Temporal relationship between decrease in antimicrobial prescription for Danish pigs and the "Yellow Card" legal intervention directed at reduction of antimicrobial use.

The potential effects of the "Yellow Card" intervention, enforced by Danish authorities in December 2010, on the antimicrobial prescription in the Danish pig production were investigated. Data on antimicrobial prescription for pigs during 2002-2012 was obtained from the national database on veterinary prescribed medicines, VetStat. Descriptive analysis of temporal trends in quantitative antimicrobial prescription for pigs on national level was performed for each administration route, age group and disease group. In addition, prescription patterns of the three most prescribed antimicrobial classes (tetracyclines, macrolides and pleuromutilins) for weaners and finishers were studied at herd level. A 25% decline in the total antimicrobial use per pig produced occurred between 2009 and 2011. A decline was observed both in sows and piglets (31%), weaners (34%) and finishers (19%). Reduced prescription of tetracycline, macrolides and pleuromutilins for oral use, mainly for gastrointestinal disease (GI) in weaners and finishers, explained 76% of the total reduction. In 2012, the overall antimicrobial use increased by 10%, as a partial reversal of the preceding changes in prescription pattern. On herd level, the decline and subsequent increase was mainly related to changes in number of herds receiving regular monthly prescriptions. This study demonstrated that the steep decrease in antimicrobial use in the Danish pig production was temporally related with the announcement and introduction of the Yellow Card intervention.

A long-lasting outbreak of Salmonella Typhimurium U323 associated with several pork products, Denmark, 2010.

This paper shows that control of foodborne disease outbreaks may be challenging even after establishing the source of infection. An outbreak of Salmonella Typhimurium U323 infections occurred in Denmark from March to September 2010, involving 172 cases. Before the detection of human cases, several positive isolates of the outbreak strain had been found in a particular pig slaughterhouse and thus early traceback, investigation and control measures were possible. Several batches of pork and pork products were recalled and the slaughterhouse was closed twice for disinfection. No single common food item was identified as the outbreak source, but repeated isolation of the outbreak strain from the slaughterhouse environment and in pork and products as well as patient interviews strongly suggested different pork products as the source of infection. Furthermore, a matched case-control study identified a specific ready-to-eat spreadable pork sausage (teewurst) as the source of a sub-outbreak (matched odds ratio 17, 95% confidence interval 2·1-130).

An outbreak of Salmonella Typhimurium infections in Denmark, Norway and Sweden, 2008.

In November-December 2008, Norway and Denmark independently identified outbreaks of Salmonella Typhimurium infections characterised in the multiple-locus variable number of tandem repeats analysis (MLVA) by a distinct profile. Outbreak investigations were initiated independently in the two countries. In Denmark, a total of 37 cases were identified, and multiple findings of the outbreak strain in pork and pigs within the same supply chain led to the identification of pork in various forms as the source. In Norway, ten cases were identified, and the outbreak investigation quickly indicated meat bought in Sweden as the probable source and the Swedish authorities were alerted. Investigations in Sweden identified four human cases and two isolates from minced meat with the distinct profile. Subsequent trace-back of the meat showed that it most likely originated from Denmark. Through international alert from Norway on 19 December, it became clear that the Danish and Norwegian outbreak strains were identical and, later on, that the source of the outbreaks in all three countries could be traced back to Danish pork. MLVA was instrumental in linking the outbreaks in the different countries and tracing the source. This outbreak illustrates that good international communication channels, early alerting mechanisms, inter-sectoral collaboration between public health and food safety authorities and harmonised molecular typing tools are important for effective identification and management of cross-border outbreaks. Differences in legal requirements for food safety in neighbouring countries may be a challenge in terms of communication with consumers in areas where cross-border shopping is common.

Large outbreaks of Salmonella Typhimurium infection in Denmark in 2008.

An outbreak of Salmonella Typhimurium phage type U292 has been ongoing in Denmark since 1 April, with 1,054 cases registered until 23 October 2008. Extensive investigations including hypothesis-generating interviews, matched case-control studies, cohort studies in embedded outbreaks, shopping list analyses, analyses of food samples from patient's homes, trace-back analyses and extensive microbiological analysis of products have not provided clear indications of a specific source of infection but the main hypothesis is that the vehicle of the outbreak are different pork products. In addition to the large U292 outbreak, at least four other S. Typhimurium outbreaks (caused by phage types U288, DT120, DT3 and DT135) have been investigated in Denmark in 2008.

A European longitudinal study in Salmonella seronegative- and seropositive-classified finishing pig herds.

Surveillance and control are important aspects of food safety assurance strategies at the pre-harvest level of pork production. Prior to implementation of a Salmonella surveillance and control programme, it is important to have knowledge on the dynamics and epidemiology of Salmonella infections in pig herds. For this purpose, 17 finishing pig herds initially classified as seropositive and 15 as seronegative, were followed for a 2-year period through serological and bacteriological sampling. The study included 10 herds from Denmark, 13 from The Netherlands, 4 from Germany and 5 from Sweden and was performed between October 1996 and May 1999. The Salmonella status of finishing pig herds was determined by an initial blood sampling of approximately 50 finishing pigs close to market weight per herd. The development of the Salmonella status of the selected herds was assessed at seven subsequent sampling rounds of 25 blood samples from finishing pigs, 25 blood samples from grower pigs and 10 pen faecal samples each, approximately 3 months apart. The odds for testing finishers seropositive, given that growers were found seropositive previously were 10 times higher than if growers were seronegative (OR 10.0, 95% CI 3.2-32.8). When Salmonella was isolated from pen faecal samples, the herd was more likely to be classified seropositive in the same sampling round, compared to no Salmonella being detected (OR 4.0, 95% CI 1.1-14.6). The stability of an initially allocated Salmonella status was found to vary noticeably with time, apparently irrespective of a seropositive or seronegative classification at onset of the study. Given the measured dynamics in the occurrence of Salmonella in pig herds, regular testing is necessary to enable producers, advisors and authorities to react to sudden increases in the Salmonella prevalence in single herds or at a national level.

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.

The occurrence and epidemiology of Salmonella in European pig slaughterhouses.

This study was part of an international research project entitled SALINPORK (FAIR CT-950400) initiated in 1996. The objectives were to investigate the occurrence of Salmonella in pig slaughterhouses and to identify risk factors associated with the contamination of pig carcasses. Data was collected from 12 slaughterhouses in five European countries. Isolates were characterized by serotyping, phage typing and antimicrobial susceptibility. In one country, no Salmonella was found. Salmonella was isolated from 5.3% of 3485 samples of pork and from 13.8% of 3573 environmental samples from the seven slaughterhouses in the four remaining countries. The statistical analyses (multi-level logistic regression) indicated that the prevalence was significantly higher during the warmer months and that the environmental contamination increased during the day of slaughter. The polishing (OR 3.74, 95% CI 1.43-9.78) and pluck removal (OR 3.63, 95% CI 1.66-7.96) processes were found to contribute significantly to the total carcass contamination, the latter especially if the scalding water also was contaminated. To reduce carcass contamination, it is recommended to ensure sufficiently high temperatures of scalding water (62 degrees C) and appropriate cleaning and disinfection of the polishing equipment at least once a day in order to reduce the level of carcass contamination and consequently the prevalence of Salmonella in pork.

Bacteriological and serological examination and risk factor analysis of Salmonella occurrence in sow herds, including risk factors for high Salmonella seroprevalence in receiver finishing herds.

A strong association between the seroprevalence in sows and the occurrence of Salmonella Typhimurium among weaners has been shown. As shown several times for finisher herds, the risk-factors, ready mixed pelleted feed and health status also apply to sow herds. Risk factors on the sow level, for high seroprevalence in finishers have been quantified. It has been shown, that isolating Salmonella in weaners is a risk factor for high seroprevalence in finishers. Feed factors; ready-mixed pelleted feed for both sows and finishers, dry feed for sows, have been shown to have a significant effect on high seroprevalence, monitored by meat juice samples at slaughter. The etiological fraction of ready-mixed pelleted feed for sows and for finishers is of the same magnitude, indicating that intervention on the sow level could prove to contribute considerably to the effect of intervention programs.

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.

Clinical observations, pathology, bioassay in mice and serological response at slaughter in pigs experimentally infected with Toxoplasma gondii.

Experimental infections of a total of 47 pigs with tachyzoites of the Toxoplasma gondii RH-strain, tissue cysts of the SSI-119 and R92 strains as well as oocysts of the SSI-119 strain were performed to determine the sensitivity of an indirect IgG-ELISA, using tachyzoite lysate of the RH-strain as antigen. The infections led to a dose dependent moderate clinical affection (inappetence, fever and poor general condition). Pigs infected with 10000 oocysts or with 1/2 mouse brain containing tissue cysts of the SSI-119 strain showed a significant decrease in weight gain compared to uninoculated pigs during the first 2 weeks p.i., followed, however, by compensatory growth during the next 6 weeks. At slaughter 3 to 4 months after inoculation 39/41 (95.1%) of pigs positive by bioassay in mice were seropositive in ELISA. Tissue cysts were not demonstrable by immunohistochemistry. ELISA OD-values obtained by analysis of meat juice from heart muscle and tongue (diluted 1:40) correlated strongly with OD-values by analysis of serum (diluted 1:400) (r heart juice = 0.942; r tongue juice = 0.915). Thus, meat juice samples were shown to provide a suitable alternative to serum for serological detection of Toxoplasma infection in pigs.

The time course of the specific antibody response by various ELISAs in pigs experimentally infected with Toxoplasma gondii.

With the aim of developing routine serological tests for monitoring the Toxoplasma infection status of Danish swine herds, four ELISAs based on tachyzoite antigen were set up: (1) an indirect ELISA for IgG-antibody; (2) a blocking ELISA for antibody to the membrane antigen, P30; (3) an indirect ELISA for IgM; (4) a reverse, antibody-catching IgM-ELISA. Groups of pigs (number between 6 and 10) were inoculated with tachyzoites of the RH-strain, tissue cysts of two complete strains, or oocysts in two doses (10(3) and 10(4). All inoculations were tolerated well. Irrespective of strain and stage used for inoculation, specific IgG and anti-P30 blocking activity appeared after 1-2 weeks, with OD-values stabilizing after 3-6 weeks and persisting throughout the study period (3-4 months). Specific IgM appeared quickly, but was short-lived (approximately 2 weeks). A cut-off OD-value of 0.36 for positive seroreaction in the indirect IgG-ELISA was determined on the basis of 69 sera from four herds, investigated in the dye-test (serum dilution 1:10) and ELISA. The chosen cut-off gave optimal combined sensitivity and specificity of 0.94 and 0.92, respectively, using the dye-test as a standard. Corresponding figures for the blocking ELISA were 37% inhibition as cut-off, with sensitivity and specificity of 0.94 and 0.94, respectively. Sera from a total of 87 pigs, experimentally infected with bacteria of the genera Salmonella, Yersinia or Actinobacillus and with the parasites Isospora suis, Trichinella spiralis or Ascaris suum, in no case produced cross-reactions in the IgG-ELISA. However, 3/9 pigs inoculated with 50 000 sporocysts of Sarcocystis miescheriana gave maximal OD-readings of 0.40-0.45 during the 13-15 weeks observation period. None of the sera from heterologously infected animals produced inhibitions in the anti-P30 blocking ELISA exceeding 36%.

Elimination of Salmonella typhimurium infection by the strategic movement of pigs.

Three field investigations were carried out to assess the feasibility of raising salmonella-free finishers from pigs born in infected herds, by moving the pigs to clean and disinfected facilities before their expected exposure to the bacteria from the environment. Three herds with persistently high levels of subclinical infection with S typhimurium in the finishing pigs were used. They practised all-in all-out management in the nurseries and in the grower units. A total of 844 pigs were moved, either at weaning, from the nursery, or from the grower unit to newly built or rigorously cleaned and disinfected finishing units with no known history of salmonella infection. No detectable infection was observed at slaughter either serologically or bacteriologically by random testing of the pigs which had been moved, whereas a proportion of the pigs raised at the same time in the continuous systems on the farms were found to be infected.

Time course of the serological response to Yersinia enterocolitica O:3 in experimentally infected pigs.

A total of 25 pigs inoculated with Yersinia enterocolitica serovar O:3 and 25 un-inoculated controls were followed weekly by sampling blood and faeces for 70 days post infection (p.i.). All inoculated pigs were faeces culture positive from day 5 to 21 p.i., whereafter shedding of bacteria declined to < 10% of the pigs at day 49 p.i. and to 0% at day 68 p.i. All control pigs remained Y. enterocolitica O:3 culture negative. When examined in an indirect ELISA using purified LPS from Y. enterocolitica 0:3, sera from all inoculated pigs showed significantly higher optical densities (OD) as compared to the control group. All inoculated pigs had seroconverted at day 19 p.i. and remained seropositive until slaughter at day 70 p.i. The maximum mean anti-LPS response was observed at day 33 p.i. with a positive/negative ratio of 780. No cross-reactions were observed with sera from 21 pigs, infected with Salmonella typhimurium. At necropsy at day 70 p.i., Y. enterocolitica O:3 was isolated from the tonsils of 20 inoculated pigs, whereas the rest of the gastrointestinal tract and associated lymph nodes were culture negative. The remaining inoculated pigs and all control pigs were culture negative at necropsy at day 70 p.i. The ELISA seems to be a promising alternative to bacteriological culture for detection of Y. enterocolitica O:3 infection in pig herds.

Intracapsular and atmospheric pressure in the dynamics and stability of the hip. A biomechanical study.

A cadaver study was undertaken to evaluate (a) the relations between the rotation around the axis of the neck of the femur, intracapsular effusion, and intracapsular pressure; and (b) the importance of the atmospheric pressure in stabilizing the hip joint. The following conclusions were reached: (1) There is no increase in intracapsular pressure within the normal range of rotation ("flexion") around the axis of the neck of the femur. (2) Intracapsular fluid (e.g., blood, pus, synovial edema and/or free synovial fluid) decreases this pressureless range of rotation, a likely cause of pain and subsequently flexion contractures. (3) Joint stability is primarily maintained by the atmospheric pressure within the normal range of rotation. The joint capsule is tightened only in extreme extension or flexion and contributes to stability only in these positions. (4) The traction force needed to overcome the stabilizing effect of the atmospheric pressure and thus subluxate the adult joint is approximately 200 N, in a child less, proportional to the square of the diameter of the femoral head. We also propose that intracapsular fluid makes the joint potentially unstable, a prerequisite for unfavorable mechanical cartilage load. These findings have clinical implications in synovitis, septic and juvenile arthritis, congenital dislocation of the hip, arthroplasty, and trauma.