Usefulness of serological examinations in the analysis of Salmonella infections in pig herds

The development of the antibody concentration against lipopolysaccharide (LPS) of S. Typhimurium und S. Choleraesuis in rearing pigs during the fattening period and in breeding sows of the corresponding age was recorded. The studies revealed the following results. Antibodies of isotypes IgG1 and IgG2 revealed a more pronounced specificity against the according Salmonella serovar than IgM antibodies. The calculated "antibody percent value" based on the total amount of Salmonella antibodies is mainly determined by the IgM antibodies in sera and meat juice, respectively. In fattening pigs a significant increase of antibodies against IgM and total Ig was observed between week 3 and 10 after beginning of the rearing period. In breeding pigs this increase was detectable already earlier. In only 3 out of 10 groups an increase of IgG1 and IgG2 was also seen. The detected significant increase of total Ig and IgM in the other groups might be the result of a less intensive exposure to salmonellas or it might be due to an increase of unspecific antibodies induced by other antigens. Serological investigations represent a valuable tool to record the intensity and development in time of the Salmonella exposure in pigs farms. Examination of total Ig is an appropriate method to detect pig herds with a high level of Salmonella exposure, for detailed epidemiological studies in pig farms the examination of antibody isotypes will give more comprehensive information.     

Development and application of an enzyme-linked immunosorbent assay to detect antibodies against prevalent Salmonella serovars in swine in southern Brazil.

The implementation of Salmonella control programs in the pork production chain demands rapid and cost-effective methods to assess the prevalence of infection in pig herds. The objective of the present study was to develop an in-house enzyme-linked immunosorbent assay (ELISA) based on S. Typhimurium lipopolysaccharides (LPS) to measure the prevalence of infection caused by Salmonella in swine herds. Coating antigen was produced by phenol extraction of S. Typhimurium culture. After standardization of ELISA test conditions, the assay was validated by testing serum samples on different animal categories: pigs orally inoculated with S. Typhimurium and sentinel animals in contact with them, naturally infected animals, colostrum-deprived piglets, and bacterin-immunized pigs. Seroconversion was observed in inoculated pigs (7 days postinfection [DPI]) and in the sentinels (21 DPI). Nonspecific reactions were not detected in the sera of colostrum-deprived animals. Serum samples from animals immunized with Salmonella Agona, Salmonella Derby, Salmonella Panama, and Salmonella Bredeney bacterins showed marked cross-reaction with the LPS from the serovar Typhimurium. Moreover, positive results obtained with the in-house ELISA were associated with Salmonella isolation in 75 infected pig herds. Comparisons with 2 commercial kits showed a linear correlation coefficient of 0.847 between the in-house ELISA and kit A and 0.922 with kit B but a low agreement in the qualitative results. In conclusion, the newly developed in-house ELISA based on S. Typhimurium LPS can be a useful tool to determine the intensity of Salmonella sp. infection in swine herds.     

Nationwide surveillance of salmonella in the faeces of pigs in Japan

The prevalence of faecal carriage of salmonella in 5393 pigs reared on 218 pig farms located in 31 of 47 prefectures in Japan over the period July 2003 to June 2005 was investigated. We isolated 172 strains belonging to 20 serovars and one untypable Salmonella enterica from 169 pig faecal samples (3.1%) collected from 48 farms (22.0%). The most prevalent type of S. enterica was untypable O4,12:d:- which lacks phase 2 flagellar antigen, representing 29.1% (50/172) of all isolates. Of 26 S. enterica serovar Typhimurium isolates, 16 strains appeared to be definitive phage type 104 (DT104) by polymerase chain reaction.     

Isolation of Salmonella from diarrheic feces of pigs

A survey of Salmonella was carried out in fecal samples of 887 pigs with diarrhea collected from 235 pig farms between April 1996 and March 2001. Salmonella was isolated from 84 feces (9.5%) of 887 pigs and from 45 (19.1%) of 235 farms. The higher prevalence was found in weaned pigs (12.4%) and fattening pigs (17.3%) than in sows (4.2%) and suckling pigs (4.5%). Isolation rates of S. Typhimurium were higher from weaned and fattening pigs than from the others. Therefore, risk of horizontal infection of S. Typhimurium will increase, if no adequate health managements are practiced when weaned and fattening pigs have diarrhea.     

Immunochemical analyses of serum antibodies from pig herds in a Salmonella non-endemic region.

In a large comparative survey of Danish and Swedish slaughter pig herds performed prior to this work, it was unexpectedly found that some Swedish herds harbored seropositive pigs. Serum samples from the Swedish herds had moderate responses in the Salmonella mix-ELISA (detecting serogroup B and C1 infections) compared to the Danish herds classifying some of them as seropositive using a cut-off value at 40 OD%. In Sweden, extensive Salmonella control is carried out by bacteriological screening of feces and lymph nodes, and the overall prevalence has been proven to be below 0.1%. The serological positive results were therefore unexpected; hence the reactivities of the Swedish sera were studied by a number of immunochemical analyses (Western blot, indirect ELISA, inhibition ELISA, avidity ELISA) and compared to sera from Danish pig herds with verified Salmonella infections ("the reference sera").In Western blot, the Swedish sera had high binding reactivities against Salmonella Typhimurium LPS of different molecular weights, and gave binding patterns similar to that of the reference sera. Pre-incubation with free S. Typhimurium LPS or PS (the polysaccharide part of LPS) was able to inhibit the reactivity of the Swedish sera in the mix-ELISA. Reactivities against other related bacterial LPS such as Citrobacter freundii LPS and Yersinia enterocolitica O:3 LPS were observed in the Swedish sera, but these LPS antigens were unable to inhibit the reactivities in the mix-ELISA as efficiently as S. Typhimurium LPS. Furthermore, the Swedish sera did not bind Salmonella LPS of another serogroup (S. Meleagridis LPS, serogroup E1) or rough Salmonella LPS, both lacking the specific O-antigenic parts of S. Typhimurium LPS. The avidity of the Swedish sera was much lower than the avidity of the reference sera, which could indicate the presence of transient low-dose infections or stimulation by inactivated bacteria in feed. The results obtained in this investigation strongly indicate that the Swedish sera contain antibodies directed against the O-antigenic part of LPS from S. Typhimurium or possibly on as yet unknown bacterium.     

Distribution of Salmonella serovars and phage types on 80 Ontario swine farms in 2004

The objective of this study was to describe the distribution of Salmonella spp. on Ontario grower-finisher pig farms. Eighty swine farms were visited from January through July 2004. On each farm, fecal samples were collected from 5 pens, 2 rectal samples and 1 pooled sample from fresh manure on the floor per pen. Salmonella was isolated from 91 (11%) of the 800 rectal samples and 73 (18%) of the 397 pooled samples. Overall, Salmonella was recovered from 37 (46%) of the 80 farms. On each positive farm, Salmonella was cultured from 1 to 7 pigs or 1 to 5 pens. Of the 37 farms, 18, 13, 5, and 1 yielded 1, 2, 3, and 4 serovars, respectively. The most common serovars were S. Typhimurium var. Copenhagen, S. Infantis, S. Typhimurium, S. Derby, S. Agona, S. Havana, and S. enterica subsp. I:Rough-O. The 3 most frequent phage types were PT 104, PT 104a, and PT 104b. There was a statistically fair agreement between samples collected directly from pigs and pooled pen samples in determining the Salmonella status at the pen and farm level (kappa = 0.6, P < 0.0001). However, in 62 pens, Salmonella status, serovars, or phage types differed between the pig and pooled pen samples. The distribution of Salmonella on the swine farms in this study indicates that, in developing an intervention strategy, priority should be given to farms positive for S. Typhimurium var. Copenhagen. Also, the variation in Salmonella status between pig and pooled pen samples deserves consideration in a sampling strategy.     

Development of a complete ELISA using Salmonella lipopolysaccharides of various serogroups allowing to detect all infected pigs

Although poultry is recognized as the major source of food-poisoning caused by Salmonella, pork also contributes to human infections. This study was therefore undertaken in order to develop a reliable serological method for the evaluation of the Salmonella status of piglets. A complete ELISA was performed using lipopolysaccharides of Salmonella Typhimurium, Anatum, Hadar and Infantis because these serovars were representative of the serogroups isolated from 30 contaminated fattening farms. S. Enteritidis was also added because of its importance in human infection and to include the O:9 antigen. This method potentially detects 100% of infected pigs. A significant correlation was found between this serological method and the bacteriological data from mesenteric lymph nodes (p = 0.01). In addition, both sensitivity and specificity were high (97% and 94% respectively). The ELISA test was therefore used in a cross-sectional study on 4 farms to evaluate when pigs became contaminated: seropositive pigs were only found for the 20 week old finishing pigs. The antibody response to Salmonella in piglets was also investigated: maternal antibodies persisted until 7 weeks of age and post-Salmonella contamination seroconversion was detected from 8 weeks of age onwards.     

Salmonella serovars and antimicrobial resistance patterns on a sample of high seroprevalence pig farms in England and Wales (2003-2008)

Following the introduction of a national abattoir-based monitoring programme for Salmonella in pigs, advisory visits were made to pig farms in England and Wales with high Salmonella seroprevalence assessed by muscle tissue fluid (meat juice) ELISA. Samples (n = 15 790), including pooled pen floor faeces (n = 12 136), were collected for Salmonella culture from 296 farms, between October 2003 and February 2008. Salmonella was isolated from 4489 (28%) of all samples collected, including 3301 (27%) of pooled pen floor faecal samples, from 270 (91%) of farms visited. Salmonella Typhimurium and S. Derby were the most prevalent serovars, representing 64% and 16% of isolates serotyped, respectively. The main phage types of S. Typhimurium identified were U288 and DT193. Antimicrobial resistance (AMR) was seen in 92% of isolates tested, with the highest frequencies of resistance occurring to tetracyclines (T), sulphonamide compounds (SU), ampicillin (AM), sulphamethoxazole/trimethoprim (SXT), streptomycin (S) and chloramphenicol (C). Fifty-nine AMR patterns were observed, the most frequent of these being T, AM, SXT, C, S, SU, seen in 35% of isolates tested. Multi-drug resistance was commonly found, with 67% of isolates submitted for AMR testing showing resistance to between four and nine antimicrobials.     

Excretion in feces and mucosal persistence of Salmonella ser. Typhimurium in pigs subclinically infected with Oesophagostomum spp

OBJECTIVE: To determine interactions between Oesophagostomum spp and Salmonella ser. Typhimurium in pigs. ANIMALS: 30 healthy 5- to 6-week-old pigs. PROCEDURE: Pigs were allotted to 3 groups (n = 10 pigs/group) and treated as follows: group A was given Oesophagostomum dentatum and O quadrispinulatum; group B was given O dentatum, O quadrispinulatum, and S Typhimurium; and group C was given S Typhimurium only. Pigs in groups A and B were trickle infected with Oesophagostomum spp 3 times weekly throughout the study. After 19 days, groups B and C were inoculated once with S Typhimurium. One pig from each group was euthanatized on the day of Salmonella exposure and 2 and 4 days after Salmonella exposure. The remaining pigs were euthanatized on days 16 and 17 after Salmonella exposure. RESULTS: Pigs with dual infections of nematodes and bacteria (group B) excreted significantly higher amounts of S Typhimurium in feces, compared with nematode-free pigs (group C). In addition, group-B pigs excreted S Typhimurium on more days than pigs in group C. Salmonella Typhimurium was detected in the cecum and colon in the majority of pigs in group B, whereas S Typhimurium was only detected in the colon in pigs in group C. Immunohistochemical examination detected S Typhimurium in 7 of 9 pigs in group B but only 2 of 9 pigs in group C. CONCLUSIONS AND CLINICAL RELEVANCE: Interactions between intestinal nematodes and bacteria may play an important role in the dynamics of S Typhimurium infections.     

2016～2018年江苏省规模猪场PRRS血清学调查

为了解2016年1月~2018年12月期间江苏省规模猪场猪繁殖与呼吸障碍综合征(porcine reproductive and respiratory syndrome,PRRS)流行动态,本研究对该省27家规模猪场不同批次送检的2062份未免疫PRRS疫苗血清样本,采用ELISA方法进行了猪繁殖与呼吸障碍综合征病毒(Porcine reproductive and respiratory syndrome virus,PRRSV)抗体检测,并对抗体阳性率≥80%的猪群阶段,依据PRRSV抗体S/P分布频段选取135份血清,采用RT-qPCR方法检测并统计PRRSV阳性率,进行血清学调查。结果显示,27家未免疫PRRS疫苗猪场抗体总阳性率为68.82%。不同地区抗体阳性率较高的为宿迁和南通,分别为72.04%和71.09%,连云港地区最低为58.82%。2016~2018年呈现逐年下降的趋势,从76.41%下降至57.72%。不同猪群阶段中以公猪、后备母猪、12~16周龄育肥猪和18~25周龄育肥猪抗体阳性率较高,分别为80.95%、92.86%、86.84%和98.09%。在上述4个抗体阳性率≥80%的猪群阶段,RT-qPCR检测结果显示,24份PRRSV阳性血清样本C t值与抗体S/P值高低无相关性。血清中PRRSV阳性率以后备母猪最高为20.58%,在PRRSV抗体S/P值<0.4和S/P值≥2.5异常分布频段,血清PRRSV阳性率均≥15.38%,而0.4≤S/P值<2.5正常范围内PRRSV阳性率均≤10%,差异显著,具有统计学意义(P<0.05)。表明江苏省规模化猪场不同地区、不同规模和不同阶段猪群普遍存在 PRRSV 感染,该研究结果为规模猪场PRRS的防控提供了参考。     

Distribution of immunoglobulin isotypes and Salmonella antibodies in blood serum and meat juice of pigs

Using the close linear regression between the logarithm of the dilution degree of a sample and the logarithm of the extinction measured in an ELISA both the relative concentrations of immunoglobulines of the isotypes IgG, IgM and IgA and of the LPS antibodies against S. Typhimurium of the different isotypes in blood sera and meat juice of 15 slaughtered pigs were detected and compared. Furthermore the total concentration of antibodies against LPS of S. Typhimurium according to the "meat juice ELISA" were compared. Distribution of immunoglobulines between serum and meat juice revealed individual differences between the animals as well as between the different immunoglobulin-isotypes. Within the same isotype the ratio of the concentrations of anti-LPS Salmonella Typhimurium antibodies between serum and meat juice was significantly closer than relating the whole of immunoglobulines of the referred isotype. In order to detect pig herds with a high level of Salmonella exposure a comparison of the 1:30 diluted meat juice samples with the 1:400 diluted blood sera is justified, however, for detailed epidemiological or scientific studies there is a need to consider the existing differences between the immunoglobuline-isotypes as well as between the specificity of antibodies and of total immunoglobulines. While the concentration of Salmonella antibodies of the isotypes IgG1, IgG2 and IgA showed a clear and statistically significant correlation between both one below the other and with the total amount of Salmonella antibodies, this connection could not be established for the total amount of immunoglobulines of different isotypes and the IgM-antibodies.     

Phenotypic and genetic characterization of Salmonella enterica subsp. enterica serovar Typhimurium isolated from pigs in Rio Grande do Sul, Brazil

This study aimed to investigate the relatedness of porcine Salmonella enterica subsp. enterica (S.) serovar Typhimurium strains isolated in Southern Brazil. Sixty-six isolates from pigs belonging to three commercial companies were submitted to phage typing, XbaI-macrorestriction (PFGE), IS200 hybridization, rep-PCR, antimicrobial susceptibility testing, and PCR assay targeting the spvR region. All strains presented a unique rep-PCR pattern and 63 strains had a common IS200 profile. One pulse-type (XA) was the most prevalent (39/66 strains) and included strains of phage types DT177, DT192, DT194 and RDNC. The spvR region was detected in three strains, which harboured plasmids of 90 kb. High rates of tetracycline, sulfonamide and streptomycin resistance were found. Isolates from farms located in different geographic regions but associated to the same commercial companies clustered together and presented a common resistance profile. Results suggested that clonal groups of S. Typhimurium are present in pig commercial companies in Southern Brazil.     

A cross-sectional study of Salmonella in pre-slaughter pigs in a production compartment of northern Thailand

A cross-sectional study was conducted to determine the prevalence of Salmonella and to associate management factors in fattening pigs in a production compartment of northern Thailand. A total of 194 fecal samples and 166 environmental samples were collected from 22 fattening pig herds for isolation and identification of Salmonella. An additional 427 serum samples were collected from the same herds to determine Salmonella antibodies using ELISA. A questionnaire was used to collect management factors likely to be associated with Salmonella identification. Prevalence of Salmonella in each sample and its confidence interval was adjusted for clustering by herds using linearization technique. A generalized estimating equation was used to determine the odds ratio and significance level for each management factor in a logistic regression model. Salmonella was found in all 22 study pig herds with a fecal sample prevalence of 63% (95%CI: 56-69%) and a serum sample prevalence of 72%. However, isolation results were not significantly different from ELISA results. The most isolated serotype was Salmonella Rissen (49%) followed by Salmonella Typhimurium (19%), Salmonella Stanley (12%) and Salmonella Weltevreden (4%) being significantly different in the different specimens collected (p=.024). The final logistic regression model with isolation results as outcome showed that medium herd size (OR=2.32, p=0.003), quality certification according to the Department of Livestock Development standard (OR=1.88, p=0.000), use of effective microorganisms (OR=1.51, p=0.022), slurry waste management (OR=2.17, p=0.000) and less number of pigs per pen (OR=1.12, p=0.000) were significantly associated with positive Salmonella isolation; with positive ELISA results, however, only the use of effective microorganisms was significantly associated (OR=2.63, p=0.011).     

Salmonella spp. in Bavarian liquid pig manure: occurrence and relevance for the distribution of antibiotic resistance

In a representative study, 380 manure samples of pig farms distributed all over Bavaria (Germany) were screened for the presence of Salmonella spp. at the time of manure application to soil using methods adapted to DIN EN ISO 6579. The isolates were tested according to DIN 58940 for their susceptibility towards 26 antimicrobial substances - such substances partly administered in animals, but mainly used in human therapy. Six out of 380 manure samples and, in addition, the only separated liquid manure sample examined, contained Salmonella isolates. Serotypes represented S. Typhimurium (n = 5), S. Derby (n = 1) and S. Infantis/S. Serogroup C1-(6,7:r:-)-form (each n = 1). Within the serovar S. Typhimurium, the most common phage type was DT104 (n = 3). All Salmonella isolates originated from 'big' farms (>30/45 sows on combined/breeding farms or >220 fattening pigs). Four out of six manure samples contained resistant isolates; all resistant Salmonellae were multi-resistant. Two out of three DT104-isolates showed the typical penta-resistance pattern often found in S. Typhimurium DT104, which was, furthermore, supplemented by other resistances. One Escherichia coli isolated together with a phage type DT104 S. Typhimurium also expressed the same penta-resistance pattern.     

Salmonella enterica infections in Spanish swine fattening units

The present study is the first conducted in Spain to estimate the bacteriological herd prevalence of Salmonella enterica in fattening units and to describe the Salmonella serovar diversity on these farms using a sample representative of the entire swine population. For this purpose, 10 faecal samples were collected from 10 different pens containing pigs close to market weight in a total of 232 fattening units. Total sample size was proportionally distributed according to the fattener census in each of the regions of the country and all the samples were examined by culture of 25 g of faecal material. One hundred (43.1%) farms had at least one Salmonella-positive sample (95% CI: 37-49.1%). Salmonella enterica was detected in 290 (12.5%) pooled faecal floor samples (95% CI: 11.2-13.8%). The apparent herd prevalence of salmonellosis was similar among multi-site, finishing and farrow to finish farms. Overall, 24 different serovars were identified, with S. Typhimurium, S. Rissen and S. Derby being the most common both at herd and sample level. Results of phage typing were available for the 91 isolates of S. Typhimurium. A total number of 10 different phage types were identified, with DT 193 being the most frequent. Phage types DT 104, DT 104b and DT U302, which have been associated with several multi-resistant patterns, accounted for 23% and 29% of the Typhimurium total isolates or Typhimurium infected farms respectively.     

Herd prevalence of Salmonella spp. in Danish pig herds after implementation of the Danish Salmonella Control Program with reference to a pre-implementation study

The problems addressed are: (1) comparison of prevalences of Salmonella spp. in different herd types in the Danish pig population after implementation of the Danish Salmonella Control Program (DSCP), and (2) to make a reference to a study from 1993/1994 (pre-implementation) with a discussion of possible biases when diagnostic methods differ slightly. The objectives were to present the prevalences of Salmonella spp., Salmonella Typhimurium, and multiresistant S. Typhimurium DT104 in Danish pig herds in 1998. Further, to discuss how herd prevalences may be compared to a previous study.A bacteriological study in 1998 comprised: (a) a random sample of slaughter pig producing herds (N=1962); (b) a random sample of farrow-to-grower (sow) herds (N=305); and (c) all breeding and multiplying (genetic) herds (N=366). A previous bacteriological study on Salmonella presence in 1993/1994 served as a model for the present study. The results of the study were that multiresistant S. Typhimurium DT104 was detected in one herd producing slaughter pigs. The herd apparent prevalences (HAPs) of Salmonella spp. were 11.7, 16.7 and 11.4% in genetic, sow, and slaughter pig herds, respectively. The conclusion of the study was that prevalence of multiresistant S. Typhimurium DT104 was low in the examined slaughter pig herds. The herd true prevalence (HTP) of Salmonella spp. in pigs had declined from before the start of the DSCP in 1993/1994 to 4 years later (1998).     

Meat juice ELISA for determination of Salmonella incidence in slaughter pig herds in Bavaria

Meat samples from diaphragm pillars were randomly taken from 3,048 pigs of 52 Bavarian herds after slaughtery. Meat-juice was collected and tested for salmonella antibodies in an indirect ELISA. The number of samples was calculated according to the annual production of slaughter pigs of a farm outlined in the "Leitlinien für ein Programm zur Reduzierung des Eintrags von Salmonellen durch Schlachtschweine in die Fleischgewinnung" from February 05th, 1998 (< 100 slaughter pigs: 45 samples, 100-200 slaughter pigs: 50 samples, > 200 slaughter pigs: 60 samples per year). Salmonella antibodies were detected in 48 carcasses (1.6%) of 12 farms (23.1%). However, 33 (68.8%) of these carcasses were originated from a single farm which had to be classified into category III (prevalence of > 40% in the samples). No bacteria could be isolated from this farm in a follow up examination. The 51 other farms (98%) were classified into category I (prevalence of < 20% in the samples). Farms with in/out-management showed a higher degree of reagents (2.1T%) than farms with continuous stabling (0.8T%). In a pig experimentally immunized with LPS-antigen preparations of Salmonella typhimurium it was shown that antibodies induced were nearly at the same level in all meat samples and even in selected organs (liver, kidney, parotis, mesenteric lymph nodes).     

Effects of the antimicrobial growth promoter tylosin on subclinical infection of pigs with Salmonella enterica serotype Typhimurium

OBJECTIVE: To determine whether feeding tylosin, an antimicrobial growth promoter, to pigs was associated with increased risk of infection with and excretion of Salmonella enterica serotype Typhimurium. ANIMALS: 17 healthy pigs. PROCEDURE: A commercial pelleted dry feed was given in 2 feeding trials. In trial A, 11 pigs were given feed with tylosin, 11 pigs were given feed without tylosin, and 11 pigs were given feed with tylosin before and feed without tylosin after inoculation with S Typhimurium. In trial B, 44 pigs were given feed that contained tylosin, and 44 pigs were given feed without tylosin. Three weeks after the start of each trial, pigs were orally inoculated with approximately 5 x 10(6) colony-forming units of S Typhimurium. Feces were examined for S Typhimurium, using semiquantitative microbiologic techniques before and for 5 or 6 weeks after inoculation. Serum antibody titers against S enterica were measured by use of ELISA. RESULTS: None of the pigs developed clinical signs of salmonellosis. However, after inoculation, S Typhimurium was isolated from feces of most pigs, and all but 2 pigs developed serum antibodies against S enterica. Significant differences were not detected between experimental and control groups in either trial. CONCLUSIONS AND CLINICAL RELEVANCE: Results indicate that tylosin fed as an antimicrobial growth promoter to pigs may not be an important factor in promoting infection with or excretion of S enterica serotype Typhimurium.     

Direct and indirect transmission of four Salmonella enterica serotypes in pigs

Background

Feed-borne spread of Salmonella spp. to pigs has been documented several times in recent years in Sweden. Experiences from the field suggest that feed-associated serotypes might be less transmittable and subsequently easier to eradicate from pig herds than other serotypes more commonly associated to pigs. Four Salmonella serotypes were selected for experimental studies in pigs in order to study transmissibility and compare possible differences between feed-assoociated (S Cubana and S Yoruba) and pig-associated serotypes (S Derby and S Typhimurium).

Methods

Direct contact transmission was studied in four groups of pigs formed by six 10-week-old salmonella negative pigs commingled with two fatteners excreting one of the four salmonella serotypes. Indirect transmission was studied by putting six 10-week-old salmonella negative pigs in each of four salmonella contaminated rooms. Each room had previously housed a group of pigs, excreting one of the four selected serotypes.All pigs were monitored for two weeks with respect to the faecal excretion of salmonella and the presence of serum antibodies. At the end of the trial, eight samples from inner tissues and organs were collected from each pig at necropsy.

Results

In the four direct transmission groups, one pig shed Salmonella (Cubana) at one occasion. At necropsy, S Typhimurium was isolated from one pig.In the indirect transmission groups, two pigs in the Yoruba room and one pig in each of the other rooms were excreting detectable levels of Salmonella once during the study period of two weeks. At necropsy, S Derby was isolated from one of six pigs in the Derby room and S Typhimurium was isolated from four of the six pigs in the Typhimurium room.No significant serological response could be detected in any of the 48 pigs.

Conclusions

These results show that all four selected serotypes were able to be transmitted in at least one of these field-like trials, but the transmission rate was low in all groups and no obvious differences between feed-associated and pig-associated serotypes in the transmission to naïve pigs and their subsequent faecal shedding were revealed. However, the post mortem results indicated a higher detection of S Typhimurium in the ileocecal lymph nodes of pigs introduced into a contaminated environment in comparison with the other three serotypes.     

Prevalence of Salmonella spp. on Canadian pig farms using liquid or dry-feeding

The objective of this study was to determine whether the shedding and antibody titre to Salmonella was lower for pig herds provided liquid-feed compared to those on traditional dry rations. Twenty liquid-feeding farms and 61 dry-feeding farms were selected. The amount of antibodies to Salmonella in sera from 15 finisher pigs on each of 80 Ontario swine farms was analyzed by means of enzyme-linked immunosorbent assay (ELISA). In addition, the presence of Salmonella on the 20 liquid-feeding farms and 21 of the dry-feeding farms was assessed by culture of 15 fecal samples taken directly from finisher pigs and five pooled pen-fecal samples at each farm.

A cut-off of OD% 10 was used. The Salmonella sero-prevalence differed between the two groups of farms. At least one pig tested sero-positive on 98% of the dry-feeding farms and 84% of the liquid-feeding farms (P < 0.05). A multi-variable mixed linear regression model with the farm as a random variable and farm factors as the fixed effects was fitted. Crude optical density (OD) of the individual pig was considered as the continuous dependent variable. Dry-feeding and antimicrobial daily usage was associated with crude OD (P < 0.05). In addition, crude OD increased with increasing herd size (P < 0.05).

Salmonella was isolated from 25 out of 420 fecal samples (6%) from dry-feeding farms compared to three out of 400 samples (0.8%) from liquid-feeding farms. Eight of the dry-feeding farms (38%) tested positive compared to only three of the liquid-feeding farms (15%). Salmonella was also recovered from the pen environment on five dry-feeding farms but were not isolated from the facilities using liquid-feeding. Salmonella Typhimurium was isolated from four farms in the dry-feed group and on one farm with liquid-feeding. The one S. Typhimurium isolate from the liquid-feeding farm exhibited no antimicrobial resistance, but those from dry-feeding farms were resistant to four or more antimicrobial agents. The results of the logistic regression, with farm as a random effect showed that dry-feeding [OR = 2.7 (1.1–15.1)] and continuous flow system [OR = 2.3 (1.2–12.7)] increased risk of finding Salmonella in the individual pig.

These findings indicate that liquid-feeding and all-in all-out management of the grower–finisher barns can reduce the Salmonella prevalence.