Pathology of experimental pneumonia in pigs produced by Salmonella cholerae-suis

Nonspecific protection of heat-inactivated Mycobacterium bovis against Salmonella Choleraesuis infection in pigs

Trained immunity is the capacity of innate immune cells to produce an improved response against a secondary infection after a previous unrelated infection. Salmonellosis represents a public health issue and affects the pig farming industry. In general, vaccination against salmonellosis is still facing problems regarding the control of distinct serovars. Therefore, we hypothesized that an immunostimulant based on heat inactivated Mycobacterium bovis (HIMB) could have an immune training effect in pigs challenged with Salmonella enterica serovar Choleraesuis (S. Choleraesuis) and decided to explore the amplitude of this non-specific immune response. For this purpose, twenty-four 10 days-old female piglets were randomly separated in three groups: immunized group (n = 10) received orally two doses of HIMB prior to the intratracheal S. Choleraesuis-challenge, positive control group (n = 9) that was only challenged with S. Choleraesuis, and negative control group (n = 5) that was neither immunized nor infected. All individuals were necropsied 21 days post-challenge. HIMB improved weight gain and reduced respiratory symptoms and pulmonary lesions caused by S. Choleraesuis in pigs. Pigs immunized with HIMB showed higher cytokine production, especially of serum TNFα and lung CCL28, an important mediator of mucosal trained immunity. Moreover, immunized pigs showed lower levels of the biomarker of lipid oxidation malondialdehyde and higher activity of the antioxidant enzyme superoxide dismutase than untreated challenged pigs. However, the excretion and tissue colonization of S. Choleraesuis remained unaffected. This proof-of-concept study suggests beneficial clinical, pathological, and heterologous immunological effects against bacterial pathogens within the concept of trained immunity, opening avenues for further research.

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.

Outbreaks of antimicrobial resistant Salmonella Choleraesuis in wild boars piglets from central-western Spain

Salmonella enterica serovar Choleraesuis is the aetiological agent of swine paratyphoid being a highly invasive zoonotic pathogen. Wild boar natural populations are experiencing a demographical expansion as well as some farms are breeding this species to release for hunting with management sometimes identical to that of domestic pigs, including supplementation, grouping, and antibiotic treatments. This situation increases the chance of contact between wild boars and livestock, and potentially induces stress, with different sanitary consequences. The present work aims to describe the clinical features of recent outbreaks caused by S. Choleraesuis in wild boar from central-western Spain, as well as the antimicrobial resistance and phylogenetic relationships of isolates involved. 28 strains of S. Choleraesuis were isolated from 28 different wild boars belonging to 10 different game states located in central western Spain and submitted to the Clinical Veterinary Hospital (CVH) of the University of Extremadura. Samples were taken from different organs and cultured according to the ISO 6579:2002 procedure. Suspicious colonies were identified by PCR and antimicrobial resistance was evaluated by disc diffusion susceptibility test and the presence of the main resistance genes as well as 18 plasmid replicons frequently found among the Enterobacteriaceae was verified by PCR. Pulsed field gel electrophoresis was applied to determine the genetic relationship between isolates. The outbreaks under study were characterized by high mortality (35%-84%) and a septicaemic presentation. S. Choleraesuis was isolated from all the wild boars analysed, and 26 of the 28 isolates presented resistance to at least one antibiotic. The predominant resistances found were against sulphonamide, streptomycin, tetracycline, and doxicicline and sul1, strA-strB, and tetA were the most prevalent resistance genes among isolates. 10 strains carried FIIA, FIB+H/1 or FIIA+H/1 plasmids. PFGE classified the isolates into four different profiles, grouped into two clusters. This results show that prevention against S. Choleraesuis must be considered in the sanitary programs of the wild boar breeders.

An update on the epidemiology and pathology of African swine fever

African swine fever (ASF) is one of the most important infectious diseases of swine and has major negative consequences for affected countries. ASF is present in many sub-Saharan countries, Sardinia and several countries of eastern and central Europe, where its continuous spread has the swine industry on heightened alert. ASF is a complex disease for which no vaccine or treatment is available, so its control is based on early detection and rapid control of spread. For a robust and reliable early detection programme it is essential to be able to recognize the clinical signs and pathological changes of ASF, keeping in mind that in most cases the first introductions don't show high mortality nor characteristic clinical signs or lesions, but fever and some hemorrhagic lymph nodes. Knowledge of the main characteristics of this infection, including its current distribution and routes of transmission, is also essential for preventing and controlling ASF. This review addresses each of these topics and aims to update knowledge of the disease in order to improve early detection of ASF in the field and allow implementation of public health programmes.

Swine Diseases and Disorders

Swine diseases and disorders that are significant in modern, commercial swine production systems are organized by body system; the reader will need to know basic anatomy and physiology. The industry significance, etiology, epidemiology, pathogenesis, clinical signs, postmortem and histpathologic lesions, diagnostic testing, and generic treatment, control, and prevention are described. Diseases of a particular system are summarized in a differential diagnosis table.

Infecção experimental por Salmonella enterica subespécie enterica sorotipo Panama e tentativa de transmissão nasonasal em leitões desmamados

O objetivo deste experimento foi produzir uma infecção experimental de Salmonella enterica subespécie. enterica sorotipo Panama e verificar a importância da via nasonasal na transmissão entre leitões desmamados. Foram utilizados seis leitões recém-desmamados, adquiridos de granja livre de Salmonella spp. Utilizaram-se baias isoladoras, que proporcionavam o contato nasonasal e eliminavam a possibilidade de outras vias de transmissão e de contaminação externa. Três grupos foram formados: controle, sentinela e infectado. Não foram encontradas amostras positivas para Salmonella spp. em leitões do grupo-controle e sentinelas, e nos animais infectados foi isolada Salmonella Panama em suabes retais e tecidos necropsiados. Os resultados revelaram não haver a transmissão pela via nasonasal entre leitões desmamados, pois, em nenhum momento, o agente foi isolado dos animais sentinelas

Reproduction of fowl typhoid by respiratory challenge with Salmonella Gallinarum

Fowl typhoid is a disease of adult chickens and is caused by Salmonella Gallinarum infection via the alimentary tract. The experimental reproduction of fowl typhoid per os (PO) requires artificial conditions to minimize the effect of gastric acid, and several Salmonella serovars have been known to be transmitted via the respiratory route. Therefore, we have hypothesized the existence of a respiratory route for Salmonella Gallinarum infection and have attempted to reproduce fowl typhoid via intratracheal challenge. In accordance with our hypothesis, the intratracheal challenges of Salmonella Gallinarum reproduced exactly same lesions as fowl typhoid and induced higher mortality and morbidity than those of the PO challenge. Therefore, this study represents the first reproduction of fowl typhoid via respiratory route, and our findings may be useful for understanding the transmission of Salmonella Gallinarum in the field.

Indirect transmission of Escherichia coli O157:H7 occurs readily among swine but not among sheep

Transmission of Escherichia coli O157:H7 among reservoir animals is generally thought to occur either by direct contact between a naïve animal and an infected animal or by consumption of food or water containing the organism. Although ruminants are considered the major reservoir, there are two reports of human infections caused by E. coli O157:H7 linked to the consumption of pork products or to the contamination of fresh produce by swine manure. The objective of this study was to determine whether E. coli O157:H7 could be transmitted to naïve animals, both sheep and swine, that did not have any direct contact with an infected donor animal. We recovered E. coli O157:H7 from 10/10 pigs with nose-to-nose contact with the infected donor or animals adjacent to the donor and from 5/6 naïve pigs that were penned in the same room as the donor pig but 10 to 20 ft away. In contrast, when the experiment was repeated with sheep, E. coli O157:H7 was recovered from 4/6 animals that had nose-to-nose contact with the infected donor or adjacent animals and from 0/6 naïve animals penned 10 to 20 ft away from the donor. These results suggest that E. coli O157:H7 is readily transmitted among swine and that transmission can occur by the creation of contaminated aerosols.

Experimental airborne transmission of Salmonella Agona and Salmonella Typhimurium in weaned pigs

This study tested the hypothesis of airborne transmission of Salmonella Agona (Trial I) and Salmonella Typhimurium (Trial II) in weaned pigs. The trials were performed using stainless-steel/glass isolation cabinets connected by air ducts to permit an unidirectional airflow from cabinet 1 (two control pigs) to cabinet 3 (two sentinel pigs), passing through cabinet 2 (two inoculated pigs). Air samples, pooled faecal samples from the floor and rectal swabs were collected daily and assessed by culture and PCR. A fumigation chamber and rubber gloves coupled to the cabinets allowed sampling without opening the system. Trials I and II lasted 15 and 19 days respectively. The recovery of S. Agona and S. Typhimurium and detection of seroconversion in sentinel pigs indicate that airborne Salmonella transmission in weaned pigs over short distances is possible. Further studies on the role of aerosols in the epidemiology of Salmonella in intensive pig production should be performed.

Salmonella Epidemiology and Pathogenesis in Food-Producing Animals

This review reviews the pathogenesis of different phases of Salmonella infections. The nature of Salmonella infections in several domesticated animal species is described to highlight differences in the epidemiology and pathogenesis of salmonellosis in different hosts. The biology of Salmonella serovar host specificity is discussed in the context of our current understanding of the molecular basis of pathogenesis and the potential impact of different virulence determinants on Salmonella natural history. The ability to colonize the intestine, as evidenced by the shedding of relatively large numbers of bacteria in the feces over a long period, is shared unequally by Salmonella serovars. Studies probing the molecular basis of Salmonella intestinal colonization have been carried out by screening random transposon mutant banks of serovar Typhimurium in a range of avian and mammalian species. It is becoming increasingly clear that Salmonella pathogenicity island 2 (SPI2) is a major virulence factor during infection of food-producing animals, including cattle and poultry. The prevalence of Salmonella serovars in domestic fowl varies in different countries and with time. Although chickens are the natural hosts of serovars Gallinarum and Pullorum, natural outbreaks caused by these serovars in turkeys, guinea fowl, and other avian species have been described. There are two possible explanations to account for the apparent host specificity of certain Salmonella serovars. Environmental factors may increase exposure of particular animal species to certain serovars. Alternatively, there are genetic differences between these serovars, which allow them to survive and/or grow in specific niches only found within ruminants or pigs.

Pneumonia of pigs: a review

Pneumonia of pigs is one of the more important disease factors limiting pig production. Of the varieties of pneumonia affecting this species enzootic pneumonia caused by Mycoplasma spp. is the most common and most important. The major effects of this disease are lowered food conversion ratio and poor weight gain. Deaths are usually the result of secondary infection by necrotising, pus-forming bacteria. Eradication of the disease is expensive and requires depopulation and restocking. Control and treatment by antimicrobial agents is most effective if the drug combination used takes regard of the bacteria complicating the disease on any particular property. Other forms of pneumonia such as those caused by Haemophilus pleuropneumoniae, Salmonella cholerae-suis and Aujeszky's disease virus can be important on individual farms. The role of other agents such as Bordetella bronchiseptica and adenoviruses in respiratory disease of pigs remain to be clarified.

Analysis of Salmonella enterica serotype-host specificity in calves: avirulence of S. enterica serotype gallinarum correlates with bacterial dissemination from mesenteric lymph nodes and persistence in vivo

Host and bacterial factors that determine whether Salmonella serotypes remain restricted to the gastrointestinal tract or penetrate beyond the mucosa and cause systemic disease remain largely undefined. Here, factors influencing Salmonella host specificity in calves were assessed by characterizing the pathogenesis of different serotypes. Salmonella enterica serotype Dublin was highly virulent intravenously, whereas S. enterica serotype Choleraesuis was moderately virulent. Both serotypes were virulent in calves infected orally. In contrast, S. enterica serotypes Gallinarum and Abortusovis were avirulent by either route. Serotypes Dublin, Gallinarum, and Abortusovis colonized the intestinal tract 24 h after oral inoculation, yet only serotype Dublin was consistently recovered from systemic tissues. Serotypes Dublin and Gallinarum invaded bovine intestines in greater numbers and induced greater enteropathogenic responses than serotypes Choleraesuis and Abortusovis. However, only serotype Dublin was able to persist within the intestinal mucosa, and use of a novel cannulation model demonstrated that serotype Dublin was able to pass through the mesenteric lymph nodes in greater numbers than serotype Gallinarum. Together, these results suggest that initial interactions with the intestinal mucosa do not correlate with host specificity, although persistence within tissues and translocation via efferent lymphatics appear to be crucial for the induction of bovine salmonellosis.

Synergism between porcine reproductive and respiratory syndrome virus (PRRSV) and Salmonella choleraesuis in swine

Porcine reproductive and respiratory syndrome virus (PRRSV) and Salmonella choleraesuis are two leading causes of economic loss in the swine industry. While respiratory disease is common in both S. choleraesuis and PRRSV infections, the factors that contribute to its development remain largely undefined. We investigated the interaction of PRRSV, S. choleraesuis, and stress in 5-week-old swine. All combinations of three factors (inoculation with S. choleraesuis on Day 0, PRRSV on Day 3, and treatment with dexamethasone on Days 3-7) were used to produce eight treatment groups in two independent trials. Fecal samples, tonsil and nasal swabs, serum samples and postmortem tissues were collected for bacteriologic and virologic examinations. No clinical signs were observed in pigs inoculated with only PRRSV or only S. choleraesuis. In contrast, pigs which were dually infected with S. choleraesuis and PRRSV exhibited unthriftiness, rough hair coats, dyspnea, and diarrhea. The pigs which received all three treatment factors were the most severely affected and 43% (three of seven) of the animals in this group died. Individuals in this group shed significantly higher quantities of S. choleraesuis in feces and had significantly higher serum PRRSV titers compared to other treatments (p < or = 0.05). In addition, S. choleraesuis and PRRSV were shed longer and by more pigs in this group than other groups and S. choleraesuis was recovered from more tissues in this group on Day 21 post inoculation. These results suggested that PRRSV, S. choleraesuis, and dexamethasone acted synergistically to produce a syndrome similar to that observed in the field.

Natural transmission of Salmonella choleraesuis in swine

This experiment was designed to study the natural transmission of Salmonella choleraesuis in swine. Forty pigs were divided into three groups. Group 1 (n = 12) was challenged with 10(8) CFU of S. choleraesuis per ml by intranasal inoculation. One day postinoculation (p.i.), group 2 (n = 24) was commingled with group 1. Group 3 (n = 4) served as uninoculated controls. Serum samples were collected weekly. Blastogenesis assays and necropsies were performed at 1, 2, 4, 6, 9, and 12 weeks p.i., and 16 tissue samples per pig were collected and cultured. Environmental (pooled feces from the pen floor) levels of S. choleraesuis were 2.61 log10 CFU/g of feces at 24 h p.i. (immediately prior to commingling). Severe clinical signs were observed in groups 1 and 2. The results indicated that at least 16% of group 2 pigs were shedding S. choleraesuis within 24 h of commingling. At 1 week p.i., 32 of 32 group 1 and 39 of 62 group 2 tissue samples were positive for S. choleraesuis. Only 3 of 12 group 2 pigs were positive at 6, 9, and 12 weeks (1 pig for each week), indicating that only a small proportion of infected swine become long-term carriers. At 12 weeks p.i., only the colon and colonic lymph node samples of one pig from group 2 were positive. Humoral, mucosal, and cellular immune responses were similar between groups 1 and 2. These data demonstrate that a few pigs shedding low levels of Salmonella organisms before slaughter can result in rapid transmission and subsequent shedding by many swine.

Influence of inoculation route on the carrier state of Salmonella choleraesuis in swine

This study was designed to investigate the carrier state of swine infected with Salmonella choleraesuis. Thirty-five pigs were divided into 3 groups. Groups 1 (n = 15) and 2 (n = 16) were challenged with 10(8) CFU of S. choleraesuis intranasally or by gastric route, respectively. Group 3 (n = 4) served as uninoculated controls. Pigs were necropsied at 2, 4, 6, and 12 weeks post inoculation. Clinical signs and microscopic lesions were more severe for group 1. Salmonella choleraesuis was recovered from a greater percentage of tissue samples for group 1 versus group 2 at 2, 4, and 6 weeks post inoculation. No differences were observed between groups at 12 weeks post inoculation. Regardless of route of inoculation, S. choleraesuis was most often recovered from the ileocolic junction, ileocolic lymph node, cecal contents, tonsil, lung and colon. Both groups shed S. choleraesuis in the feces sporadically throughout the 12 week period indicating that a carrier state is maintained for at least 12 weeks. However, group 1 shed higher numbers of S. choleraesuis initially. Serum IgG, IgM, and IgA antibody responses to S. choleraesuis lipopolysaccharide and heat extract antigens were observed for both groups. Higher serum IgG antibody titers to S. choleraesuis lipopolysaccharide were observed for group 2. Intestinal antibody responses for both groups included IgG and IgM responses but not an IgA response. Both routes of inoculation stimulated peripheral blood B-cells while the intranasal route (group 1) was more effective at simulating peripheral blood T-cells. The reduction in levels of tissues infection and shedding observed for both groups coincided with the development of the host immune response. These data indicate that route of inoculation affects the development of humoral and cellular immunity, influences levels of Salmonella shed into the environment and the distribution of Salmonella within tissue.

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

Transmission of Salmonella typhimurium in swine is traditionally believed to occur by the fecal-oral route, with invasion through the intestinal wall and Peyer's patches. However, involvement of the upper respiratory tract may be equally important. An esophagotomy was performed on 6- to 8-week-old pigs. Esophagotomized pigs were challenged intranasally with 10(9) CFU of S. typhimurium cells and necropsied at 3, 6, 12, and 18 h postinoculation (p.i.). By 3 h p.i., S. typhimurium was recovered from cecum, colon, head, and thoracic tissues and from the middle ileum involving a large number of Peyer's patches. The ileocolic lymph nodes and ileocolic junction were not positive for S. typhimurium until 6 and 12 h p.i., respectively. Additional pigs were inoculated transthoracically with 10(9) CFU of S. typhimurium and necropsied at 3 and 18 h p.i. By 3 h p.i., all tissues were positive for S. typhimurium. Tonsil explants seeded with 10(9) CFU of S. typhimurium indicated that within 6 h p.i., S. typhimurium was located within the tonsilar crypts. These data show that after intranasal inoculation, S. typhimurium rapidly appears in the gut tissues and suggest that the tonsils and lung may be important sites for invasion and dissemination of Salmonella species.

The effects of O-antigen character and enterobacterial common antigen content on the in vivo persistence of aromatic-dependent Salmonella sp. live-vaccine strains

Aromatic-dependent (aro) derivatives of Salmonella choleraesuis like aro S. typhimurium are non-virulent but, unlike them, are ineffective as live vaccines in mice, given i.p. An aro derivative of S. choleraesuis did not persist in the liver and spleen (RES) of mice after i.p. inoculation whereas a similar derivative of S. typhimurium persisted. S. choleraesuis (O group C1; O-6,7) and S. typhimurium [O group B; O-(1),4(5),12] differ in O antigen of LPS, determined by chromosomal locus, rfb. Three pairs of nearly-isogenic aro derivatives, one member O-6,7 and the other O-(1),4,(5),12, were constructed in two lines of S. typhimurium by replacement of their B-rfb genes with the C1-rfb genes of S. choleraesuis. In tests for persistence after mixed or separate i.p. inoculation of equal doses into BALB/c mice the O-(1),4,(5),12 member of each pair was recovered as CFU in the RES at ca. 100-fold greater number than the O-6,7 member at 24 hours post-inoculation and subsequently. O-6,7 derivatives of S. typhimurium constructed as described above by a simple replacement of group B with group C-rfb locus synthesise only trace (tr) amounts of enterobacterial common antigen (ECA). An ECA+ (able to make normal levels of ECA) derivative of one aro, O-6,7 S. typhimurium strain was constructed by replacement of its B-rfe locus with the C-rfe locus of S. choleraesuis. Tested by mixed inoculation i.p. this strain persisted in the RES in numbers 10-fold greater than its O-6,7 ECAtr but 5-10-fold lesser than its O-(1),4,(5),12 cousins. Thus both O-specificity and ECA contribute to the survival of salmonella species in mice as determined by in vivo persistence of non-multiplying aro derivatives.

Test of the virulence and live-vaccine efficacy of auxotrophic and galE derivatives of Salmonella choleraesuis

Aromatic compound-dependent (aro) derivatives of three mouse-virulent strains of Salmonella choleraesuis (Salmonella cholerae-suis) were constructed and shown to be nonvirulent for mice (intraperitoneal [i.p.] 50% lethal dose [LD50], greater than 5 X 10(6) CFU). A pur derivative, and a thy derivative, each of a different virulent parent, remained moderately virulent (i.p. LD50S for BALB/c mice, ca. 10(5) and 5 X 10(4) CFU, respectively). Tested as live vaccines i.p., the aro strains were ineffective in salmonella-susceptible BALB/c and C57BL/6 mice but were somewhat effective in salmonella-resistant CBA/J mice and in outbred CD-1 mice. The pur and thy strains were effective as live vaccines in BALB/c mice when given in sublethal doses. Two previously isolated nonvirulent galE derivatives of S. choleraesuis (i.p. LD50 in BALB/c mice, greater than 10(6) CFU) were also ineffective as live vaccines in BALB/c and C57BL/6 mice. The main antigenic difference between S. choleraesuis (O-6,7) and S. typhimurium (O-4,12) is in O-antigen character, thought to largely determine the specificity of protection in salmonellosis. Paired, nearly isogenic O-6,7 and O-4,12 derivatives were constructed from an aro S. typhimurium strain of proven efficacy as a live vaccine. Used as live vaccines, the O-4,12 member protected BALB/c mice against challenge with virulent S. typhimurium, whereas the O-6,7 member did not protect against virulent S. choleraesuis. However, BALB/c mice vaccinated with the O-6,7 member and mice vaccinated with an aro S. choleraesuis strain were protected against challenge with a moderately virulent (LD50, 5 X 10(4) CFU) O-6,7 derivative of an S. typhimurium strain.