Survival and infectivity of Salmonella choleraesuis in swine feces

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.

Salmonella enterica subspecies enterica serovar Choleraesuis in a Swedish gilt-producing herd, a case report

BACKGROUND

When Salmonella enterica subspecies enterica serovar Choleraesuis (S. Choleraesuis) was detected in faecal samples collected within the Swedish Salmonella surveillance program from a gilt multiplying herd in September 2020, S. Choleraesuis had not been detected in domestic pigs or wild boar in Sweden for over 40 years. This report describes the subsequent investigation, identification of possible entry routes and measures undertaken to eliminate the pathogen from the herd.

CASE PRESENTATION

In accordance with Swedish regulations, pig movements to and from the farm were restricted, internal biosecurity measures were enhanced, and a test-and-remove strategy was implemented. Testing included repeated faecal sampling, tissue samplings from all dead or euthanized pigs, and serological sampling of replacement gilts. Epidemiological investigations included scrutinising of production records, employee interviews, analysing feed and environmental samples, faecal samples from the herd's purebred gilt supplier, and tissue and faecal samples from wild boars in the adjacent area. Testing of in-contact herds receiving gilts (n = 15) or 30-kg pigs (n = 7) from the multiplier included whole-herd faecal sampling and tissue cultures from pigs that died with signs of septicaemia. In total, S. Choleraesuis was detected in 12/4200 faecal and 5/1350 tissue samples from the herd, and the corresponding groups of pigs were euthanized. All feed and environmental samples as well as samples from the gilt supplier were negative. Testing of contact herds resulted in the identification and culling of one group of S. Choleraesuis-positive gilts. Replacement gilts introduced to the herd from January until May 2021 remained serologically negative during a surveillance-period of five months.

CONCLUSION

Although speculative, the epidemiological investigation identified indirect transmission from wild boar as possible source of introduction to the herd. Whole-genome sequencing of S. Choleraesuis isolates from wild boar in the area showed that they clustered with isolates from the herd. Repeated testing of the herd indicated that the test-and-remove strategy was successful. In August 2021, all restrictions were removed, and the herd was re-instated as a gilt producing herd. Compensation from the Swedish state to the farmer for production losses, culled animals and extra costs associated with the elimination cost totalled SEK 7 992 234.

First Detection of Salmonella enterica Serovar Choleraesuis in Free Ranging European Wild Boar in Sweden

Following the first detection of Salmonella enterica subsp. enterica, serovar Choleraesuis (S. Choleraesuis) in a Swedish pig herd for more than 40 years and subsequent detection of the same serotype in an enclosure with kept wild boar, a national surveillance for S. Choleraesuis in free living wild boar was launched. A total of 633 wild boar sampled within the active and the enhanced passive surveillance were examined for Salmonella enterica serovars by culture. Of these, 80 animals were culture positive for S. Choleraesuis var. Kunzendorf. All positive animals, including those in the original outbreaks, originated from counties located in the southern and eastern parts of Sweden. Fifty-eight isolates were selected for sequence typing, revealing a relatively homogenous population of S. Choleraesuis with two distinct genetic clusters containing isolates from the southern counties in one and the counties further northeast in the other. Sequenced isolates from domestic pig farms all clustered with wild boar in the same region. S. Choleraesuis appears highly contagious in dense wild boar populations, making it a relevant model for other infectious diseases that may be transmitted to pigs. The many potential routes of introduction and spread of S. Choleraesuis warrant further investigations in order to prepare for other disease threats.

Bacterial and viral enterocolitis in horses: a review

Enteritis, colitis, and enterocolitis are considered some of the most common causes of disease and death in horses. Determining the etiology of these conditions is challenging, among other reasons because different causes produce similar clinical signs and lesions, and also because some agents of colitis can be present in the intestine of normal animals. We review here the main bacterial and viral causes of enterocolitis of horses, including Salmonella spp., Clostridium perfringens type A NetF-positive, C. perfringens type C, Clostridioides difficile, Clostridium piliforme, Paeniclostridium sordellii, other clostridia, Rhodococcus equi, Neorickettsia risticii, Lawsonia intracellularis, equine rotavirus, and equine coronavirus. Diarrhea and colic are the hallmark clinical signs of colitis and enterocolitis, and the majority of these conditions are characterized by necrotizing changes in the mucosa of the small intestine, colon, cecum, or in a combination of these organs. The presumptive diagnosis is based on clinical, gross, and microscopic findings, and confirmed by detection of some of the agents and/or their toxins in the intestinal content or feces.

Survival of Salmonella in Various Wild Animal Feces That May Contaminate Produce

ABSTRACT

Heightened concerns about wildlife on produce farms and possible introduction of pathogens to the food supply have resulted in required actions following intrusion events. The purpose of this study was to evaluate the survival of Salmonella in feces from cattle and various wild animals (feral pigs, waterfowl, deer, and raccoons) in California, Delaware, Florida, and Ohio. Feces were inoculated with rifampin-resistant Salmonella enterica cocktails that included six serotypes: Typhimurium, Montevideo, Anatum, Javiana, Braenderup, and Newport (104 to 106 CFU/g). Fecal samples were stored at ambient temperature. Populations were enumerated for up to 1 year (364 days) by spread plating onto tryptic soy agar supplemented with rifampin. When no colonies were detected, samples were enriched. Colonies were banked on various sampling days based on availability of serotyping in each state. During the 364-day storage period, Salmonella populations decreased to ≤2.0 log CFU/g by day 84 in pig, waterfowl, and raccoon feces from all states. Salmonella populations in cattle and deer feces were 3.3 to 6.1 log CFU/g on day 336 or 364; however, in Ohio Salmonella was not detected after 120 days. Salmonella serotypes Anatum, Braenderup, and Javiana were the predominant serotypes throughout the storage period in all animal feces and states. Determination of appropriate risk mitigation strategies following animal intrusions can improve our understanding of pathogen survival in animal feces.

HIGHLIGHTS

Salmonella enterica subspecies enterica serovar Choleraesuis in a German wild boar population: occurrence and characterisation

BACKGROUND

The swine-adapted serovar Choleraesuis of Salmonella enterica subspecies enterica is found rarely in domestic pigs in Germany. However, a considerable and increasing number of S. Choleraesuis organisms have been isolated from wild boars in Germany in recent years. To investigate a possible epidemiological context, S. Choleraesuis strains from a regional German wild boar population and other hosts were characterised by genotyping methods.

RESULTS

Macrorestriction analysis, biochemical differentiation and antimicrobial susceptibility typing enabled the identification of several clusters of S. Choleraesuis. Some clusters occurred almost permanently in a certain district, whereas other groups circulated among different wild boar herds in larger regions. Non-porcine hosts were infected with the same cluster as the wild boars.

CONCLUSIONS

The emergence of S. Choleraesuis in wild boars might be caused by a higher prevalence in the wild boar population, but also the higher awareness to infections with African swine fever may have resulted in a higher number of examined animals. Separation of wild boar populations and, as a result, also the diverse S. Choleraesuis organisms might be due to natural barriers and artificial barriers like arterial roads. The findings of S. Choleraesuis in domestic pigs emphasize the importance of strict biosecurity measures to prevent transmission from wild boars of this but also other pathogens. To avoid risks for humans by zoonotic pathogens regular inspections of meat from wildlife need to be conducted.

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.

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 Live Salmonella Gallinarum Vaccine Candidate Secreting an Adjuvant Protein Confers Enhanced Safety and Protection Against Fowl Typhoid

Live attenuated vaccines are used for effective protection against fowl typhoid (FT) in domestic poultry. In this study, a lon/cpxR/asd deletion mutant of Salmonella Gallinarum expressing the B subunit of a heat labile toxin (LTB) from Escherichia coli, a known adjuvant, was cloned in a recombinant p15A ori plasmid, JOL1355, and evaluated as a vaccine candidate in chickens. The plasmid was shown to be stable inside the attenuated Salmonella Gallinarum cell after three successive generations. Moreover, from an environmental safety point of view, apart from day 1 the JOL1355 strain was not detected in feces through day 21 postinoculation. For the efficacy of JOL1355, a total of 100 chickens were equally divided into two groups. Group A (control) chickens were intramuscularly inoculated with phosphate-buffered saline at 4 and 8 wk of age. Group B chickens were primed and boosted via the intramuscular route with 200 μL of a bacterial suspension of JOL1355 containing 1 × 10(8) colony forming units. All the chickens in Group A and B were challenged at 3 wk postbooster by oral inoculation with a wild-type Salmonella Gallinarum strain, JOL420. The JOL1355-immunized group showed significant protection and survival against the virulent challenge compared to the nonimmunized group. In addition, Group B exhibited a significantly higher humoral immune response, and the chickens remained healthy without any symptoms of anorexia, diarrhea, or depression. Group B also exhibited a significantly lower mortality rate of 4% compared to the 46% of the control group, which can be attributed to higher immunogenicity and better protection. The Group B chickens had significantly lower lesion scores for affected organs, such as the liver and spleen, compared to those of the control chickens (P < 0.01). These findings suggest that JOL1355 is a promising candidate for a safe and highly immunogenic vaccine against FT.

From the bench to modeling--R0 at the interface between empirical and theoretical approaches in epidemiology of environmentally transmitted infectious diseases

For environmentally transmitted infectious diseases (ETIDs), which spread through the contaminated environment (such as foods, surfaces and fomites), there is a lack of consensus about the mathematical approach to derive R0, leading to inconsistent predictions about the spread and control of these infections in their host populations. The objective of this study was to explain three current, though conflicting, approaches to derive a theoretical expression for R0 for ETIDs and assess their validity through comparison with available empirical data. Salmonella Typhimurium in laboratory mice was used as a theoretical and empirical model system. The three conflicting theoretical expressions for R0 were derived using the next generation matrix approach according to three unverified hypotheses about the role of the environmental phase in the transmission of ETIDs. The hypotheses assume that the environment contaminated with a pathogen is: (H1) an extension of the host's infectious period, (H2) a reservoir for the infectious agent, or (H3) has both of these characteristics. For the parameter values describing the empirical model system, the theoretical values of R0 corresponding to the hypotheses H2 and H3 were very similar (1.38 and 1.62, respectively) and their values were approximately half of the value of R0 for hypothesis H1 (2.94). The theoretical R0 values were compared with an empirical R0 (1.58, 95% confidence interval: 1.14, 2.02) estimated using a Martingale method from published experimental data on Salmonella Typhimurium transmission in mice. The results of the comparison suggested that hypothesis H1 is unlikely to hold true but it could not be rejected with confidence because of uncertainty in the value of the pathogen growth rate in the environment. The hypotheses H2 and H3 were both equally strongly supported with the empirical data suggesting that either of them could be valid. A sensitivity analysis identified critical information gaps about the indirect transmission rate of infection and the pathogen growth rate in the environment. Moreover, we identified experimental conditions for which the theoretical R0 predictions based on the hypotheses H2 and H3 differ greatly, which would assist their discrimination and conclusive validation against future empirical studies. Once a valid theoretical R0 is identified for Salmonella Typhimurium in mice, its generalizability to other host-pathogen-environment systems should be tested. The present study may serve as a template for integrated empirical and theoretical research of R0 in the epidemiology of ETIDs.

Airborne Microorganisms From Livestock Production Systems and Their Relation to Dust

Large amounts of airborne microorganisms are emitted from livestock production. These emitted microorganisms may associate with dust, and are suspected to pose a risk of airborne infection to humans in vicinity and to animals on other farms. However, the extent to which airborne transmission may play a role in the epidemic, and how dust acts as a carrier of microorganisms in the transmission processes is unknown. The authors present the current knowledge of the entire process of airborne transmission of microorganisms-from suspension and transportation until deposition and infection-and their relation to dust. The sampling and the mitigation techniques of airborne microorganisms and dust in livestock production systems are introduced as well.

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.

Effectiveness of simulated interventions in reducing the estimated prevalence of Salmonella in UK pig herds

Salmonella spp are a major foodborne zoonotic cause of human illness. Consumption of pork products is believed to be a major source of human salmonellosis and Salmonella control throughout the food-chain is recommended. A number of on-farm interventions have been proposed, and some have been implemented in order to try to achieve Salmonella control. In this study we utilize previously developed models describing Salmonella dynamics to investigate the potential effects of a range of these on-farm interventions. As the models indicated that the number of bacteria shed in the faeces of an infectious animal was a key factor, interventions applied within a high-shedding scenario were also analysed. From simulation of the model, the probability of infection after Salmonella exposure was found to be a key driver of Salmonella transmission. The model also highlighted that minimising physiological stress can have a large effect but only when shedding levels are not excessive. When shedding was high, weekly cleaning and disinfection was not effective in Salmonella control. However it is possible that cleaning may have an effect if conducted more often. Furthermore, separating infectious animals, shedding bacteria at a high rate, from the rest of the population was found to be able to minimise the spread of Salmonella.

Semi-stochastic models for Salmonella infection within finishing pig units in the UK

A multi-group semi-stochastic model is formulated to describe Salmonella dynamics on a pig herd within the UK and assess whether farm structure has any effect on the dynamics. The models include both direct transmission and indirect (via free-living infectious units in the environment and airborne infection). The basic reproduction number R0 is also investigated. The models estimate approximately 24.6% and 25.4% of pigs at slaughter weight will be infected with Salmonella within a slatted-floored and solid-floored unit respectively, which corresponds to values found in previous abattoir and farm studies, suggesting that the model has reasonable validity. Analysis of the models identified the shedding rate to be of particular importance in the control of Salmonella spread, a finding also evident in an increase in the R0 value.

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.

Informing surveillance programmes by investigating spatial dependency of subclinicalSalmonellainfection

The aim of this paper is to investigate local spatial dependency with regard toSalmonellaseropositivity in data from the Danish swine salmonellosis control programme and its application in informing surveillance strategies. We applied inhomogeneous and observed-differenceK-function estimation, and geo-statistical modelling to data from the Danish swine salmonellosis control programme. Slaughter-pig farm density showed large variation at both the country-wide and local level in Denmark (median 0·23, range 0·02–0·47 farms/km2). The spatial distribution of pig farms followed a random inhomogeneous Poisson process but was not aggregated. We found evidence for aggregation ofSalmonellacase farms over that of all farms at distances of up to 6 km and semivariogram analyses ofSalmonellaseropositivity revealed spatial dependency between pairs of farms up to 4 km apart. The strength of the spatial dependency was positively associated with slaughter-pig farm density. We proposed sampling more intensively those farms within a 4 km radius of farms that were identified with a highSalmonellastatus, and reduced sampling of farms that are within this radius of ‘Salmonella-free’ farms. Our approach has the potential to optimize sampling strategies while maintaining consumer confidence in food safety and also has potential to be used for other zoonotic disease surveillance systems.

Approaches for reducing Salmonella in pork production

Salmonellosis is an important disease in humans and is associated with contaminated food, including pork products. Salmonella infection is invasive in humans, but it usually remains latent within the swine population, creating reservoirs for carcass contamination. Although abattoirs implement stringent procedures during carcass processing, some raw pork products still have Salmonella contamination. To reduce the presence of Salmonella, a dynamic picture of the pork production chain is needed that includes management practices aimed at health and welfare of swine and practices within swine operations that affect the environment and community health. Swine practices indirectly influence the spread of zoonotic enteric pathogens. Pathogens in food animals can escape detection, and critical control points often are missed. Preharvest growth of swine by enhancement of normal gut flora and targeting intestinal pathogens through nonantibiotic approaches might improve food safety and reduce antibiotic residues. In light of the threat posed by multidrug-resistant pathogens, old dogma is being revisited with optimism for potential utility in promoting pre- and postharvest pork safety. This review includes possible approaches that can be implemented in swine operations and postslaughter during pork processing with simultaneous omission of subtherapeutic antibiotics to control Salmonella. We emphasize the vital roles of the veterinarians, pig producers, industry, food research scientists, and government guidelines for the strategic implementation of approaches to Salmonella control across the pork production and processing chains.

Prevalence, distribution and characterisation of ceftiofur resistance in Salmonella enterica isolated from animals in the USA from 1999 to 2003

Third-generation cephalosporin (3GC) antimicrobials are the drugs of choice for treatment of salmonellosis in children. Salmonella isolated in the USA are assayed by the National Antimicrobial Resistance Monitoring System (NARMS) for resistance to antimicrobials including first-, second- and third-generation cephalosporins. From 1999 to 2003, 34,411 Salmonella were isolated from animals in the USA, of which 10.9% were found to be resistant to ceftiofur, a 3GC used in animals, whilst only 0.3% were resistant to ceftriaxone, a 3GC used in human medicine. Ceftiofur resistance rose from 4.0% in 1999 to 18.8% in 2003. Isolates from diagnostic laboratories had higher levels of resistance (18.5%), whereas levels in isolates from on-farm (3.4%) and slaughter (7.1%) sources were lower. Animals with a higher than average proportion of resistant Salmonella included cattle (17.6%), horses (19.2%) and dogs (20.8%). Levels in turkeys (6.8%), chickens (7.1%), eggs (3.6%) and swine (4.6%) were lower. Resistance varied between Salmonella serotypes. A few serotypes had significantly high levels, e.g. S. Newport was 70.4% ceftiofur resistant. Resistance was predominantly associated with bla(CMY-2)-encoding plasmids. These data suggest that the acquisition of resistance plasmids and the spread of specific serotypes harbouring these plasmids are driving the observed resistance to ceftiofur in Salmonella animal isolates.

Rapid aerosol transmission of Salmonella among turkeys in a simulated holding-shed environment

Once turkeys arrive at Midwest processing plants, they are usually held in large open-sided sheds for 1 to 4 h, waiting to be unloaded. In hot, humid weather, large fans are used to cool the birds. The resultant air currents distribute a significant amount of dust to the turkeys. The dust created in this environment could be a factor in the number of Salmonella-contaminated turkeys entering slaughter plants. The objective of this study was to determine if rapid transmission of Salmonella in turkeys could occur from exposure to Salmonella-contaminated dust similar to what may be experienced in holding sheds or in other high-dust environments prior to slaughter. In the first experiment, trials of 3 different concentrations of Salmonella (1.2 x 10(9), 2.6 x 10(7), and 2.6 x 10(5) cfu/g) were conducted to determine if transmission of Salmonella enterica serovar Typhimurium var. typhimurium(chi)4232 to turkeys 2 to 4 h after aerosol exposure to contaminated feces is possible. Results showed that turkeys became infected after 2 h of exposure to airborne-contaminated feces with a concentration level of 2.6 x 10(5) cfu of Salmonella Typhimurium/g. In the second experiment, consisting of 3 trials, 1 bank (5 cages wide and 3 cages high) of turkeys (n = 15 birds per trial) was exposed to another bank of cages of S. Typhimurium-inoculated (n = 15) birds for 2 to 4 h using a fan similar to the type in processing-plant cooling sheds. Results from this experiment demonstrated that birds could be contaminated with S. Typhimurium after 2 h of exposure. Results of both studies implicate contaminated dust as a route of rapid airborne transmission of Salmonella in turkeys. Processes that generate significant dust prior to slaughter should be regarded as critical control points for Salmonella.

Impact of heat stress on the fecal shedding patterns of Salmonella enterica Typhimurium DT104 and Salmonella enterica infantis by 5-week-old male broilers

The objective of this study was to determine if there is an impact of heat stress of broiler chickens on number and survival of two types of Salmonella shed in the chicken's feces after an oral challenge. The data from this study indicate that heat stress did not result in higher levels or longer survival of Salmonella spp. shed in feces. It is possible that the duration or intensity of the heat stress employed was not sufficient or that heat stress does not alter the number or survivability for these particular strains of Salmonella spp. Feces stored at room temperature after collection, resulted in the numbers of both strains of Salmonella increasing by one to three logs in the first week. This finding indicates that there could be an increase in environmental contamination under certain conditions.

Influence of Salmonella in pigs preharvest and during pork processing on human health costs and risks from pork

Salmonellosis in humans is a costly disease traditionally assumed to be associated with exposure to contaminated food. We have developed a farm-to-fork model that allows estimation of the human health costs and risks associated with Salmonella in pork. This analysis focuses on the stages of the pork production chain up to the point of producing a chilled pork carcass. The model predicts the number of human cases of salmonellosis associated with pork (mean, 99,430; 90% confidence interval, 20,970 to 245,560) and the corresponding social costs (mean, $81.53 million; 90% confidence interval, $18.75 million to $197.44 million). Sensitivity and scenario analyses suggest that changes in Salmonella status during processing are more important for human health risk and have a higher benefit:cost ratio when compared with on-farm strategies for Salmonella control. Specifically, benefit:cost ratios are less than 1 (indicating they are not likely to be profitable from a social economic perspective) for the on-farm strategies of vaccination and meal feeding, whereas rinsing carcasses at various temperatures with and without sanitizer all have benefit:cost ratios greater than 1 (indicating they are profitable from a social economic perspective). This type of modeling is useful for evaluation of the relative cost effectiveness of interventions at different points in the food chain when allocating limited food safety dollars and is best used for examining trends and alternative strategies rather than for providing definitive dollar value estimates of risk. The dollar value estimates must be considered in the context of the wide confidence intervals.

Salmonella enterica serotype Choleraesuis: epidemiology, pathogenesis, clinical disease, and treatment

Nontyphoid Salmonella strains are important causes of reportable food-borne infection. Among more than 2,000 serotypes, Salmonella enterica serotype Choleraesuis shows the highest predilection to cause systemic infections in humans. The most feared complication of serotype Cholearesuis bacteremia in adults is the development of mycotic aneurysm, which previously was almost uniformally fatal. The advances in diagnostic techniques, surgical care, and antimicrobial therapy have greatly improved the survival of these patients. However, the recent emergence of serotype Choleraesuis that is resistant to ampicillin, chloramphenicol, trimethoprim-sulfamethoxazole, and, notably, fluoroquinolone antibiotics has aroused concern about the use of these agents for the empirical treatment of systemic infection caused by this organism. In view of the serious implications of the situation, the chain of transmission and mechanism of resistance should be carefully studied to reduce the spread of infection and threat to human health. To date, there are no vaccines available to prevent serotype Choleraesuis infections in humans. The availability, in the near future, of the genome sequence of serotype Cholearesuis will facilitate the development of effective vaccines as well as the discovery of new targets for novel antimicrobial agents.

Preslaughter holding environment in pork plants is highly contaminated with Salmonella enterica

The objective of this study was to determine whether abattoir pens can provide a Salmonella enterica infection source during the 2 to 4 h of preharvest holding. Previous work has suggested that pigs may be getting infected, but little has been reported on the environmental contamination of abattoir holding pens. For 24 groups of pigs studied ( approximately 150 animals/group) at two high-capacity abattoirs, six pooled fecal samples (n, 10 per pool) were collected from each transport trailer immediately after pigs were unloaded. Holding pens were sampled (one drinking water sample and six pooled floor samples consisting of swabs, residual liquid, and feces) prior to entry of study pigs for the routine holding period ( approximately 2.5 h). After slaughter, cecal contents and ileocecal lymph nodes were collected, on the processing line, from 30 pigs in each studied group. All samples were cultured for the isolation and identification of S. enterica by primary enrichment in GN-Hajna and tetrathionate broths, secondary enrichment in Rappaport-Vassiliadis broth, and plating on brilliant green sulfa and xylose-lysine-tergitol-4 agars, followed by biochemical and serological identification. The study pens were highly contaminated with S. enterica; all holding pens sampled had at least one positive sample. Additionally, 33% (8 of 24) of drinking water samples were positive for S. enterica. All 24 groups of pigs had S. enterica-positive cecal contents and ileocecal lymph nodes, including those groups from transport trailers with no positive samples. From pigs, trailers, and pens, 586 isolates representing 36 different Salmonella serovars were isolated. Of the 353 isolates from pigs (109 from ileocecal lymph nodes plus 244 from cecal contents), 19% were identified as belonging to the same serovars as those isolated from the respective pens; 27% were identified as belonging to the same serovars as those isolated from the trailers. Sixteen percent of the unique serovars were isolated from both pigs and pens, suggesting that pens served as the infection source. This study demonstrates highly contaminated abattoir holding pens and watering sources. It also demonstrates that holding pens can serve as an infection source. This study identifies the abattoir holding pens as a significant hazard and a potential control point for Salmonella contamination in the preharvest pork production chain.

Persistence of Salmonella enteritidis phage type 4 in the environment and arthropod vectors on an empty free-range chicken farm

The persistence of S. Enteritidis PT4 was studied on a free-range breeding chicken farm which had been depopulated following identification of the organism in breeding birds. The site was sampled periodically for 26 months after depopulation and the organism was found to persist in litter, dried faeces and feed, but not in dust within empty poultry houses, for the whole of that period. Salmonella Enteritidis PT4 was also found in soil samples after 8 months but not 13 months and in faeces from wild mice, foxes and cats but not wild birds or badgers. The organism was also found in adult and larval forms of ground beetles and centipedes. Addition of pullets to a contaminated pen or inclusion of contaminated litter, feed or beetles/larvae to feed did not result in acquisition of infection by birds.