Risk factors for Salmonella enterica subsp. enterica shedding by market-age pigs in French farrow-to-finish herds

Fattening-pigs carriers of Salmonella enterica are believed to be a main source of carcass and pork contamination at the later steps of the meat process. We did a prospective study in 2000-2001 in 105 French farrow-to-finish pig farms. In each farm, a batch of contemporary fattening pigs housed in the same room was followed throughout the fattening period. Salmonella shedding was assessed on environmental samples of faecal material (taken by means of pairs of gauze socks) analysed by classical bacteriological methods. 36.2% of the batches studied had at least one contaminated environmental sample and therefore were classified as Salmonella-shedding batches. Logistic regression was used to assess the association between managerial and hygiene practices and health status and the shedding risk at the end of the finishing period. Emptying the pit below the slatted floor after the previous batch of sows was removed and frequent removal of sow dung during the lactation period were protective. Presence of residual Salmonella contamination of the floor and pen partitions in the fattening rooms before loading the growing pigs also was a risk factor. The risk for Salmonella shedding at the end of the fattening period was increased when dry feed (versus wet feed) was provided during the fattening period. Lastly, Lawsonia intracellularis seroconversion and PRRSV seropositivity during the fattening period also was a risk factor for Salmonella shedding.     

Impact of the Salmonella status of market-age pigs and the pre-slaughter process on Salmonella caecal contamination at slaughter

The aim of this study was to evaluate the impact of the pre-slaughter process on Salmonella caecal contamination of pigs at slaughter. An observational study was carried out in 2001 on 101 conventional farrow-to-finish pig farms. On each farm, one batch of contemporary pigs was followed from the end of the fattening period until slaughter. The Salmonella bacteriological status of the batches was assessed by environmental samples of faecal material. The serological Salmonella status was obtained on 30 individually identified market-age pigs using an indirect ELISA test. At the slaughterhouse, 25 g of caecal contents were taken from 10 of the identified pigs. Faecal and caecal material were analysed according to a classical bacteriological method. A questionnaire was designed to obtain information about the type of feeding during the fattening period (dry versus wet), the duration of fasting on the farm before leaving for the slaughterhouse, the duration of transport between the farm and the slaughterhouse, the holding time in lairage at the slaughterhouse and loading and unloading conditions on the farm and at the slaughterhouse. To assess the relationships between these factors and the Salmonella caecal status of the pigs and the batches, two logistic models were fitted at the individual and at the batch level, respectively. The first analysis was performed using a random effects logistic regression model. The second analysis was based on a cumulative logit model with a positive caecal rate classified into three classes as the outcome variable. The results showed that the Salmonella status of market-age pigs assessed on the farm either by serological or bacteriological examinations and the time spent in lairage before slaughtering played a crucial role on caecal contamination. In the light of these results, actions should be considered both on the farm and at the slaughterhouse to decrease the risk of Salmonella contamination of the caecal contents.     

Listeria monocytogenes contamination of finishing pigs: an exploratory epidemiological survey in France

Listeria monocytogenes is a foodborne pathogen of major concern for public health in industrialised countries. Since L. monocytogenes carriage by pigs at the herd level could be a primary source for carcass contamination, control measures should be designed to reduce the L. monocytogenes load at the pre-harvest stage. For this purpose, an exploratory analytical survey was carried out in 2000-2001 in 93 French farrow-to-finish pig farms concerning L. monocytogenes contamination in pigs before they left for the slaughterhouse. On each farm, the L. monocytogenes status of a batch of contemporary fattening pigs housed in the same room was assessed on faecal material samples taken by means of gauze swabs wiped on the perianal region of the pigs. Fourteen percent of the batches studied had at least one contaminated sample and were therefore classified as L. monocytogenes contaminated batches. Two logistic regression models were used to assess the association between managerial and hygiene practices and the risk of L. monocytogenes contamination of the batch at the end of the finishing period on the whole data set (n = 93) and in the wet feeding farms only (n = 57). Wet feeding during the fattening period was identified as a risk factor for L. monocytogenes contamination. Risk factors related to the introduction of L. monocytogenes in pig facilities were identified for both the general and wet feeding farm data sets. Poor care paid to hygiene on the farms was found to increase the risk of being infected (boots cleaning, change room presence). When the duration of the empty period prior to the introduction of growing pigs was less than one day in the fattening section, the risk of L. monocytogenes contamination was significantly increased. For wet feeding farms, a distribution pipeline cleaning procedure including disinfection was found to be associated with a higher risk of contamination than no cleaning or a procedure consisting of rinsing with water only.     

Evaluation of the Salmonella surveillance program in Belgian pig farms

Since July 2007, Belgium has implemented a national surveillance and control program for Salmonella in pigs. Pig farms are designated as Salmonella high risk farms based on serological profiles and are obliged to subsequently take part in a Salmonella specific action plan (SSAP). The SSAP was evaluated and potential risk factors for the persistence of Salmonella on the farm were investigated. First, the Kaplan-Meier method was used in order to study the period during which a farm maintains a Salmonella high risk status. Farms recovered more slowly from their high risk status before the SSAP was implemented compared to after the program was implemented (p<0.001). However, results showed that 29% of the farms were withdrawn from the program possibly only because of sampling error. The program should thus be adapted to accommodate for this. Secondly, the influence of several risk factors (type of farm, season of entrance into the SSAP, size of farm and farm density of the municipality) on the time to withdrawal from the high risk status was evaluated using univariable methods and a Cox multiple regression model for survival data. A statistically significant association was identified between the type of farm and the time to withdrawal from the high risk status. At any point in time after the onset of the SSAP, withdrawals from the high risk status occurred at a 39% and 28% higher rate in mixed (p=0.01) and fattening farms (p=0.05), respectively, compared to closed farms. The risk attributed to closed pig farms is related to the presence of sows in this particular type of structure, which underlines the importance of implementing control measures in this category of animals.     

Effect of introducing piglets from farrow-to-finish breeding farms into all-in all-out fattening batches in Spain on productive parameters and economic profit

A prospective study was conducted to assess the effect of introduction of piglets from farrow-to-finish farms on the global performance of all-in all-out fattening batches in Galicia (NW Spain). Two hundred and thirty-nine fattening batches from 48 fattening farms integrated in a cooperative were used in the study. All-in all-out fattening batches were classified according to the category of farm that supplied the piglets. Origin F was a fattening batch where all feeder piglets came from one or more farrow to feeder units versus origin FF, in case a group of piglets or all piglets of the batch came from farrow-to-finish farms. Productive parameters of fattening batches included in the study were recorded. Crude comparisons of performance of 37 fattening batches from origin F and 202 from origin FF were made. Mixed multiple linear regression models were used to assess the association between type of origin of feeder piglets and the following parameters: feed consumed per market hog, percentage of deaths (mortality) and time to slaughter. In all models, variables with presumable relationships with the outcomes were offered to the models as well as the biologically plausible interaction terms.

Mortality was higher in fattening batches with piglets coming from farrow-to-finish farms (0.67% higher than origin F; P < 0.05). Time to slaughter was longer when feeder piglets were from origin FF (3.1 days longer; P < 0.05).

We found a significant effect of type of origin on feed consumed per marketed hog. Additionally, a significant interaction was found: feed consumed per marketed hog was higher for fattening batches with all piglets from farrow-to-finish farms if slaughtered before 109 days and vice versa. A Monte Carlo simulation model was used to assess the economic impact of using origin F or FF as source of piglets. Results of the model indicated that the difference in expected profit per marketed hog between the types of sources of piglets was small (€11.50, S.D. 1.79 for origin F versus €10.44, S.D. 2.72, for origin FF).     

Farm-level risk factors for the presence of Salmonella in 89 Alberta swine-finishing barns

This study investigated potential risk factors for the presence of Salmonella on 89 Alberta swine-finishing farms with the use of a questionnaire. Salmonella status was regressed on each fixed effect in a logistic mixed regression model, with farm as the random effect. Eleven variables were significant at the 10% level: farm type, number of square feet per pen, number of pigs per pen, source of feed, ration type, dust control measures, cat presence, reported effective mouse-control measures, time required to be away from pigs before visiting the farm, precautions taken when entering or leaving the farm, and reported use of antimicrobials through water. Three factors remained significant at the 5% level in the multivariable analysis: farm type, ration type, and precautions taken when entering or leaving the farm. Finishing barns at multisite operations or individual grow-to-finish farms had a greater risk of the presence of Salmonella at a single visit than did finishing barns at farrow-to-finish farms. The use of pelleted and wet feed was associated with higher odds of the presence of Salmonella than was the use of meal feed. Farms that required their personnel or visitors to shower before entering and before leaving had increased odds of the presence of Salmonella compared with farms that provided boots and coveralls; no significant difference was observed between the latter category and farms that used boot disinfection. Further work is necessary to better understand the effectiveness of all-in/all-out pig management and disinfection practices in reducing the presence of Salmonella in swine and to evaluate the association with certain types of feed.     

Longitudinal serological responses to Salmonella enterica of growing pigs in a subclinically infected herd

A longitudinal survey was conducted in France in a subclinically Salmonella-infected farrow-to-finish pig farm to describe the time-course of the serological response to Salmonella enterica in growing pigs. We used three batches of sows and their corresponding litters (n = 31 litters). Among these, 256 pigs randomly selected and individually identified were followed from the first week of age until slaughter. Serial individual blood samples were submitted to indirect Salmonella-ELISA testing. Salmonella shedding was investigated by bacteriological testing of faecal material regularly collected from the sows and pigs and by environment swabs taken from the pens. Caecal contamination was checked at the slaughterhouse. Information about litter composition (filiation), location of the pigs in post-weaning and fattening pens, sanitary events, sex and body weights was recorded. 11.6% of the pigs shed S. enterica; 52% of pigs seroconverted before slaughter. The age-related variation of the natural logarithm of calibrated optical densities (COD) of pigs was described with two linear mixed models. From 8 to 61 days of age, the decrease in COD with age was fitted with a model including random effects of the animal and the dam on the intercept and slope, a batch random effect on the intercept and an individual birth-weight fixed effect on the intercept. The dam random effect was explained by the parity of the sow, Salmonella shedding by the sow during the farrowing phase and the value of the optical density of colostrum collected at parturition. A second model fitting the increase in COD from 61 days of age until slaughter included the random effect on intercept of the batch and the random effects on slope and intercept of the animal, the dam and the pen in which the followed animals were located during the fattening phase and the environmental contamination as fixed effect. In this second model, no relation was found between individual slaughter-bacteriological results and increasing COD values. Considering seroconversion time between 61 days of age and slaughter, survival function were constructed using the Cox proportional-hazards model. Both methods suggested that seroconversions generally occurred during the last third of the fattening phase (from 140 days of age to slaughter), while shedding was observed during the first half of the fattening period. The fitted models suggest the existence of clusters (such as pen and litter of origin).     

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.     

Intra-unit correlations in seroconversion to Actinobacillus pleuropneumoniae and Mycoplasma hyopneumoniae at different levels in Danish multi-site pig production facilities

In this paper, multilevel logistic models which take into account the multilevel structure of multi-site pig production were used to estimate the variances between pigs produced in Danish multi-site pig production facilities regarding seroconversion to Actinobacillus pleuropneumoniae serotype 2 (Ap2) and Mycoplasma hyopneumoniae (Mh). Based on the estimated variances, three newly described computational methods (model linearisation, simulation and linear modelling) and the standard method (latent-variable approach) were used to estimate the correlations (intra-class correlation components, ICCs) between pigs in the same production unit regarding seroconversion. Substantially different values of ICCs were obtained from the four methods. However, ICCs obtained by the simulation and the model linearisation were quite consistent. Data used for estimation were collected from 1161 pigs from 429 litters reared in 36 batches at six Danish multi-site farms chronically infected with the agents. At the farms, weaning age was 3-4.5 weeks, after which batches of pigs were reared using all-in/all-out management by room. Blood samples were collected shortly before: weaning, transfer from weaning-site to finishing-site, and sending the first pigs in the batch for slaughter (third sampling). Few pigs seroconverted at the weaning-sites, whereas considerable variation in seroconversion was observed at the finishing-sites. Multilevel logistic models (initially including four levels: farm, batch, litter, pig) were used to decompose the variation in seroconversion at the finishing-site. However, there was essentially no clustering at the litter level-leading to the use of three-level models. In the case of Ap2, clustering within batch was so high that the data eventually were reduced to two levels (farm, batch). For seroconversion to Ap2, ICC between pigs within batches was approximately 90%, whereas the ICC between pigs within batches for Mh was approximately 40%. This indicates that the possibility for Mh to spread between pigs within batches is lower than for Ap2. The diversity in seroconversion between batches within the same farm was large for Ap2 (ICC approximately 10%), whereas there was a relative strongly ICC (approximately 50%) between batches for Mh. This indicates that the transmission of Mh is more consistent within a farm, whereas the presence of Ap2 varies between batches within a farm.     

Risk factors for Aujeszky's disease in pig herds and detection of field virus antibodies in fattening pigs in the state of Yucatan, Mexico

Two epidemiological studies were conducted from August 1997 to May 1998: a case-control study to identify herd level risk factors for antibodies to Aujeszky's disease virus (ADV) in sows in the state of Yucatan, Mexico and a cross-sectional study to determine the prevalence of antibodies against ADV in fattening pigs. In the case-control study, data on herd management and biosecurity were obtained from all the 27 ADV known field-virus-seropositive farms (cases) and 62 randomly selected seronegative farms (controls) by questionnaire. Breeding animals of these seropositive farms had received a gE-deletion vaccine. In the cross-sectional study, 26 farrow-to-finish farms of the 27 seropositive farms were used and blood samples taken from 60 fattening pigs per herd (15 pigs for each stage of production). Serum samples were analyzed by the screening-ELISA and gE-ELISA tests. In the case-control study, three of the 15 risk factors were significant. Odds ratios for distance to the nearest farm (< or = 2.5km), not sampling for the detection of ADV and herds with origin of breeding animals within the state were 9.5, 18.1 and 8.7. In the cross-sectional study, 11 (42.3%) of the 26 sampled farms were seropositive to vaccine antibodies. None of the piglets were positive to antibodies against field virus risk--suggesting that the strategy of vaccinating only the breeding animals reduced the ADV infection of the piglets.     

Herd-level risk factors for faecal shedding of Salmonella enterica in Spanish fattening pigs

Herd-level risk factors for faecal shedding of Salmonella enterica were investigated in a cross-sectional study on Spanish finishing units. 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. The total sample size was proportionally distributed according to the fattener census in each of the regions and provinces of the country in order to ensure a sample representative of the entire swine population. All samples were individually examined by culture of 25 g of faecal material. Data regarding characteristics and management of each fattening unit were collected by means of a questionnaire. Logistic regression was used to detect relationships between the detection of faecal shedding of S. enterica and potential herd-level risk factors. The feeding of pelleted feed was associated with an increased risk of culture-positive faecal samples (OR = 2.28; 95% CI: 1.22, 4.26). The odds of a farm being Salmonella positive were associated with its size. Fattening units that slaughtered more than 3500 pigs per year had a higher risk for Salmonella faecal shedding (OR = 1.78; 95% CI: 0.96, 3.31). Interventions at these two points should be considered when designing or managing growing pig facilities to reduce Salmonella faecal shedding by fatteners.     

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.     

Cattle and environmental sample-level factors associated with the presence of Salmonella in a multi-state study of conventional and organic dairy farms

The objective of this study was to evaluate associations between cattle-level factors and environmental samples with the isolation of Salmonella from dairy farms in Minnesota, Wisconsin, Michigan, and New York. The study farms included 129 conventional and organic farms enrolled without regard to previous history of Salmonella infection. Herds were sampled at two-month intervals over a one-year period. Cattle groups more likely to be associated with Salmonella shedding (compared to preweaned calves) were cows designated as sick by farm personnel (OR=2.5, 95% CI: 1.7, 3.7), cows within 14 days of calving (OR=1.8, 95% CI: 1.1, 2.8), and cows due for culling within 14 days (OR=1.9, 95% CI: 1.0, 3.4). State of origin was also associated with the presence of Salmonella in samples from cattle and the farm environment; Midwestern states were more likely to have Salmonella-positive samples compared to New York. Cattle treated with antimicrobials within 14 days of sampling were more likely to be Salmonella-negative compared with nontreated cattle (OR=2.0, 95% CI: 1.1, 3.4). Farms with at least 100 cows were more likely to have Salmonella-positive cattle compared with smaller farms (OR=2.6, 95% CI: 1.4, 4.6). Season was associated with Salmonella shedding in cattle, and compared to the winter period, summer had the highest odds for shedding (OR=2.4, 95% CI: 1.5, 3.7), followed by fall (OR=1.9, 95% CI: 1.2, 3.1) and spring (OR=1.8, 95% CI: 1.2, 2.6). Environmental samples significantly more likely to be Salmonella-positive (compared to bulk tank milk) included, in descending order, samples from sick pens (OR=7.4, 95% CI: 3.4, 15.8), manure storage areas (OR=6.4, 95% CI: 3.5, 11.7), maternity pens (OR=4.2, 95% CI: 2.2, 8.1), haircoats of cows due to be culled (OR=3.9, 95% CI: 2.2, 7.7), milk filters (OR=3.3, 95% CI: 1.8, 6.0), cow waterers (OR=2.8, 95% CI: 1.4, 5.7), calf pens (OR=2.7, 95% CI: 1.3, 5.3), and bird droppings from cow housing (OR=2.4, 95% CI: 1.3, 4.4). Parity, stage of lactation, and calf age were not associated with Salmonella shedding.     

Noninfectious factors associated with pneumonia and pleuritis in slaughtered pigs from 143 farrow-to-finish pig farms

A cross-sectional study involving 143 farrow-to-finish herds was carried out to identify herd-level noninfectious factors associated with pneumonia and pleuritis in slaughter pigs. Data related to herd characteristics, biosecurity, management and housing conditions were collected by questionnaire during a farm visit. Climatic conditions were measured over 20 h in the post-weaning and finishing rooms where the slaughter pigs were kept. After these on-farm investigations, the finishing pigs were examined at slaughter for lung lesions. A sample of 30 randomly selected pigs per herd was scored for pneumonia and pleuritis. Herds were grouped into three categories according to their pneumonia median score (class 1: ≤ 0.5; class 2: 0.53.75). For pleuritis, a herd was deemed affected if at least one pig had a high pleuritis score (≥ 3). A multinomial logistic regression model was used to identify factors associated with pneumonia classes 2 and 3. A logistic regression for binary outcome was used to identify risk factors for severe pleuritis. An interval of less than four weeks between successive batches (OR=4.5, 95% confidence interval (95% CI): 1.5-13.6, p<0.01), large finishing room size (OR=4.3, 95% CI: 1.6-11.6, p<0.01) and high mean CO(2) concentration in the finishing room (OR=4.2, 95%CI: 1.6-11.3, p<0.01), significantly increased the odds for a herd to be in class 2 for pneumonia. The same risk factors were found for class 3 and, in addition, a direct fresh air inlet from outside or from the corridor in the post-weaning room vs an appropriate ceiling above the pigs (OR=5.1, 95% CI: 1.4-18.8, p=0.01). The risk for a herd to have at least one pig with a high pleuritis score was increased when the farrowing facilities were not disinsected (OR=2.7, 95% CI: 1.2-5.8, p=0.01), when tail docking was performed later than 1.5 days after birth (OR=2.6, 95% CI: 1.2-5.7, p=0.01) and if the piglets were castrated when more than 14 days old (OR=2.7, 95%CI: 1.1-6.8, p=0.03). A temperature range of less than 5°C for the ventilation control rate in the farrowing room (OR=2.7, 95% CI: 1.2-5.9, p=0.01), a mean temperature in the finishing room below 23°C (OR=3.0, 95% CI: 1.3-6.8, p<0.01) and large herd size (OR=3.1, 95% CI: 1.4-6.9, p<0.01) were also associated with increased risk of pleuritis. The factors affecting pneumonia and pleuritis seemed to be different. All rearing steps from farrowing to finishing must be taken into account in any health programme aimed at controlling pneumonia and pleuritis and lung health may be improved through several pathways, i.e. correcting managerial and hygienic factors, implementing an appropriate and well-functioning ventilation in order to offer favorable climatic conditions.     

Main risk factors for Salmonella-infections in pigs in north-western Germany

Salmonellosis is one of the major zoonotic, food-borne diseases, among others, caused by pig derived food products. As infected pigs are one of the main sources of the introduction of the bacterium into the food chain, scientific research in the last years has focussed on identifying risk factors for infection as well as developing mitigation strategies on this level of production. In order to update the knowledge of the German situation by incorporating recent changes in the German pig industry, a case-control study was set up to identify the key contributing risk factors for farms located in the western part of Lower Saxony, the region with the highest pig density in Germany. Based on an extensive and systematic literature search, a comprehensive questionnaire with 302 questions concerning such topics as personnel hygiene, animal management, biosecurity, feeding management as well as cleaning and disinfection routines was utilized in a face-to-face interview on 104 case and 67 control farms. Within a stepwise forward selection process the preliminary identified factors were grouped contextually, associations between variables were calculated and multivariable logistic regression models were conducted. Identified risk factors were: the moving of individual animals during the fattening period (OR 5.3, CI 95% 1.35-20.35), not having a separate transporter for different age groups (OR 11.4, CI 95% 1.94-66.18) and pigs having contact to other animals (OR 4.3, CI 95% 1.39-12.96). The following factors were identified as being protective: not cleaning the transporter (OR 0.2, CI 95% 0.05-0.72) and not having clean boots available (OR 0.2, CI 95% 0.07-0.64). While this study was able to identify some factors which influence the Salmonella-infection of a herd, overall the process of analysis showed that the control of Salmonella on farm is due to a series of individual factors and therefore remains extremely complex.     

Longitudinal study of Salmonella species in 90 Alberta swine finishing farms

The aim of this study was to determine the farm prevalence of Salmonella in 90 Alberta finishing swine farms over a 5-month period, to evaluate Salmonella distribution in the farm environment and to describe Salmonella serovar diversity on these farms. Ten veterinary practitioners selected 90 Alberta swine farms based on an annual production of > or =2000 market pigs per farm and the willingness of the producers to participate in the study. Between May and September 2000, twenty samples were collected from finishing swine and the environment of each farm. The annual production of selected farms represented approximately 25% of the market swine production in Alberta. Participating farms were geographically representative of major swine production areas in Alberta. Sixty (66.7%) farms had at least one Salmonella-positive sample, with confidence interval (CI) of 57.1-77.2%. Salmonella were detected in 14.3% of fecal and 20.1% of environmental samples. The number of Salmonella-positive samples per farm ranged from 1 to 19. Among environmental samples, Salmonella were most frequently recovered from boots (38.6%) and the main drain (31.8%). Twenty-two serovars were detected on the 60 Salmonella-positive farms. Serovars Typhimurium (78 isolates), Derby (71 isolates) and Infantis (47 isolates) were the most common. A single serovar was detected on 58 farms, while 2, 3 and >3 serovars were detected on 15, 10 and 7 farms, respectively. The Salmonella farm status changed frequently over the 5-month period indicating the dynamic nature of Salmonella infections on these farms.     

Longitudinal study of hepatitis E virus infection in Spanish farrow-to-finish swine herds

Hepatitis E is a zoonotic disease and is highly prevalent in European swine livestock. There is a need to compare the infection dynamics of hepatitis E virus (HEV) between herds with the same production system and determine the percentage of animals that could arrive infected at slaughter age. Therefore, a longitudinal study was performed in six Spanish farrow-to-finish affected farms. Twenty piglets per farm were monitored from nursery to slaughter. RT-PCR and serology techniques were applied to analyze longitudinally collected sera and/or faecal samples. Liver and bile samples were also taken at the abattoir. Anti-HEV IgM were firstly detected at 7 weeks of age in 5 farms whereas at 13 weeks of age in 1 farm (farm 2). At slaughter age 50–100% of pigs had seroconverted to anti-HEV IgG in the former 5 farms whereas in the other herd only 5% of pigs were IgG seropositive (farm 2). Six out of 96 livers and 5 out of 80 biles analyzed were HEV positive at the abattoir (total percentage of infected animals: 11.5%). All these positive animals had already seroconverted except 2 pigs of farm 2. Hence, pigs can be seronegative at slaughter age being infected during the latest fattening period. Manipulation of HEV-infected livers or other organs from pigs could be considered a possible route of transmission in Spanish abattoirs. This study represents the first longitudinal survey on swine HEV infection dynamics conducted in different herds.     

Epidemiological study of risk factors for Mycoplasma bovis infections in fattening calves

To establish the role of Mycoplasma bovis as an agent of respiratory disease in fattening calves, an epidemiologic study was undertaken. A recently validated commercially available ELISA was used to diagnose M. bovis infection by seroconversion in paired sera obtained for each animal at entry in the fattening herd and at follow-up seven weeks later. Management data as well as relevant clinical and epidemiological variables were prospectively recorded. The overall seroconversion rate observed among the 415 calves in 23 fattening herds on 13 farms was 54.7%. Significant risk factors for seroconversion were the mixing of fattening herds of different age groups (risk ratio RR 1.70, 95% confidence interval (CI) 1.48 to 1.96), and the presence of at least one seropositive animal in the fattening herd (RR: 2.02; CI: 1.69 to 2.40). The proportion of clinical episodes of respiratory disease attributable to M. bovis infection was 50.3%. The average weight gain during the observation period was reduced by 7.6% in seroconverting calves and these animals had about 2 times more antibiotics prescribed by a veterinarian than calves remaining negative for M. bovis throughout follow-up (RR 1.83). Maternal antibodies against M. bovis were detected in 39% of newborn calves born from seronegative cows and had a half-life of 20 days, potentially limiting the usefulness of vaccines against M. bovis in this age group.     

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.     

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.