicrobial use were complex with multiple drivers motivating decisions. There was no consensual opinion on what farming systems resulted in either a low or high antimicrobial requirement however, farmers reported that good management practices, low stocking densities, and a high health status were associated with low antimicrobial use. Farmers expressed desire to avoid the long-term use of in-feed antimicrobials, but identified barriers to discontinuing such behaviors, such as pig morbidity, mortality, and economic losses. The high cost of antimicrobials was described as a motivation toward seeking alternative methods of controlling disease to prophylactic use; however, this expense was balanced against the losses from an increased burden of disease. The high financial costs involved in pig production alongside the economic uncertainty of production and pressure from retailers, were identified as limiting the scope for improvements in pig accommodation and facilities which could reduce the antimicrobial requirements on farm. Long-term, sustainable and economically stable relationships between retailers and farmers may allow farmers to make necessary investments in improving management and housing in order to reduce antimicrobial use. Greater use and more widespread deployment of effective vaccinations were highlighted by farmers as being a feasible alternative to antimicrobial use in preventing disease.

Infection, colonization and shedding of Campylobacter and Salmonella in animals and their contribution to human disease: A review

Livestock meat and offal contribute significantly to human nutrition as sources of high-quality protein and micronutrients. Livestock products are increasingly in demand, particularly in low- and middle-income settings where economies are growing and meat is increasingly seen as an affordable and desirable food item. Demand is also driving intensification of livestock keeping and processing. An unintended consequence of intensification is increased exposure to zoonotic agents, and a contemporary emerging problem is infection with Campylobacter and Salmonella spp. from livestock (avian and mammalian), which can lead to disease, malabsorption and undernutrition through acute and chronic diarrhoea. This can occur at the farm, in households or through the food chain. Direct infection occurs when handling livestock and through bacteria shed into the environment, on food preparation surfaces or around the house and surroundings. This manuscript critically reviews Campylobacter and Salmonella infections in animals, examines the factors affecting colonization and faecal shedding of bacteria of these two genera as well as risk factors for human acquisition of the infection from infected animals or environment and analyses priority areas for preventive actions with a focus on resource-poor settings.

Persistent Infection and Long-Term Carriage of Typhoidal and Nontyphoidal Salmonellae

The ability of pathogenic bacteria to affect higher organisms and cause disease is one of the most dramatic properties of microorganisms. Some pathogens can establish transient colonization only, but others are capable of infecting their host for many years or even for a lifetime. Long-term infection is called persistence, and this phenotype is fundamental for the biology of important human pathogens, including Helicobacter pylori, Mycobacterium tuberculosis, and Salmonella enterica Both typhoidal and nontyphoidal serovars of the species Salmonella enterica can cause persistent infection in humans; however, as these two Salmonella groups cause clinically distinct diseases, the characteristics of their persistent infections in humans differ significantly. Here, following a general summary of Salmonella pathogenicity, host specificity, epidemiology, and laboratory diagnosis, I review the current knowledge about Salmonella persistence and discuss the relevant epidemiology of persistence (including carrier rate, duration of shedding, and host and pathogen risk factors), the host response to Salmonella persistence, Salmonella genes involved in this lifestyle, as well as genetic and phenotypic changes acquired during prolonged infection within the host. Additionally, I highlight differences between the persistence of typhoidal and nontyphoidal Salmonella strains in humans and summarize the current gaps and limitations in our understanding, diagnosis, and curing of persistent Salmonella infections.

Assessing the contributions of intraspecific and environmental sources of infection in urban wildlife: Salmonella enterica and white ibis as a case study

Conversion of natural habitats into urban landscapes can expose wildlife to novel pathogens and alter pathogen transmission pathways. Because transmission is difficult to quantify for many wildlife pathogens, mathematical models paired with field observations can help select among competing transmission pathways that might operate in urban landscapes. Here we develop a mathematical model for the enteric bacteria Salmonella enterica in urban-foraging white ibis ( Eudocimus albus) in south Florida as a case study to determine (i) the relative importance of contact-based versus environmental transmission among ibis and (ii) whether transmission can be supported by ibis alone or requires external sources of infection. We use biannual field prevalence data to restrict model outputs generated from a Latin hypercube sample of parameter space and select among competing transmission scenarios. We find the most support for transmission from environmental uptake rather than between-host contact and that ibis-ibis transmission alone could maintain low infection prevalence. Our analysis provides the first parameter estimates for Salmonella shedding and uptake in a wild bird and provides a key starting point for predicting how ibis response to urbanization alters their exposure to a multi-host zoonotic enteric pathogen. More broadly, our study provides an analytical roadmap to assess transmission pathways of multi-host wildlife pathogens in the face of scarce infection data.

A cost-benefit assessment of Salmonella-control strategies in pigs reared in the United Kingdom

Pork and pork products are a major source of human salmonellosis in the United Kingdom (UK). Despite a number of surveillance programmes, the prevalence of Salmonella in the UK slaughter pig population remains over 20%. Here, we present the results of a Cost-Benefit Analysis comparing five on-farm control strategies (where the cost is the cost of implementation and the benefits are the financial savings for both the human health and pig industries). The interventions considered were: wet feed, organic acids in feed, vaccination, enhanced cleaning and disinfection and movement of outdoor breeding units. The data originate from published papers and recent UK studies. The effectiveness was assessed by adapting a previous risk assessment, originally developed for the European Food Safety Authority. Using this method, none of the intervention strategies produced a net cost-benefit. Our results suggest that the cost of implementation outweighed the savings for all interventions, even if the effectiveness could be improved. Therefore, to achieve a net cost-benefit it is essential to reduce the cost of interventions. Analyses concluded that large cost reductions (up to 96%) would be required. Use of organic acids required the smallest reduction in cost (22.7%) to achieve a net cost benefit. Uncertainty analysis suggested that a small net gain might be possible, for some of the intervention measures. But this would imply that the model greatly underestimated some key parameters, which was considered unlikely. Areas of key uncertainty were identified as the under-reporting factor (i.e. the proportion of community cases of Salmonella) and the source attribution factor (i.e. the proportion of human Salmonella cases attributable to pork products).

Study of the impact on Salmonella of moving outdoor pigs to fresh land

Anecdotal evidence has suggested that outdoor-kept pigs show an improvement to health and productivity after being moved to a new site. This study explores whether Salmonella occurrence reduced and was sustained after moving to a new site. Nine farms were followed for a year in which four sampling visits were completed. The highest detection of Salmonella was from pooled faecal dropping from pigs, run-off/ pooled water, rodents and wild birds. Descriptive summaries showed that the prevalence of both all Salmonella and serovars of public health importance were lower at all visits after the move. Some variability was shown in results from individual farms, but a year after the move, six farms still maintained a lower prevalence. A risk factor model showed that the prevalence at visits 2 and 3 after the move was significantly lower than baseline, after accounting for a number of significant factors that were included in the model. These were sample type and seasonality (included as a priori), presence of coughing in the sampled group and Glasser's disease on the farm, and the use of tent or kennel accommodation. This finding provides important evidence that more frequent site moves may help reduce Salmonella prevalence in outdoor herds.

Assessing the Effectiveness of On-Farm and Abattoir Interventions in Reducing Pig Meat-Borne Salmonellosis within E.U. Member States

As part of the evidence base for the development of national control plans for Salmonella spp. in pigs for E.U. Member States, a quantitative microbiological risk assessment was funded to support the scientific opinion required by the EC from the European Food Safety Authority. The main aim of the risk assessment was to assess the effectiveness of interventions implemented on-farm and at the abattoir in reducing human cases of pig meat-borne salmonellosis, and how the effects of these interventions may vary across E.U. Member States. Two case study Member States have been chosen to assess the effect of the interventions investigated. Reducing both breeding herd and slaughter pig prevalence were effective in achieving reductions in the number of expected human illnesses in both case study Member States. However, there is scarce evidence to suggest which specific on-farm interventions could achieve consistent reductions in either breeding herd or slaughter pig prevalence. Hypothetical reductions in feed contamination rates were important in reducing slaughter pig prevalence for the case study Member State where prevalence of infection was already low, but not for the high-prevalence case study. The most significant reductions were achieved by a 1- or 2-log decrease of Salmonella contamination of the carcass post-evisceration; a 1-log decrease in average contamination produced a 90% reduction in human illness. The intervention analyses suggest that abattoir intervention may be the most effective way to reduce human exposure to Salmonella spp. However, a combined farm/abattoir approach would likely have cumulative benefits. On-farm intervention is probably most effective at the breeding-herd level for high-prevalence Member States; once infection in the breeding herd has been reduced to a low enough level, then feed and biosecurity measures would become increasingly more effective.

A Farm Transmission Model for Salmonella in Pigs, Applicable to E.U. Member States

The burden of Salmonella entering pig slaughterhouses across the European Union is considered a primary food safety concern. To assist E.U. member states with the development of national control plans, we have developed a farm transmission model applicable to all member states. It is an individual-based stochastic susceptible-infected model that takes into account four different sources of infection of pigs (sows, feed, external contaminants such as rodents, and new stock) and various management practices linked to Salmonella transmission/protection (housing, flooring, feed, all-in-all-out production). A novel development within the model is the assessment of dynamic shedding rates. The results of the model, parameterized for two case study member states (one high and one low prevalence) suggest that breeding herd prevalence is a strong indicator of slaughter pig prevalence. Until a member state's' breeding herd prevalence is brought below 10%, the sow will be the dominant source of infection to pigs raised for meat production; below this level of breeding herd prevalence, feed becomes the dominant force of infection.

A Transport and Lairage Model for Salmonella Transmission Between Pigs Applicable to EU Member States

A model for the transmission of Salmonella between finisher pigs during transport to the abattoir and subsequent lairage has been developed, including novel factors such as environmental contamination and the effect of stress, and is designed to be adaptable for any EU Member State (MS). The model forms part of a generic farm-to-consumption model for Salmonella in pigs, designed to model potentially important risk factors and assess the effectiveness of interventions. In this article, we discuss the parameterization of the model for two case study MSs. For both MSs, the model predicted an increase in the average MS-level prevalence of Salmonella-positive pigs during both transport and lairage, accounting for a large amount of the variation between reported on-farm prevalence and reported lymph-node prevalence at the slaughterhouse. Sensitivity analysis suggested that stress is the most important factor during transport, while a number of factors, including environmental contamination and the dose-response parameters, are important during lairage. There was wide variation in the model-predicted change in prevalence in individual batches; while the majority of batches (80-90%) had no increase, in some batches the increase in prevalence was over 70% and in some cases infection was introduced into previously uninfected batches of pigs. Thus, the model suggests that while the transport and lairage stages of the farm-to-consumption exposure pathway are unlikely to be responsible for a large increase in average prevalence at the MS level, they can have a large effect on prevalence at an individual-batch level.

Evaluating the risk of pathogen transmission from wild animals to domestic pigs in Australia

Wild animals contribute to endemic infection in livestock as well as the introduction, reintroduction and maintenance of pathogens. The source of introduction of endemic diseases to a piggery is often unknown and the extent of wildlife contribution to such local spread is largely unexplored. The aim of the current study was to quantitatively assess the probability of domestic pigs being exposed to different pathogens from wild animals commonly found around commercial piggeries in Australia. Specifically, this study aims to quantify the probability of exposure to the pathogens Escherichia coli, Salmonella spp. and Campylobacter spp. from European starlings (Sturnus vulgarus); Brachyspira hyodysenteriae, Lawsonia intracellularis and Salmonella spp. from rats (Rattus rattus and Rattus norvegicus); and Mycoplasma hyopneumoniae, Leptospira spp., Brucella suis and L. intracellularis from feral pigs (Sus scrofa). Exposure assessments, using scenario trees and Monte Carlo stochastic simulation modelling, were conducted to identify potential pathways of introduction and calculate the probabilities of these pathways occurring. Input parameters were estimated from a national postal survey of commercial pork producers and from disease detection studies conducted for European starlings, rats and feral pigs in close proximity to commercial piggeries in Australia. Based on the results of the exposure assessments, rats presented the highest probability of exposure of pathogens to domestic pigs at any point in time, and L. intracellularis (median 0.13, 5% and 95%, 0.05-0.23) and B. hyodysenteriae (median 0.10, 0.05-0.19) were the most likely pathogens to be transmitted. Regarding European starlings, the median probability of exposure of domestic pigs to pathogenic E. coli at any point in time was estimated to be 0.03 (0.02-0.04). The highest probability of domestic pig exposure to feral pig pathogens at any point in time was found to be for M. hyopneumoniae (median 0.013, 0.007-0.022) and L. intracellularis (median 0.006, 0.003-0.011) for pigs in free-range piggeries. The sensitivity analysis indicates that the presence and number of wild animals around piggeries, their access to piggeries and pig food and water, and, in the case of feral pigs, their proximity to piggeries, are the most influential parameters on the probability of exposure. Findings from this study support identification of mitigation strategies that could be implemented at on-farm and industry level to minimize the exposure risk from European starlings, rats and feral pigs.

Managing Salmonella Typhimurium and Escherichia coli O157:H7 in soil with hydrated lime - An outdoor study in lysimeters and field plots

An outbreak of Salmonella Typhimurium or E. coli O157:H7 among domestic animals can have great financial consequences for an animal enterprise but also be a threat for public health as there is a risk for transmission of the infection through the environment. In order to minimize disease transmission, it is important to treat not only the affected animals but also the areas on which they have been kept. In the present study, the effect of hydrated lime as a treatment for Salmonella Typhimurium or E. coli O157:H7 contaminated soil was investigated. The study was performed outdoors, in a lysimeter system and in field plots. The soils were spiked with Salmonella Typhimurium and/or E. coli O157:H7 and hydrated lime was added at three different concentrations (0.5, 1 and 2%). Sampling was performed over one month, and the levels of bacteria were analyzed by standard culture methods. In addition, the soil pH was monitored throughout the study. The results showed that application of 0.5-1 kg hydrated lime per m(2) reduced both Salmonella Typhimurium and E. coli O157:H7 numbers to below the detection limit (2 log10 CFU g-1 soil) in 3-7 days. Lower application rates of hydrated lime did not reduce pathogen numbers in the lysimeter study, but in the field plots no E. coli O157:H7 was detected at the end of the four-week study period regardless of hydrated lime application. A recommended strategy for treating a Salmonella Typhimurium or E. coli O157:H7 contaminated soil could therefore be to monitor the pH over the time of treatment and to repeat hydrated lime application if a decrease in pH is observed.

Extracellular DNA inhibits Salmonella enterica Serovar Typhimurium and S. enterica Serovar Typhi biofilm development on abiotic surfaces

Extracellular DNA (eDNA) was identified and characterized in a 2-day-old biofilms developed by Salmonella enterica ser. Typhimurium SR-11 and S. enterica ser. Typhi ST6 using confocal laser scanning microscopy (CLSM) and enzymatic extraction methods. Results of microtitre plate assay and CLSM analysis showed both Salmonella strains formed significantly more biofilms in the presence of DNase I; Furthermore, a remarkable decrease of biofilm formation was observed when eDNA was added in the inoculation. However, for the pre-established biofilms on polystyrene and glass, no significant difference was observed between the DNase I treated biofilm and the corresponding non-treated controls. In conclusion, these results demonstrate that eDNA is a novel matrix component of Salmonella biofilms. This is the first evidence for the presence of eDNA and its inhibitive and destabilizing effect during biofilm development of S. enterica ser. Typhimurium and S. enterica ser. Typhi on abiotic surfaces.

Interaction between the microbial community and invading Escherichia coli O157:H7 in soils from vegetable fields

The survival of Escherichia coli O157:H7 in soils can contaminate vegetables, fruits, drinking water, etc. However, data on the impact of E. coli O157:H7 on soil microbial communities are limited. In this study, we monitored the changes in the indigenous microbial community by using the phospholipid fatty acid (PLFA) method to investigate the interaction of the soil microbial community with E. coli O157:H7 in soils. Simple correlation analysis showed that the survival of E. coli O157:H7 in the test soils was negatively correlated with the ratio of Gram-negative (G(-)) to Gram-positive (G(+)) bacterial PLFAs (G(-)/G(+) ratio). In particular, levels of 14 PLFAs were negatively correlated with the survival time of E. coli O157:H7. The contents of actinomycetous and fungal PLFAs in the test soils declined significantly (P, <0.05) after 25 days of incubation with E. coli O157:H7. The G(-)/G(+) ratio declined slightly, while the ratio of bacterial to fungal PLFAs (B/F ratio) and the ratio of normal saturated PLFAs to monounsaturated PLFAs (S/M ratio) increased, after E. coli O157:H7 inoculation. Principal component analysis results further indicated that invasion by E. coli O157:H7 had some effects on the soil microbial community. Our data revealed that the toxicity of E. coli O157:H7 presents not only in its pathogenicity but also in its effect on soil microecology. Hence, close attention should be paid to the survival of E. coli O157:H7 and its potential for contaminating soils.

Understanding the role of cleaning in the control of Salmonella Typhimurium in grower-finisher pigs: a modelling approach

Salmonella Typhimurium (STM) infection in pigs represents a considerable food safety concern. This study used mathematical modelling to evaluate the effectiveness of cleaning (faeces removal) as a measure to control STM spread among grower-finisher pigs. A modified Susceptible-Infected-Recovered-Susceptible (SIRS) model of STM transmission through a contaminated environment was developed. Infected pigs were divided into three states according to the pathogen level being shed in their faeces. Infection transmission was evaluated using the basic reproduction number (R 0) and the prevalence of infectious pigs at slaughter age. Although increased frequency and efficiency of cleaning did reduce the prevalence of STM shedding at the time of slaughter, these efforts alone were not capable of eliminating the infection from the population. The level of STM faecal shedding by infectious pigs strongly influenced the infection spread and prevalence at slaughter. To control STM in pigs, cleaning should be combined with vaccination and/or isolation of high-level shedders.

Longitudinal study of distributions of similar antimicrobial-resistant Salmonella serovars in pigs and their environment in two distinct swine production systems

The aim of this longitudinal study was to determine and compare the prevalences and genotypic profiles of antimicrobial-resistant (AR) Salmonella isolates from pigs reared in antimicrobial-free (ABF) and conventional production systems at farm, at slaughter, and in their environment. We collected 2,889 pig fecal and 2,122 environmental (feed, water, soil, lagoon, truck, and floor swabs) samples from 10 conventional and eight ABF longitudinal cohorts at different stages of production (farrowing, nursery, finishing) and slaughter (postevisceration, postchill, and mesenteric lymph nodes [MLN]). In addition, we collected 1,363 carcass swabs and 205 lairage and truck samples at slaughter. A total of 1,090 Salmonella isolates were recovered from the samples; these were isolated with a significantly higher prevalence in conventionally reared pigs (4.0%; n = 66) and their environment (11.7%; n = 156) than in ABF pigs (0.2%; n = 2) and their environment (0.6%; n = 5) (P < 0.001). Salmonella was isolated from all stages at slaughter, including the postchill step, in the two production systems. Salmonella prevalence was significantly higher in MLN extracted from conventional carcasses than those extracted from ABF carcasses (P < 0.001). We identified a total of 24 different serotypes, with Salmonella enterica serovar Typhimurium, Salmonella enterica serovar Anatum, Salmonella enterica serovar Infantis, and Salmonella enterica serovar Derby being predominant. The highest frequencies of antimicrobial resistance (AR) were exhibited to tetracycline (71%), sulfisoxazole (42%), and streptomycin (17%). Multidrug resistance (resistance to ≥ 3 antimicrobials; MDR) was detected in 27% (n = 254) of the Salmonella isolates from the conventional system. Our study reports a low prevalence of Salmonella in both production systems in pigs on farms, while a higher prevalence was detected among the carcasses at slaughter. The dynamics of Salmonella prevalence in pigs and carcasses were reciprocated in the farm and slaughter environment, clearly indicating an exchange of this pathogen between the pigs and their surroundings. Furthermore, the phenotypic and genotypic fingerprint profile results underscore the potential role played by environmental factors in dissemination of AR Salmonella to pigs.

Evaluating the occurrence of host-specific , general fecal indicators, and bacterial pathogens in a mixed-use watershed

Fecal contamination of water is very common, and, in the United States, prevention is complicated by the colossal span of waterways (>3.5 million miles), heterogeneous sources of pollution, and competing interests in water monitoring. The focus of this study was the Upper Sugar Creek Watershed, a mixed-use watershed with many headwater streams and one of the most contaminated waterways in Ohio. Quantitative polymerase chain reaction (qPCR) and host-specific PCR for were evaluated for the potential to discern sources of fecal contamination. Pathogen-specific qPCR and culturable by most probable number (MPN) were compared at 21 established water quality monitoring sites in the watershed headwaters. Lower numbers of ruminant-specific markers were detected in the base flow water samples compared with the human-specific marker, suggesting the presence of hotspots of human fecal contamination. qPCR and MPN showed significant correlation ( = 0.57; < 0.001). Correlation between general fecal indicator and pathogen concentrations was weak or nonexistent. Coexistence of and human-specific was common ( = 0.015). qPCR may have a greater potential for predicting fecal contamination due to its sensitivity, rapid analysis, and availability of host-specific assays. However, the lack of a strong correlation between pathogens and general fecal indicators suggests that assessment of health risk associated with fecal contamination will require a complement of approaches.

A Review of the Use of Organic Amendments and the Risk to Human Health

Historically, organic amendments—organic wastes—have been the main source of plant nutrients, especially N. Their use allows better management of often-finite resources to counter changes in soils that result from essential practices for crop production. Organic amendments provide macro- and micronutrients, including carbon for the restoration of soil physical and chemical properties. Challenges from the use of organic amendments arise from the presence of heavy metals and the inability to control the transformations required to convert the organic forms of N and P into the minerals available to crops, and particularly to minimize the losses of these nutrients in forms that may present a threat to human health. Animal manure and sewage biosolids, the organic amendments in greatest abundance, contain components that can be hazardous to human health, other animals and plants. Pathogens pose an immediate threat. Antibiotics, other pharmaceuticals and naturally produced hormones may pose a threat if they increase the number of zoonotic disease organisms that are resistant to multiple antimicrobial drugs or interfere with reproductive processes. Some approaches aimed at limiting N losses (e.g. covered liquid or slurry storage, rapid incorporation into the soil, timing applications to minimize delay before plant uptake) also tend to favor survival of pathogens. Risks to human health, through the food chain and drinking water, from the pathogens, antibiotics and hormonal substances that may be present in organic amendments can be reduced by treatment before land application, such as in the case of sewage biosolids. Other sources, such as livestock and poultry manures, are largely managed by ensuring that they are applied at the rate, time and place most appropriate to the crops and soils. A more holistic approach to management is required as intensification of agriculture increases.

Integrating survey and molecular approaches to better understand wildlife disease ecology

Infectious wildlife diseases have enormous global impacts, leading to human pandemics, global biodiversity declines and socio-economic hardship. Understanding how infection persists and is transmitted in wildlife is critical for managing diseases, but our understanding is limited. Our study aim was to better understand how infectious disease persists in wildlife populations by integrating genetics, ecology and epidemiology approaches. Specifically, we aimed to determine whether environmental or host factors were stronger drivers of Salmonella persistence or transmission within a remote and isolated wild pig (Sus scrofa) population. We determined the Salmonella infection status of wild pigs. Salmonella isolates were genotyped and a range of data was collected on putative risk factors for Salmonella transmission. We a priori identified several plausible biological hypotheses for Salmonella prevalence (cross sectional study design) versus transmission (molecular case series study design) and fit the data to these models. There were 543 wild pig Salmonella observations, sampled at 93 unique locations. Salmonella prevalence was 41% (95% confidence interval [CI]: 37-45%). The median Salmonella DICE coefficient (or Salmonella genetic similarity) was 52% (interquartile range [IQR]: 42-62%). Using the traditional cross sectional prevalence study design, the only supported model was based on the hypothesis that abundance of available ecological resources determines Salmonella prevalence in wild pigs. In the molecular study design, spatial proximity and herd membership as well as some individual risk factors (sex, condition score and relative density) determined transmission between pigs. Traditional cross sectional surveys and molecular epidemiological approaches are complementary and together can enhance understanding of disease ecology: abundance of ecological resources critical for wildlife influences Salmonella prevalence, whereas Salmonella transmission is driven by local spatial, social, density and individual factors, rather than resources. This enhanced understanding has implications for the control of diseases in wildlife populations. Attempts to manage wildlife disease using simplistic density approaches do not acknowledge the complexity of disease ecology.

Salmonella fecal shedding and immune responses are dose- and serotype- dependent in pigs

Despite the public health importance of Salmonella infection in pigs, little is known about the associated dynamics of fecal shedding and immunity. In this study, we investigated the transitions of pigs through the states of Salmonella fecal shedding and immune response post-Salmonella inoculation as affected by the challenge dose and serotype. Continuous-time multistate Markov models were developed using published experimental data. The model for shedding had four transient states, of which two were shedding (continuous and intermittent shedding) and two non-shedding (latency and intermittent non-shedding), and one absorbing state representing permanent cessation of shedding. The immune response model had two transient states representing responses below and above the seroconversion level. The effects of two doses [low (0.65×10⁶ CFU/pig) and high (0.65×10⁹ CFU/pig)] and four serotypes (Salmonella Yoruba, Salmonella Cubana, Salmonella Typhimurium, and Salmonella Derby) on the models' transition intensities were evaluated using a proportional intensities model. Results indicated statistically significant effects of the challenge dose and serotype on the dynamics of shedding and immune response. The time spent in the specific states was also estimated. Continuous shedding was on average 10–26 days longer, while intermittent non-shedding was 2–4 days shorter, in pigs challenged with the high compared to low dose. Interestingly, among pigs challenged with the high dose, the continuous and intermittent shedding states were on average up to 10–17 and 3–4 days longer, respectively, in pigs infected with S. Cubana compared to the other three serotypes. Pigs challenged with the high dose of S. Typhimurium or S. Derby seroconverted on average up to 8–11 days faster compared to the low dose. These findings highlight that Salmonella fecal shedding and immune response following Salmonella challenge are dose- and serotype-dependent and that the detection of specific Salmonella strains and immune responses in pigs are time-sensitive.

Roles of diet and the acid tolerance response in survival of common Salmonella serotypes in feces of finishing pigs

The persistence of Salmonella in the environment is an important factor influencing the transmission of infection in pig production. This study evaluated the effects of acid tolerance response (ATR), organic acid supplementation, and physical properties of feed on the survival of a five-strain Salmonella mixture in porcine feces held at 4 and 22°C for 88 days. Acid-adapted or non-acid-adapted nalidixic acid-resistant Salmonella strains were used to inoculate feces of pigs fed four different diets, which consisted of a nonpelleted, finely ground meal feed or a finely ground, pelleted feed that was left unsupplemented or was supplemented with K-diformate. Organic acid supplementation and physical properties of feed markedly influenced Salmonella survival, but the effects were highly dependent on storage temperature; survival was unaffected by ATR. The most pronounced effects were observed at 22°C, a temperature similar to that of finishing pig houses. The supplementation of meal diets with K-diformate significantly reduced the duration of survival (P < 0.1) and increased rates of decline (P < 0.0001) of salmonellae in feces compared to survival in feces of pigs fed unsupplemented meal. The pelleting of feed, compared to feeding meal, significantly reduced (P < 0.1) the duration of survival in feces held at 22°C. Only minor effects of feed form and acid supplementation on survivor numbers were observed at 4°C. Differences in the fecal survival of Salmonella could not be related to diet-induced changes in fecal physiochemical parameters. The predominant survival of S. enterica serovar Typhimurium DT193 and serotype 4,[5],12:i:- in porcine feces demonstrates the superior ability of these serotypes to survive in this environment. Fecal survival and transmission of Salmonella in pig herds may be reduced by dietary approaches, but effects are highly dependent on environmental temperature.

An outbreak of Salmonella enterica serotype Choleraesuis in goitered gazelle (Gazella subgutrosa subgutrosa) and a Malayan tapir (Tapirus indicus)

An outbreak of Salmonella enterica serotype Choleraesuis enteritis occurred in two juvenile goitered gazelles and an adult Malayan tapir over a period of 5 wk at the Minnesota Zoo. Diagnosis was made postmortem on one gazelle and one tapir, and a second gazelle was diagnosed via fecal culture. The death of the tapir was attributed to S. enterica serovar Choleraesuis septicemia, while salmonellosis was considered to be a contributing factor besides ostertagiasis for the death of one goitered gazelle and for the diarrhea of another goitered gazelle. A third gazelle became ill in the same time period, but Salmonella infection was not confirmed by culture. All exhibited the clinical signs of profuse, watery diarrhea. The gazelles developed a protein-losing enteropathy, and the tapir showed signs of sepsis and endotoxemia. Serotyping and pulsed-field gel electrophoresis revealed the Salmonella isolates to be indistinguishable from each other. One year prior to this outbreak, Salmonella sp. was cultured from a Visayan warty pig (Sus cebifrons) housed in the same building as the tapir. After further investigation into the outbreak, spread of this pathogen was speculated to be associated with human movement across animal areas.

Development of a self-regulated dynamic model for the propagation of Salmonella Typhimurium in pig farms

A self-regulated epidemic model was developed to describe the dynamics of Salmonella Typhimurium in pig farms and predict the prevalence of different risk groups at slaughter age. The model was focused at the compartment level of the pig farms and it included two syndromes, a high and a low propagation syndrome. These two syndromes generated two different classes of pigs, the High Infectious and the Low Infectious, respectively, which have different shedding patterns. Given the two different classes and syndromes, the Infectious Equivalent concept was used, which reflected the combination of High and Low Infectious pigs needed for the high propagation syndrome to be triggered. Using the above information a new algorithm was developed that decides, depending on the Infectious Equivalent, which of the two syndromes should be triggered. Results showed that the transmission rate of S. Typhimurium for the low propagation syndrome is around 0.115, pigs in Low Infectious class contribute to the transmission of the infection by 0.61-0.80 of pigs in High Infectious class and that the Infectious Equivalent should be above 10-14% of the population in order for the high propagation syndrome to be triggered. This self-regulated dynamic model can predict the prevalence of the classes and the risk groups of pigs at slaughter age for different starting conditions of infection.

Analysis of meat juice ELISA results and questionnaire data to investigate farm-level risk factors for Salmonella infection in UK pigs

The study set out to explore risk factors for Salmonella infection in pigs, based on seroprevalence amongst slaughtered pigs, using a large study population of holdings and a comprehensive list of farm characteristics. Farm data were collected from pig quality assurance schemes and supplemented by a postal questionnaire. These data were used with meat juice serology results from ongoing abattoir Salmonella surveillance, for a multivariable risk factor analysis, modelling the ELISA sample to positive ratio directly (ELISA ratio). The study population contained 566 farms, covering a geographically representative spread of farms within the United Kingdom, with a mean average of 224 sample results per holding over a 4-year period. The model highlighted that temporal factors (quarterly and yearly cycles) and monthly meteorological summaries for rainfall, sunshine and temperature were associated with Salmonella presence (P < 0.01). The ELISA ratio was found to be highest in autumn and lowest in spring and summer, whereas yearly averages showed a greater degree of variation than seasonal. Two feed variables (homemix and barley) were found to be protective factors, as was a conventional, rather than organic or freedom foods, farm enterprise type. The number of annual pig deliveries and dead stock collections, and the main cause of pig mortality on the farm were found to be associated with Salmonella infection. Scottish farms had a lower ELISA ratio than other regions, and an increased number of pig farms within a 10-km radius was associated with a higher ELISA ratio. The study demonstrated that the analysis of routinely collected data from surveillance and quality assurance schemes was cost-effective, with sufficient power to detect modest associations between Salmonella and exposure variables. The model results can be used to inform on-farm Salmonella control policies and could target-specific geographical regions and seasons to assist the efficiency of surveillance.

Intensive swine production and pork safety

Major structural changes in livestock production in developed countries, particularly intensive confinement production and increases in herd and flock sizes, have raised several societal concerns about the future directions and implications of livestock food production, including the safety of meat products. This review of the major parasitic and bacterial foodborne pathogens associated with pork production indicates that pork safety in the United States has improved demonstrably over recent decades. Most notably, changes in swine production methods have been associated with virtual elimination of risk of the foodborne parasites Taenia solium, Trichinella spiralis, and Toxoplasma gondii from pigs reared on modern intensive farms. This represents a substantial public health achievement that has gone largely unheralded. Regulatory changes have led to demonstrably lower prevalence of Salmonella on pork carcasses, but control of bacterial foodborne pathogens on farms remains a significant challenge. Available evidence does not support the hypothesis that intensive pork production has increased risk for the major bacterial foodborne pathogens that are common commensals of the pig (Salmonella, Campylobacter, Listeria, and Yersinia enterocolitica), or that pigs produced in alternative systems are at reduced risk of colonization with these organisms. However, pigs raised in outdoor systems inherently confront higher risks of exposure to foodborne parasites, particularly T. gondii.

Transfer of enteric pathogens to successive habitats as part of microbial cycles

Escherichia coli O157:H7 gfp and Salmonella enterica Typhimurium gfp passed through six successive habitats within a microbial cycle. Pathogen cultures were introduced into cow dung or fodder. Microscopically observed cells and CFUs were monitored in fodder, dung, dung-soil mix, rhizosphere and phyllosphere of cress or oat plants grown in infested dung-soil mix, and in excrements of snails or mice fed with contaminated cress or oat shoots. Both methods were sensitive enough to monitor cells and CFUs throughout the chain. There was a positive correlation between cells and CFUs. Both pathogens declined through the successive habitats, but with unexpected increased densities on plants compared to dung-soil mix. Pathogen densities were higher in the phyllosphere than the rhizosphere of cress, but for oat plants this was reverse. Survival in dung was better after passage through the digestive tract of cows than after introduction of cultures into dung. Positive correlations between pathogens and copiotrophic bacteria (CB) and dissolved organic carbon (DOC) were observed in dung and dung-soil mixtures, but at low DOC contents CB densities were higher than pathogen densities. Thus, the pathogens are able to cycle through different habitats, surviving or growing better at high DOC concentrations, but maintaining population densities that are sufficiently high to cause disease in humans.

Examination of Salmonella and Escherichia coli translocation from hog manure to forage, soil, and cattle grazed on the hog manure-treated pasture

Use of hog (Sus scrofa) manure as a fertilizer is a practical solution for waste re-utilization, however, it may serve as a vehicle for environmental and domestic animal contamination. Work was conducted to determine whether pathogens, naturally present in hog manure could be detected in cattle (Bos taurus) grazed on the manure-treated pasture, and whether forage contamination occurred. During two 3 mo summer trials manure was applied to yield < or = 124 kg available N per hectare in a single spring or split spring and fall application. Samples of hog manure, forage, soil, and cattle feces were analyzed for naturally occurring Salmonella, Yersinia enterocolitica, and Escherichia coli. To follow movement of Salmonella in the environment isolates were identified to serovar and serotyped. Transfer of E. coli from hog manure to soil and cattle was examined by randomly amplified polymorphic DNA (RAPD) analysis of >600 E. coli isolates. While Y. enterocolitica was absent from all samples, in both years S. enterica Derby and S. enterica Krefeld were found in most hog manure samples, but were only on forage samples in the second year. Salmonella enterica Typhimurium, absent from hog manure was present on some forage in the first year. Cattle feces and soil samples were consistently Salmonella negative. These contaminations could not be traced to manure application. During this study, Salmonella and E. coli found in hog manure had different RAPD genomic profiles from those found in the feces of cattle grazing on manure-treated pasture.

Differential attachment to and subsequent contamination of agricultural crops by Salmonella enterica

U.S. salmonellosis outbreaks have occurred following consumption of tomato and cantaloupe but not lettuce. We report differential contamination among agricultural seedlings by Salmonella enterica via soil. Members of the family Brassicaceae had a higher incidence of outbreak than carrot, lettuce, and tomato. Once they were contaminated, phyllosphere populations were similar, except for tomato. Contamination differences exist among tomato cultivars.

Role of soil, crop debris, and a plant pathogen in Salmonella enterica contamination of tomato plants

BACKGROUND

In the U.S., tomatoes have become the most implicated vehicle for produce-associated Salmonellosis with 12 outbreaks since 1998. Although unconfirmed, trace backs suggest pre-harvest contamination with Salmonella enterica. Routes of tomato crop contamination by S. enterica in the absence of direct artificial inoculation have not been investigated.

METHODOLOGY/PRINCIPAL FINDINGS

This work examined the role of contaminated soil, the potential for crop debris to act as inoculum from one crop to the next, and any interaction between the seedbourne plant pathogen Xanthomonas campestris pv. vesicatoria and S. enterica on tomato plants. Our results show S. enterica can survive for up to six weeks in fallow soil with the ability to contaminate tomato plants. We found S. enterica can contaminate a subsequent crop via crop debris; however a fallow period between crop incorporation and subsequent seeding can affect contamination patterns. Throughout these studies, populations of S. enterica declined over time and there was no bacterial growth in either the phyllosphere or rhizoplane. The presence of X. campestris pv. vesicatoria on co-colonized tomato plants had no effect on the incidence of S. enterica tomato phyllosphere contamination. However, growth of S. enterica in the tomato phyllosphere occurred on co-colonized plants in the absence of plant disease.

CONCLUSIONS/SIGNIFICANCE

S. enterica contaminated soil can lead to contamination of the tomato phyllosphere. A six week lag period between soil contamination and tomato seeding did not deter subsequent crop contamination. In the absence of plant disease, presence of the bacterial plant pathogen, X. campestris pv. vesicatoria was beneficial to S. enterica allowing multiplication of the human pathogen population. Any event leading to soil contamination with S. enterica could pose a public health risk with subsequent tomato production, especially in areas prone to bacterial spot disease.

Comparative Investigation of Prevalence and Antimicrobial Resistance of Salmonella Between Pasture and Conventionally Reared Poultry

The objective of this study was to compare Salmonella prevalence and antimicrobial resistance between pasture and conventional poultry farms. We collected the first Salmonella prevalence and antimicrobial resistance data on pasture poultry farms. Fecal droppings were collected from 31 farms from Wisconsin (nine farms from each production type) and the Southeast (North Carolina, Virginia, and South Carolina; five conventional and 10 pasture poultry farms) in a 1-yr period. The specimens were cultured for Salmonella and tested for resistance to 12 antimicrobials. A univariate analysis was conducted to determine the significant differences in prevalence and resistance. At the farm level, no significant difference in Salmonella prevalence was found on 33% pasture and 47% conventional poultry farms (P= 0.4928). On an individual specimen level, flocks reared conventionally had higher prevalence than in pasture (P < 0.0001). Of all the isolates found to have resistance, 80% were from the Southeast. Of all the pasture isolates tested, 5% (8 of 162) were resistant to ceftriaxone, which is higher than previously reported from any production setting. None of the isolates from conventional flocks showed resistance to ceftriaxone. Multidrug resistance (resistance to three or more classes of antimicrobials) was found in 69% of the isolates from conventional farms and 11% on pasture farms in the Southeast (P < 0.0001), with the predominant resistance type of AmCSSuTeAx (ampicillin, chloramphenicol, streptomycin, sulfasoxazole, tetracycline, amoxicillin/clavulanic acid; 62%). About 5% of the pasture isolates from the Southeast showed the AmAxCFCRO (ampicillin, amoxicillin/clavulanic acid, cephalothin, ceftriaxone) multidrug resistance pattern. None of the isolates from Wisconsin were found to be multidrug resistant.

The occurrence and characterization of Campylobacter jejuni and C. coli in organic pigs and their outdoor environment

The occurrence and species distribution of thermophilic Campylobacter was investigated in organic outdoor pigs. An increased exposure of outdoor pigs to C. jejuni from the environment may cause a shift from a normal dominance of C. coli to more C. jejuni, which may imply a concern of reduced food safety. Bacteriological methods for determination of Campylobacter excretion level were combined with colony-blot hybridization and real-time PCR for specific detection of C. jejuni in pigs. Campylobacter was isolated from pigs (n=47), paddock environment (n=126) and wildlife (n=44), identified to species by real-time PCR and sub-typed by serotyping (Penner) and pulse-field gel electrophoresis (PFGE) genotyping. All pigs excreted Campylobacter (10(3)-10(7) CFU g(-1) faeces) from the age of 8-13-weeks old. C. jejuni was found in 29% of pigs in three consecutive trials and always in minority to C. coli (0.3-46%). C. jejuni and C. coli were isolated from 10% and 29% of the environmental samples, respectively, while crow-birds and rats harboured C. jejuni. Individual pigs hosted several strains (up to nine serotypes). The paddock environment was contaminated with C. coli serotypes similar to pig isolates, while most of the C. jejuni serotypes differed. C. jejuni isolates of different origin comprised few similar serotypes, just one identical genotype was common between pigs, environment and birds. In conclusion, the occurrence of C. jejuni varied considerably between the three groups of outdoor pigs. Furthermore, transfer of C. jejuni to the outdoor pigs from the nearby environment was not predominant according to the subtype dissimilarities of the obtained isolates.