Prevalence of intestinal pathogens in Danish finishing pig herds

Our aim was to determine the prevalence of the intestinal bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Serpulina intermedia, Brachyspira innocens, Brachyspira pilosicoli, pathogenic Escherichia coli (serogroups O138, O139, O141 and O149) and Salmonella enterica in Danish finishing pig herds. A total of 79 herds was randomly selected and visited during 1998. From each herd, 20 faecal samples were collected from individual pigs weighing 30–50 kg. Furthermore, 10 pooled pen samples were collected and examined for S. enterica. In total, 1580 faecal samples and 790 pen samples were collected and examined by polymerase chain reaction (PCR) or culture. L. intracellularis was found in 74 herds (93.7%), B. hyodysenteriae in two herds (2.5%), S. intermedia in 10 herds (12.7%), B. innocens in 27 herds (34.2%), B. pilosicoli in 15 herds (19.0%), pathogenic E. coli in 19 herds (24.1%) and S. enterica in eight herds (10.1%). The within-herd prevalences of L. intracellularis and B. hyodysenteriae were 25–30%; the within-herd prevalences of the other agents were 5–10%. Three herds (4%) were not infected with any of the bacteria and 25 herds (32%) were only infected with L. intracellularis.     

Nation-wide Salmonella enterica surveillance and control in Danish slaughter swine herds

A nation-wide Salmonella enterica surveillance and control programme was initiated in Danish finishing herds over the first quarter of 1995. In Denmark, all swine for slaughter are identifiable by a unique herd code. For each herd code, and depending on the herd's annual kill, random samples ranging from four to more than 60 swine are obtained quarterly at the abattoir. A meat sample from each pig is frozen, and meat juice (harvested after thawing) is examined for specific antibodies against S. enterica using an indirect enzyme-linked immunosorbent assay (ELISA). The ELISA combines several S. enterica O-antigens, and allows detection of antibody response after a variety of different S. enterica serovar infections. Results are transferred to a central database, which each month (based on meat-juice tests obtained in the previous 13 weeks) assigns all herds into three S. enterica infection levels: Level 1, in which the S. enterica prevalence is deemed low and acceptable; Level 2, where there is a moderate prevalence of S. enterica seroreacl.ors (from > 50% in the smallest to > 10% in the largest herds); Level 3, in which S. enterica seroreactor prevalence is clearly unsatisfactory ( > 50% for most herd sizes). Irrespective of Salmonella level, all herds receive a monthly update on the current results of the S. enterica test results. If a herd is categorized in Level 2 or 3, it must receive an advisory visit by a practising veterinarian and a local swine extension specialist, and certain management hygiene precautions must be taken. If a herd is categorized in Level 3, the finishers from the herd must additionally be slaughtered under special hygiene precautions. This is supervised by the veterinary authorities.

During 1995, 604000 samples were tested for S. enterica, corresponding to 3.0% of the total kill. In December 1995, 15522 herds (representing > 90% of the national production) were categorized into one of the three levels: 14551 herds (93.7%) in Level 1; 610 herds (3.9%) in Level 2; 361 herds (2.3%) in Level 3. The proportion of serologically positive meat-juice samples collected during 1995 ranged from a mean of 2.9% in smaller herds (101–200 swine slaughtered per year) to 6.1% in relatively large herds (more than 5000 swine slaughtered per year).     

Data-quality issues and alternative variable-screening methods in a questionnaire-based study on subclinical Salmonella enterica infection in Danish pig herds

Our aim was to determine risk factors for subclinical Salmonella enterica infection in Danish finishing-pig herds. In this paper, the evaluation, combining and initial reduction of variables is presented, along with assessment of the hypotheses in the preliminary statistical testing.The first group of herds was selected at random with no former knowledge of S. enterica infection. Both the herd prevalence and the within-herd prevalence among these herds turned out to be low; hence, some additional herds were selected from The Danish Salmonella Control program, based on their high seroprevalence. This resulted in a hybrid case-"control" design of the study and therefore, five different methods of categorising the data were used to ensure that variables were not wrongfully excluded as a result of using an improper design.Our questionnaire focused on management, infection-limiting precautions and feed and feeding procedures. To establish the prevalence of S. enterica infection within herds at the time of the visit, 50 blood samples from each herd were collected and serologically examined. The reliability of each variable from the questionnaire was assessed and it was decided which variables should be selected, disregarded, combined with other variables and/or recoded. In the simple statistical testing (2x2 tables, cut-off: P=0.25) herds were defined as subclinically S. enterica infected if the within-herd proportion of individual pigs with OD%>10 was more than 20%.The results included questionnaires from 96 randomly selected and 39 high-seroprevalence herds and 6814 blood samples. The initial 95 variables originally included in the questionnaires were reduced to 21 by critical check, combination, recoding and preliminary screening. We failed to demonstrate "herd size" as a risk factor for subclinical S. enterica infection in pig herds.     

Herd-level risk factors for Salmonella enterica subsp. enterica in U.S. market pigs

Midwest U.S. herds (n = 63) were studied to identify risk factors for harboring Salmonella enterica among slaughter-weight pigs. Samples collected on farms (feces) and at slaughter (distal colonic content, cecal content and ileocolic lymph nodes) were cultured using conventional means. Approximately 15 pigs were studied per herd, for a total of 3754 samples. The proportion of pigs positive in one or more samples was calculated for each herd. Herd characteristics were described by a combination of interview and written survey. Logistic regression was used to detect relationships between the detection of Salmonella and potential herd-level risk factors. The mean individual pig prevalence was 5% for feces, 4% for distal colonic content, 15% for ileocolic lymph nodes, and 17% for cecal contents. One or more Salmonella isolates were detected in at least one sample type in every herd. The five most common serovars were S. Agona, S. Derby, S. Schwarzengrund, S. Typhimurium and S. Senftenberg, with 25 additional serovars detected. Salmonella prevalence estimates were positively correlated among all samples except distal colonic content and ileocolic lymph nodes. Pigs with culture positive fecal samples were at increased odds of being detected positive for each of the slaughter-collected samples examined, namely distal colonic content (OR = 30.5), ileocolic lymph nodes (OR = 12.9) and cecal content (OR = 23.2). Herds with positive fecal sample(s) had increased odds of having positive cecal content (OR > 1.5), distal colonic content (OR = 15.3) and ileocolic lymph nodes (OR = 12.7). Pigs from herds with at least some bowl drinkers had eight-fold higher odds of testing Salmonella positive than did pigs from herds with only nipple drinkers. Pigs from herds with only dry feeders had five-fold higher odds of testing Salmonella positive when compared with pigs from herds with combinations of wet/dry style feeders. Interventions at these two points should be considered when designing growing pig facilities to reduce Salmonella shedding.     

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.     

A longitudinal study of Salmonella enterica infections in high-and low-seroprevalence finishing swine herds in The Netherlands

The purpose of this investigation was to study the incidence and course of Salmonella infections in finishing pig herds in order to asses the stability of a given Salmonella herd status. Five low- and 7 high-seroprevalence herds were followed for seven sampling rounds. Each round, blood and faecal samples were tested in an indirect ELISA and by bacteriological culturing, respectively. In high-seroprevalence herds a positive Salmonella status was an indication of a long-term problem and the status was relatively stable over time. The herds experiencing clinical salmonellosis were not necessarily the herds with the highest seroprevalence. It is possible to deliver sero-negative finishers to the slaughterhouse, even though these pigs were seropositive as growers. In three out of five low-prevalence herds, major infection incidents occurred, indicating that changes in the Salmonella status should be anticipated. Low-prevalence herds can remain negative over a longer period of time as a result feeding a complete liquid feed containing fermented by-products.     

The new classification system for slaughter-pig herds in the Danish Salmonella surveillance-and-control program

The Danish surveillance-and-control program for Salmonella in slaughter pigs was introduced in 1995. The key element of the program is a quick and correct identification of herds with high seroprevalence. After 5 years, the classification scheme was evaluated--and a revision was made. Data from two Salmonella screenings including a total of 1902 slaughter pig herds were used. For each herd, information was available on Salmonella status based on both microbiology and serology. Based on analyses of these data, suitable changes in the scheme were identified and their effect estimated by use of data from the Danish Salmonella Database including all herds in 2000. The classification scheme has been adjusted on the following points. (1) The sampling has been simplified into 60, 75, or 100 samples per herd per year depending on herd size. This means more-precise estimates for the seroprevalence among smaller herds. (2) Herds with an annual kill or=index 40, and the limit between Levels 2 and 3 to >or=index 70. If the Danish swine producers are interested, a Level 0 may be introduced (consisting of seronegative herds as an indication of a negligible Salmonella prevalence). The classification scheme was introduced in August 2001.     

Seroprevalence of Actinobacillus pleuropneumoniae serovars 2, 3 and 9 in slaughter pigs from Belgian fattening farms

Fifty randomly selected fattening pig herds were studied to investigate the epidemiological characteristics of infections with Actinobacillus pleuropneumoniae serovars 2, 3 and 9, and to identify risk factors for their within-herd seroprevalences. Information about 13 farm characteristics was obtained by means of a questionnaire and used to assess potential risk factors for the percentage of slaughter pigs with antibodies against each of the three serovars. The presence of antibodies was measured with an indirect ELISA. The median within-herd seroprevalence for serovar 2 was 58 per cent (range 0 to 100 per cent), for serovar 3, 53 per cent (range 10 to 95 per cent), and for serovar 9, 35 per cent (range 5 to 100 per cent). All but one farm tested positive for A pleuropneumoniae serovar 2, and all the farms were positive for A pleuropneumoniae serovars 3 and 9. There was a positive association (P < 0.05) between each pair of serovars. The within-herd seroprevalence of serovar 2 was significantly associated with the density of pig herds in the municipality (odds ratio [OR] = 1.60; P < 0.05) and with the absence of preventive medication at the start of the fattening period (OR = 2.77; P < 0.10). No significant risk factors were found for serovar 3. The percentage of pigs positive for serovar 9 was significantly associated with a slaughter date in June (OR = 2.30; P < 0.10) and with herds in which the finishing houses were not divided into separate compartments (OR = 2.99; P < 0.05).     

Herd prevalence of Salmonella enterica infections in Danish slaughter pigs determined by microbiological testing

As a part of a nationwide programme to survey and control salmonella in pig herds, a microbiological survey of 1363 pig herds was performed in Denmark. A total of 13 468 slaughter pigs were examined at slaughter by culture of 5 g of caecal contents. Overall, 30 different serotypes of Salmonella enterica were isolated from 832 pigs (6.2%). The predominant serotype was S. Typhimurium, comprising 536 (64.4%) of the isolates. Four hundred and forty-eight isolates of S. Typhimurium were examined by phage typing, resulting in detection of 17 different phage types (definitive types, DT) with DT12 being the most frequent (49.1%).

Salmonella enterica was found in 302 herds (22.2%), S. Typhimurium was found in 61.1% of these. 279 (23.1%) large herds (producing more than 2600 slaughter pigs per year) were found to be salmonella positive compared with 23 (14.7 %) small herds (annual production of 500 to 550 slaughter pigs). Practical constraints in the study design did not allow for a firm conclusion on the interplay among herd size, geographical location and occurrence of salmonella.

In 284 of 302 infected herds (94.0%) only one serotype was detected. Infections with two different serovars were seen in 18 herds (6.0%).     

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.     

Herd characteristics and management practices associated with seroprevalence of Mycobacterium avium subsp paratuberculosis infection in dairy herds

OBJECTIVE: To investigate herd characteristics and management practices associated with a high seroprevalence of Mycobacterium avium subsp paratuberculosis (MAP) in dairy herds in central California. SAMPLE POPULATION: 60 randomly selected cows from each of 21 dairy herds. PROCEDURES: Sera of selected cows were tested for antibodies against MAP by use of an ELISA test kit. Cows with a test sample-to-positive control sample (S:P) ratio of > or = 0.25 were considered seropositive, and herds with > or = 4% seropositive cows were considered high-seroprevalence herds. Data on herd characteristics and management practices were collected via interviews with owners. Bayesian logistic regression was used to model the predictive probability of a herd having a high seroprevalence on the basis of various herd characteristics and management practices. RESULTS: 9 of 21 (43%) herds were classified as high-seroprevalence herds. Five variables (history of previous signs of paratuberculosis in the herd, herd size, exposing cattle to water from manure storage lagoons, feeding unsalable milk to calves, and exposing heifers < or = 6 months old to manure of adult cows) were included in the predictive model on the basis of statistical and biological considerations. In large herds, the predictive probability of a high seroprevalence of MAP infection decreased from 0.74 to 0.39 when management changed from poor to good practices. In small herds, a similar decrease from 0.64 to 0.29 was predicted. CONCLUSIONS AND CLINICAL RELEVANCE: The seroprevalence of MAP infection in California dairies may be reduced by improvements in herd management practices.     

Factors associated with Neospora caninum serostatus in cattle of 20 specialised Costa Rican dairy herds

Twenty-five specialised Costa Rican dairy farms (located in the Poás area) were used to determine neosporosis seroprevalence and the association of seropositivity with environmental and management factors. The farms involved were selected intentionally and all of them use VAMPP 5.1 (Veterinary Automated Management and Production Control Programme) as management-information system. Holstein–Friesian, Jersey and crosses between them were the most-frequent breeds in these herds. The number of females per farm varied from 41 to 296. Our cross-sectional study had two phases. In the first phase, we determined the presence or absence of seropositivity at herd level. For the second phase, all females in 20 seropositive farms were bled. Serum samples were tested for antibodies to Neospora caninum using an indirect enzyme-linked immunosorbent assay (ELISA). A questionnaire with factors mentioned in the literature was administered to the farmers. Logistic regression (LR with herd as random effect) was used to assess the relationships of the serostatus at the individual level with characteristics of the cows and environmental factors. In the first phase all herds had >20% seropositive females; therefore, all herds were eligible for the second phase. In the second phase, the overall prevalence was 39.7% (1191/3002), and within-herd prevalences were between 25.0 and 70.5%. Age 3–6 years, parity ≤2 of the dam of the cow, Jersey breed and lack of purposive sampling to diagnose abortive infectious disease were associated with positive serostatus; other management and environmental factors did not show significant associations. The lack of association between management and environmental factors with serostatus might be because all farms were exposed to a considerable number of potential factors. That all herds of this study were seropositive for neosporosis and the within-herd prevalence was considerable raises questions about how far the infection is spread in other dairy areas of Costa Rica.     

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.     

Quantification of vertical and horizontal transmission of Neospora caninum infection in Dutch dairy herds

Ninety-six of 108 randomly selected Dutch dairy herds had one or more cows with a positive serostatus for N. caninum. In these 96 herds, we have quantified the probabilities of vertical transmission (VT) and horizontal transmission (HT) of N. caninum infection by combining serostatus and pedigree data in 4091 dam-daughter pairs. The probability of animals infected by vertical transmission during pregnancy (Prob(VT)) was calculated as the proportion of seropositive daughters among daughters of seropositive dams. The probability of animals infected by horizontal transmission (Prob(HT)) was the proportion of seropositive daughters among daughters of seronegative dams. These probabilities were calculated after the frequencies of observed dam-daughter combinations were corrected for (1) imperfect test-characteristics, (2) underestimation of horizontal transmission in situations that seronegative dams were horizontally infected after the birth of their daughters and (3) overestimation of vertical transmission in situations that seronegative daughters born from seropositive dams were horizontally infected. The incidence rate for horizontal transmission was calculated based on Prob(HT) and the average age of the animals in these herds. Based on the analysis of dam-daughter serology, Prob(VT) was 61.8% (95% CI: 57.5-66.0%) and Prob(HT) was 3.3% (95% CI: 2.7-3.9%). After adjusting the observed frequencies for imperfect test-characteristics, underestimation of horizontal transmission and overestimation of vertical transmission, Prob(VT) decreased to 44.9% (95% CI: 40.0-49.9%) while Prob(HT) increased to 4.5% (95% CI: 3.9-5.2%). Prob(HT) corresponded with an incidence rate for horizontal transmission of 1.4 (95% CI: 1.2-1.7) infections per 100 cow-years at risk. When stratifying herds for the presence of farm dogs, Prob(HT) was higher (5.5% (95% CI: 4.6-6.4%)) in herds with farm dogs than in herds without farm dogs (2.3% (95% CI: 1.5-3.4%)). When stratifying for within-herd seroprevalence, Prob(HT) was higher (10.3% (95% CI: 8.6-12.2%)) in herds with high (> or =10%) within-herd seroprevalence compared with herds with low (<10%) within-herd seroprevalence (2.0% (95% CI: 1.5-2.6%)). Although there was this relation between Prob(HT) and within-herd seroprevalence (crude OR(PREV) = 5.7 (95% CI: 4.0-7.9)), in herds without farm dogs, this relationship was no longer statistical significant (OR(PREV|DOG-) = 1.9 (95% CI: 0.7-5.5)). It indicated that the association between seroprevalence and Prob(HT) depended largely on the presence of farm dogs. In addition, when looking for the presence of specific age-groups with significantly higher seroprevalence compared with the rest of the herd, there were 7 herds in which two or more horizontally-infected animals were present in specific age-groups. This was an indication of a recent point-source exposure to N. caninum. These results reiterate the current control strategies to apply strict dog-management measures as well as to minimize within-herd seroprevalence by monitoring serostatus of animals.     

Diagnostic performance of the Pourquier ELISA for detection of antibodies against Mycobacterium avium subspecies paratuberculosis in individual milk and bulk milk samples of dairy herds

The objective of the study was to determine the diagnostic performance of the Pourquier ELISA for detection of antibodies against Mycobacterium avium subsp. paratuberculosis (Map) in individual milk samples and in bulk milk samples. For individual milk samples the specificity of the Pourquier ELISA was estimated by testing a panel of individual milk samples from certified Map-free herds. The relative sensitivity of the assay in individual milk samples and agreement of the results with those of serum samples was estimated by testing panels of paired serum-milk samples from seropositive cattle, whole-herd investigations, and moderate or heavy shedders. The specificity of the ELISA for individual milk samples was still 99.8% at a cut-off of 20% sample to positive (S/P) value, clearly lower than the cut-off defined by the manufacturer (30% S/P). The relative sensitivity for individual milk samples as compared with positive serum samples was 87% for a cut-off of 20% S/P, and 80% for a cut-off of 30% S/P. The sensitivity of this ELISA for detection of high shedders was >90% both for individual milk and serum samples, also agreement was very good (kappa=0.91 for all paired samples). The specificity of the Pourquier ELISA in bulk milk samples was investigated by testing bulk milk samples from certified Map-free herds. Feasibility of bulk milk testing was investigated by titrating ELISA positive individual milk samples in negative milk. In addition, 383 bulk milk samples from herds with a known within-herd seroprevalence were tested. The specificity of the ELISA for bulk milk samples was 100% at a cut-off of 12.5% S/P. At the cut-off recommended by the manufacturer (30% S/P) performance of the bulk milk ELISA related to herd status (> or =2 seropositive cows) was rather poor, corresponding with a sensitivity of 24% and a specificity of 99% relative to serology. However, at the revised cut-off for bulk milk of 12.5% S/P and a within-herd seroprevalence of > or =3%, sensitivity and specificity relative to serology were 85% and 96%, respectively. Given the current herd-level seroprevalence in The Netherlands, these test characteristics corresponded with positive and negative predictive values for bulk milk of 67% and 94%, respectively. In conclusion, the diagnostic performance of the Pourquier ELISA for individual milk samples creates opportunities for a cheaper and more feasible testing scheme, while the diagnostic performance for bulk milk samples warrants further consideration.     

A longitudinal study of seroprevalence and seroconversion of Neospora caninum infection in dairy cattle in northeast Thailand

A long-term study was carried out in 11 dairy herds in the Khon Kaen province of northeast Thailand between August 2001 and November 2004. The objective was to investigate seroprevalence dynamics of Neospora caninum infection in the herds and to demonstrate patterns of seroconversion in individual cattle. Each herd was visited once a year, in total four times, and sera from cattle > 3 months of age and farm dogs as well as a sample from the bulk milk were collected. All samples were analysed for presence of specific antibodies by an N. caninum iscom ELISA. The overall percentage of antibody-positive cattle was constant and varied only between 10 and 13% over the 4 years, but the variation in within-herd seroprevalence between herds was substantial. Two herds had > or = 20% seropositive animals at all samplings and consistently high bulk milk OD, whereas two herds had no seropositive animal at the last two samplings and low bulk milk OD. Five herds had a decreasing trend of within-herd seroprevalence, whereas the remaining six herds had a higher portion of test-positive individuals at the end of the study. A total of 424 individuals were sampled more than once; 344 (81%) and 32 (8%) were consistently antibody-negative and antibody-positive, respectively. The proportions of animals that changed from being seronegative to seropositive and from being seropositive to seronegative between the years were 3.9-4.6% and 19-39%, respectively. Apparent vertical and horizontal transmission rates were 58% (95% CI; 44-71%) and 5% (95% CI; 3-7%), respectively. In conclusion, the overall percentage of N. caninum antibody-positive cattle was constant over the years, but the within-herd seroprevalence varied substantially between the herds. Seroconversions were likely to occur in individual cattle although most animals had consistent serological status throughout the study.     

Longitudinal study of Salmonella infection in Italian farrow-to-finish swine herds

A longitudinal study of Salmonella enterica infection was carried out in five Italian farrow-to-finish swine herds previously known to be infected by Salmonella. Five litters were randomly selected from each herd and in each litter six piglets were randomly selected and individually identified. Thus, the study included 30 pigs from each farm. At weaning, individual blood samples were collected for serological examination from all selected piglets and on the same day from all sows in the farrowing unit. Piglets were bled again at approximately 60, 90, 150, 210 and 270 days of life whereas the last blood sample was collected at slaughtering. In one of the herds, in which the duration of productive cycle was about 12 months, the last blood samples were collected at 350 days of life. With the same time scheduling, five pen pooled faecal samples were collected from each herd for bacteriological examination. At slaughtering, mesenteric lymph nodes were collected from each ear-tagged pig. Sero-prevalence (cut off S/P ratio 0.25) in sows varied from 93.8% to 100%. In four herds, sero-prevalence in piglets showed a similar profile with complete decline of maternal antibodies at day 60 and clear sero-conversion between day 90 and day 150. In one herd, sero-conversion was observed earlier and 56% of piglets were positive at day 90. The peak of sero-prevalence was observed between day 210 and day 270. Sero-prevalence at slaughtering varied from 66% to 100%. Salmonella was isolated from faecal samples in four of five herds. No Salmonella was isolated from mesenteric lymph nodes at slaughter in two of the herds. Culture prevalence from mesenteric lymph nodes in the other three herds ranged from 3.3% to 30%. This longitudinal study provides original information about epidemiological dynamics of Salmonella enterica infection in Italian swine herds in consideration of the unique extended fattening period typical of the Italian production.     

Prevalence of bovine herpesvirus-1 in the Belgian cattle population

The national bovine herpesvirus 1 (BHV-1) seroprevalence (apparent prevalence) in the Belgian cattle population was determined by a serological survey that was conducted from December 1997 to March 1998. In a random sample of herds (N=556), all cattle (N=28 478) were tested for the presence of antibodies to glycoprotein B of BHV-1. No differentiation could be made between vaccinated and infected animals, because the exclusive use of marker vaccines was imposed by law only in 1997 by the Belgian Veterinary Authorities. Twenty-one percent of the farmers vaccinated continuously against BHV-1.

In the unvaccinated group, the overall herd, individual-animal and median within-herd seroprevalences were estimated to be 67% (95% confidence interval (CI)=62–72), 35.9% (95% CI=35.0–36.8) and 33% (quartiles=14–62), respectively.

Assuming a test sensitivity and specificity of 99 and 99.7%, respectively, the true herd, individual-animal and median within-herd prevalence for the unvaccinated group of herds were estimated to be 65, 36 and 34%, respectively. The true herd prevalence for dairy, mixed and beef herds were respectively, 84, 89 and 53%; the true individual-animal prevalence for those types of herds were, respectively, 35, 43 and 31%; whereas, the true median within-herd prevalences were 36, 29 and 38%.     

Schmallenberg virus in Dutch dairy herds: Potential risk factors for high within-herd seroprevalence and malformations in calves,and its impact on productivity

In November 2011, the new orthobunyavirus Schmallenberg virus (SBV) was identified in dairy cows that had induced fever, drop in milk production and diarrhoea in the Netherlands (Muskens et al., 2012. Tijdschrift voor Diergeneeskunde 137, 112–115) and a drop in milk production in cows in Northwestern Germany (Hoffmann et al., 2012. Emerging Infectious Diseases 18 (3), 469–472), in August/September 2011. This study aimed at quantifying risk factors for high within-herd prevalence of SBV and SBV-induced malformations in newborn calves in dairy herds in the Netherlands. Additionally, the within-herd impact of SBV infection on mortality rates and milk production was estimated.A case-control design was used, including 75 clinically affected case herds and 74 control herds. Control herds were selected based on absence of malformations in newborn calves and anomalies in reproductive performance. SBV-specific within-herd seroprevalences were estimated. Risk factors for high within-herd SBV seroprevalence (>50%) and the probability of malformed newborn calves in a herd were quantified. In addition, within-herd impact of SBV with regard to milk production and mortality was estimated.Animal-level seroprevalence was 84.4% (95% confidence interval (CI): 70.8–92.3) in case herds and 75.8% (95% CI: 67.5–82.5) in control herds. Control herds that were completely free from SBV were not present in the study. Herds that were grazed in 2011 had an increased odds (OR 9.9; 95% CI: 2.4–41.2)) of a high seroprevalence (>50%) compared to herds that were kept indoors. Also, when grazing was applied in 2011, the odds of malformations in newborn calves tended to be 2.6 times higher compared to herds in which cattle were kept indoors. Incidence of malformations in newborn calves at herd level was associated with both within-herd seroprevalence and clinical expression of the disease in adult cattle.The rate of vertical transmission of SBV to the fetus once a dam gets infected seemed low. A total of 146 stillborn or malformed calves were submitted by 65 farmers during the study period, of which 19 were diagnosed as SBV-positive based on pathological investigation and/or RT-qPCR testing of brain tissue. Based on these results combined with calving data from these herds we roughly estimated that at least 0.5% of the calves born between February and September 2012 have been infected by SBV.A drop in milk production was observed between the end of August 2011 and the first half of September (week 35–36), indicating the acute phase of the epidemic. During a 4-week period in which SBV infection was expected to have occurred, the total loss in milk production in affected dairy herds was around 30–51 kg per cow. SBV had no or limited impact on mortality rates which was as expected given the relatively mild expression of SBV in adult cows and the low incidence of malformations in newborn calves.