Effect of maternally derived antibodies on the clinical signs and immune response in pigs after primary and secondary infection with an influenza H1N1 virus

The aim of this study was to determine the role of maternally derived antibodies (MDA) against an influenza H1N1 virus in the clinical protection of piglets and especially their effect on the development of the active immunity after an infection with a homologous influenza H1N1 virus. Twenty piglets with MDA and 10 piglets without MDA were housed together and inoculated twice with influenza H1N1 virus, at 7 and 15 weeks of age. Nine piglets without MDA were added to these groups at 12 weeks of age to be inoculated at 15 weeks of age only. Clinical signs, body temperature, growth performance, virus excretion, antibody responses, and influenza-specific T-cell response were monitored. It was shown that MDA protect piglets against the clinical consequences of a primary influenza infection, but that this protection is not complete. A short but significant rise in body temperature was observed and growth seemed to be inhibited due to the infection. Piglets with MDA shed virus for a longer period after an infection than piglets without MDA. Piglets with and without MDA were protected against the clinical consequences of a secondary infection. However, both after primary and secondary infection significant differences in immune responses were observed that indicated that pigs with MDA developed a weaker immunity than pigs without MDA. Furthermore, overall growth performances from weaning to slaughter show a trend in favour of pigs without maternal antibodies, compared to pigs with maternal antibodies, mainly caused by a significant better performance in the second half of the finishing period. The results of this study provide us insight in the role of MDA in clinical protection and their influence on active immunity after an influenza virus infection of pigs. Furthermore, it leads us to the discussion about the profitability of massive sow herd vaccinations in an attempt to increase MDA levels in piglets, taking into account the overall performance of these piglets and the possible effects on antigenic drift.

Estimating the incidence of influenza-virus infections in Dutch weaned piglets using blood samples from a cross-sectional study

A cross-sectional study was carried out on 32 Dutch breeding herds to estimate the incidence of influenza-virus infections in piglets before the start of the finishing period, at the age of approximately 10 weeks. Longitudinal studies on two herds (8 and 10 litters, respectively) were done to obtain an average decay function for maternal antibodies.Each participating farm in the cross-sectional study was visited twice within 5 months; each time, blood samples were taken randomly from one compartment (a separate room with separate air flow) of 4-5-week-old piglets and one compartment of 8-9-week-old piglets. These blood samples (a total of 2598; 16-23 per compartment, depending on its size) were tested in a haemagglutination inhibition test for antibodies against influenza-virus subtypes H1 and H3. Samples from 8-9-week-old piglets from the first sampling period (n=660) were also tested in an IgM ELISA. For each individual herd and each influenza-virus subtype separately, the decay function derived from the longitudinal studies was used to calculate an expected seroprevalence in 8-9-week-old piglets, which was then compared to the observed seroprevalence. Depending on subtype and sampling period, between 10 and 15 of the 32 herds were suspected of virus circulation during the weaning period because the observed seroprevalence was significantly higher than the expected seroprevalence (P<0.05). In the first sampling period the IgM ELISA confirmed six of these outbreaks. However, due to the small window of detection of the IgM ELISA (compared to the length of the weaning period), it will always underestimate the number of infections. Infections in the first half of the weaning period will no longer be detectable because IgM antibodies have already disappeared. In individual pigs, an incidence of 16-17% was estimated for each subtype over a 4-week period between the age of 4-5 and 8-9 weeks. For each influenza subtype, 80% of the piglets will enter the finishing facilities without antibodies or with decaying maternal antibodies. These piglets may be susceptible to an infection with influenza virus.

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.

Administration of acidified drinking water to finishing pigs in order to prevent Salmonella infections

The aim of the study was to test whether acidified drinking water, with two millilitres of an acid mixture per litre, was able to reduce the number of Salmonella infections in finishing pig herds. In each compartment, half of the pens were supplied with acidified water and the other pens served as negative control. In three herds the required dose was not applied to the pigs as a result of various practical problems. In another herd, all pigs remained seronegative throughout the study. Analysis of the remaining three herds showed a large and significant treatment effect in one herd (P<0.001). As a result of the small number of observations and the overall lower seroprevalence in the control groups, the other two herds only showed a statistical trend to a treatment effect (0.10<P<0.05). The main practical problem was the clogging of drinking nipples as a result of fungal growth in the pipelines.

Salmonella seroprevalence at the population and herd level in pigs in The Netherlands

The aim of this study was to provide baseline data on the population and herd Salmonella seroprevalence in sows and finishers. For the population estimates in 1996 and 1999 and the herd prevalences for sows and gilts, blood samples from swine vesicular disease (SVD) and pseudorabies monitoring programmes were used and tested in an indirect Salmonella enzyme-linked immunosorbent assay (ELISA). The herd prevalence for finishers was determined using blood samples collected at two slaughterhouses. The population prevalence for finishers in 1996 and 1999 was 23.7 and 24.5%, respectively, and for sows 40.5 and 60.4%, respectively. The prevalence in free range (FR) finishers was significantly higher (44.6%) than in intensively housed finishers in 1999, identifying a hazard group for possible extra pork and pork product contamination. Of 406 finishing herds, 9% were completely seronegative for Salmonella (cut-off OD%>10). Of these 406 finishing herds, 69.7% had Salmonella-status I (low prevalence), 21.7% status II (moderate prevalence) and 8.6% status III (high prevalence) (cut-off OD%>40). In 46 multiplying sow herds, 20 breeding sow herds and 20 matching replacement gilt herds, the average herd prevalences were 54, 44.4 and 19.3%, respectively. Two gilt herds were completely seronegative. The prevalence in the gilt herds was never higher than in the matching breeding sow herds. Agreement on methodology and calibration of ELISA tests would make these results comparable between countries and is a prerequisite for a co-ordinated and integrated program to reduce Salmonella in pork in the European Union.

Herd level husbandry factors associated with the serological Salmonella prevalence in finishing pig herds in The Netherlands

A national program to reduce Salmonella in pork and pork products should include monitoring and intervention at farm level. To develop an adequate intervention strategy at farm level, risk factors for Salmonella infections in finishing pigs have to be determined. In this study, blood samples were collected randomly at two slaughterhouses from slaughter pigs. Samples were tested by the Dutch Salmonella ELISA, based on the O-antigens 1, 4, 5, 6, 7 and 12, using a cut-off of OD%=10. This ELISA has been calibrated against the Danish ELISA to give comparable results. Workers from herds from which at least forty blood samples had been collected, were asked to participate in a questionnaire. In total, 353 questionnaires were obtained and analysed. Significant risk factors associated with the proportion of seropositive samples were identified by multiple linear logistic regression. The feeding of a complete liquid feed containing fermented by-products and the omission of disinfection after pressure washing a compartment as part of an all-in/all-out procedure, were both associated with a lower Salmonella seroprevalence. A small to moderate herd size (<800 finishing pigs), a previous diagnosis of clinical Salmonella infection in the herd, the use of tylosin as an antimicrobial growth promoter in finishing feed, or herds which had more than 16% of the livers of their pigs condemned at the slaughterhouse as a result of white spots were associated with a higher Salmonella seroprevalence. Hypothetical intervention strategies based on these risk factors can be studied for their effect on the Salmonella seroprevalence and practical applicability in field studies.

Experimental quantification of the transmission of Sarcoptes scabiei var. suis among finishing pigs

In this study, the rate of S. scabiei var. suis transmission among finishing pigs was quantified in a contact transmission experiment. Forty piglets originating from a mange free farrow-to-finish herd were randomly allocated to three groups and one S. scabiei var. suis infested finishing pig was subsequently added to each of these groups. After 35 days, the three seeder pigs were removed from the groups and the remaining 40 pigs were re-allocated to five pens. Ear scrapings, to be examined for mites, were collected from each pig on days 1, 14, 28, 42, 56, and 84 of the experiment. Blood samples, to be tested for antibodies against S. scabiei, were collected from each pig on days 0, 14, 28, 42, 56, 70, 84 and 112 after the introduction of the seeder pigs. From the results of the ear scrapings and the blood samples the number of susceptible (not infested) and infested pigs was derived at the time of each sample collection and the number of new infestations in the intervals between the sample collections. From these data the infestation rate parameter beta (average number of new infestations per infested pig per day) was estimated by use of a Generalised Linear Model (GLM) and accordingly, beta was estimated at 0.056 (95% CI: 0.037-0.085) infestations per infested pig per day.Next, by use of beta, the transmission of S. scabiei was simulated in a population of 100 finishing pigs for 100 days after the introduction of a single infested pig. For this purpose, 500 simulations were done. The 90% confidence interval of the number of infested pigs at day 100 ranged from 12 to 88 (median: 63). It was concluded that transmission of S. scabiei among finishing pigs is slow. Due to the presumed lower contact rate between sows as compared to finishing pigs, it is anticipated that transmission of S. scabiei among sows will even be slower than among finishers These findings are of particular interest for the development of surveillance programmes for S. scabiei free herds.

[Effect of the Stellamune Mycoplasma vaccine on growth, energy conversion, death, and medication use in fattening pigs on a pig farm chronically infected with Mycoplasma hyopneumoniae]

The effect of Stellamune Mycoplasma vaccine, administered to piglets aged 2-15 days and then 13-15 days later, on daily weight gain, energy conversion, and use of medication was examined in fattening pigs on a chronically Mycoplasma hyopneumoniae infected pig farm. Half of the piglets were vaccinated and the other half acted as controls. In the study design, half of the pens in the fattening unit were allocated to vaccinated pigs; the other half to non-vaccinated pigs, pen was the experimental unit. In the fattening pens sows and castrated boars were separated. The study consisted of a total of 37 pens with vaccinated, and 37 pens with non-vaccinated pigs in 12 different compartments within the pig herd. In the finishing period, mean growth performance and mean energy conversion (EV/kg) of vaccinated animals was 65 grams/day higher and 0.07 EV/kg lower than in control pigs. Furthermore, the incidence of individual curative medication against respiratory problems was more than 4 times higher in control pigs than in vaccinated pigs. There was a tendency for a higher number of group medications against respiratory problems in control pigs than in vaccinated pigs. It is concluded that, in this herd, vaccination against M. hyopneumoniae was successful from an economic point of view.

Production performance and pruritic behaviour of pigs naturally infected by Sarcoptes scabiei var. suis in a contact transmission experiment

Reports on the effects of mange on the production performance of pigs are conflicting. So far, studies have used experimental infections, by depositing encrusted lesions from chronically infected pigs into the ears of experimental pigs. However, this is a poor representation of what happens under natural field conditions. The purpose of our study was to quantify the effects of sarcoptic mange on production performance and pruritus in pigs that were infected by contact with S. scabiei var. suis-infected pigs. A total of 80 piglets were matched by sex and weight and randomly divided between experimental and control compartments. In the experimental compartment, each of three naturally S. scabiei var. suis-infested pigs were randomly allocated to three pens with 13 susceptible pigs each. From day 0 to 35, the growth performance of pigs in the experimental compartment was significantly (P=0.04) worse (35 g/d) than of pigs in the control compartment. From day 35 to 112, there was a statistical trend (P=0.10) that the growth performance of pigs in the experimental compartment was lower (50 g/d) than that of pigs in the control compartment. For the complete fattening period (0-112 or more days), the growth performance of pigs in the experimental compartment was significantly (P=0.05) worse (41 g/d) than that of pigs in the control compartment. Mean feed conversion ratio (kg feed per kg gain) was 2% higher in the experimental compartment compared with the control compartment. Pigs in the experimental compartment had a nine times (95% CI: 2 - 44) higher chance of showing pruritic behaviour than pigs in the control compartment.

Aujeszky's disease virus eradication campaign successfully heading for last stage in The Netherlands

The Aujeszky's disease virus (ADV) eradication campaign in The Netherlands is based on compulsory vaccination and certification of ADV-free herds and consists of three stages: reduction of transmission of ADV, tracing and elimination of remaining sources of ADV, and, in the last stage prohibition of vaccination. This paper summarizes the progress made in the first two stages of the eradication. Between 1994-1999, ADV seroprevalence decreased sharply in all four regions in The Netherlands, both in the sow and the finishing pig population. In the sow population, the mean ADV prevalence in the northern, eastern and western regions decreased to less than 0.5% in the first quarter of 1998, and to approximately 1% in the southern region. For the finishing pig population, the mean ADV prevalence decreased to less than 0.6% in all four regions in the first quarter of 1998. The proportion of sow herds that were certified ADV-free increased steadily from approximately 40% in the last quarter of 1996 to 96% in the first quarter of 1999. The proportion of finishing pig herds that were certified ADV-free showed the same spectacular increase as in the sow population: from approximately 14% in the last quarter of 1996 to 90% in the first quarter of 1999. It is anticipated that the last stage of the ADV eradication campaign, stopping vaccination, will be achieved very soon. Monitoring wild boars for ADV between 1994 and 1999 indicated that ADV is uncommon within the wild boar population. Therefore, it seems that ADV infection in the wild boar population is not an important reservoir in The Netherlands.

Validation of ELISAs for the detection of antibodies to Sarcoptes scabiei in pigs

An Enzyme-linked ImmunoSorbent Assay (ELISA) was developed for the detection of antibodies to Sarcoptes scabiei. This 'Animal Health Service'-ELISA (AHS-ELISA) was compared with a commercial test (Checkit(R) Sarcoptest) using experimental and field sera. The experimental study was a contact infestation experiment. Eighty piglets were randomly divided between the experimental and control group. After introduction of three Sarcoptes scabiei var. suis infested pigs in the experimental group, both groups were monitored by determining scratching indices, taking ear scrapings and blood samples in Weeks 0, 2, 4, 6, 8, 12 and 16. Four pigs in the control group were immunised with either Dermatophagoides pteronyssinus (Dp) antigens (n=2), or Acarus siro (As) antigens (n=2). In the control group all (non-immunised) pigs were negative in all tests. In the experimental group only slightly elevated scratching indices were observed, with a maximum in Week 8. After 2 weeks for the first time an ear scraping was positive (2.5%). In Week 8 the highest number of positive ear scrapings were found (25.0%). Positive results in the Sarcoptest were first obtained in Week 12 (10.5% positive), while eventually 29.0% of the finishing pigs were positive after 16 weeks. The AHS-ELISA first detected a serological response after 6 weeks (5. 0% positives), increasing until after 16 weeks a large proportion (74.2%) of the finishing pigs were seropositive, making the AHS-ELISA the most sensitive test. In the AHS-ELISA one As-immunised pig remained seronegative, but the other hyper-immunised pigs crossreacted. In the Sarcoptest, only Dp-immunised pigs had elevated Optical Densities (OD's) albeit below the cut-off level. Although hyper-immunisation is not a representation of field conditions, it cannot be excluded that the AHS-ELISA is not 100% specific.Field samples were taken from 20 sows in 30 herds, classified as mange-free, suspect, or infested. On a herd level there was high agreement among the ELISAs. Both serological tests were suitable to distinguish mange-free herds from infested herds. In one infested herd the decline of maternal antibody in piglets was studied by sampling 40 piglets from 20 different litters. The lowest average OD using the AHS-ELISA was found at 5 weeks of age, followed by a significant increase at 7 weeks. The average OD with the Sarcoptest was at a minimum level at 3 weeks, but no increase was found later. For screening of herds, interference of maternal antibodies is avoided by sampling at an age of 7 weeks or older.

Survey of infectious agents involved in acute respiratory disease in finishing pigs

Outbreaks of respiratory disease constitute a major health problem in herds of finishing pigs and their aetiology often remains unclear. In this study, 16 outbreaks of respiratory disease with acute clinical signs in finishing pigs were investigated to determine which infectious agents were involved. From each herd four diseased and two clinically healthy pigs were examined pathologically and for the presence of viruses, bacteria and mycoplasmas. In addition, paired blood samples from 10 groupmates of the diseased pigs were tested for antibodies against commonly known causal agents of respiratory disease. A clear diagnosis was possible in 12 of the 16 outbreaks. Seven were due to an infection with influenza virus and five were due to an infection with Actinobacillus pleuropneumoniae. A combination of influenza virus and A pleuropneumoniae may have caused one other outbreak, but no clear cause could be established for the other three outbreaks.

Salmonella infections in finishing pigs in The Netherlands: bacteriological herd prevalence, serogroup and antibiotic resistance of isolates and risk factors for infection

Salmonellae are wide spread in man and animals world wide and are of increasing significance as causative agents of foodborne diseases in man. The European Union, national authorities and the pig industry are therefore more and more interested in the Salmonella status of the pig population. The aim of this study was to estimate the bacteriological prevalence of Salmonella in finishing pig herds, the serogroup and the resistance to antibiotics of the isolated Salmonellae and a preliminary risk analysis of factors associated with infection. For this, 317 finishing pig herds were randomly selected from a database containing 1500 herds in the southern part of the Netherlands. In each herd 24 samples of fresh faeces were collected from two compartments with pigs close to market weight. Per compartment 12 samples of faeces were pooled into one pooled sample. Pooled samples were cultured in duplicate. Salmonella spp. were recovered from 71 out of 306 herds (23%) in which two compartments could be sampled. A total of 108 isolated Salmonella's were serotyped: 71 serogroup B, 3 serogroup C1, 6 serogroup C2, 22 serogroup D1, and 6 isolates neither serogroup B, C or D1. Of a total of 115 Salmonella isolates tested, none were resistant to colistin, enrofloxacin, flumequin or gentamicin. Automated liquid feeding of by-products, and membership of an Integrated Quality Control (IQC) production group were associated with a decreased risk of infection, while use of trough feeding was associated with an increased risk of infection. It is necessary to test these presumed risk factors in intervention studies to evaluate their potency to reduce the Salmonella prevalence in finishing pigs and thereby reduce the risk of Salmonellosis in people consuming pork.

Effect of hammer mill screen size and addition of fibre or S-methylmethionine-sulphonium chloride to the diet on the occurrence of oesophagogastric lesions in fattening pigs

Four groups of about 86 pigs from a common source were fed a grower diet from 25 kg to 45 kg liveweight, and then from 45 to 107 kg liveweight they were offered one of four diets ad libitum: A) normal commercial feed, ground through a 3 mm screen (the control diet), B) the same diet ground through a 6 mm screen, C) the control diet to which lucerne meal was added before the diet was ground to increase its crude fibre content, and D) the control diet to which was added 400 ppm S-methylmethionine-sulphonium chloride (MMSC). All the diets were pelleted. Approximately 21 per cent of the animals fed the control diet had severe oesophagogastric erosions and/or ulcers after slaughter. The addition of 400 ppm MMSC decreased (P = 0.066) the proportion of severe oesophagogastric erosions and/or ulcers by about 50 per cent compared with the control diet. The diet with the higher crude fibre content (but finely ground) did not have a significant effect on the proportion of severe oesophagogastric erosions and/or ulcers. There was a tendency for the pigs fed the diet ground through a 6 mm screen instead of a 3 mm screen, to have fewer severe oesophagogastric erosions and/or ulcers. However, there were only small differences between the particle size distribution obtained from the wet sieve analysis of the two diets. As a result, the observed tendency for a decrease in the proportion of severe oesophagogastric erosions and/or ulcers in pigs fed the diet milled through the larger screen size was of questionable significance.(ABSTRACT TRUNCATED AT 250 WORDS)

Prevalence and development of antibodies neutralizing the haemolysin and cytotoxin of Actinobacillus pleuropneumoniae in three infected pig herds

Sero-epidemiological studies were carried out in pigs aged 1 to 24 weeks in three herds in which Actinobacillus pleuropneumoniae was endemic. The sera were tested in the complement-fixation test and for their ability to neutralize the haemolytic and cytotoxic activities of the A. pleuropneumoniae serotypes isolated from the herds. Almost all (98%) sera from 1-week-old piglets neutralized the haemolytic and cytotoxic activities but only 21% fixed complement. At the end of the finishing period, most pigs (82%) had sera that neutralized haemolytic and cytotoxic activities and only 22% fixed complement. In longitudinal studies the neutralization titres decreased during the first 12-13 weeks of age. Thereafter, 75% of the pigs had increased titres in the haemolysin- and cytotoxin-neutralization tests and only 5% of the pigs had increased titres in the complement-fixation test. In none of these pigs were clinical signs of pleuropneumonia seen. Thus in these endemically infected herds the prevalence of complement-fixing antibodies was low, whereas the prevalence of neutralizing antibodies was high. The fact that serum-neutralizing titres are low in 12-week-old pigs might be the reason that pigs of this age are the most vulnerable to the disease.

An observational study into herd-level risk indicators of return to oestrus more than five days after insemination in sow herds

In a study population of 90 sow herds in the southern Netherlands, the occurrence of sows returning to oestrus more than five days after insemination (SRO) was investigated. In these herds information with regard to the herd system, herd size, and breeding management was recorded. The occurrence of SRO was recorded with the on-farm computer management system CBK-plus. The incidence of SRO was defined as the average number of gilts or sows returning to oestrus more than five days after insemination per 100 first inseminations. The average incidence of SRO in the study population was 18.3 per 100 first inseminations. Multivariate analysis resulted in a model with a significant effect of herd operation (herds with only sows had a lower incidence of SRO than herds with sows and finishing pigs), breeding strategy (herds with two or more inseminations per oestrus in a sow had a lower incidence of SRO than herds with one insemination per oestrus) and percentage of sows artificially inseminated (a higher percentage of artificial insemination was associated with a higher incidence of SRO).

Estimating sample sizes for a two-stage sampling survey of seroprevalence of pseudorabies virus (PRV)-infected swine at a regional level in The Netherlands

In the European Union, vaccination campaigns against Pseudorabies virus (PRV) in swine have been started to eradicate PRV. Specific sampling designs are needed to monitor PRV seroprevalence at a regional level. This paper demonstrates how sampling theory can be applied to design a disease seroprevalence survey, using PRV as an example. In the spring of 1994, the four regions in the Netherlands covered by the regional Animal Health Services were monitored with respect to PRV seroprevalence. Per region, blood samples from approximately 1400 herds, with two animals per herd, were collected. The sampling design accounted for stratification by fattening pig and sow population within each region. The regional PRV seroprevalence of swine in the Southern region was the highest (24.9%), closely followed by the PRV seroprevalence of swine in the Eastern region (20.5%). These regions have the highest density of swine in the Netherlands. The PRV seroprevalence in the Western and Central region (11.7%) was about half of the seroprevalence in the Southern and Eastern regions; the lowest regional PRV seroprevalence was observed in the Northern region (3.5%). The Northern part also has the lowest pig density. The PRV seroprevalence was approximately two times higher in sows than in fattening pigs.

Reduction of the prevalence of pseudorabies virus-infected breeding pigs by use of intensive regional vaccination

The influence of an intensive vaccination program on prevalence of pseudorabies virus (PRV)-infected breeding pigs was examined in a region where the disease was enzootic. In a 2-year period, significantly (P < 0.005) greater decrease in the prevalence of PRV-infected breeding pigs was observed in herds participating in the regional vaccination program and in herds outside the trial region that intensified PRV vaccination during the study than in herds that applied routine PRV control measures. In the regional vaccination program, introduction of breeding stock from outside the area was significantly (P < 0.05) associated with higher prevalence of PRV-infected pigs at the end of the study. These results indicate that transmission of PRV can be markedly reduced by use of an accurately applied intensive vaccination program.

Intensive regional vaccination with a gI-deleted vaccine markedly reduces pseudorabies virus infections

The development of marker vaccines against pseudorabies virus (PRV) and companion diagnostic tests have enabled us to perform a unique field trial. In this study, the effect of intensive regional vaccination on pig-finishing herd immunity was directly measured by comparing the seroprevalence of antibodies to glycoprotein I in trial and control groups. The seroprevalence of infected finishing herds in the trial region decreased from 81% at the start of the trial to 19% after 2 years (p < 0.001). The mean seroprevalence of infected pigs in these herds diminished from 49 to 5% (p < 0.001). In the control group, representing routine PRV control, no significant change in seroprevalences was noticed.

Spread of Aujeszky's disease virus within pig herds in an intensively vaccinated region

An intensive vaccination programme with the glycoprotein I (gI) and thymidine kinase-deleted vaccine strain 783 was applied on all the pig farms in a region with a high pig density. To monitor the spread of Aujeszky's disease virus within breeding herds in that region, all the breeding stock in nine herds were examined for antibodies to gI six times at intervals of four months. The prevalence of gI-seropositive sows decreased greatly in all nine herds. The mean percentage of gI-seropositive sows decreased from 56.4 per cent (range 80.0 to 13.6 per cent) at the start, to 20.3 per cent (range 29.1 to 1.6 per cent) after two years. Nevertheless, seroconversions to gI were detected in all the herds, and in six out of the nine breeding herds even during the second year of the study. The intensive regional vaccination apparently did not completely prevent Aujeszky's disease virus infections within these herds. The source of the virus responsible for these infections was not identified. However, because in most herds only a few sows seroconverted, the virus either circulated at a low level within the herds, or its introduction or reactivation did not lead to an extensive spread of the virus.

Prophylaxis of pleuropneumonia in pigs by in-feed medication with oxytetracycline and the subsequent transmission of infection

The prophylactic effect of in-feed medication with oxytetracycline was tested by using an Actinobacillus pleuropneumoniae aerosol challenge model. Groups of 10 conventional pigs were provided with feed containing 400, 800, 1200 or 1600 mg oxytetracycline/kg and fed ad libitum. After six days of medication the pigs were challenged and clinical signs were recorded. Two groups of four unmedicated pigs served as controls and were euthanased 36 to 48 hours after challenge and dissected. The feed medication was continued for nine days after the challenge, and the different treatment groups were then moved to separate accommodation where they were mixed with seronegative tracer pigs. The steady state concentrations of oxytetracycline in the pigs' serum after six days medication with feed containing 400, 800, 1200 or 1600 mg oxytetracycline/kg ranged from 0.07 to 0.13, 0.21 to 0.46, 0.27 to 0.46 and 0.35 to 0.56 microgram/ml, respectively. One of the eight unmedicated control pigs died, and the other seven showed signs of pleuropneumonia post mortem. Medication with feed containing 400 mg and 800 mg oxytetracycline/kg failed to prevent pleuropneumonia in the challenged pigs, and the mortality rates in these groups were two out of 10 and one out of nine pigs, respectively. All the pigs given feed containing 1200 and 1600 mg oxytetracycline/kg survived and only two of the pigs in the first treatment group showed mild clinical signs. No clinical signs were observed in the tracer pigs which were mixed with the pigs medicated with 400, 800 or 1200 mg oxytetracycline/kg.(ABSTRACT TRUNCATED AT 250 WORDS)

Variation in seropositivity for some respiratory disease agents in finishing pigs: epidemiological studies on some health parameters and farm and management conditions in the herds

The relationship between the extent of seropositivity for Aujeszky's disease virus (ADV), Actinobacillus pleuropneumoniae (App.) serotype 2 and porcine influenza (PI) viruses serotype H1N1 and H3N2 in pigs on the one hand and the health status of the pigs and some farm and management conditions in the herds on the other hand was studied in 45 pig finishing herds, all members of one integration group. The health status was assessed by the extent of clinical signs, the use of veterinary drugs and the prevalence of pathological lesions in pigs at slaughter. There was no relationship between the extent of seropositivity on the one hand and clinical signs and use of veterinary drugs on the other hand. However, there was a positive relationship between the extent of seropositivity and the percentage of pigs with lesions of the respiratory tract at slaughter. Furthermore, the study indicates that the variation in seropositivity between pigs herds is associated with management related factors that particularly influence the possibility of the spreading of viruses. A sero-epidemiological investigation in 14 pig herds with recurrent pneumonia problems revealed a high percentage of seropositive pigs per herd. Furthermore, in a large number of herds, pigs were simultaneously seropositive for ADV and App. serotype 2, for ADV and PI serotype H1N1 or for ADV and PI serotype H3N2.

Studies on the possibility of rearing seronegative animals within a breeding and rearing herd infected with Actinobacillus pleuropneumoniae serotype 2

In two sanitation trials it was not possible to rear seronegative animals within a breeding and rearing herd heavily infected with Actinobacillus pleuropneumoniae serotype 2. Neither medication with sulphonamides-trimethoprim of the sows and piglets or the sows alone nor a strictly applied all-in all-out system reduced the percentage of seropositive animals.

Sero-epidemiological screening of pig sera collected at the slaughterhouse to detect herds infected with Aujeszky's disease virus, porcine influenza virus and Actinobacillus (Haemophilus) pleuropneumoniae in the framework of an integrated quality control (IQC) system

Over a period of six months, approximately 4700 blood samples were collected from 97 pig-finishing farms in the provinces of Noord-Brabant and Gelderland and screened for antibodies with respect to Aujeszky's disease virus (ADV), porcine influenza virus (PI) and Actinobacillus (Haemophilus) pleuropneumoniae (App). There were significant differences in the percentages of seropositive pigs between the two provinces, which may be related to the difference in the density of the pig population in the two provinces. In practice, it was possible to perform a reliable sera collecting procedure at the slaughterhouse. No farms remained seronegative with respect to most of the disease agents during the sampling period. There was a high degree of variation in the percentages of seropositive pigs per farm as to most of the disease agents. Evidence was found that animals that were seropositive with respect to ADV were significantly more susceptible to becoming seropositive with respect to App. serotype 2, and vice versa. The same connection was observed for PI serotype H1N1 and PI serotype H3N2. Furthermore, evidence was found that pigs seropositive with respect to PI serotype H1Ni only, or to PI serotype H1N1 and ADV or PI serotype H3N2 show a significant decrease in average daily weight gain compared to pigs that were seronegative.

[Serological study of the presence of Actinobacillus pleuropneumoniae antibodies serotype 2 and 9 on pig-breeding farms in the provinces of North Brabant and Overijssel (The Netherlands)]

Serological studies for the presence of CFT antibodies to Actinobacillus pleuropneumoniae, both to serotype 2 and serotype 9, were done in twenty-five sows on each of thirty pig-breeding farms in the provinces of North Brabant and Overijssel. Antibodies to serotype 2 and/or serotype 9 were detected in one or several sows on forty-two out of sixty farms. Similar findings were recorded on eighteen and twenty-four farms respectively in the provinces of Overijssel and North Brabant; the number of herds showing positive reactions to serotype 2 was sixteen and twenty-three in these provinces respectively, that showing positive reactions to serotype 9 being six and five respectively. An average proportion of nineteen per cent of the samples taken on the farms having serologically positive animals was positive for serotype 2, and twelve per cent for serotype 9. Only one of the twenty-five animals on twelve farms was found to be positive; serotype 2 was present in ten cases and serotype 9 in two cases. A marked effect of the size of the herds on the serological status of the farms was not observed in the present studies. This was also true of the purchasing policy; there was no difference between farms which had no longer purchased any breeding pigs for an average period of seventeen years and for one year respectively. Clinical symptoms of an infection due to Actinobacillus pleuropneumoniae were only reported as occurring on two farms having serologically positive animals.

[Log book registration of farms for slaughtering pigs in the Integrated Quality Control Project. I. Use of drugs and vaccines]

Log book recording was done for twelve months on approximately 100 pig finishing farms in an Integrated Quality Control (IQC) project. This recording was designed to gain a better understanding of the extent and nature of the medication and vaccination on these farms. Vaccination against Aujeszky's disease was done on the majority of farms. This vaccination mainly consisted in a single, frequently intramuscular, injection. Vaccinations against swine influenza and infections due to Actinobacillus (Haemophilus) pleuropneumoniae were merely sporadic. The animals were dewormed in 58 per cent of the finishing periods, whereas they were given preventive treatment for sarcoptic mange in 23 per cent of the finishing periods. Not a single pig was treated with antibiotics and/or chemotherapeutic agents in 12.5 per cent of the finishing periods. The majority of finishing periods in which treatment was not carried out, were those having closed pig herds. To the extent that the farms were supplied with piglets by more breeders, there were fewer finishing periods during which treatment was omitted. The great majority of cases in which individual therapy was given, were treated for respiratory disorders. On 27 per cent of the farms, more than 10 per cent of the animals per finishing period were treated for respiratory disorders. Group medication was much less frequent: intestinal disorders did not have to be treated on 31 per cent of the farms, and 16 per cent did not require treatment for respiratory disorders. In the great majority of cases in which group treatment was required, this was given during the first sixty days of the finishing period. In view of the fact that there are marked differences in the degree to which pigs have to be medicated on the farms, recording the use of veterinary drugs on farms, could fulfil the function of a signal. On the basis of these signals, measures may be suggested in herd management programmes to ensure an effective and minimum use of veterinary drugs. Using a log book will also enable the pig farmer to estimate whether groups of animals may be sent to the slaughter-house without involving risks to public health.

[Study of the possibility of breeding serologically negative animals from a breeding farm infected with serotype 2 Actinobacillus pleuropneumoniae]

Two sanitation trials showed that it was possible to rear serologically negative animals from pigs on a breeding farm infected with Actinobacillus pleuropneumoniae serotype 2. This was achieved by the medication of sows and piglets during the farrowing-house period and by isolating the piglets from the infected stock of pigs immediately after weaning. Medication of the sows consisted in administering sulphamethoxazole-trimethoprim in the drinking water for a period from five days before to eight days after farrowing. The piglets were treated by injections of sulphadoxine-trimethoprim on days 3, 10, 17 and 24.

[Serologic studies on the presence of antibodies against Haemophilus (Actinobacillus) pleuropneumoniae at swine breeding farms in North Brabant]

Serological screening for the presence of antibodies to both H. pleuropneumoniae serotype 2 and serotype 9 using the complement fixation test was carried out on twenty-nine piglets production farms of an integrated group in the province of North Brabant. Antibodies to H. pleuropneumoniae serotype 2 and serotype 9 were not detected on six of the twenty-nine farms when a single screening was performed. The proportions of farms with animals serologically positive in regard to serotypes 2 and 9 were 59 and 34 per cent respectively. Of the specimens on farms with seropositive animals, those positive for serotype 2 averaged 13 per cent, those positive for antibodies to serotype 9 averaging 9 per cent. When a re-examination was made within two months after the first screening, animals showing antibodies to serotype 2 or serotype 9 were present on three of the six pig-breeding farms which were negative for these antibodies at first examination. When a third investigation was carried out within two months after the re-examination, antibodies to serotypes 2 or 9 were also detected on the remaining farms which were negative for antibodies in the two previous investigations.

[Serological studies on swine. Significance and interpretation of laboratory results for clinical practice]

Establishing a diagnosis in swine herds on the basis of previous histories, clinical symptoms and/or pathological lesions is becoming increasingly difficult for veterinarians. The services of a laboratory for performing serological examinations are therefore increasingly enlisted. Some aspects are described in the present paper, which are essential to an optimum serodiagnosis of Haemophilus pleuropneumoniae infections, Aujesky's disease, influenza and parvovirus infections.

Incidence, economic effects, and control of Haemophilus pleuropneumoniae infections in pigs

This thesis synopsis reports the results of investigations on: the incidence of clinical and subclinical H. pleuropneumoniae infections on pig farms in North Brabant; the economic loss on fattening farms; the effect of husbandry; the possibility of eradicating H. pleuropneumoniae on infected breeding farms on the basis of serological testing; the possibility of control on fattening farms by means of vaccination. The principal findings were as follows: Clinical and subclinical H. pleuropneumoniae infections are widespread on pig farms in North Brabant: The greatest economic loss was due to mortality and veterinary fees; the daily weight again was not found to be affected. The effect of husbandry. Less mortality occurred: on farms where the animals were not shifted during the fattening period; in compartments where the all-in all-out method was systematically used; in compartments with thermostatically controlled warming of the incoming air; in compartments meeting all standards of a good housing climate. Various sanitation measures on infected breeding farms were not successful. Only one experimental vaccine afforded good protection, but because of a high percentage of injection abscesses this vaccine was unsuitable for use in practice.

[Some aspects of the control of atrophic rhinitis (author's transl)]

The results obtained by a number of methods adopted in the control of atrophic rhinitis in herds in which this disease occurred, are reviewed. The long-term results may be described as disappointing. A number of possible causes of these disappointments are discussed.

[Scours in piglets during the first four weeks of life. Studies on the incidence and the effect of various features of management on the appearance of scours (author's transl)]

On 793 farms, studies were done on: --the incidence of scours on commercial farms. --The differences between groups of animals, such as the difference of age and the differences between litters of primiparae and multiparae. --Various features of herd management as factors in the incidence of scours, such as the size of the farm, the use of straw-bedding in the farrowing house, hygienic procedures, supplementary feeding and supply of drinking-water. Investigations were carried out during the periods of February and March 1975 and August and September 1975. The total number of litters of piglets taking part in the studies was 7,692. Some of the most important conclusions drawn from these studies were: --The incidence of scours was highest during the second week of life, namely in 34 per cent of the litters. --The litters of primiparae, scours was commoner than it was in litters of multiparae. This difference was most marked during the first week of life. --When straw-bedding was used in the farrowing houses, much fewer cases of scours were observed. --Supplementary feeding and supplying drinking water-during the first week of life resulted in a higher incidence of scours. --Hygienic procedures such as washing the sow and cleaning the farrowing house prior to farrowing reduced the proportion of litters showing scours.