Chronic pleuritis in Danish slaughter pig herds

Respiratory disease is considered the most serious disease problem in modern pig production and the risk has increased with intensification of pig production. We quantified risk factors for chronic pleuritis (CP) in Danish pig herds in terms of herd and herd-owner characteristics, management and neighbourhood factors. The occurrence of CP was investigated in 540,104 slaughter pigs from 259 farrow-to-finish or finishing herds during the mandatory post-mortem meat inspection at 18 Danish abattoirs. The monthly herd- and abattoir-specific prevalences of CP were estimated for the months January through August 2000. Meat-inspection data, herd characteristics and neighbourhood factors were obtained from databases at the Danish Bacon and Meat Council. Data on herd-owner characteristics and management factors were obtained by telephone interviews. Data were analysed using a mixed model accounting for repeated measurements. Four factors were associated with increased herd prevalence of CP: low health status of the herd, pig density within a 5 km radius, mingling of pigs during the production period and the month of slaughter. Two factors protected against CP: feeding with only dry feed and practising all-in-all-out production.     

Sampling plan for the establishment of a serologic Salmonella surveillance for slaughter pigs with meat juice ELISA

The guidelines of the German Ministery of Food, Agriculture and Forestry outlining a Salmonella surveillance programme, "Leitlinien für ein Programm zur Reduzierung des Eintrags von Salmonellen durch Schlachtschweine in die Fleischgewinnung" (February 5th, 1998), provide a staggered spot-check size depending on the annual production of slaughtery pigs. A classification of farms into three quality categories (< 20%, 20-40%, and > 40%) is performed by salmonella antibody levels detected in meat samples using ELISA. Beside a fundamental inquiry into the salmonella status, the programme ought to lead to a decreased burden on slaughtery pigs and finally to a reduced salmonella entry into meat handling and processing companies. The spot-check plan is based on an unfavourable initial position and does not consider the real situation of salmonella load in pig fattening farms. For many farms the procedure will lead to an unjustified expenditure of examinations. In simple model calculations it is shown how a significant reduction of testing amount can be reached and statistical reliability is guaranteed, too. At the same time, we attempt to find a compromise between optimal spot check size and practicability. For reasons of free enterprise, an additional category would be desirable containing farms without any positive antibody titres in the samples. The results achieved so far indicate that a large number of German slaughter pig producers would fall into this category, without the necessity of a higher examination effort.     

Necessity of double testing of meat juice samples from pigs using ELISA for the determination of Salmonella status in pig farms]

According to the test protocol of the "meat juice ELISA" for detection of salmonella antibodies in pigs, all meat juice samples and serum controls are to be tested in duplicate. Results from routine investigations of repeatedly double tested meat juice and serum samples have been used to analyze the effect of double testing versus single testing with regard to the reliability of the final result. In case of an individual animal, testing of samples in duplicate increases the reliability of the results significantly, especially, if samples are retested at different occasions. In contrast, such a difference between mono and double testing of samples is not of importance when a group of animals is tested in order to determine the mean antibody rate in a herd. Here, results from double testing practically do not contribute to a higher reliability of the final result. This observation provides the possibility to reduce the costs for investigation programmes drastically.     

Use of herd information for predicting Salmonella status in pig herds

Salmonella surveillance-and-control programs in pigs are highly resource demanding, so alternative cost-effective approaches are desirable. The aim of this study was to develop and evaluate a tool for predicting the Salmonella test status in pig herds based on herd information collected from 108 industrial farrow-to-finish pig herds in Portugal. A questionnaire including known risk factors for Salmonella was used. A factor analysis model was developed to identify relevant factors that were then tested for association with Salmonella status. Three factors were identified and labelled: general biosecurity (factor 1), herd size (factor 2) and sanitary gap implementation (factor 3). Based on the loadings in factor 1 and factor 3, herds were classified according to their biosecurity practices. In total, 59% of the herds had a good level of biosecurity (interpreted as a loading below zero in factor 1) and 37% of the farms had good biosecurity and implemented sanitary gap (loading below zero in factor 1 and loading above zero in factor 3). This implied that they, among other things, implemented preventive measures for visitors and workers entering the herd, controlled biological vectors, had hygiene procedures in place, water quality assessment, and sanitary gap in the fattening and growing sections. In total, 50 herds were tested for Salmonella. Logistic regression analysis showed that factor 1 was significantly associated with Salmonella test status (P = 0.04). Herds with poor biosecurity had a higher probability of testing Salmonella positive compared with herds with good biosecurity. This study shows the potential for using herd information to classify herds according to their Salmonella status in the absence of good testing options. The method might be used as a potentially cost-effective tool for future development of risk-based approaches to surveillance, targeting interventions to high-risk herds or differentiating sampling strategies in herds with different levels of infection.     

Recovery of Salmonella enterica from seropositive finishing pig herds

The aim of this study was to assess the probability of detecting Salmonella from pen faecal samples in seropositive classified finishing pig herds. The study involved 77 herds from Denmark (20), The Netherlands (20), Greece (17) and Germany (20). The serological herd status was determined by the blood-sampling of 50 finishing pigs. Bacteriological sampling was performed by 20 pen faecal samples per herd. Over-all, 47% of the blood samples had an OD% larger than 10 and 23% larger than 40. Salmonella was isolated from 135 (9.3%) pen faecal samples in 32 herds (42%). Twenty-eight of these herds (87.5%) had a within-herd seroprevalence larger than 50% at sample cut-off OD% > 10. In our study, there was an increasing probability of recovering Salmonella with increasing within-herd seroprevalence. However, this was only a moderate correlation. A correlation coefficient of 0.62 was found between the proportion of culture positive- and seropositive samples in a herd at cut-off OD%> 10 and of 0.58 at cut-off OD% > 40. Serology is a measure of historical exposure, which may or may not correlate closely to the microbiological burden at the time of sampling. Due to the low sensitivity of culture methods, apparent 'false-positive' serological results may well represent real infections not detected by bacteriological testing. For screening purposes, serological testing provides an indication of exposure to Salmonella, which forms the basis for targeted sampling, intervention and logistic slaughter procedures.     

Salmonella in sows: a longitudinal study in farrow-to-finish pig herds

Besides finishing pigs, sows are also believed to be important in the epidemiology of Salmonella. The study objective was to investigate the prevalence of Salmonella excretion in sows during an entire reproductive cycle. In 3 farrow-to-finish herds, groups of 34, 40 and 32 sows, respectively, were sampled serially. Faecal samples, environmental swabs and feed samples were taken and submitted to a qualitative Salmonella isolation. All isolates were characterised using RAPD and a representative number of isolates was serotyped. The prevalence of Salmonella excretion was < 10% during gestation, around farrowing and during lactation, but a significant increase in the number of Salmonella excreting sows was found in herds A (p < 0.01) and C (p = 0.02) after weaning. S. Infantis was the most prevalent serotype in herd A, S. Derby in herds B and C. Except for the S. Infantis group in herd A, all isolates within each group of the RAPD analysis belonged to the same serotype. Three sows in herd A and 1 sow in herd C shed different serotypes at different time points. The present results indicate that sows can maintain Salmonella infections in farrow-to-finish herds and that culled sows, leaving the herd after weaning, may constitute a substantial risk for contamination of their carcasses with Salmonella.     

Factors associated with variation in bulk-tank-milk Salmonella Dublin ELISA ODC% in dairy herds

Our objective was to determine factors that contribute to variation in bulk-tank-milk Salmonella Dublin enzyme-linked immunosorbent assays (ELISA) corrected optic-density measurements (ODC%) in dairy herds. We constructed hierarchical mixed models with repeated bulk-tank-milk ELISA ODC% in 31 Danish dairy herds. Four models included different combinations of explanatory factors, and we compared how well these models described the variation in the data. Herd was included as a random effect nested within Salmonella status and barn type.

Detection of Salmonella Dublin or Salmonella Typhimurium by bacteriological culture of individual faecal samples or of slurry samples was associated with higher bulk-tank-milk ELISA ODC%, as was apparent Salmonella prevalence, the mean ELISA ODC% or mean-yield-corrected ELISA ODC% in milk samples collected from all individual cows. However, combinations of risk factors that included number or prevalence of cows with a very high ELISA ODC% provided better models, indicating that the effect of the cow-level explanatory variables on the bulk-tank-milk ELISA ODC% was related to the activity of the infection in the herd. Barn type (loose housing or tie stalls) was not associated with the variation in bulk-tank-milk ELISA ODC% in these models, which might be useful in planning of surveillance programs and intervention strategies.     

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.     

Seroprevalence and antibiotic sensitivity of serotypes of Salmonella enterica in Greek pig herds

Blood samples were taken from 50 pigs in each of 59 farrow-to-finish production herds and from 40 pigs in each of four of five registered multiplying herds. Samples of feed and faeces were also collected from 17 of the production herds and from the four multiplying herds. The sera were tested for antibodies to Salmonella enterica by the Danish mix-ELISA, and the organisms were isolated, serotyped and sensitivity tested by standard techniques. The average within-herd seroprevalence was 3.4 per cent and at least one pig tested seropositive in 21 of the 59 herds. In the multiplying herds, only a single seroreactor was detected. Salmonellae were isolated from only five of 95 feed samples, from two of the 17 herds sampled, Salmonella tennessee in four of five samples from one herd and an untypable strain in one of five samples from another. Four infected faecal samples were detected in four herds; they harboured Salmonella typhimurium, Salmonella bredeney or Salmonella london. No salmonellae were isolated from the samples of feed and faeces taken from the multiplying herds. The S london and S typhimurium had a low sensitivity to streptomycin, kanamycin and neomycin, and the S typhimurium also had low sensitivity to amoxycillin, ticarcillin, piperacillin, amoxycillin + clavulanic acid, cefalotin and cefoperazone. The other isolates were sensitive to all the antimicrobial agents tested.     

A new Salmonella surveillance and control programme in Danish pig herds and slaughterhouses

The Danish Salmonella Surveillance and Control Programme for pigs operates at all stages of the production chain and has been applied nationally since 1995. Due to the program the level of Salmonella in Danish pork has declined from 3.5% in 1993 to 0.7% in the year 2000. Simultaneously, the number of human cases with salmonellosis due to pork has declined from approximately 1,144 in 1993 to 166 in 2000. In year 2001, the programme has been improved at a number of stages. A new classification scheme for the serological surveillance of finisher herds has been developed. The individual test cut-off in the mix-ELISA has been reduced to 20 OD%. Only herds producing more than 200 finishers/year are sampled. Based on the serological result from the last 3 months a new weighted salmonella index is calculated: The Danish Bacon and Meat Council has agreed on a new stricter penalty system. Level 2 and 3 herds get a penalty of 2% and 4% of the value per slaughter carcass, respectively. A new method of Salmonella testing on carcasses has been introduced; 5 carcasses per slaughter day are swabbed at 3 defined areas at 100 cm2 for each sample. This method is more sensitive than the one used previously. Herds infected with multiresistant Salmonella Typhimurium DT104 have to follow special restrictions. These include a requirement for a herd intervention plan, restriction on livestock trade, and a requirement for special slurry handling. Carcasses from DT 104 herds must be heat-treated or decontaminated with hot water.     

Evaluation of recombinant Bhlp29.7 as an ELISA antigen for detecting pig herds with swine dysentery

Swine dysentery (SD) results from infection of the porcine large intestine with the anaerobic intestinal spirochaete Brachyspira hyodysenteriae. Diagnosis of SD traditionally has relied on detecting the spirochaete in the faeces of acutely affected pigs. To date simple and reliable serological assays that can be applied as a diagnostic tool at the herd level have not been available. In the current study a recombinant histidine tagged 29.7 kDa lipoprotein of B. hyodysenteriae (His6-Bhlp29.7) was used as an ELISA plate-coating antigen. Sera (n=1121) from slaughter-aged pigs on 19 farms were tested in this ELISA. Following optimization of the ELISA conditions using hyperimmune control sera, a set of 464 sera from slaughter-aged pigs from five herds where SD did not occur was tested. From these results a suitable cut-off value for herd negativity was defined as the mean optical density reading plus three standard deviations. Testing of 337 pig sera from six farms with SD then showed that the sensitivity of the test at the herd level was 100%, with all six farms having one or more serum samples exceeding the cut-off value for negativity. Finally, 320 sera from eight herds suspected of having SD were examined. Four of these herds were shown to have pigs with titres consistent with SD. The true health status of the other four herds that were serologically negative could not be confirmed. In conclusion, when used on sets of 40 sera from slaughter-aged pigs the His6-Bhlp29.7 ELISA as established proved to be a useful adjunct to the diagnosis of SD at the herd level.     

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.     

Chemiluminescent immunoassay as a microtiter system for the detection of Salmonella antibodies in the meat juice of slaughter pigs

Chemiluminescent immunoassay (CLIA) was applied in the screening of swine meat juice samples obtained from different laboratories in Germany, using the indirect enzyme linked immunosorbent assay (ELISA) as test for comparison. Out of the 1350 samples tested, 987 were found acceptable for validation of results. A good level of agreement between the two tests was obtained with a kappa value of 0.824 at 20% cut-off and 0.798 at 40% cut-off. At 20% and 40% cut-off levels, a sensitivity of 96.2% and 97.3%, respectively, and a specificity of 94.6% and 95.1%, respectively, were demonstrated between CLIA and ELISA. The detecting lipopolysaccharide (LPS) antigen was tested for specificity and a cross-reaction with two Escherichia coli and Yersinia strains was found when tested with ELISA. This reaction was not observed in CLIA, possibly because of the broader measurement spectrum of this test, which allows a more distinctive definition of immunologic reactions. The same explanation can be given for the increased number of meat juice samples which were positively detected only in ELISA but not in CLIA. Because of the wide detection range in CLIA, a normalization scheme was necessary to obtain reproducible results in this test system. The samples positively classified in screening were further tested for reciprocal titres in both test systems, and a higher correlation between screening and titration results was obtained for CLIA. Based on the results of this study, CLIA can be used as a reference method in detecting Salmonella antibodies in the meat juice of slaughter pigs.     

Herd factors associated with the seroprevalences of four major respiratory pathogens in slaughter pigs from farrow-to-finish pig herds

The objective of this study was to investigate sero-epidemiological aspects of Mycoplasma hyopneumoniae (Mh), influenza H1N1 and H3N2 viruses and Aujeszky disease virus (ADV) in fattening pigs from 150 randomly selected farrow-to-finish pig herds. Different herd factors were examined as potential risk indicators for the percentage of pigs with antibodies against the 4 pathogens. The median within-herd seroprevalences of the pathogens were: Mh 76%, H1N1 100%, H3N2 40% and ADV 53%. There was a positive association between the seroprevalences of both influenza viruses, and a negative association between the seroprevalences of ADV and H1N1. The percentage of pigs seropositive for Mh increased with the purchase of gilts and with the season (slaughter date in March-April). The within-herd seroprevalences of both influenza viruses were higher in the case of a higher density of pig herds in the municipality. A higher number of fattening pigs per pen additionally increased the risk of being seropositive for H3N2. The percentage of pigs with anti-gE-antibodies against the wild type ADV increased with higher airspace stocking density in the finishing unit, increasing herd size, increasing number of pig herds in the municipality and slaughter date in March-April. Increased seroprevalences for these 4 respiratory pathogens were mostly associated with pig density in the herd and its vicinity, the winter period, and with the purchase of gilts. Purchase of gilts, number of fattening pigs per pen and airspace stocking density are risk factors that can be managed directly by farmers striving to attain a high respiratory health status of pigs.     

Serological Salmonella monitoring in German pig herds: results of the years 2003-2008

The implementation of the European regulations regarding zoonoses demands objective and scientific statements regarding the status of the Salmonella prevalence in the national pig herds of all EU member states. Since 2002, the "QS Qualit?t und Sicherheit GmbH" has carried out serological Salmonella monitoring in German finishing pig herds. All data generated within the monitoring system are entered into the central database Qualiproof(?) (Qualitype AG, Dresden). The dataset investigated included 5,324,532 samples taken between January 1, 2003 and December 31, 2008, originating from 22,490 herds. Blood sera or meat juices were sampled following a standardized sampling scheme (up to 60 samples per year and herd, depending on herd size) using one of four evaluated ELISA-tests. Herds were classified into three categories I (0-20%), II (>20-40%), or III (>40%) by their percentage of yearly positive samples, which was re-calculated quarterly. The number of participating herds increased continuously since the start of the monitoring programme, with regional differences in the degree of participation. In 2008, 10.8% of all samples were positive. Adjusted for the distribution of samples in the German districts, the Salmonella prevalence in Germany was 7.9%. In general the distribution of herds in the categories was relatively stable over time. In the fourth quarter of 2008, 81.9% of the herds were allocated to category I, 14.0% to category II, and 4.0% to category III. However, the prevalence of Salmonella tended to decrease in herds that participated over a longer period. Differences could be found between German geographical regions. Seroprevalences were higher in the Northwest and the Northeast than in the South. This might be due to the relationship between Salmonella seroprevalences and farm densities per district, which were both higher in Northern than in Southern Germany. The Salmonella monitoring system will contribute to the reduction of the Salmonella prevalence in German pork production, when it is supplemented by control measures.     

Estimating the number of undetected multi-resistant Salmonella Typhimurium DT104 infected pig herds in Denmark

In Denmark, the detection of multi-resistant Salmonella Typhimurium DT104 (MRDT104)-infected pig herds relies on the national Salmonella surveillance programme at the farm and slaughterhouse levels of production. With the surveillance sampling protocol and the diagnostic methods currently used, some herds might remain undetected. The number of undetected Danish pig herds infected with MRDT104 in the period 1 August 2001–31 July 2002 was estimated and compared with the number of culture-confirmed detected herds. A flow chart was constructed to illustrate where infected herds will go undetected in the surveillance system and Monte Carlo simulation was used to model the actual number of pig herds infected with MRDT1104. We estimated that 52 (90% CI [28, 178]) finisher herds were infected with MRDT104 compared to 23 (44%) detected. Among sow herds with production of weaners or growers, we estimated that 38 (90% CI [23, 74]) were infected with MRDT104 compared to 7 (18%) actually detected. Among breeder and multiplier herds, we estimated that five (90% CI [3, 8]) herds were infected with MRDT104 compared to three (60%) detected. In total, we estimated that 102 pig herds were infected with MRDT104 from 1 August 2001 till 31 July 2002 (90% CI [63, 228]). In comparison, 33 (32%) infected herds were detected in this period. The predicted proportion of undetected herds varied considerably with herd type. We infer that the proportion of detected MRDT104 infected herds depended on the intensity of the combined serological and bacteriological testing.