Alternate routes of invasion may affect pathogenesis of Salmonella typhimurium in swine

Infection biology of Salmonella enterica

Salmonella enterica is the leading cause of bacterial foodborne illness in the USA, with an estimated 95% of salmonellosis cases due to the consumption of contaminated food products. Salmonella can cause several different disease syndromes, with the most common being gastroenteritis, followed by bacteremia and typhoid fever. Among the over 2,600 currently identified serotypes/serovars, some are mostly host-restricted and host-adapted, while the majority of serotypes can infect a broader range of host species and are associated with causing both livestock and human disease. Salmonella serotypes and strains within serovars can vary considerably in the severity of disease that may result from infection, with some serovars that are more highly associated with invasive disease in humans, while others predominantly cause mild gastroenteritis. These observed clinical differences may be caused by the genetic make-up and diversity of the serovars. Salmonella virulence systems are very complex containing several virulence-associated genes with different functions that contribute to its pathogenicity. The different clinical syndromes are associated with unique groups of virulence genes, and strains often differ in the array of virulence traits they display. On the chromosome, virulence genes are often clustered in regions known as Salmonella pathogenicity islands (SPIs), which are scattered throughout different Salmonella genomes and encode factors essential for adhesion, invasion, survival, and replication within the host. Plasmids can also carry various genes that contribute to Salmonella pathogenicity. For example, strains from several serovars associated with significant human disease, including Choleraesuis, Dublin, Enteritidis, Newport, and Typhimurium, can carry virulence plasmids with genes contributing to attachment, immune system evasion, and other roles. The goal of this comprehensive review is to provide key information on the Salmonella virulence, including the contributions of genes encoded in SPIs and plasmids during Salmonella pathogenesis.

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.

Quantitative Microbial Risk Assessment (QMRA) of Workers Exposure to Bioaerosols at MSW Open Dumpsites

The bioaerosol exposure data from the study by Akpeimeh, Fletcher, and Evans (2019) was used to compute the risk of infection from the exposure of dumpsite workers to Aspergillus fumigatus and Escherichia coli O157:H7. A stochastic (Markov Chain) model was used to model the transport of the inhaled dose though the human respiratory system and then integrated into the beta-Poisson dose-response model to estimate workers risks of respiratory and gastrointestinal (GI) infection. The infection risk was computed based on workers exposure to E. coli O157:H7 at 10-50% pathogen ingestion rate and pathogen-indicator ratio (P:I) of 1:10³ and 1:10⁴ , while exposure to A. fumigatus was based solely on the average initial exposure dose. The results showed that after 11 hours of exposure, workers engaged in scavenging, waste sorting, and site monitoring were at risk of respiratory and GI infection in the magnitude of 10^-1 . However, the risk estimates associated with specific areas of the dumpsite showed that, the risk of GI infection at the active area ranged between 3.23 × 10^-3 -1.56 × 10^-2 and 3.25 × 10^-4 -1.62 × 10^-3 ; dormant area 2.06 × 10^-3 -1.01 × 10^-2 and 2.09 × 10^-4 -1.04 × 10^-3 ; entrance 1.85 × 10^-3 -9.09 × 10^-3 and 1.87 × 10^-4 -9.27 × 10^-4 ; boundary 1.82 × 10^-3 -8.82 × 10^-3 and 2.09 × 10^-4 -8.94 × 10^-4 for P:I = 1:10³ and 1:10⁴ respectively, while the risk of respiratory infection risks were in the magnitude of 10^-1 for all four locations. The estimated risk of workers developing respiratory and gastrointestinal infections were high for all activities assessed at the dumpsite.

Vaccination and Infection of Swine With Salmonella Typhimurium Induces a Systemic and Local Multifunctional CD4+ T-Cell Response

The gram-negative facultative intracellular bacteria Salmonella Typhimurium (STM) often leads to subclinical infections in pigs, but can also cause severe enterocolitis in this species. Due to its high zoonotic potential, the pathogen is likewise dangerous for humans. Vaccination with a live attenuated STM strain (Salmoporc) is regarded as an effective method to control STM infections in affected pig herds. However, information on the cellular immune response of swine against STM is still scarce. In this study, we investigated the T-cell immune response in pigs that were vaccinated twice with Salmoporc followed by a challenge infection with a virulent STM strain. Blood- and organ-derived lymphocytes (spleen, tonsils, jejunal and ileocolic lymph nodes, jejunum, ileum) were stimulated in vitro with heat-inactivated STM. Subsequently, CD4⁺ T cells present in these cell preparations were analyzed for the production of IFN-γ, TNF-α, and IL-17A by flow cytometry and Boolean gating. Highest frequencies of STM-specific cytokine-producing CD4⁺ T cells were found in lamina propria lymphocytes of jejunum and ileum. Significant differences of the relative abundance of cytokine-producing phenotypes between control group and vaccinated + infected animals were detected in most organs, but dominated in gut and lymph node-residing CD4⁺ T cells. IL-17A producing CD4⁺ T cells dominated in gut and gut-draining lymph nodes, whereas IFN-γ/TNF-α co-producing CD4⁺ T cells were present in all locations. Additionally, the majority of cytokine-producing CD4⁺ T cells had a CD8α⁺CD27^- phenotype, indicative of a late effector or effector memory stage of differentiation. In summary, we show that Salmonella-specific multifunctional CD4⁺ T cells exist in vaccinated and infected pigs, dominate in the gut and most likely contribute to protective immunity against STM in the pig.

Isolation and Antimicrobial Susceptibility Profile of Escherichia coli O157 : H7 from Raw Milk of Dairy Cattle in Holeta District, Central Ethiopia

A cross-sectional study was conducted in small, medium, and large-scale dairy farms of Holeta district to isolate, identify, and antimicrobial susceptibility profile of Escherichia coli O157 : H7 in raw milk of dairy cattle. A total of 210 lactating cows were selected for raw milk samples, and 19% (40/210) were found to be positive for E. coli whereas 5.2% (11/210) were confirmed as E. coli O157 : H7 positive using the Escherichia coli O157 latex test. Accordingly, all E. coli was highly susceptible to Ciprofloxacin (100%), Gentamycin (100%), Oxytetracycline (100%), and Tetracycline (63.63%). Furthermore, the resistance of 72.73%, 54.54%, 54.54%, and 45.45% was developed to Cefoxitin, Sulphamethoxazole, Cloxacillin, and Streptomycin, respectively. Factors such as parity, age, body condition, herd size, milk yield, udder hygiene, and udder lesion showed a statistically significant ( $p<0.05$ ) association with the occurrence of E. coli infection in dairy cattle. In conclusion, in this study, a higher prevalence of Escherichia coli O157 : H7 and its drug susceptibility profile is an alarm for the health of the public, and awareness creation to the farm owners and the community is recommended.

Salmonella Typhimurium Infection Along the Porcine Gastrointestinal Tract and Associated Lymphoid Tissues

Salmonella is a major foodborne pathogen and pork is one of the main sources of human salmonellosis. Understanding the pathogenesis and progression of the infection within the host is of interest to establish potential approaches to control the disease in pigs. The present study evaluates factors such as intestinal colonization, fecal shedding, and pathogen persistence by 2 studies using experimental challenge with Salmonella Typhimurium in weaned pigs and euthanasia at different time points (1, 2, and 6 and 2, 14, and 30 days postinfection [dpi], respectively). Histopathology of intestine at early time points (1 dpi and 2 dpi) showed severe damage to the epithelium together with an increase in polymorphonuclear cells and macrophages (P < .001), particularly in jejunum and ileum. Large quantities of Salmonella were detected within the contents of the ileum, cecum, and colon in early infection. Salmonella could also be observed in the medulla of tonsils and mesenteric lymph nodes. From 6 dpi onward, signs of recovery were observed, with progressive restoration of the epithelium, reduction of the inflammatory infiltrate, and elimination of Salmonella from the mucosa. Concentration of Salmonella in feces and ileum content decreased, but shedding did not cease even at 4 weeks after infection. Persistence of the bacteria in mesenteric lymph nodes was identified within the connective tissue at 14 and 30 dpi. Our results demonstrate a recovery of the disease after an initial acute phase but also show persistence within the lumen and surrounding lymphoid tissue. These findings are relevant to developing effective control strategies.

Prevalence of Salmonella spp. in tonsils, mandibular lymph nodes and faeces of wild boar from Spain and genetic relationship between isolates

The importance of wild boars as game species in Spain is well known. Their feeding habits and intrusive behaviour, together with a progressively wider spreading of populations, increases the interactions of these animals with livestock and humans. Considering that wild boars could have a potential role in the transmission of certain pathogens as salmonellae, the aims of this study were to determine the prevalence of Salmonella spp. in wild boars hunted in central-western Spain, the occurrence of this pathogen in tonsils, mandibular lymph nodes and faeces (as markers for transmission risk), and to define the phylogenetic relationships among isolated strains, in order to investigate the circulation pathways of bacteria among tissues, animals and estates. Samples from 1,041 hunted wild boars were analysed for the presence of Salmonella spp. by bacteriological culture. Isolates were confirmed by PCR and serotyped in the Spanish national reference laboratory. The genetic relationships between strains were determined by PFGE. The results showed a 7.7% of positive animals (81 wild boars), being tonsils the organ most frequently colonised by Salmonella spp. (18.7%), followed by lymph nodes (5.1%) and faecal samples (2.9%). Serovars Enteritidis and Newport were the most frequent amongst the 34 different serovars obtained. The pulsed-field gel electrophoresis (PGFE) analysis showed a great genetic diversity, with serovars that exhibited different pulsotypes when isolated from different estates and multiple serovars in the same estate. In conclusion, this study reveals the importance of wild boars as carriers and possible transmitters of virulent and/or antimicrobial-resistant clones of Salmonella spp. to livestock and humans.

Chlortetracycline Enhances Tonsil Colonization and Fecal Shedding of Multidrug-Resistant Salmonella enterica Serovar Typhimurium DT104 without Major Alterations to the Porcine Tonsillar and Intestinal Microbiota

Salmonella spp. are estimated to cause 1.2 million cases of human foodborne illness each year in the United States, and pigs can often be asymptomatically colonized with Salmonella spp. (>50% of farms). Recent reports state that 18.3% of Salmonella enterica serovar Typhimurium isolates are resistant to ≥3 antimicrobial classes, and multidrug-resistant (MDR) strains are associated with an increased hospitalization rate and other complications. Chlortetracycline is commonly used in swine production to prevent/treat various diseases; therefore, chlortetracycline treatment of pigs unknowingly colonized with MDR Salmonella may have collateral effects on Salmonella spp. (and other gut bacteria). In this study, we determined the effect of in-feed chlortetracycline (400 g/ton) on shedding and colonization of pigs challenged with the MDR S Typhimurium strain DT104 (n = 11/group). We also assessed the impact on the fecal microbiota over the 12-day experimental period and on the ileum, cecum, and tonsil microbiota at 7 days postinoculation (dpi). In MDR S Typhimurium-inoculated pigs, chlortetracycline administration significantly increased fecal shedding at 2 dpi (+1.4 log₁₀ CFU/g; P < 0.001) and enhanced tonsil colonization (+3.1 log₁₀ CFU/g; P < 0.001). There were few major alterations detected in the gut or tonsillar microbiota of pigs treated with MDR S Typhimurium and/or chlortetracycline. The tonsillar transcriptome was largely unaffected despite increased colonization by MDR S Typhimurium following inoculation of the chlortetracycline-treated pigs. These results highlight the idea that chlortetracycline administration can enhance shedding and colonization of MDR S Typhimurium in pigs, which could increase the risk of environmental dissemination of MDR Salmonella strains.IMPORTANCE Salmonella spp. are an important cause of foodborne illness in North America, and pork products are associated with sporadic cases and outbreaks of human salmonellosis. Isolates of Salmonella may be resistant to multiple antibiotics, and infections with multidrug-resistant (MDR) Salmonella spp. are more difficult to treat, leading to increased hospitalization rates. Swine operations commonly use antimicrobials, such as chlortetracycline, to prevent/treat infections, which may have collateral effects on pig microbial populations. Recently, we demonstrated that chlortetracycline induces the expression of genes associated with pathogenesis and invasion in MDR Salmonella enterica serovar Typhimurium in vitro In our current study, we show increased tonsillar colonization and fecal shedding of the MDR S Typhimurium strain DT104 from pigs administered chlortetracycline. Therefore, pigs unknowingly colonized with multidrug-resistant Salmonella spp. and receiving chlortetracycline for an unrelated infection may be at a greater risk for disseminating MDR Salmonella spp. to other pigs and to humans through environmental or pork product contamination.

Salmonella fecal shedding in pigs from birth to market and its association with the presence of Salmonella in palatine tonsils and submandibular lymph nodes at slaughter

Salmonella is an important cause of foodborne illnesses in humans. Food-producing animals, including swine, are a major source of Salmonella in food products. This study investigated on farm Salmonella fecal shedding in pigs at different production stages - from weaning to marketing - and its association with the presence of Salmonella in tissues at slaughter. Fourteen groups from 8 commercial farrowing sources (N = 809 pigs) were monitored 5 times from birth to slaughter. Fecal and tissue samples were collected from pigs and cultured for Salmonella. A survey was conducted to collect farm management information. A multi-level mixed-effects logistic regression modelling method was used to analyze Salmonella shedding over time and the association between Salmonella shedding and the presence of Salmonella in tissue samples. Salmonella was recovered from 13% (421/3339) of fecal samples collected from 809 pigs over the course of the study. Overall, 35% (284) of pigs shed Salmonella at least once, while 12% (99) shed more than once. Salmonella shedding increased as pigs aged (P = 0.01) and increased in the summer months (P < 0.01). Salmonella was isolated from tissue samples collected from 23% (134/580) of pigs; however, the presence of Salmonella at slaughter was not associated with on farm shedding. The seasonal trend in Salmonella shedding and its association with age may be used to identify high-risk groups and implement more effective control measures accordingly. The identification of repeat shedders warrants interventions that target this source of infection on swine farms.

Colonization of Pigs Experimentally Infected with a Monophasic Variant of Salmonella Typhimurium

The monophasic variant of Salmonella Typhimurium is highly prevalent in human and in pork. However, little is known about colonization dynamics and serology in pigs. We orally inoculated 24 seven-week-old piglets with 10⁹ CFU/pig of a porcine strain of monophasic Salmonella Typhimurium in an experimental trial. Three groups of eight piglets were orally inoculated and monitored for 21, 49, or 84 days post-inoculation until necropsied. From 3 days post-inoculation to necropsy, individual feces were sampled twice weekly and blood once weekly. At necropsy, the tonsils, mesenteric lymph nodes, and the contents of the duodenum, jejunum, ileum, and cecum were collected from each pig. We determined the number of CFU/g in all the samples and measured also Salmonella antibodies in OD% in all blood samples. At different times during the trial, we tested by MLVA (Multilocus Variable Number Tandem Repeat Analysis) the genomic stability of the strain after passing through the intestinal tract. Salmonella was continuously excreted by pigs, ranging from 1.4 to 5.8 log₁₀ CFU/g. At necropsy, Salmonella was present in all samples, but the tonsils were particularly infected. Salmonella antibodies were detected in five pigs 7 days post-inoculation. At 49 days post-inoculation, all the pigs were seropositive. We observed new MLVA types for 3.3% of the isolates tested over the trial. Our study allowed us to show the serovar's ability to persist in pigs after infection up to 84 days post-inoculation. We demonstrated that Salmonella seroconversion appeared earlier than in naturally infected pigs and that the strain's genome can evolve after passing through the digestive tract of pigs.

Salmonella in the pork production chain and its impact on human health in the European Union

Salmonella spp. comprise the second most common food-borne pathogens in the European Union (EU). The role of pigs as carriers of Salmonella has been intensively studied both on farm and at slaughter. Salmonella infection in pigs may cause fever, diarrhoea, prostration and mortality. However, most infected pigs remain healthy carriers, and those infected at the end of the fattening period could pose a threat to human health. Contamination of pig carcasses can occur on the slaughter line, and it is linked to cross-contamination from other carcasses and the presence of Salmonella in the environment. Therefore, Salmonella serovars present on pig carcasses can be different from those detected in the same bathes on the farm. In recent years, S. Typhimurium, S. Derby and S. serotype 4,[5],12:i:- (a monophasic variant of S. Typhimurium) have been the most common serovars to be detected in pigs in EU countries, but S. Rissen, S. Infantis, S. Enteritidis and S. Brandenburg have also been reported. In humans, several cases of salmonellosis have been linked to the consumption of raw or undercooked pork and pork products. Among the main serovars of porcine origin detected in confirmed human cases, S. Typhimurium, the monophasic variant S. 4,[5],12:i:- and S. Derby are certainly the most important.

Investigation of in-feed organic acids as a low cost strategy to combat Salmonella in grower pigs

Salmonella carriage in pigs is a significant food safety issue. Dietary supplementation with organic acids has previously been shown to reduce shedding and transmission of Salmonella. Therefore, this study aimed to examine the effect of three commercially available organic acid-based products on Salmonella levels in grower pigs, using a model of experimental infection that closely mimics natural exposure to the organism. Seven week old trial pigs (n=40) with a mean weight of 14.7kg were placed in one of four pens with 10 pigs/pen. Pens had previously been contaminated with Salmonella Typhimurium 4,[5],12;i;- via seeder pigs. Trial pigs received one of four diets for 28days: 1, control diet; 2, sodium butyrate supplemented diet; 3, benzoic acid supplemented diet and 4, formic-citric acid supplemented diet. A further 10 pigs were placed in a Salmonella-free pen receiving the control diet. Pigs were weighed and blood sampled on days 0 and 28. Faeces was collected on day 0, 2, 3, 5, 7, 14, 21 and 28 and examined for Salmonella. On day 28, 5 pigs/group were euthanised and ileocaecal lymph nodes (ILN) and caecal contents sampled for culture. The remaining 5 pigs/pen were then fed the control diet and faeces were collected on days 35 and 42. On day 42 pigs were euthanised and ILN and caecal contents tested for Salmonella levels. The trial was repeated once. Within the first two days of exposure to the contaminated environment, 96% (77/80) of pigs became infected. Most pigs shed Salmonella at levels of between 10⁰-10³ CFU/g faeces for at least 7days post-exposure. A significant reduction in Salmonella faecal concentration was observed after supplementation with sodium butyrate (p=0.001) and a formic citric acid blend (p<0.0001). Average daily weight gain (ADWG) was significantly increased in all groups fed the supplemented feed when compared to the positive control group. The use of sodium butyrate or a blend of formic and citric acid in feed could be considered a cost-effective control measure to reduce Salmonella faecal shedding and improve ADWG in Salmonella infected herds.

Towards an understanding ofSalmonella entericaserovar Typhimurium persistence in swine

Salmonella entericais an important food borne pathogen that is frequently carried by swine. Carrier animals pose a food safety risk because they can transmitS. entericato finished food products in the processing plant or by contamination of the environment. Environmental contamination has become increasingly important as non-animal foods (plant-based) have been implicated as sources ofS. enterica. The prevalence ofS. entericain swine is high and yet carrier animals remain healthy.S. entericahas developed a highly sophisticated set of virulence factors that allow it to adapt to host environments and to cause disease. It is assumed thatS. entericaalso has developed unique ways to maintain itself in animals and yet not cause disease. Here we describe our research to understand persistence. Specifically, data are presented that demonstrates that detection of most carrier animals requires specific stresses that causeS. entericato be shed from pigs. As well, we describe a phenotypic phase variation process that appears to be linked to the carrier state and a complex set of factors that control phenotypic phase variation. Finally, we describe how the composition of the gut bacterial microbiome may contribute to persistence and at the least howS. entericamight alter the composition of the gut bacterial microbiome.

Salmonella in Swine: Microbiota Interactions

For the important foodborne pathogen Salmonella enterica to cause disease or persist in pigs, it has evolved an intricate set of interactions between itself, the host, and the indigenous microflora of the host. S. enterica must evade the host's immune system and must also overcome colonization resistance mediated by the pig's indigenous microflora. The inflammatory response against S. enterica provides the bacteria with unique metabolites and is thus exploited by S. enterica for competitive advantage. During infection, changes in the composition of the indigenous microflora occur that have been associated with a breakdown in colonization resistance. Healthy pigs that are low-level shedders of S. enterica also exhibit alterations in their indigenous microflora similar to those in ill animals. Here we review the literature on the interactions that occur between swine, S. enterica, and the indigenous microflora and discuss methods to reduce or prevent colonization of pigs with S. enterica.

Evaluation of an Alternative Experimental Infection Method, Which Closely Mimics the Natural Route of Transmission of Monophasic Salmonella Typhimurium in Pigs

Salmonella carriage in pigs is a significant food safety issue. This study describes a new protocol of Salmonella infection based on exposure to an artificially contaminated environment that closely mimics natural exposure to the organism. The aim of the study was to develop and evaluate the effectiveness of this protocol, which could then be used as a tool in the investigation of control measures. In addition, Salmonella shedding pattern and growth performance of the pigs were examined. Trial pigs (n = 10) were placed in a pen that had been previously contaminated by housing two pigs experimentally challenged with a monophasic Salmonella Typhimurium (mST). A further 10 pigs were placed in a Salmonella-free pen. Pigs were weighed on days 0 and 28. Feces was collected on days 0, 2, 3, 5, 7, 14, 21, and 28 and examined for the presence and quantity of Salmonella. The trial was replicated once. All pigs in the contaminated pens shed Salmonella within the first 2 days of exposure with values ranging from 10⁰ to 10⁴ CFU/g. The noninfected pigs had significantly higher final body weights on day 28 than those exposed to the Salmonella contaminated environment in both replicates. The pigs in the Salmonella-free pen had significantly higher average daily weight gain over the 28-day period compared to the infected animals (p < 0.001). Although not significant, numerical improvements in average daily feed intake and feed conversion efficiency were observed in the Salmonella-free pigs when compared to the contaminated pigs. The approach used was successful in infecting pigs with Salmonella without the need for direct inoculation or exposure to seeder pigs. This "natural" method of infection in which pigs are exposed to low levels of environmental contamination with Salmonella may be an effective tool that could be utilized when investigating control measures.

Application of slightly acidic electrolyzed water for decontamination of stainless steel surfaces in animal transport vehicles

The effectiveness of slightly acidic electrolyzed water (SAEW) in reducing Escherichia coli, Salmonella typhimurim, Staphylococcus aureus or bacterial mixtures on stainless steel surfaces was evaluated and compared its efficacy with composite phenol solution for reducing total aerobic bacteria in animal transport vehicles. Stainless steel surfaces were inoculated with these strains individually or in a mixture, and sprayed with SAEW, composite phenol, or alkaline electrolyzed water for 0.5, 1, 1.5 and 2min. The bactericidal activity of SAEW increased with increasing available chlorine concentration and spraying duration. The SAEW solution of 50mgl^-1 of available chlorine concentration showed significantly higher effectiveness than composite phenol in reducing the pathogens on stainless steel surfaces (P<0.05). Complete inactivation of pathogens on stainless steel surfaces were observed after treatment with alkaline electrolyzed water followed by SAEW at 50mgl^-1 of available chlorine concentration for 2min or alkaline electrolyzed water treatment followed by SAEW treatment at 90mgl^-1 of available chlorine concentration for 0.5min. The efficacy of SAEW in reducing total aerobic bacteria in animal transport vehicles was also determined. Vehicles in the disinfection booth were sprayed with the same SAEW, alkaline electrolyzed water and composite phenol solutions using the automatic disinfection system. Samples from vehicle surfaces were collected with sterile cotton swabs before and after each treatment. No significant differences in bactericidal efficiency were observed between SAEW and composite phenol for reducing total aerobic bacteria in the vehicles (P>0.05). SAEW was also found to be more effective when used in conjunction with alkaline electrolyzed water. Results suggest that the bactericidal efficiency of SAEW was higher than or equivalent to that of composite phenol and SAEW may be used as effective alternative for reducing microbial contamination of animal transport vehicles.

Regulation signature of miR-143 and miR-26 in porcine Salmonella infection identified by binding site enrichment analysis

Salmonella infects many vertebrate species, and pigs colonized with Salmonella are typically Salmonella carriers. Transcriptomic analysis of the response to Salmonella infection in whole blood has been reported for the pig. The objective of this study is to identify the important miRNAs involved in Salmonella infection using binding site enrichment analysis. We predicted porcine microRNA (miRNA) binding sites in the 3' UTR of protein-coding genes for all miRNA families. Based on those predictions, we analyzed miRNA-binding sites for mRNAs expressed in peripheral blood to investigate the functional importance of miRNAs in Salmonella infection in pig. Enrichment analysis revealed that binding sites of five miRNAs (including miR-143, -9839, -26, -2483, and -4335) were significantly over represented for the differentially expressed gene sets. Real-time PCR results indicated that selected members of this miRNA group (miR-143, -26, and -4335) were differentially expressed in whole blood after Salmonella inoculation. The luciferase reporter assay showed that ATP6V1A and IL13RA1 were targets of miR-143 and that miR-26 regulates BINP3L and ARL6IP6. The results strongly suggest that miR-143 and miR-26 play important regulatory roles in the development of Salmonella infection in pig.

Chicken egg yolk antibodies (IgY) as non-antibiotic production enhancers for use in swine production: a review

In recent years, the use of in-feed antibiotics for growth and disease prevention in livestock production has been under severe scrutiny. The use and misuse of in-feed antibiotics has led to problems with drug residues in animal products and increased bacterial resistance. Chicken egg yolk antibodies (IgY) have attracted considerable attention as an alternative to antibiotics to maintain swine health and performance. Oral administration of IgY possesses many advantages over mammalian IgG such as cost-effectiveness, convenience and high yield. This review presents an overview of the potential to use IgY immunotherapy for the prevention and treatment of swine diarrhea diseases and speculates on the future of IgY technology. Included are a review of the potential applications of IgY in the control of enteric infections of either bacterial or viral origin such as enterotoxigenic Escherichia coli, Salmonella spp., rotavirus, porcine transmissible gastroenteritis virus, and porcine epidemic diarrhea virus. Some potential obstacles to the adoption of IgY technology are also discussed.

Chicken egg yolk antibodies (IgY) as non-antibiotic production enhancers for use in swine production: a review

In recent years, the use of in-feed antibiotics for growth and disease prevention in livestock production has been under severe scrutiny. The use and misuse of in-feed antibiotics has led to problems with drug residues in animal products and increased bacterial resistance. Chicken egg yolk antibodies (IgY) have attracted considerable attention as an alternative to antibiotics to maintain swine health and performance. Oral administration of IgY possesses many advantages over mammalian IgG such as cost-effectiveness, convenience and high yield. This review presents an overview of the potential to use IgY immunotherapy for the prevention and treatment of swine diarrhea diseases and speculates on the future of IgY technology. Included are a review of the potential applications of IgY in the control of enteric infections of either bacterial or viral origin such as enterotoxigenic Escherichia coli, Salmonella spp., rotavirus, porcine transmissible gastroenteritis virus, and porcine epidemic diarrhea virus. Some potential obstacles to the adoption of IgY technology are also discussed.

Biology and Diseases of Swine

Swine are used in biomedical research as models for biomedical research and for teaching. This chapter covers normative biology and behavior along with common and emerging swine diseases. Xenotransplantation is discussed along with similarities and differences of swine immunology.

Estimation of costs for control of Salmonella in high-risk feed materials and compound feed

INTRODUCTION

Feed is a potential and major source for introducing Salmonella into the animal-derived food chain. This is given special attention in the European Union (EU) efforts to minimize human food-borne Salmonella infections from animal-derived food. The objective of this study was to estimate the total extra cost for preventing Salmonella contamination of feed above those measures required to produce commercial feed according to EU regulation (EC) No 183/2005. The study was carried out in Sweden, a country where Salmonella infections in food-producing animals from feed have largely been eliminated.

METHODS

On the initiative and leadership of the competent authority, the different steps of feed production associated with control of Salmonella contamination were identified. Representatives for the major feed producers operating in the Swedish market then independently estimated the annual mean costs during the years 2009 and 2010. The feed producers had no known incentives to underestimate the costs.

RESULTS AND DISCUSSION

The total cost for achieving a Salmonella-safe compound feed, when such a control is established, was estimated at 1.8-2.3 € per tonne of feed. Of that cost, 25% relates to the prevention of Salmonella contaminated high-risk vegetable feed materials (mainly soybean meal and rapeseed meal) from entering feed mills, and 75% for measures within the feed mills. Based on the feed formulations applied, those costs in relation to the farmers' 2012 price for compound feed were almost equal for broilers and dairy cows (0.7%). Due to less use of protein concentrate to fatten pigs, the costs were lower (0.6%). These limited costs suggest that previous recommendations to enforce a Salmonella-negative policy for animal feed are realistic and economically feasible to prevent a dissemination of the pathogen to animal herds, their environment, and potentially to human food products.

Salmonella pathogenicity and host adaptation in chicken-associated serovars

Enteric pathogens such as Salmonella enterica cause significant morbidity and mortality. S. enterica serovars are a diverse group of pathogens that have evolved to survive in a wide range of environments and across multiple hosts. S. enterica serovars such as S. Typhi, S. Dublin, and S. Gallinarum have a restricted host range, in which they are typically associated with one or a few host species, while S. Enteritidis and S. Typhimurium have broad host ranges. This review examines how S. enterica has evolved through adaptation to different host environments, especially as related to the chicken host, and continues to be an important human pathogen. Several factors impact host range, and these include the acquisition of genes via horizontal gene transfer with plasmids, transposons, and phages, which can potentially expand host range, and the loss of genes or their function, which would reduce the range of hosts that the organism can infect. S. Gallinarum, with a limited host range, has a large number of pseudogenes in its genome compared to broader-host-range serovars. S. enterica serovars such as S. Kentucky and S. Heidelberg also often have plasmids that may help them colonize poultry more efficiently. The ability to colonize different hosts also involves interactions with the host's immune system and commensal organisms that are present. Thus, the factors that impact the ability of Salmonella to colonize a particular host species, such as chickens, are complex and multifactorial, involving the host, the pathogen, and extrinsic pressures. It is the interplay of these factors which leads to the differences in host ranges that we observe today.

Polynucleotide phosphorylase (PNPase) is required for Salmonella enterica serovar Typhimurium colonization in swine

The pnp gene encodes polynucleotide phosphorylase, an exoribonuclease involved in RNA processing and degradation. A mutation in the pnp gene was previously identified by our group in a signature-tagged mutagenesis screen designed to search for Salmonella enterica serovar Typhimurium genes required for survival in an ex vivo swine stomach content assay. In the current study, attenuation and colonization potential of a S. Typhimurium pnp mutant in the porcine host was evaluated. Following intranasal inoculation with 10(9) cfu of either the wild-type S. Typhimurium χ4232 strain or an isogenic derivative lacking the pnp gene (n = 5/group), a significant increase (p < 0.05) in rectal temperature (fever) was observed in the pigs inoculated with wild-type S. Typhimurium compared to the pigs inoculated with the pnp mutant. Fecal shedding of the pnp mutant was significantly reduced during the 7-day study compared to the wild-type strain (p < 0.001). Tissue colonization was also significantly reduced in the pigs inoculated with the pnp mutant compared to the parental strain, including the tonsils, ileocecal lymph nodes, Peyer's Patch region of the ileum, cecum and contents of the cecum (p < 0.05). The data indicate that the pnp gene is required for S. Typhimurium virulence and gastrointestinal colonization of the natural swine host.

Role of slaughtering in Salmonella spreading and control in pork production

Salmonella is one of the major foodborne pathogens worldwide. Pork products are among the main sources of Salmonella infection in humans, and several countries have established Salmonella surveillance and control programs. The role of slaughtering in carcass contamination has been indicated by studies focused on the slaughterhouse environment. In this review, we examine and discuss the information available regarding the influence that farm status, pig transport, and lairage have on the carriage of Salmonella by pigs entering the slaughter line. The evolution of carcass contamination throughout the slaughtering process, the main sources of contamination in the dirty and clean zones of the slaughter line, and previously reported prevalence of Salmonella on carcasses and factors affecting this prevalence also are discussed. The importance of implementing interventions at the slaughter level is discussed briefly. Consistent with the information available, pigs from infected farms and newly acquired or recrudescent infections in pigs at the subsequent stages of transport and lairage are important sources of Salmonella at the slaughtering plant. The continuous introduction of Salmonella into the slaughterhouse and the potential for resident flora constitute a risk for carcass contamination. At the slaughterhouse, some dressing activities can reduce carcass contamination, but others are critical control points that jeopardize carcass hygiene. This information indicates the importance of considering slaughter and previous stages in the pork production chain for controlling Salmonella in swine production.

Profiling the gastrointestinal microbiota in response to Salmonella: low versus high Salmonella shedding in the natural porcine host

Controlling Salmonella in the food chain is complicated by the ability of Salmonella to colonize livestock without causing clinical symptoms/disease. Salmonella-carrier animals are a significant reservoir for contamination of naïve animals, the environment, and our food supply. Salmonella carriage and shedding in pigs varies greatly both experimentally and on-farm. To investigate the dynamics between the porcine intestinal microbiota and Salmonella shedding, we temporally profiled the microbiota of pigs retrospectively classified as low and high Salmonella-shedders. Fifty-four piglets were collectively housed, fed and challenged with 10(9)Salmonella enterica serovar Typhimurium. Bacterial quantitation of Salmonella in swine feces was determined, and total fecal DNA was isolated for 16S rRNA gene sequencing from groups of high-shedder, low-shedder, and non-inoculated pigs (n=5/group; 15 pigs total). Analyses of bacterial community structures revealed significant differences between the microbiota of high-shedder and low-shedder pigs before inoculation and at 2 and 7 days post-inoculation (d.p.i.); microbiota differences were not detected between low-shedder and non-inoculated pigs. Because the microbiota composition prior to Salmonella challenge may influence future shedding status, the "will-be" high and low shedder phylotypes were compared, revealing higher abundance of the Ruminococcaceae family in the "will-be" low shedders. At 2d.p.i., a significant difference in evenness for the high shedder microbiota compared to the other two groups was driven by decreases in Prevotella abundance and increases in various genera (e.g. Catenibacterium, Xylanibacter). By 21 d.p.i., the microbial communities of high-shedder and low-shedder pigs were no longer significantly different from one another, but were both significantly different from non-inoculated pigs, suggesting a similar Salmonella-induced alteration in maturation of the swine intestinal microbiota regardless of shedding status. Our results correlate microbial shifts with Salmonella shedding status in pigs, further defining the complex interactions among the host, pathogen, and microbiota of this important public health issue and food safety concern.

Effect of cattle on Salmonella carriage, diversity and antimicrobial resistance in free-ranging wild boar (Sus scrofa) in northeastern Spain

Salmonella is distributed worldwide and is a pathogen of economic and public health importance. As a multi-host pathogen with a long environmental persistence, it is a suitable model for the study of wildlife-livestock interactions. In this work, we aim to explore the spill-over of Salmonella between free-ranging wild boar and livestock in a protected natural area in NE Spain and the presence of antimicrobial resistance. Salmonella prevalence, serotypes and diversity were compared between wild boars, sympatric cattle and wild boars from cattle-free areas. The effect of age, sex, cattle presence and cattle herd size on Salmonella probability of infection in wild boars was explored by means of Generalized Linear Models and a model selection based on the Akaike's Information Criterion. Prevalence was higher in wild boars co-habiting with cattle (35.67%, CI 95% 28.19-43.70) than in wild boar from cattle-free areas (17.54%, CI 95% 8.74-29.91). Probability of a wild boar being a Salmonella carrier increased with cattle herd size but decreased with the host age. Serotypes Meleagridis, Anatum and Othmarschen were isolated concurrently from cattle and sympatric wild boars. Apart from serotypes shared with cattle, wild boars appear to have their own serotypes, which are also found in wild boars from cattle-free areas (Enteritidis, Mikawasima, 4:b:- and 35:r:z35). Serotype richness (diversity) was higher in wild boars co-habiting with cattle, but evenness was not altered by the introduction of serotypes from cattle. The finding of a S. Mbandaka strain resistant to sulfamethoxazole, streptomycin and chloramphenicol and a S. Enteritidis strain resistant to ciprofloxacin and nalidixic acid in wild boars is cause for public health concern.

Defining the "core microbiome" of the microbial communities in the tonsils of healthy pigs

BACKGROUND

Porcine tonsils are the colonization site for many pathogenic as well as commensal microorganisms and are the primary lymphoid tissue encountered by organisms entering through the mouth or nares. The goal of this study was to provide an in-depth characterization of the composition and structure of the tonsillar microbial communities and to define the core microbiome in the tonsils of healthy pigs, using high throughput bar-coded 454-FLX pyrosequencing.

RESULTS

Whole tonsils were collected at necropsy from 12 16-week-old finisher pigs from two healthy herds. Tonsil brushes were also used to collect samples from four of these animals. Bacterial DNA was isolated from each sample, amplified by PCR with universal primers specific for the bacterial 16S rRNA genes, and the PCR products sequenced using pyrosequencing. An average of 13,000 sequences were generated from each sample. Microbial community members were identified by sequence comparison to known bacterial 16S rRNA gene sequences.The microbiomes of these healthy herds showed very strong similarities in the major components as well as distinct differences in minor components. Pasteurellaceae dominated the tonsillar microbiome in all animals, comprising ~60% of the total, although the relative proportions of the genera Actinobacillus, Haemophilus, and Pasteurella varied between the herds. Also found in all animals were the genera Alkanindiges, Peptostreptococcus, Veillonella, Streptococcus and Fusobacterium, as well as Enterobacteriaceae and Neisseriaceae. Treponema and Chlamydia were unique to Herd 1, while Arcanobacterium was unique to Herd 2.Tonsil brushes yielded similar results to tissue specimens, although Enterobacteriaceae and obligate anaerobes were more frequently found in tissue than in brush samples, and Chlamydia, an obligately intracellular organism, was not found in brush specimens.

CONCLUSIONS

We have extended and supported our previous studies with 16S clone libraries, using 16S rRNA gene pyrosequencing to describe the microbial communities in tonsils of healthy pigs. We have defined a core microbiome, dominated by Pasteurellaceae, in tonsil specimens, and have also demonstrated the presence of unique minor components of the tonsillar microbiome present in each herd. We have validated the use of non-invasive tonsil brushes, in comparison to tonsil tissue, which will facilitate future studies.

Distinct peripheral blood RNA responses to Salmonella in pigs differing in Salmonella shedding levels: intersection of IFNG, TLR and miRNA pathways

Transcriptomic analysis of the response to bacterial pathogens has been reported for several species, yet few studies have investigated the transcriptional differences in whole blood in subjects that differ in their disease response phenotypes. Salmonella species infect many vertebrate species, and pigs colonized with Salmonella enterica serovar Typhimurium (ST) are usually asymptomatic, making detection of these Salmonella-carrier pigs difficult. The variable fecal shedding of Salmonella is an important cause of foodborne illness and zoonotic disease. To investigate gene pathways and biomarkers associated with the variance in Salmonella shedding following experimental inoculation, we initiated the first analysis of the whole blood transcriptional response induced by Salmonella. A population of pigs (n = 40) was inoculated with ST and peripheral blood and fecal Salmonella counts were collected between 2 and 20 days post-inoculation (dpi). Two groups of pigs with either low shedding (LS) or persistent shedding (PS) phenotypes were identified. Global transcriptional changes in response to ST inoculation were identified by Affymetrix Genechip® analysis of peripheral blood RNA at day 0 and 2 dpi. ST inoculation triggered substantial gene expression changes in the pigs and there was differential expression of many genes between LS and PS pigs. Analysis of the differential profiles of gene expression within and between PS and LS phenotypic classes identified distinct regulatory pathways mediated by IFN-γ, TNF, NF-κB, or one of several miRNAs. We confirmed the activation of two regulatory factors, SPI1 and CEBPB, and demonstrated that expression of miR-155 was decreased specifically in the PS animals. These data provide insight into specific pathways associated with extremes in Salmonella fecal shedding that can be targeted for further exploration on why some animals develop a carrier state. This knowledge can also be used to develop rational manipulations of genetics, pharmaceuticals, nutrition or husbandry methods to decrease Salmonella colonization, shedding and spread.

Investigation of Salmonella enterica in Sardinian slaughter pigs: prevalence, serotype and genotype characterization

In order to improve the knowledge about the presence of Salmonella in pork meat in Sardinia (Italy), the prevalence and the sources of Salmonella at 5 pig slaughterhouses (slaughtered pigs and environment) were investigated and the isolates were characterised. A total of 462 samples were collected, 425 from pigs at slaughter and 41 from the slaughterhouse environment. Salmonella was isolated from 26/85 (30.5%) mesenteric lymph nodes, 14/85 (16.4%) colon contents, and from 12/85 (14.1%) carcasses and livers. Salmonella prevalence was 38% (8/21) in samples from surfaces not in contact with meat, and 35% (7/20) in those from surfaces in contact with meat. Thirty-one pigs were identified as carriers of Salmonella in lymph nodes and/or colon content, but of these, only 8 carcasses were positive. A total of 103 Salmonella isolates were serotyped and genotyped. Eight different serotypes were detected; the most common were S. Derby (44/103, 42.7%) and S. Typhimurium (24/103, 23.3%). The most prevalent S. Typhimurium phage type was DT193. Thirty-two isolates were found to be resistant to more than one antimicrobial (MDR). Pulse-field gel electrophoresis (PFGE) permitted the resolution of XbaI macrorestriction fragments of the Salmonella strains into 20 distinct pulsotypes. Combined application of a plasmid profiling assay (PPA) and PFGE gave useful additional information to assist in tracing the routes of Salmonella contamination in abattoirs. To reduce Salmonella prevalence some preventive measures should be encouraged: the origin of infected slaughter animals should be identified and direct and cross-contamination of carcasses should be avoided by adhering to HACCP principles in association with good hygiene procedures (GHP).

SALMONELLA TYPHIMURIUM EM LINFONODOS MESENTÉRICOS DE OVINOS AO ABATE

RESUMO O rebanho de ovinos no Brasil está estimado em mais de 16 milhões de cabeças. Embora o consumo da carne desta espécie ainda seja pequeno, comparado ao de outros países, o consumo de carne, inclusive ovina, tem sido associado às doenças transmitidas por alimentos, em especial a salmonelose. No presente estudo, investigou-se a ocorrência de salmonelas em linfonodos mesentéricos e conteúdo intestinal de 175 ovinos ao abate. “Pools” constituído por cinco amostras de contéudo fecal ou 5 amostras de linfonodos de 25 g foram pre-enriquecidos em 250 mL de água peptonada tamponada e incubados a 37° C por 18-24 horas. Uma alíquota de 0,1 mL do pré-enriquecimento foi transferida para 9,9 mL de caldo de enriquecimento Rappaport-Vassiliadis e 1,0 mL do pré-enriquecimento foi transferido para 10 mL de caldo tetrationato Muller-Kaufmann, incubados a 42° C for 24h. 10 μL do caldo de enriquecimento foi semeado superfície de placas de ágar BPLS e ágar XLT4 incubadas a 37º C for 24-48h. Colônias suspeitas de salmonela foram testadas por provas bioquímicas e serologicas. Os testes bioquímicos utilizados para identificação de Salmonella foram TSI (triple sugar iron àgar), LIA (lysine iron àgar) e ágar ureia. Sorotipagem foi realizada no Laboratório de Enterobactérias do Instituto Osvaldo Cruz. Isolou-se Salmonella Tiphymurium de um pool de linfonodos mesentéricos, provenientes de cinco animais. O fato de se observar a ocorrência de salmonela em ovino portador sadio alerta para necessidade de monitorar este micro-organismo também nesta espécie, especialmente quando destinada ao abate, com vistas à produção de alimentos seguros.

A mutation in the poxA gene of Salmonella enterica serovar Typhimurium alters protein production, elevates susceptibility to environmental challenges, and decreases swine colonization

Control of foodborne Salmonella within the farm-retail continuum is a complex issue since over 2500 serovars of Salmonella exist, the host range of Salmonella spp. varies greatly, and Salmonella is environmentally ubiquitous. To identify Salmonella enterica serovar Typhimurium (Salmonella Typhimurium) genes important for pathogen survival, our research group previously screened a signature-tagged mutagenesis bank in an ex vivo swine stomach content assay. A mutation in the poxA gene, a member of the gene family encoding class-II aminoacyl-tRNA synthetases, decreased survival of Salmonella Typhimurium in the ex vivo swine stomach content assay. In the current study, complementation with a plasmid-encoded poxA gene restored survival of the poxA mutant to the level of the parental, wild-type strain. In vivo analysis of the poxA mutant in the natural porcine host revealed significantly reduced fecal shedding of Salmonella, decreased colonization of the tonsils, and decreased detection of the mutant strain in the cecal contents of the pigs at 7 days postinoculation (p < 0.05). Body temperature (fever) of the pigs inoculated with wild-type Salmonella Typhimurium was significantly higher than that of pigs inoculated with the poxA mutant (p < 0.05). Two-dimensional gel electrophoresis revealed characteristic differences in the protein profile of the poxA mutant relative to the wild-type strain, indicating that deletion of poxA in Salmonella Typhimurium exerts selective effects on translation and/or posttranslational modifications of mRNA species that are necessary for stress survival and colonization of the natural swine host.

Immunological, physiological, and behavioral effects of Salmonella enterica carriage and shedding in experimentally infected finishing pigs

Finishing pigs infected with Salmonella pose significant food safety risks by carrying the pathogen into abattoirs. This study was conducted to determine the dynamics of Salmonella infection in finishing pigs, and associated immunological, physiological, and behavioral alterations, by longitudinally comparing infected to noninfected pigs during 6 weeks postinfection (p.i.). Bacteriological data revealed that all inoculated pigs started shedding Salmonella within 2 h p.i., and persistently shed the bacteria up to the end of the study. Ileal and cecal contents, as well as mesenteric lymph node samples, were all positive throughout the study, containing 3-4 log(10) cfu/g of Salmonella at 24 h p.i., and 4-5 log(10) cfu/g of Salmonella up to 4 weeks p.i. Levels of Salmonella dropped markedly (p < 0.05) in all samples at 5 weeks p.i. There was no difference between groups for blood cell counts. Tumor necrosis factor-α was greater (p < 0.05) in infected pigs: (1) in the mesenteric lymph nodes by 48 h p.i.; (2) at 24 h and 3 weeks p.i. in the ileum; and (3) in the cecum and spleen at 3 weeks p.i. Interleukin-12, interleukin-1 and its antagonist, and a porcine-specific antimicrobial peptide RNA expression in tissues changed over time, but were not different between groups. Infected pigs spent more time in ventral recumbency, standing, and sitting than controls (p < 0.01). Infected pigs were also more active (p < 0.01), and approached a novel object more quickly than control pigs (p < 0.05). No treatment differences were detected for rectal temperature or plasma cortisol (p > 0.10). This study shows that finishing pigs can carry high levels of Salmonella for up to 4 weeks p.i. in the gastrointestinal contents and mesenteric lymph nodes, shedding high levels of the bacteria without developing clinical symptoms, but developing an immune response throughout the intestinal tract. Moreover, subtle behavioral changes measured as postures were detected, and therefore warrant additional investigation.

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.