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1.
In 2001, the first case of Postweaning Multisystemic Wasting Syndrome (PMWS) was reported in the Danish pig population. During subsequent years, the number of affected farms increased exponentially. The aim of this study was to determine how this increase influenced the use of antimicrobials between 2002 and 2004. We used national register data of herd characteristics, antimicrobial usage and disease occurrence. The analysis included data on antimicrobial usage in 3371 pig herds with weaners and 7434 pig herds with finishers, which accounted for 56 and 82% of the national amount of antimicrobials prescribed to weaners (prescribed by 347 practitioners) and finishers (prescribed by 522 practitioners), respectively.The estimation of the effect of PMWS was done by comparing the amount of antimicrobials (measured as Animal Defined Daily Doses (ADDkg) used per pig-day at risk each month in each herd) used in herds before and after an outbreak of PMWS, and by comparing the amount of antimicrobials used in herds experiencing PMWS with the amount of antimicrobials used in herds not experiencing PMWS. The effects were estimated in a three-level (veterinarian/herd/study-month) linear mixed regression model with an autoregressive correlation of order 1 (AR1).We found that after a herd had experienced an outbreak of PMWS, the antimicrobial usage in weaners was increased for a year. During the first 3 months post outbreak the usage increased by 22%, followed by an increase of 7% during the next 4th to 12th month when compared to the pre-outbreak usage. There was a significant variation between herds in this effect. Additionally, in herds experiencing an outbreak of PMWS, the usage of antimicrobials before the outbreak was 37 and 19% higher in herds with weaners and finishers, respectively, compared to herds not experiencing PMWS.Generalisation of the results to the entire Danish pig population indicated that the increase of PMWS infected herds from almost zero to about 20% during a 4-year period resulted in a national increase of 4–5% in antimicrobials usage in weaners. The effect of PMWS on usage of antimicrobials in finishers was unclear.  相似文献   

2.
A retrospective cohort study of 116 British pig farms was undertaken to investigate the epidemiological risk factors associated with herd breakdowns with postweaning multisystemic wasting syndrome (PMWS). Farmers reported the PMWS status of their herd (case definition 1) and, where applicable, when the disease was first suspected and what they observed; they described a prolonged increase in mortality in six to 16-week-old pigs that was not attributable to any disease known to be on their farm. There was over 90 per cent agreement on the farmers' PMWS status between the farmers and their veterinarians. Approximately 70 per cent of the breakdowns were confirmed at the laboratory (case definition 2) except during the outbreak of foot-and-mouth disease (FMD) in 2001 when it was reduced to 30 per cent. Porcine circovirus type 2 antigen was detected in pigs examined postmortem (case definition 3) in approximately 90 per cent of the farms with increased mortality. The breakdowns occurred initially in the south of England and spread west and north, as well as locally in a radial pattern from the affected farms, and there was strong statistical evidence that there was non-random space-time clustering. The risk of herd breakdowns with PMWS was not constant; therefore, for each case definition, three survival models were developed with outcome variable time to breakdown of between January 2000 and January 2001, February 2001 to September 2001 (during FMD) or October 2001 to December 2003. Exposures with a bivariable significance of P<0.20 were tested in three multivariable Cox proportional hazard models. From January 2000 to January 2001 the risk of a herd breakdown with PMWS for definitions 1, 2 and 3 was greater for farms with 600 or more breeding sows, and for definitions 1 and 3 there was an increased risk associated with the purchase of replacement gilts rather than using homebred replacements. For definitions 1 and 3 the farms where the nearest pig farm had no breeding pigs were at greater risk of a breakdown than those where the nearest farm had breeding stock, as were the farms where visitors were not requested to avoid pigs for more than three days before visiting the farm during the FMD outbreak. From October 2001, the associated risks were identical for all three case definitions; farms were at greater risk when they had 600 or more breeding sows, if visitors had not avoided contact with pigs for more than three days before visiting the farm, and when there was a farm with PMWS less than five miles away. The affected farms were more likely to have disease associated with porcine parvovirus, porcine reproduction and respiratory syndrome virus, erysipelas, Escherichia coli and salmonella. These exposures were positively associated with large herds and the farm being close to other pig farms, but did not remain in the final models for breakdown with PMWS, indicating that such farms may be at greater risk of many infectious diseases.  相似文献   

3.
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4.
In 1992, the porcine reproductive and respiratory syndrome virus (PRRSV) of European type (PRRSV-EU) was introduced in Denmark. By 1996, the virus had spread to approximately 25% of the Danish herds. In January 1996, a modified-live vaccine based on the American type of the virus (PRRSV-US) was used in replacement boars for Danish artificial insemination (AI) centres and from July 1996, the vaccine was used in PRRSV-EU infected herds for prevention of disease. Soon after vaccine introduction, PRRSV non-infected herds experienced outbreaks of disease due to infection with PRRSV-US. In this study, we investigated the risk factors (biosecurity level, animals, exposure from PRRSV-US-infected neighbour herds, semen, herd size, pig density and herd density) for infection with PRRSV-US in a cohort of 1071 sow herds; we used a nested case-control study. The retrospective observation period lasted from June 1996 (when they all were non-infected) to October 1997. Seventy-three non-vaccinated, closed sow herds became infected with the vaccine strain during this period. Each case herd was matched with two control herds from the cohort (controls had not been infected at the time of infection in the case herds). The data were analysed using a Cox-regression model. The hazard of infection increased significantly with exposure from PRRSV-US-infected neighbouring herds, purchase of animals from herds incubating PRRSV-US infection, increasing herd size and purchase of semen from boars at PRRSV-US-infected AI centres. The results are consistent with the modified-live vaccine strain spread to other herds by trade with animals and semen and by neighbour (area) transmission. We suggest that virus spread by aerosols was a frequent mode of transmission.  相似文献   

5.
The problems addressed are: (1) comparison of prevalences of Salmonella spp. in different herd types in the Danish pig population after implementation of the Danish Salmonella Control Program (DSCP), and (2) to make a reference to a study from 1993/1994 (pre-implementation) with a discussion of possible biases when diagnostic methods differ slightly. The objectives were to present the prevalences of Salmonella spp., Salmonella Typhimurium, and multiresistant S. Typhimurium DT104 in Danish pig herds in 1998. Further, to discuss how herd prevalences may be compared to a previous study.A bacteriological study in 1998 comprised: (a) a random sample of slaughter pig producing herds (N=1962); (b) a random sample of farrow-to-grower (sow) herds (N=305); and (c) all breeding and multiplying (genetic) herds (N=366). A previous bacteriological study on Salmonella presence in 1993/1994 served as a model for the present study. The results of the study were that multiresistant S. Typhimurium DT104 was detected in one herd producing slaughter pigs. The herd apparent prevalences (HAPs) of Salmonella spp. were 11.7, 16.7 and 11.4% in genetic, sow, and slaughter pig herds, respectively. The conclusion of the study was that prevalence of multiresistant S. Typhimurium DT104 was low in the examined slaughter pig herds. The herd true prevalence (HTP) of Salmonella spp. in pigs had declined from before the start of the DSCP in 1993/1994 to 4 years later (1998).  相似文献   

6.

Background

Despite that PMWS commonly affects pigs aged eight to sixteen weeks; most studies of PMWS have been conducted during the period before transfer to finishing herds. This study focused on PCV2 load and antibody dynamics in finishing herds with different PMWS status.

Methods

Sequentially collected blood samples from 40 pigs in each of two Swedish (A and B) and one Norwegian (C) finishing herds were analysed for serum PCV2-load and -antibodies and saliva cortisol. The two Swedish herds differed in PMWS status, despite receiving animals from the same sow pool (multi-site production). However, the PMWS-deemed herd (A) had previously also received pigs from the spot market. ResultsThe initial serum PCV2 load was similar in the two Swedish herds. In herd A, it peaked after two weeks in the finishing herd and a high number of the pigs had serum PCV2 levels above 107 per ml. The antibody titres increased continually with exception for the pigs that developed PMWS, that had initially low and then declining antibody levels. Pigs in the healthy herd B also expressed high titres of antibodies to PCV2 on arrival but remained at that level throughout the study whereas the viral load steadily decreased. No PCV2 antibodies and only low amounts of PCV2 DNA were detected in serum collected during the first five weeks in the PMWS-free herd C. Thereafter a peak in serum PCV2 load accompanied by an antibody response was recorded. PCV2 from the two Swedish herds grouped into genotype PCV2b whereas the Norwegian isolate grouped into PCV2a. Cortisol levels were lower in herd C than in herds A and B.

Conclusions

The most obvious difference between the Swedish finishing herds and the Norwegian herd was the time of infection with PCV2 in relation to the time of allocation, as well as the genotype of PCV2. Clinical PMWS was preceded by low levels of serum antibodies and a high load of PCV2 but did not develop in all such animals. It is notable that herd A became affected by PMWS after errors in management routine, emphasising the importance of proper hygiene and general disease-preventing measures.  相似文献   

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

8.
Porcine circovirus type 2 (PCV2) is the primary cause of Postweaning Multisystemic Wasting Syndrome (PMWS) in pigs. PCV2, however, is found in both PMWS-affected herds and non-affected herds. The objective of this study was to clarify if PCV2 genome nucleotide sequences isolated from pigs from PMWS-affected herds and non-affected herds cluster phylogenetically in two separate groups. All isolates (45) belonged to PCV2 group 1 and shared a nucleotide sequence identity of 99.4-100% indicating a very homogeneous PCV2 population in Denmark. Phylogenetic analysis of the PCV2 isolates revealed no distinctive clustering of case- and control-herds suggesting that there is no link between PCV2 sequences and herd disease status. The appearance of only PCV2 group 1 isolates in this study (isolates from 2003/2004) led us to determine if PCV2 nucleotide sequences had changed in Denmark over time. Interestingly, all PCV2 isolates from before the first outbreak of PMWS (2001) belonged either to a new PCV2 group identified for the first time in this study and named group 3 (isolates from 1980, 1987 and 1990) or PCV2 group 2 (isolates from 1993 and 1996). The shift from PCV2 group 2 to 1 was confirmed on a more global scale by placing all full genome PCV2 sequences submitted to GenBank from 1997 to 2006 in either of the groups by phylogenetic analysis. The analysis showed that the shift happened in 2003 or even earlier. This may indicate that PCV2 group 1 is a more adapted form of PCV2 and possibly could be more pathogenic.  相似文献   

9.
In order to test the hypothesis that a putative co-factor for the development of postweaning multisystemic wasting syndrome (PMWS) in pigs could be of viral origin, we performed extensive virological examinations on organ material from pigs diagnosed with PMWS originating from within a Danish PMWS-transmission study. Virus isolation attempts were carried out on a large panel of different cell types including primary pig kidney cells and lung macrophages, primary rabbit kidney cells and seven established cell lines (MARC-145, ST117, PK15, BHK21, HeLa, Vero, and MDCK). Although these represent cells with susceptibility to a wide range of known viruses, the results did not provide evidence for a specific virus other than PCV2 contributing to the development of PMWS. Furthermore, in order to test whether specific genotypes of PCV2 may trigger the switch from PCV2 infection to clinical disease, we compared complete DNA genome sequences of PCV2 derived from PMWS-positive as well as PMWS-negative pigs. On the basis of the DNA sequences, the PCV2 isolates were divided into two groups. Group 1 consisting of one isolate originating from a herd unaffected by PMWS, with group 2 consisting of nine isolates originating from four PMWS-affected herds, four PMWS-positive pigs plus one unaffected herd. The PCV2 genomes from the two groups showed 95.5% identity. Alignment analyses of the sequences encoding the replicase and capsid protein from group 1 and group 2 PCV2 isolates showed two amino acid differences encoded in the replicase protein, while 19 amino acid differences were predicted among the capsid protein sequences. The PCV2 DNA sequence analysis supports recent observations from studies in USA as well as Europe, which suggest that strain variations may influence the clinical outcome of PCV2 infection.  相似文献   

10.
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11.
In Denmark, a serological Salmonella surveillance programme in finishing pig herds has been in place since 1995. The programme was founded on data from experimental studies, which demonstrated a strong association between Salmonella serology and the prevalence of these bacteria. The current study was carried out in three Danish abattoirs to evaluate the correlation under field conditions. A total of 160 Danish finishing pig herds were included. Seven out of these were examined twice, yielding a total of 167 observations. The herds were selected according to their herd serology based on data from the national surveillance. From each herd, samples were taken from 10 finishers at slaughter. The prevalence of Salmonella bacteria was measured at four sites: (1) caecal-content; (2) carcass surface; (3) pharynx; and (4) caecal lymph nodes. A logistic regression model was constructed for each sampling site. Abattoir, sanitary slaughter and herd seroprevalence were used as explanatory variables. The results demonstrated that there was a strong association between herd serology and the prevalence of Salmonella bacteria measured at three of the sampling sites: caecal-content, pharynx, and carcass surface. For these sites, the odds for being culture-positive for Salmonella varied from 1.3 to 1.5 for each increase of 10% in herd serology (P < 0.0001). For caecal lymph nodes, however, no linear association was found.  相似文献   

12.
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13.
In this study, 60 pigs with clinical signs of post-weaning multisystemic wasting syndrome (PMWS) from 20 different pig herds and 180 control pigs (without clinical signs of PMWS) were examined to get more insights into the frequencies of porcine circovirus 2 infections and the presence of co-infections in pigs with and without clinical signs of PMWS in the Netherlands. Porcine circovirus type 2 was detected in 100% of the pigs with clinical signs of PMWS by virus isolation and/or PCR and in 50% of the pigs from PMWS-free herds. There was an association between the levels of infectious PCV2 and/or PCV2 DNA load and the severity of clinical signs as described for PMWS. A high variation in PCV2 antibody titres was found in the clinically affected pigs, and 27% of these pigs did not mount PCV2 antibody titres higher than 1:200. A concurrent infection of PCV2 and porcine reproductive and respiratory syndrome virus (PRRSV) was found in at least 83% of the pigs with clinical signs of PMWS and in 35% of the pigs from PMWS-free herds. Co-infections of European- and American-type PRRSV were detected only in PMWS herds and in one control herd with a history of PMWS clinical signs.  相似文献   

14.
A study was conducted in 1994-96 with the aim of assessing the serological prevalence of Border Disease (BD) among sheep and goats in Denmark and to investigate possible relations to herd factors. From each of 1000 herds, 2 blood samples were obtained from animals older than 1 year. The examination for antibodies was performed using a blocking ELISA detecting antibodies to pestivirus. Data from 815 herds were analysed statistically by the maximum likelihood method in a multinomial model. The estimated herd prevalence was 0.083 and the estimated individual prevalence within the positive herds was 0.50. There was no difference between the prevalence in sheep and goat herds. Records for well over half of the herds could be combined with data from the Danish Central Husbandry Register. No association between occurrence of BD and herd size was found. Cattle were registered as contemporarily present on 135 out of 521 herds which was shown to be strongly associated to BD. The estimated herd prevalences of BD among farms with and without contemporary cattle were 0.24 and 0.042, respectively.  相似文献   

15.
Postweaning multisystemic wasting syndrome (PMWS) is causally associated with porcine circovirus type 2 (PCV2) infection of pigs. PCV2 was first demonstrated in Swedish pigs in 1993, although the virus was almost certainly present in pigs in the country before that. Despite this, no signs of PMWS were observed in pigs of Sweden until the first outbreak was reported in 2003. The accumulated number of PMWS-affected herds have increased via 16 (2004) and 41 (2005) to 123 in December 2006. Of these herds, 30 (25%) have now been declared free from PMWS. However, a number of other herds have had individual pigs that have fulfilled the demands for PMWS at necropsy and 52 of these herds have been declared negative on herd basis after treatment for intestinal or respiratory diseases, and/or by correcting shortcomings in management of the herd including feed. Thus, individual cases of the disease have been observed in around 200 herds by the end of 2006 and PMWS is now regarded as an endemic disease in Sweden. The pig population of Sweden is geographically isolated, the density of pigs and the pathogen load in the country is low and the use of growth promoters (low dose antibiotics in feed) was prohibited in 1986. Additionally, the trade of animals in Sweden is organised in a restricted way. Because of these factors it is possible to conduct meaningful real-time studies on the transformation of PMWS in Sweden from being an exotic to an endemic disease in a three year time scale. Initially the PMWS cases were concentrated in the southern part of Sweden, but have gradually spread north. The PMWS-positive herds have, in general, had an effective production, but some management errors have constantly been observed in affected herds. Physical links between affected herds are often missing, and the data generated to date on the PMWS outbreaks in Sweden do not suggest an introduction of a new contagious microbe into the country that is responsible for the PMWS outbreaks, nor does PMWS appear to be spread via semen. In Sweden, intensity in rearing, disease preventing measures and immaturity of the piglets appear to be important as predisposing factors to PMWS and, as such, are discussed in this article.  相似文献   

16.
Respiratory disease is considered the most serious disease problem in modern pig production and the risk has increased with intensification of pig production. We quantified risk factors for chronic pleuritis (CP) in Danish pig herds in terms of herd and herd-owner characteristics, management and neighbourhood factors. The occurrence of CP was investigated in 540,104 slaughter pigs from 259 farrow-to-finish or finishing herds during the mandatory post-mortem meat inspection at 18 Danish abattoirs. The monthly herd- and abattoir-specific prevalences of CP were estimated for the months January through August 2000. Meat-inspection data, herd characteristics and neighbourhood factors were obtained from databases at the Danish Bacon and Meat Council. Data on herd-owner characteristics and management factors were obtained by telephone interviews. Data were analysed using a mixed model accounting for repeated measurements. Four factors were associated with increased herd prevalence of CP: low health status of the herd, pig density within a 5 km radius, mingling of pigs during the production period and the month of slaughter. Two factors protected against CP: feeding with only dry feed and practising all-in-all-out production.  相似文献   

17.
A comparative serologic and virologic study was performed in pigs from 5 herds with postweaning multisystemic wasting syndrome (PMWS) and 2 herds without PMWS in Quebec. In each herd, 60 blood samples were collected at 4-wk intervals from pigs from 3 to 23 wk of age. The serum was evaluated for the presence of antibodies to porcine circovirus type 2 (PCV2) and porcine reproductive and respiratory syndrome virus (PRRSV), as well as for the presence of nucleic acid of PCV2, PRRSV, and porcine parvovirus (PPV), by means of the polymerase chain reaction (PCR). Serologic profiles for PCV2 were very similar in 6 of the 7 herds, including the 2 without PMWS, and were characterized by a gradual decrease in antibody titres from 3 until 11 wk of age, followed by seroconversion at 15 wk, and high PCV2 antibody titres thereafter in all pigs. Only starting at 11 to 15 wk of age could PCV2 viremia be detected, except in 1 herd, in which clinical signs were observed at 6 to 7 wk of age. A PCV2 viremia could be detected within the same pigs for a minimum of 8 wk, and the virus could still be detected in 41% of the serum samples obtained at 23 wk of age. The antibody level did not appear to influence the occurrence of disease, since titres were similar in pigs in the herds with or without PMWS. Infection with PRRSV, as demonstrated by PCR and seroconversion, preceded that of PCV2 by at least 1 mo in both types of herd. Both PRRSV and PCV2 were detected in some pigs in 5 of the 7 herds, including 1 herd without PMWS. Porcine parvovirus could be detected in serum by PCR in 2 herds with PMWS after the onset of clinical signs and also in 1 herd without PMWS. Genomic analysis of PCV2 strains identified in the herds without PMWS indicated complete or very high homology (99.4% to 100%) with the PCV2 strains identified in 4 herds with PMWS. In our field study, the triggering of PMWS in the herds could not be linked to coinfection with either PRRSV or PPV or to the use of a specific immunostimulant, such as vaccines, or to particular genomic differences between the PCV2 strains identified.  相似文献   

18.
AIMS: To determine the frequency with which porcine reproductive and respiratory syndrome (PRRS) virus (PRRSv) would become established in a non-commercial pig herd in New Zealand due to illegal feeding of uncooked food waste containing virus-contaminated pigmeat. To determine the likelihood of a single incursion resulting in a multi-farm outbreak of the disease, and describe the spatio-temporal characteristics of such an outbreak. METHODS: A Monte Carlo simulation model was constructed to determine the expected annual frequency of PRRSv infection being initiated in a non-commercial pig herd as a result of inadvertent feeding of pigmeat imported from countries endemically infected with the disease. Once the likelihood of PRRSv becoming established in a single pig herd was determined, stochastic spatially explicit infectious disease modelling software was utilised to model the temporal and spatial characteristics of the resulting epidemic. RESULTS: Assuming the proportion of imported pigmeat remained at current levels, consumption patterns of pigmeat in households in New Zealand remained steady, and limited compliance with recently reintroduced regulations to prevent feeding of uncooked food waste, at least 4.3 pig herds per year were predicted to become infected with PRRSv. Simulation modelling of PRRSv epidemics related to initial infection of a non-commercial farm produced an estimate that 36% of these incursions would spread from the initial herd, and that these outbreaks would involve 93 herds on average in the first year. By increasing the estimated persistence of PRRSv infection in small herds, an average of 205 herds became infected in the first year. CONCLUSIONS: Given a mean of 4.3 infected premises per year and a 36% probability of infection spreading beyond the initial infected herd, there was a 95% likelihood of a multi-farm PRRS outbreak occurring within 3 years. CLINICAL RELEVANCE: Introduction of PRRSv through importation of virus-contaminated pigmeat presents a high risk for establishment of the disease in the pig industry in New Zealand.  相似文献   

19.
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.  相似文献   

20.
Potential risk factors for clinical signs of post-weaning multisystemic wasting syndrome (PMWS) and porcine dermatitis and nephropathy syndrome (PDNS) in pigs in the Netherlands were investigated in a matched case-control study using a questionnaire (personal interview). Eighty-two pig farmers were questioned about management, hygiene, husbandry systems, disease history, and preventive health care. In this study, 30 pig herds with (cases) and 30 pig herds without (controls) characteristic clinical signs of PMWS were compared. For PDNS, 11 pig herds with (cases) and II pig herds without (controls) characteristic clinical signs of PDNS were compared. Univariate analysis (P < 0.10) showed that the following occurred relatively more often in the PMWS case herds than in the control herds: 1) clinical signs of PDNS, porcine reproductive and respiratory syndrome (PRRS), porcine parvovirus (PPV) infections, meningitis, coccidiosis, and pre-weaning diarrhoea observed by the farmer; 2) vaccination against PRRS and mycoplasma; 3) non-optimal climatic conditions in the nursery rooms, a large variation in weaning age, a high occurrence of cross-fostering of piglets, a large number of sows with lactation problems, poor colostrum intake by piglets; and 4) (historical) use of breeding stock (including semen for artificial insemination) of Anglo-Saxon origin. In the final multivariate statistical model, one variable remained significantly associated with PMWS case herds, namely, the presence of clinical signs of PRRS (and/or the associated use of vaccination against PRRS). It should be noted that in almost all cases animals were vaccinated against PRRS because of clinical signs of PRRS that appeared a few months after the first occurrence of clinical signs of PMWS. This excludes PRRS vaccination as a primary factor in causing PMWS. Analysis of the PDNS case-control data showed comparable results with those of the PMWS study. In the final statistical model, the presence of clinical signs of PRRS (and/or the associated use of vaccination against PRRS) was significantly associated with PDNS case herds.  相似文献   

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