Héctor Argüello

Swine dysentery: aetiology, pathogenicity, determinants of transmission and the fight against the disease.

Swine Dysentery (SD) is a severe mucohaemorhagic enteric disease of pigs caused by Brachyspira hyodysenteriae, which has a large impact on pig production and causes important losses due to mortality and sub-optimal performance. Although B. hyodysenteriae has been traditionally considered a pathogen mainly transmitted by direct contact, through the introduction of subclinically infected animals into a previously uninfected herd, recent findings position B. hyodysenteriae as a potential threat for indirect transmission between farms. This article summarizes the knowledge available on the etiological agent of SD and its virulence traits, and reviews the determinants of SD transmission. The between-herds and within-herd transmission routes are addressed. The factors affecting disease transmission are thoroughly discussed, i.e., environmental survival of the pathogen, husbandry factors (production system, production stage, farm management), role of vectors, diet influence and interaction of the microorganism with gut microbiota. Finally, prophylactic and therapeutic approaches to fight against the disease are briefly described.

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.

Prevalence, serotypes and resistance patterns of Salmonella in Danish pig production

The objective of this paper is to analyse in further detail the Danish results of the EFSA baseline studies in slaughter pigs and breeding herds, and compare them with the results obtained in (1) the pre-implementation study that was carried out to establish the initial prevalence values in fattening herds as part of the Danish Salmonella control programme, and (2) the study performed four years later in breeding and finishing herds to obtain information about the prevalence in breeding farms and the status of the finishers after the first years of the National Salmonella Control Programme. In the slaughter pigs Salmonella was detected in a 7.4% of 1218 ileocaecal lymph nodes and on 3.2% of 438 carcasses examined. Among the breeding herds examined by floor faecal or swab samples 122 of 298 (40.9%) were positive in at least one of the ten samples collected. The most prevalent serotypes were Salmonella Typhimurium in finishers and Salmonella Derby in breeding herds while the most prevalent phage types of the S. Typhimurium isolates were DT 12 and DT 120. The antimicrobial resistance analysis yielded a 35.2% of the isolates from the slaughter pigs resistant to one or more antimicrobials while 19.3% were resistant to four or more antimicrobials. A significantly higher percentage of resistance to antimicrobials was found in the S. Typhimurium isolates (χ(2)=4.72, p=0.029), where 42.9% presented resistance to one or more compounds. In breeding herds, just S. Typhimurium and S. 4,5],12:i: - isolates were tested. As many as 56.8% of the S. Typhimurium-like strains positive breeding farms had resistant strains, while 27% had multidrug resistant strains. The distribution of the isolates in regions showed that S. Derby is at present the predominant serotype in breeding farms from most of the regions of the country.

Characterization of the Emerging Salmonella 4,[5],12:i:- in Danish Animal Production

The monophasic Salmonella variant with the antigenic formula Salmonella 4,[5],12:i:- has emerged in the last decade as one of the main serotypes related to human salmonellosis. In the present study, a collection of 94 isolates of the S. 4,12:i:- and S. 4,5,12:i:- coming from Danish farm animals, swine (86), cattle (7), and poultry (1), with well-defined identification was further typed by polymerase chain reaction serotyping, phage typing, and molecular typing (polymerase chain reaction and multilocus variable-number tandem-repeat analysis [MLVA]). Moreover, the determination of antimicrobial resistance pattern of each isolate was tested. In 68 of the isolates the fljB gene was absent (i.e., they were true monophasic strains), whereas in 26 isolates, the gene was present despite the fact that the isolates did not express it. The results clustered the isolates in three main pulse-types. The predominant cluster was compatible with the previously described pattern STYMXB.0131. All the isolates included in this cluster lacked the fljB gene, and all the isolates except one belonged to phage type DT 193 with the AMP-STR-SMX-TET resistance pattern. MLVA analysis divided the clusters in several MLVA profiles previously reported by other studies. Finally, antimicrobial resistance and multiresistance was frequent, although no resistance was detected in critical compounds: fluoroquinolones and cephalosporins. The present study demonstrates the presence of monophasic Salmonella Typhimurium-like strains in Danish food animal production with well-characterized clones that are described by previous studies, demonstrating the emergence and spread of this serotype in Denmark.

Evaluation of protection conferred by a Salmonella Typhimurium inactivated vaccine in Salmonella-infected finishing pig farms.

The efficacy of an inactivated S. Typhimurium vaccine administered to pigs at the beginning of the fattening period was evaluated in four clinical trials (trials A, B, C and D). Faecal shedding and the systemic antibody response during fattening, as well as, the cecal contents and mesenteric lymph nodes collected after slaughtering were used to assess the outcome. Salmonella shedders prevalence in the control groups was six times higher than in the treated groups in trials A and D, both herds infected by S. Typhimurium. The risk of positive pens was also four or five times higher for the pens housing control pigs in trials A and C. Lower prevalence of Salmonella was observed in the slaughter samples from the vaccinated pigs in trial D and in the cecal content samples in trial A, when just the S. Typhimurium results were compared. The results suggest the effective homologous protection of the vaccinated pigs; however, the high humoral response elicited in the vaccinated pigs complicates their use in farms under serological surveillance programmes.

Sero- and genotyping of Salmonella in slaughter pigs, from farm to cutting plant, with a focus on the slaughter process

The objective of this study was to investigate the role of the slaughtering process in Salmonella carcass contamination by typing isolates recovered previously in a double study of the following: (1) a tracking survey from the farm to the slaughterhouse and (2) a survey of the slaughterhouse environment (i.e., lairage area, slaughter line, cutting plant and carcasses). The Salmonella serotypes identified on the carcasses of the 16 tracked batches were frequently linked to lairage, whereas the serotypes detected at the farm, transport or pig-related samples (i.e., caecum content and lymph nodes) were only occasionally detected at the carcass level. Multi-locus variable-number tandem repeats (MLVA) of 77 Salmonella enterica ser. Typhimurium isolates from seven of these batches confirmed the link between the isolates recovered from carcasses and holding pens. Only four of the 16 positive carcasses had profiles previously isolated from lymph nodes or caecal content. In the second part of the study, a total of 131 S. enterica ser. Typhimurium and 74 S. enterica ser. Derby isolates were further characterised by MLVA and Pulsed Field Gel Electrophoresis (PFGE), respectively. The MLVA profiles identified in carcasses varied throughout the working day and were frequently linked to those identified in samples from the slaughter line points collected close in time. PFGE and MLVA profiles identified at lairage were also detected in later processing facilities (i.e., slaughter line and cutting plant) as well as in carcasses. Finally, most of the profiles found at the cutting plants were previously identified in the slaughter line or carcass samples. The results from this study show that Salmonella contamination in pigs entering the slaughterhouse can be attributed to several sources. Typing of isolates by MLVA and PFGE clarified the sources of carcass contamination and improved the accuracy of cross-contamination attributable values. Without obviating the relevant role of infected pigs entering the slaughterhouse, the present study highlights the lairage and slaughtering as important sources of carcass contamination.

Antibacterial activity and mode of action of a commercial citrus fruit extract

This study addresses the antibacterial activity and mechanism of action of BIOLL+®, a commercial extract obtained from citrus fruits.

Effect of the Addition of Organic Acids in Drinking Water or Feed During Part of the Finishing Period on the Prevalence of Salmonella in Finishing Pigs

Pork is a major cause of foodborne salmonellosis. Consequently, effective measures that could reduce the prevalence of Salmonella at the farm are of interest. In the present study, three field trials were performed to evaluate the effect of strategic administration of organic acids, at concentrations estimated by economic criteria, on the Salmonella prevalence in finishing pigs. Pigs received either a mixture of acids (lactic, formic, propionic, and acetic) added to their drinking water at a concentration of 0.035% (trial A), or a basal diet containing 0.5% potassium-diformate, KH(COOH)₂, (trials B and C), during the last 6-7 weeks of the finishing period. Fecal Salmonella shedding and seroprevalence were monitored in the animals at four time points during the study. Mesenteric lymph nodes and cecal contents were collected from a subset of animals at the slaughterhouse and cultured for Salmonella. At the end of the finishing period in all three trials, the percentage of seropositive pigs was higher in the control group than in the experimental group, regardless of which cutoff value was used in the enzyme-linked immunosorbent assay (ELISA) assay. The frequency of fecal shedding was lower also in the treated pig groups from the trials A and B at the end of the finishing period. The results from the samples collected at the slaughterhouse did not yield differences between groups in trials A and B. However, Salmonella isolation was less frequent in the mesenteric lymph nodes from the experimental pigs in trial C. The seroprevalence reductions, together with some promising results in the reduction of shedding, support the idea that this intervention is a useful strategy to reduce Salmonella prevalence at the farm.

Salmonella Control Measures at Farm in Swine Production

Salmonella is one of the most important food-borne pathogens. Each year a high number of cases as well as outbreaks of Salmonella in humans are reported (EFSA, 2011). Despite the fact that Salmonella can cause disease in pigs mainly associated to infections by Salmonella enterica subsp. enterica serovar Cholerasuis, the importance of swine salmonellosis is related to human infections caused by pork products. During the nineties and the first years of the present century it was estimated that 10% of the human salmonellosis cases were attributed to pork products (Hald et al., 2004), classically categorized as the third most common source of human infections after poultry and turkey meat. Nevertheless with the implementation of control programs in avian production with the subsequent prevalence reduction, the role of pork products have been enhanced and nowadays it is the second most common source of human salmonellosis after laying hens (Pires et al., 2011). Regarding swine salmonellosis, control programs are not compulsory at the moment but the EU Regulation 2160/2003 has established the need for developing proper and effective measures to detect and control Salmonella at all relevant stages of pork production chain and particularly at the primary production level in order to reduce the prevalence and the risk that Salmonella poses to public health (EU Regulation 2160/2003). From our point of view, Salmonella control should start at the end of the pork production chain (slaughterhouses and finishing farms) and go back to the first steps of the production system (breeding herds and feed suppliers). The compulsory or voluntary Salmonella control programmes that have already been established in several European countries base their Salmonella evaluation on serological and carcass microbiological contamination results principally (Alban et al., 2002; Nielsen et al., 2001). At the farm level, these control programmes include the implementation of specific measures to reduce the Salmonella prevalence in those herds identified as highly contaminated according to their serological results.

Characterization of Antimicrobial Resistance Determinants and Class 1 and Class 2 Integrons in Salmonella enterica spp., Multidrug-Resistant Isolates from Pigs

Antimicrobial resistance (AMR) and Salmonella spp., are primary concerns in public health. The present study characterizes the AMR determinants of 62 multi-drug resistant (MDR) Salmonella enterica spp., isolates from swine, which were obtained between 2004–2006, a major source of human salmonellosis. The AMR determinants were investigated by PCR, checking the presence of class 1 and class 2 integrons and 29 resistance genes. Genes sul1, blaTEM1-like, aadA2, tet(A), and dfrA12 were more prevalent (p < 0.05) within the determinants that were checked for each of these antimicrobials. Co-existence of different genes conferring resistance to the same antimicrobial was common. No differences in AMR determinants prevalence were observed between Salmonella Typhimurium and other serovars from the study. Class 1 integrons were detected in 48 of 62 isolates, again with no differences being linked to any serovar. Nine different variable regions were observed, 1000 bp/aadA2-1200 bp/blaPSE-1 (13 isolates) and blaOXA-like/aadA1 (eight isolates) were the most common. Four isolates, including S. Typhimurium (2), Salmonella Bredeney (1), and Salmonella Kapemba (1) harboured a class 2 integron 2300 bp estX-sat2-aadA1. Results from the study highlight the importance of class 1 integrons and certain genes in MDR swine Salmonella isolates. The information is of relevance for monitoring in the forthcoming scope of reduction of antibiotic usage in swine production.