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.     

Studies on the interaction between Salmonella enterica ser. Typhimurium and intestinal helminths in pigs

Concomitant infections with helminths and bacteria may affect the course and the resulting disease outcome of the individual infections. Salmonella, Oesophagostomum, Trichuris and Ascaris coexist naturally in pig herds in Denmark, and possible interactions were studied. Pigs in one experiment were trickle infected with low or moderate dose levels of Oesophagostomum spp. and challenge infected with S. Typhimurium. In another experiment, pigs were inoculated with S. Typhimurium followed by a challenge exposure to either Oesophagostomum, Trichuris or Ascaris. Enhancement of the Salmonella infection was not demonstrated in either experiment. The helminth effect on the pigs was modest and may explain the lack of influence on the Salmonella infection. A previous experiment with a larger Oesophagostomum infection level resulted in enhancement of the S. Typhimurium infection. A dose dependency of the interaction is therefore suggested. However, the relatively high worm burdens in the present study suggest that infection with these common pig helminths does generally not influence the course of concurrent S. Typhimurium infections under natural conditions.     

Salmonella serotypes present on a sample of Irish pig farms

A survey of the prevalence of Salmonella species infection was conducted on 59 Irish farrow-to-finish pig herds. Faecal samples were collected from the pens of first-stage weaners (growing pigs approximately three to 10 weeks of age), second-stage weaners (approximately 10 to 17 weeks of age) and fatteners, and from the dry sow and farrowing sow houses. The prevalence of infection was estimated to within 5 per cent with a 95 per cent confidence interval. Thirty of the 59 herds were infected, 12 with Salmonella Typhimurium only, eight with Salmonella Derby only and seven with both S Typhimurium and S Derby; serotypes London, Livingstone and Infantis were each isolated from a single herd. Farms in Ireland are assigned to one of three infection categories on the basis of the antibody levels in samples of meat juice taken at slaughter. When a herd was classified as either positive or negative on the basis of the isolation of Salmonella from at least one faecal sample there was no association between the herd's category as determined by meat juice serology and the probability of the isolation of Salmonella from the faecal samples. However, there were differences in prevalence between pigs at different stages of production in herds of different categories. Farrowing sow houses in moderately infected (category 2) herds had significantly lower infection rates (P < or = 0.05) than other herd categories and other stages of production. Pigs from first-stage weaner pens in slightly infected (category 1) herds were more likely to be infected with Salmonella than pigs at any other stage of production or category of herd.     

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).     

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.     

Distribution of Salmonella in tissues following natural and experimental infection in pigs

Clinical salmonellosis associated with Salmonella is increasingly reported in finishing swine. Since S. Typhimurium is often associated with these episodes and given that this serotype is among the most often reported in humans, we were interested to determine if various tissues and carcasses from animals coming from herds that were clinically affected were more likely to be contaminated by Salmonella compared to carcasses from animals raised in herds without any history of salmonellosis. Carcasses from animals from affected herds were significantly more contaminated by Salmonella while showing increased titers in antibodies directed against this bacterium. At the opposite, caecal contents and mesenteric lymph nodes from both groups of animals were similarly contaminated by Salmonella. In the second part of the study, we studied the persistence of the bacterium in various tissues after an experimental infection with S. Typhimurium. We found that, after the infection, Salmonella persisted for as many as 7 d in many extraintestinal tissues, while it was present in the feces of infected animals for all 14 d of the experiment. These findings indicated that carcasses from animals that experienced salmonellosis during their growth phase are more likely to be contaminated by this bacterium and that precautions must be taken in order to ensure that clinically affected animals should be kept on the farm for at least 7 d before being shipped for slaughter.     

Evaluation of an enzyme-linked immunosorbent assay for diagnosis of trichinellosis in swine.

Experimental and field trials were conducted to evaluate an ELISA for its ability to detect Trichinella-infected domestic swine and to compare ELISA results with muscle-digestion test results. The ELISA used was a commercial double-antibody kit, containing an excretory-secretory antigen, and was evaluated principally for epidemiologic use. Experimentally induced infection in swine (4 groups of 3 pigs each; inoculated with 0, 50, 500 or 5,000 larvae) was detected as early as postinoculation week 4, with seroconversion of all inoculated swine by postinoculation week 8. The rate of seroconversion appeared to be affected by initial larval dose, time after inoculation, and immunocompetence of the individual host. Determination of antibody kinetics generally revealed rapidly increasing antibody titer, followed by its steady decrease in most pigs. Once seropositive, however, all pigs remained seropositive for the duration of the 10-week study. Presence of muscle larvae was confirmed in all infected pigs at termination of the study. We recognize that the experimental conditions may not be truly representative of those under which natural infection develops in pigs; however, the ELISA detected an infected pig with muscle larval density of 0.87 larvae/g of tissue. Results of a field trial (n = 310) indicated no muscle digestion test-positive pigs (35 g of diaphragm muscle digested/pig), but 3 samples tested positive by ELISA for specificity of 99.0%.     

Salmonella infections in swine herds--epidemiology and importance for human diseases]

Based on pertinent literature and research work performed by the authors, a report is presented on the presence of salmonellas in swine herds and the importance of these organisms as agents of disease in swine and source of infection for human salmonellosis. The share among human cases of salmonellosis which are caused by salmonellas originating from swine is estimated at ca. 20%. It has to be assumed that a very large proportion of swine herds is contaminated by Salmonella. Salmonellas may be introduced through infected pigs (parent animals, pigs from other herds added to the herd) or carriers among other animal species (e.g. rodent pests, birds) as well as by feeding stuffs with primary or secondary contamination. So far, the individual importance of the various routes cannot be reliably assessed. It appears that the level of Salmonella prevalence within a herd essentially depends on the hygienic conditions, the mode of keeping and the management of the animals. Serological examinations of meat juice permit conclusions as to the level of Salmonella contamination in slaughtered pigs. The results can thus be used for programmes to reduce the introduction of salmonellas into the food chain.     

Isolation and serological survey of Salmonella in pigs in Japan

A total of 267 fecal and serum samples collected from individual pigs reared on a Salmonella-positive farm were subjected to bacteriological and serological examinations of Salmonella. Salmonella was isolated from 47 pigs (17.6%) and prevalence of antibody to lipopolysaccharide (LPS) of S. Typhimurium, which was partly common to S. O4, 12: d: -, was observed in 90 pigs (33.7%). Salmonella was isolated from 26 (28.9%) of 90 antibody-positive pigs and 21 (11.9%) of 177 antibody-negative pigs. Twenty-one of 36 pigs (58.3%) positive for S. O4, 12: d: -, five of 10 pigs (50.0%) positive for S. Havana, and none for S. Anatum had antibodies. Thus, seropositive rates were higher than isolation-positive rates, and antibody prevalence was associated with serovars of the isolates. Then, we analyzed antibody prevalence among pigs on Japanese pig farms. The antibodies to LPS of S. Typhimurium were found in 195 of 1,498 pigs (13.0%) and in at least one serum sample on 35 of 52 farms (67.3%). Our results indicate that Salmonella does not seem to be so prevalent in pigs though it is widely prevalent among pig farms.     

Prevalence of Salmonella serotypes on pig carcasses from high- and low-risk herds slaughtered in three abattoirs

The aim of this study was to compare the prevalence of Salmonella serotypes at two different sites on pig carcasses from herds classified as high-risk or low-risk and to elucidate the relationship between carcass contamination levels and serological status. Caecal samples and carcass surface swabs were cultured for Salmonella from a total of 210 pigs from low risk herds (< 19% of pigs in herd Salmonella seropositive) and 209 pigs from high risk herds (> 32% of pigs in herd Salmonella seropositive) in three abattoirs. Meat juice samples were collected for analysis by ELISA. The prevalence of Salmonella in the caecal contents of "low-risk" pigs was 10%, which was significantly lower than the 19% prevalence in "high-risk" pigs (p < 0.01). The corresponding figures for skin samples collected immediately post-evisceration were 2% and 12%. The predominant Salmonella serotype in the caecal contents of both the low-risk and high-risk pigs was Salmonella Typhimurium. Salmonella Kentucky and Salmonella Derby were the most frequent isolates from the carcass surface swabs of low- and high-risk pigs respectively. There was a positive association between seropositivity of pigs from high-risk herds and caecal carriage (p < 0.05). Results showed that herd categorisation based on serological results was useful in predicting Salmonella isolation rates from caecal samples and surface swabs of slaughtered pigs.     

Rapid infection in market-weight swine following exposure to a Salmonella typhimurium-contaminated environment

OBJECTIVE: To evaluate the possibility of swine becoming infected with Salmonella Typhimurium when housed for 2 to 6 hours in an environment contaminated with Salmonella, similar to a lairage situation prior to slaughter. ANIMALS: 40 crossbred market pigs with an approximate body weight of 92 kg. PROCEDURE: Five trials were conducted (8 pigs/trial) in simulated lairage conditions. Superficial inguinal, ileocecal, and mandibular lymph nodes, cecal contents, distal portion of the ileum, and fecal samples were obtained from each pig after 2 (n = 10), 3 (10), and 6 (5) hours of exposure to an environment contaminated with feces defecated by 10 pigs intranasally inoculated with nalidixic acid-resistant Salmonella Typhimurium (chi4232). In addition, 5 control pigs that were not exposed were also evaluated in the same manner. RESULTS: Feces deposited on the floor by intranasally inoculated swine were mixed with water to form slurry with a resulting load of approximately 10(3) colony-forming units of Salmonella Typhimurium/g of material. Eight of 10, 6 of 10, and 6 of 6 pigs exposed to the slurry for 2, 3, or 6 hours, respectively, had positive results for at least 1 sample when tested for the specific strain of Salmonella Typhimurium. CONCLUSIONS AND CLINICAL RELEVANCE: Pigs can become infected during routine resting or holding periods during marketing when exposed to relatively low amounts of Salmonella organisms in the preslaughter environment. Intervention at this step of the production process may have a major impact on the safety of pork products.     

Effects of fluorequinolone treatment acidified feed, and improved hygiene measures on the occurrence of Salmonella Typhimurium DT104 in an integrated pig breeding herd

Worldwide, the use of antimicrobials in food production has been associated with drug resistance in foodborne pathogens such as Salmonella. However, little is known about the efficaciousness of fluorequinolone treatment on Salmonella Typhimurium T104 infections in pig breeding herds. A combined eradication procedure with enrofloxacin application on sows and piglets, feeding of encapsulated organic acids to sows, disinfection with peracetic acid, separation of the growers from the sows and serological discrimination using a new whole-cell-based enzyme-linked immnosorbent assay (ELISA) was evaluated for the suitability to eradicate and to control endemic S. Typhimurium DT104 infections in a closed herd. Thirty-seven sows and their piglets were treated everyday from day 14 ante partum until the day of weaning. Eighteen sows and their piglets served as controls. From the first day of life until day 168 after birth, faecal samples (n = 1671) of all piglets were analysed for Salmonella shedding. In parallel, systemic antibody responses were monitored by whole-cell-based isotype-specific ELISA systems. From birth to weaning the prevalence in both groups was between 2% and 9%. After weaning, intermittent shedding could be observed in both groups, and salmonellae could be found in up to 7.7% of the faecal samples. As a result, a dramatic increase in Salmonella-infected growers was observed, as of day 115 after birth, 47.4% of the animals of the treated group were tested positive for S. Typhimurium. Our results indicate that despite long-term antibiosis treatment and optimized hygiene measures, shedding of S. Typhimurium by the sows and the subsequent infection of their offspring could not be effectively prevented. Although it could be not shown that elimination of S. Typhimurium DT104 infection was achieved, the disinfection procedures described and the diagnostic test used are effective instruments to decrease the Salmonella load and to identify individual infected animals. Both of these are important factors for an improved consumer protection.     

Salmonella enterica serovar Typhimurium and Enteritidis infection of pigs and cytokine signalling in palatine tonsils

Pigs are considered as one of the major sources of zoonotic strains of Salmonella enterica for humans. Out of many S. enterica serovars, S. Typhimurium dominates in pigs, however, in several countries in Central Europe, S. Enteritidis is also quite frequent in pig herds. In this study we therefore compared the colonisation of pigs with S. Typhimurium and S. Enteritidis. We found that 3 weeks after infection S. Enteritidis 147 colonised the intestinal tract in higher quantities but was shed in faeces in lower quantities than S. Typhimurium 17C10. In a second experiment we found out that S. Enteritidis 147 and its SPI-1 and SPI-4 mutants increased proinflammatory cytokine (IL-1β and IL-8) signalling in the ileum 5 days post infection. On the other hand, independent of SPI-1 or SPI-4, S. Enteritidis 147 suppressed expression of IL-18, MCP1, TLR2, CD86, IL-7, IL-10 and IL-15 in the palatine tonsils. The suppression of cytokine signalling may facilitate the initial colonisation of the palatine tonsils by Salmonella. Moreover, immune suppression may also influence pig resistance to opportunistic pathogens and Salmonella infection in pigs thus may become an issue not only in terms of pork contamination but also in terms of affecting the immunological status of pig herds.     

Influence of long-time transportation stress on re-activation of Salmonella typhimurium DT104 in experimentally infected pigs

In this study a Salmonella Typhimurium infection model in swine was used in order to investigate the influence of pre-mortal stress induced by long time period transportation on the re-activation of Salmonella in experimentally infected pigs. Salmonella free pigs were exposed to a highly virulent strain of Salmonella Typhimurium DT104 by direct intragastrical administration. Clinical parameters were monitored and the shedding rate in faeces was qualitatively and quantitatively determined by standard bacteriological procedures for 21 days. The distribution of the challenge organism in 14 different internal organs of transported and nontransported animals was determined. All infected animals developed clinical signs of salmonellosis 12 to 24 hours post infection. About 88 to 100% of the fecal samples were culture-positive up to post exposure day 6, and then varied from 71 to 92% until slaughter, respectively. At necropsy S. Typhimurium was recovered most frequently from caecum and ileocolic lymph nodes (83%), colon (79%), palatine tonsils (71%) and mandibular lymph nodes (62.5%). A negative impact of transportation stress on the shedding rate and the general condition of the animals was observed.     

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.     

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).     

Experimental rapid infection in market swine following exposure to a Salmonella contaminated environment

The objective of these experiments was to evaluate the possibility of swine becoming infected with Salmonella Typhimurium after a short time interval in a contaminated environment. Two experiments were conducted. Experiment 1 consisted of five trials with eight market weight swine. Pigs were necropsied at 2 (n = 10), 3 (n = 10) and 6 (n = 5) hours after continuous exposure to an environment contaminated with feces shed by swine intranasally inoculated with nalidixic acid-resistant Salmonella Typhimurium (chi 4232). In Experiment 2, pigs were necropsied after 30 minutes (n = 6), 60 minutes (n = 6), 2 hours (n = 6), and 6 hours (n = 3). In addition, control animals with no exposure were also necropsied in both experiments. At necropsy, the superficial inguinal, ileocecal, and mandibular lymph nodes, as well as cecal contents, distal ileum portion, and feces were evaluated. All samples were cultured for the presence of the nalidixic acid-resistant Salmonella. Feces deposited on the floor by intranasally inoculated swine were mixed with water to form slurry with a resulting load of 10(3)-10(5) Salmonella Typhimurium CFU per gram. In Experiment 1, 80% percent of animals with a 2-hour, 60% of animals with a 3-hour, and 100% of animals with a 6-hour exposure to this slurry had at least one sample test positive for the marked Salmonella Typhimurium strain. In Experiment 2, 50% of the 30 minute, 50% of the 60 minute, and 33% of the 2-hour exposed pigs had at least one sample test positive. These experiments show that market swine can become infected during routine resting or holding periods when exposed to relatively low levels (10(3) CFU) of Salmonella in the simulated pre-slaughter environment, and that exposure times as short as 30 minutes are sufficient to produce contaminated gastrointestinal tracts. They also demonstrate the high risk of holding pigs longer than six hours. Intervention at this step in the swine production process may have a significant impact on the safety of pork products.     

A cross-sectional study of swine influenza in intensive and extensive farms in the northeastern region of the state of São Paulo,Brazil

Swine influenza (SI) is a seasonal infectious disease highly important to the world pig industry. Loss of daily weight gain, increased costs for the prevention and treatment of secondary infections are the main economic losses associated with the presence of this disease. However, some epidemiological features of SI remain quite unclear. This study focused on assessing the prevalence of swine influenza virus (SIV) infection in intensive and extensive pig herds and associating risk factors. A set of 601 blood samples of five intensive farrow-to-finish farms and 361 blood samples from 56 extensive farms were analyzed using an indirect ELISA kit CIVTEST SUIS INFLUENZA®, Hipra (Amer, Spain), in order to detect anti-SIV antibodies. In total, 24.13 % of samples from intensive herds were positive, while no positive samples were detected in extensive rearing herds. Sow and weaning piglets had the highest prevalence values. In the intensive rearing system, occurrence of reproductive disorders and exposure to recently introduced animals were positively associated with the disease occurrence in swine herds. The findings highlight the importance of sows in the epidemiology of the disease and bring information about risk factors involved in the occurrence of swine influenza in intensive herds.     

Development of an ELISA procedure to detect swine carriers of pathogenic Yersinia enterocolitica

An enzyme immunoassay (ELISA) was developed to detect antibodies in pigs against the lipopolysaccharidic antigen of the three serotypes of Yersinia enterocolitica mostly associated with human infections. Recent epidemiological evidence has demonstrated that pigs and pork are important sources of yersiniosis in humans. The purpose of this study was to clarify the use of an ELISA to detect swine carriers of this enteroinvasive bacteria by examining seroconversion and tissue distribution of Y. enterocolitica following experimental infection and then screening pigs at a slaughterhouse by bacterial culture and ELISA. It was observed that seroconversion occurred in animals experimentally inoculated with Y. enterocolitica but not with other enterobacteria. It was also found that 27% of swine at a slaughterhouse carried the bacterium in their tonsils and/or intestinal tract, whereas 66% showed serological evidence of previous infection. About 6% of swine at slaughter were culture-positive, but seronegative. Although, similar numbers of swine showed serological evidence of previous infection by each of the three Y. enterocolitica serotypes tested, virtually all culture isolates belonged to serotype O:3. This ELISA appears as a valuable control tool that can be used, in conjunction with culture, to identify pigs or herds infected by strains of Y. enterocolitica associated with human infections.     

Spatial distribution of antibodies to Salmonella enterica serovar Typhimurium O antigens in bulk milk from Texas dairy herds

Environmental factors that enhance either the survivability or dispersion of Salmonella enterica serovar Typhimurium (S. Typhimurium) could result in a spatial pattern of disease risk. The objectives of this study were to: (1) describe herd status based on antibody response to Salmonella Typhimurium as estimated from bulk tank milk samples and (2) to describe the resulting geographical patterns found among Texas dairy herds. Eight hundred and fifty-two bulk milk samples were collected from georeferenced dairy farms and assayed by an indirect enzyme-linked immunosorbent assay (ELISA) using S. Typhimurium lipopolysaccharide (LPS). ELISA signal-to-noise ratios for each bulk tank milk sample were calculated and used for geostatistical analyses. Best-fit parameters for the exponential theoretical variogram included a range of 438.8 km, partial sill of 0.060 and nugget of 0.106. The partial sill is the classical geostatistical term for the variance that can be explained by the herd's location and the nugget is the spatially random component of the variance. We have identified a spatial process in bulk milk tank titers for S. Typhimurium in Texas dairy herds and present a map of the expected smoothed surface. Areas with higher expected titers should be targeted in further studies on controlling Salmonella infection with environmental modifications.