Antibiotic resistance in porcine pathogenic bacteria and relation to antibiotic usage.

BACKGROUND: Optimal treatment and prudent use of antimicrobials for pigs is imperative to secure animal health and prevent development of critical resistance. An important step in this one-health context is to monitor resistance patterns of important animal pathogens. The aim of this study was to investigate the antimicrobial resistance patterns of five major pathogens in Danish pigs during a period from 2004 to 2017 and elucidate any developments or associations between resistance and usage of antibiotics. RESULTS: The minimum inhibitory concentration (MIC) for Escherichia coli, Actinobacillus pleuropneumoniae, Streptococcus suis, Bordetella bronchiseptica, and Staphylococcus hyicus was determined to representatives of antibiotic classes relevant for treatment or surveillance. Escherichia coli isolates were mostly sensitive to fluoroquinolones and colistin, whereas high levels of resistance were observed to ampicillin, spectinomycin, streptomycin, sulfonamides and tetracycline. While resistance levels to most compounds remained relatively stable during the period, resistance to florfenicol increased from 2.1% in 2004 to 18.1% in 2017, likely in response to a concurrent increase in usage. A temporal association between resistance and usage was also observed for neomycin. E. coli serovars O138 and O149 were generally more resistant than O139. For A. pleuropneumoniae, the resistance pattern was homogenous and predictable throughout the study period, displaying high MIC values only to erythromycin whereas almost all isolates were susceptible to all other compounds. Most S. suis isolates were sensitive to penicillin whereas high resistance levels to erythromycin and tetracycline were recorded, and resistance to erythromycin and trimethoprim increasing over time. For S. hyicus, sensitivity to the majority of the antimicrobials tested was observed. However, penicillin resistance was recorded in 69.4-88.9% of the isolates. All B. bronchiseptica isolates were resistant to ampicillin, whereas all but two isolates were sensitive to florfenicol. The data obtained have served as background for a recent formulation of evidence-based treatment guidelines for pigs. CONCLUSIONS: Antibiotic resistance varied for some pathogens over time and in response to usage. Resistance to critically important compounds was low. The results emphasize the need for continuous surveillance of resistance patterns also in pig pathogenic bacteria.

No evidence of enteric viral involvement in the new neonatal porcine diarrhoea syndrome in Danish pigs.

BACKGROUND: The aim of this study was to investigate whether the syndrome New Neonatal Porcine Diarrhoea Syndrome (NNPDS) is associated with a viral aetiology. Four well-managed herds experiencing neonatal diarrhoea and suspected to be affected by NNPDS were included in a case-control set up. A total of 989 piglets were clinically examined on a daily basis. Samples from diarrhoeic and non-diarrhoeic piglets at the age of three to seven days were selected for extensive virological examination using specific real time polymerase chain reactions (qPCRs) and general virus detection methods. RESULTS: A total of 91.7% of the animals tested positive by reverse transcription qPCR (RT-qPCR) for porcine kobuvirus 1 (PKV-1) while 9% and 3% were found to be positive for rotavirus A and porcine teschovirus (PTV), respectively. The overall prevalence of porcine astrovirus (PAstV) was 75% with 69.8% of the PAstV positive pigs infected with PAstV type 3. No animals tested positive for rotavirus C, coronavirus (TGEV, PEDV and PRCV), sapovirus, enterovirus, parechovirus, saffoldvirus, cosavirus, klassevirus or porcine circovirus type 2 (PCV2). Microarray analyses performed on a total of 18 animals were all negative, as were eight animals examined by Transmission Electron Microscopy (TEM). Using Next Generation de novo sequencing (de novo NGS) on pools of samples from case animals within all herds, PKV-1 was detected in four herds and rotavirus A, rotavirus C and PTV were detected in one herd each. CONCLUSIONS: Our detailed analyses of piglets from NNPDS-affected herds demonstrated that viruses did not pose a significant contribution to NNPDS. However, further investigations are needed to investigate if a systemic virus infection plays a role in the pathogenesis of NNPDS.

Postweaning multisystemic wasting syndrome in Danish pig herds: productivity, clinical signs and pathology.

A case-control study of 74 herds with postweaning multisystemic wasting syndrome (pmws) and 74 matched control herds was carried out. In the case herds the mortality rates of weaner and finisher pigs were 11.2 and 5.2 per cent respectively, compared with 3.1 and 3.2 per cent in the control herds. In most case herds, pmws developed within the first four weeks after weaning. Wasting, diarrhoea and respiratory signs were observed in 10 per cent of the weaner pigs (7 to 30 kg) in the case herds compared with 7 per cent in the control herds. The average daily gains of the weaner pigs and finisher pigs were 36 g and 52 g less in the case herds than in the control herds. By examining three weaner pigs from each herd the pmws diagnosis was confirmed by histopathology and immunohistochemistry in 78 per cent of the case herds, but at least one pmws-positive weaner pig was found in 19 of the control herds. The prevalence of pmws-positive pigs among illthriven weaner pigs was 45 per cent (101/222) in the case herds, and 12 per cent (27/222) in the control herds. Specific gross pathological findings were associated with a positive pmws diagnosis; pigs with heavy, rubber-like lungs, atonic intestines, and enlarged bronchial and inguinal lymph nodes, had a 0.7 probability of a positive pmws diagnosis by laboratory examinations. However, for illthriven pigs, this probability of having pmws was equal in the case herds and the control herds.

Comparison of bacterial culture and qPCR testing of rectal and pen floor samples as diagnostic approaches to detect enterotoxic Escherichia coli in nursery pigs.

Enterotoxigenic E. coli (ETEC) are a major cause of diarrhoea in weaned pigs. The objective of this study was to evaluate the agreement at pen level among three different diagnostic approaches for the detection of ETEC in groups of nursery pigs with diarrhoea. The diagnostic approaches used were: bacterial culturing of faecal samples from three pigs (per pen) with clinical diarrhoea and subsequent testing for virulence genes in E. coli isolates; bacterial culturing of pen floor samples and subsequent testing for virulence genes in E. coli isolates; qPCR testing of pen floor samples in order to determine the quantity of F18 and F4 genes. The study was carried out in three Danish pig herds and included 31 pens with a pen-level diarrhoea prevalence of > 25%, as well as samples from 93 diarrhoeic nursery pigs from these pens. All E. coli isolates were analysed by PCR and classified as ETEC when genes for one or more adhesin factors and one or more enterotoxins were detected. RESULTS: A total of 208 E. coli colonies from pig samples and 172 E. coli colonies from pen floor samples were isolated. Haemolytic activity was detected on blood agar plates in 111 (29.2%) of the 380 colonies that were isolated. The only adhesin factor detected in this study was F18. When comparing bacterial culture or qPCR testing of pen floor samples with detection of ETEC-positive diarrhoeic pigs by culture, agreement was found in 26 (83.9%, Kappa = 0.665) and 23 (74.2%, Kappa = 0.488) of the pens, respectively. Agreement was observed between the detection of ETEC by bacterial culture and qPCR in the same pen floor sample in 26 (83.9%, Kappa = 0.679) pens. CONCLUSION: We observed an acceptable agreement for the detection of ETEC-positive diarrhoeic nursery pigs in pen samples for both bacterial culture of pen floor samples and qPCR. This study showed that both bacterial culture and qPCR testing of pen floor samples can be used as a diagnostic approach for detecting groups of ETEC-positive diarrhoeic nursery pigs.

Association of Serpulina hyodysenteriae with the colonic mucosa in experimental swine dysentery studied by fluorescent in situ hybridization.

The localization of Serpulina hyodysenteriae in experimental swine dysentery was studied by fluorescent in situ hybridization (FISH) using an oligonucleotide probe targeting the 23S rRNA of S. hyodysenteriae. Nine 8-week-old pigs were challenged. Seven of the pigs were intragastrically dosed with 1 x 10(9) cfu S. hyodysenteriae for 3 consecutive days, whereas two pigs were infected by contact. Six non-challenged pigs served as negative controls. The challenged pigs developed clinical swine dysentery from 8 to 14 days postinfection with typical gross lesions. By FISH S. hyodysenteriae cells in huge numbers were found colonizing the mucus layer, the luminal epithelium and the crypts of the large intestinal mucosa. The orientation of the spirochaetes to the epithelium appeared to be random. Spirochaetes in clusters or as single cells were invading the epithelium and were occasionally detected in the adjacent lamina propria. The distribution of spirochaetes in the mucosa provides further evidence that S. hyodysenteriae is intimately associated with the mucus layer and the epithelium in a random pattern. Furthermore, the results demonstrate the applicability of FISH for specific detection of S. hyodysenteriae cells in clusters or as single cells in formalin-fixed tissue samples.

Identification of porcine Pneumocystis carinii as a genetically distinct organism by DNA amplification.

DNA was amplified from lung samples from three piglets infected with Pneumocystis carinii, using oligonucleotide primers designed to the P. carinii mitochondrial large subunit ribosomal RNA gene. The nucleotide sequence of the amplification product was determined and indicated lack of sequence variation among these pig-derived P. carinii samples at this locus. The data showed that porcine P. carinii was genetically distinct from P. carinii isolated from other mammalian host species.

Serological characterization and antimicrobial susceptibility of Streptococcus suis isolates from diagnostic samples in Denmark during 1995 and 1996.

At the Danish Veterinary Laboratory Streptococcus suis infections in pigs were diagnosed in 114 cases in 1995 and in 151 cases in 1996. Isolates were serotyped using specific antisera against type 1 through 28 and a total of 67 cases from 1995 and 113 cases in 1996 were tested for resistance to 11 antimicrobial agents. The majority of cases were lung diseases (57%), followed by septicaemia (16%), meningitis (15%) and endocarditis (8%). Almost 96% of the isolates could be typed using the 28 antisera. The most common serotype was serotype 2 (29%), followed by serotype 7 (17%), and serotypes 3, 4 and 8 (9-10%). The remaining serotypes were observed in frequencies of less than 5%. Serotype 7 was more commonly isolated from septicaemia than the other serotypes. Serotype 2 was more commonly isolated from pigs older than 4 weeks compared to the other serotypes. Most isolates were susceptible to amoxycillin + clavulanate, ampicillin, ceftiofur, enrofloxacin, penicillin, spectinomycin, tiamulin and trimethoprim + sulphadiazine. A high frequency (> 30%) of resistance to tetracycline was observed. Among isolates of serotype 2, 9.7% were resistant to lincomycin and 12.9% to spiramycin. Among other serotypes 56.8% were resistant to lincomycin and spiramycin. The differences in susceptibility between isolates of serotype 2 and the other serotypes were statistically significant. Compared to a previous Danish study the distribution of serotypes of S. suis causing infections among pigs in Denmark has changed during the last 15 years.

Infection dynamics of Lawsonia intracellularis in pig herds.

Little information is known about the natural course and within-herd prevalence of porcine proliferative enteropathy caused by Lawsonia intracellularis. The objective of the study was to investigate the within-herd dynamics of naturally acquired L. intracellularis infection in pigs from weaning to slaughter. The study was designed as a longitudinal survey where 100 pigs from five herds were randomly selected at weaning (approximately 4 weeks of age). Every second week until slaughter (10-12 times, i.e. 20-24 weeks) the pigs were weighed and faecal as well as blood samples were collected. Faecal shedding of L. intracellularis was assessed by real time-PCR and sero-conversion by an indirect immunofluorescence antibody test (IFAT). Clinical disease was not reported but infection was present in all herds and the PCR assay indicated infection in 75% of pigs examined. Most L. intracellularis infected pigs were shedding at 10-12 weeks of age (22-29 kg) and shed for 2-6 successive weeks. After 18 weeks of age all shedding had ceased and re-infection at PCR detectable level was not seen. Variable L. intracellularis associated impact on growth rate was observed. Immediately before bacterial shedding and during early infection the average growth rate declined whereas a compensatory impact was observed during later infection and after bacterial shedding had ceased. The performance of the IFAT resembled the bacteriological test almost perfectly. Sero-conversion was first detected at 12-14 weeks of age. Relative to the bacterial shedding, the onset of sero-conversion was a little delayed, in general, most pigs had sero-converted 2 weeks after the first shedding. Once sero-converted, 92% of the pigs remained sero-positive over the entire survey period.

Experimental airborne transmission of PRRS virus.

A series of three experiments, differing primarily in airflow volume, were performed to evaluate the likelihood of airborne transmission of Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) from infected to non-infected pigs. Pigs were housed in two units (unit A and unit B) located 1m apart and connected by pipes. The air pressure and diameter of the pipes, depending on experiments, were strictly controlled to allow desired airflow volumes from unit A to unit B. Either 25 (experiment 1 and experiment 3) or 26 (experiment 2) pigs infected recently with PRRSV, and either 25 (experiment 1 and experiment 3) or 17 (experiment 2) pigs from a PRRSV-free herd, were housed in unit A. Either 50 pigs (experiment 1 and experiment 3) or 43 pigs (experiment 2) from a PRRSV-free herd were housed in unit B. The amount of air transmitted from unit A to unit B, expressed as a percentage of ventilation intake, was approximately 70, 10, and 1% for experiment 1, experiment 2 and experiment 3, respectively. Blood samples were collected from all pigs once per week and analyzed for antibodies against PRRSV. Based on these methods, airborne transmission of PRRSV from infected to non-infected pigs was confirmed in each of the three experiments.

Demonstration of airborne transmission of Actinobacillus pleuropneumoniae serotype 2 between simulated pig units located at close range.

Airborne transmission of Actinobacillus pleuropneumoniae was studied as the percentage of air needed to establish airborne transmission from an infected pig unit into a neighbouring non-infected pig unit. The experiment was carried out in two containers constructed as pig units, placed 1m apart and connected by pipes. By manipulating the air pressure in the two units, the amount of ventilation air transferred from the infected pigs (unit A) to the non-infected pigs (unit B) was controlled and measured. In three experiments, between 48 and 50 specific pathogen free-pigs were randomly assigned to each of the two units. In unit A, five pigs (experiment 1) or eight pigs (experiments 2 and 3) were inoculated with A. pleuropneumoniae serotype 2. In experiments 1 and 3, 10% of the air was transferred from unit A to B; in experiment 2, 70% of the air was transferred. In the non-infected unit (B), 36% of the pigs seroconverted during experiment 2 (70% air transfer), whereas none of the pigs seroconverted in experiments 1 and 3 (10% air transfer). As air transmission between closely located pig units has been estimated to be less than 2% under field conditions, these results indicate that airborne transmission of A. pleuropneumoniae serotype 2 between closely located pig units is rare.

Detection of Lawsonia intracellularis, Serpulina hyodysenteriae, weakly beta-haemolytic intestinal spirochaetes, Salmonella enterica, and haemolytic Escherichia coli from swine herds with and without diarrhoea among growing pigs.

A polymerase chain reaction (PCR) was optimized to detect Lawsonia intracellularis in faeces from naturally infected pigs. By combining a boiling procedure to extract DNA and a nested PCR procedure, a detection limit at 2 x 10(2) bacterial cells per gram of faeces was achieved. The optimized PCR was used together with conventional culture techniques to detect Serpulina hyodysenteriae, weakly beta-haemolytic intestinal spirochaetes (WBHIS), Salmonella enterica, and haemolytic Escherichia coli, in a case control study to examine selected risk factors for the development of diarrhoea in growing pigs. Herds with diarrhoea were selected as cases and randomly chosen herds without diarrhoea were chosen as controls. Infection with L. intracellularis significantly enhanced the chance of diarrhoea. S. hyodysenteriae, WBHIS group IV (Serpulina pilosicoli), and S. enterica were isolated only from case herds which indicate that these species may influence the development of diarrhoea. In addition, herd-type had a significant impact, that is specific pathogen-free herds showed an odds ratio at 0.2 relative to conventional herds for the development of diarrhoea.

Serological characterization of Actinobacillus pleuropneumoniae biotype 2 strains isolated from pigs in two Danish herds.

Eight Actinobacillus pleuropneumoniae biotype 2 strains were isolated in pure culture from lungs of pigs originating from two Danish herds with growing and finishing pigs. The antigenic properties were studied by indirect haemagglutination (IHA) and immunodiffusion (ID) tests using soluble surface antigens and by enzyme-linked immunosorbent assays (ELISA) using capsular enriched fractions and LPS. In all tests the strains proved antigenically homogeneous and serologically distinct from the known biotype 1 and 2 serotypes. Thus, the strains represent a new serotype which is provisionally proposed as biotype 2 serotype 14.

Prevalence of helminth infections in swine in Denmark.

During 1982-1984 the occurrence of helminths in 66 sow herds was determined by examining faecal samples from swine of different age groups. Ascaris suum was found in 88% of the herds, while Oesophagostomum spp. and Trichuris suis were found in 58 and 23% of the herds, respectively. Strongyloides ransomi and Hyostrongylus rubidus was not identified in any of the herds. The occurrence of both A. suum and Oesophagostomum spp. was strongly related to the age of the animals. A. suum was most frequently found in growing pigs (30% of the fatteners and 25% of the gilts), whereas only 11-19% of the animals of the adult stock were excreting eggs. In contrast the prevalence of Oesophagostomum spp. increased with the age of the hosts, from 10% of the fatteners to 35 and 44% of the sows and boars, respectively. T. suis occurred only very sporadically, with the highest prevalence being 3% in the gilts. In comparison to previous Danish surveys the present mean prevalences of A. suum and Oesophagostomum spp. were low. Extremely low herd prevalences were found among large herds with intensive management and housing. In these herds, the pigs were infected at a later stage in life than pigs in more traditionally managed herds.

Relationship of the prevalence of swine helminths to management practices and anthelmintic treatment in Danish sow herds.

During 1982-1984, the occurrence of helminths in 66 sow herds in Denmark was examined by means of faecal samples. The correlations between the prevalences of Ascaris suum and Oesophagostomum spp. and management practices were analysed for fatteners and sows, respectively, resulting in four multivariate models. The helminth prevalences were in general low in large herds, specific pathogen-free (SPF) herds and herds with low weaning age. The multivariate analyses showed that only the two latter correlations were significant. The helminth prevalences of the fatteners were not correlated with anthelmintic treatment. In the sows, anthelmintic treatment was significantly correlated with low prevalences of both helminths, despite samples from recently dewormed sows indicating a rather transitory effect. The prevalences of Oesophagostomum in both fatteners and sows were significantly higher on solid floors with straw bedding than on slatted floors without straw, while this was not the case for Ascaris. Tethering of sows was not significantly correlated with helminth prevalences. Daily cleaning was significantly correlated with low helminth prevalences in fatteners, but not in the sows, while disinfection of the pens was only significantly correlated with low prevalences of Oesophagostomum in fatteners. No correlations to washing of the pens were found. The epidemiology of Ascaris and Oesophagostomum is discussed, especially why the latter is the most sensitive to intensive management.

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 30-50kg. 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.

Risk factors for intestinal pathogens in Danish finishing pig herds.

The objective of this investigation was to identify risk factors for infection with the intestinal bacteria: Lawsonia intracellularis, Brachyspira hyodysenteriae, Serpulina intermedia, Brachyspira innocens, Brachyspira pilosicoli and swine-pathogenic Escherichia coli (serogroups O138, O139, O141 and O149) 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. In total, 1580 faecal samples were collected and examined by polymerase chain reaction (L. intracellularis) or culture (all other agents). Information on feed and management procedures was collected by filling in questionnaires at the herd visits. The questionnaires included information on 29 dichotomous variables and three continuous variables. Variables with P<0.25 in a preliminary screening (chi2- or t-test) were selected for the statistical modelling. Our conclusions, based on the results of multifactorial logistic regression (cut-off: P=0.05), were the following: 1. Consistent batch production was associated with reduced prevalences of L. intracellularis and weakly -haemolytic spirochetes (S. intermedia, B. innocens, B. pilosicoli) (OR's=0.43 and 0.06, respectively). 2. Home-mixed (and/or non-pelleted) feed was associated with reduced prevalences of L. intracellularis and weakly -haemolytic spirochetes (OR's=0.6 and 0.4, respectively). 3. Providing straw to finishers was associated with a reduced prevalence of weakly -haemolytic spirochetes (OR=0.28-0.32). 4. Not using antimicrobial growth promoters for piglets was associated with an increased prevalence of S. intermedia (OR=11.11). 5. Rare occurrence of post-weaning diarrhoea (as opposed to common) was associated with an increased prevalence of weakly -haemolytic spirochetes (OR=8.3-13.7).

Detection of Lawsonia intracellularis in the tonsils of pigs with proliferative enteropathy.

The presence of Lawsonia intracellularis, the obligate intracellular bacterium causing proliferative enteropathy (PE), in the tonsils of pigs as a locus for infection or extraintestinal occurrence of the bacterium was investigated by PCR and immunohistochemistry. Tonsillar occurrence of L. intracellularis could be part of the pathogenesis of PE and an important risk factor in the spread of the disease. L. intracellularis was detected by only PCR in the tonsils of 2/32 pigs without PE at necropsy but with a clinical history of diarrhoea and detection of the bacterium in faeces 1 to 3 weeks prior to necropsy but not in four pigs with moderate PE lesions. However, L. intracellularis was detected in the tonsils of 4/9 pigs with PE complicated with necroses and in 4/4 pigs with proliferative haemorrhagic enteropathy in which L. intracellularis antigen also was demonstrated in tonsillar macrophages and as intact bacteria in the lumen of the crypts. The results show that L. intracellularis is detectable in the tonsils of pigs and that the tonsillar presence of L. intracellularis appears to be correlated to the severity of the intestinal lesions possibly as a result of local retention and not as part of the pathogenesis of PE.

Prevention of edema disease in pigs by vaccination with verotoxin 2e toxoid.

Pigs in 2 herds with persistent problems with post weaning edema disease caused by infection with verotoxin-2e (VT2e)-producing Escherichia coli O139 were treated with a VT2e-toxoid vaccine. Treatment was performed as a randomized blind field trial with parallel treatment and non-vaccinated control groups. In 1 herd, a group of pigs was injected with adjuvant alone. Pigs were vaccinated at 1 and 3 wk of age and weaned at 4 wk of age. The effect of vaccination was measured by average daily weight gain (ADG), mortality due to edema disease within the 1st 4 wk after weaning, and weight at 3-6 mo of age. Pathological and microbiological examinations were performed on all pigs that died during the 1st 4 wk post weaning. Only pigs from which VT2e+, F18+ E. coli O139 was isolated were categorized as "death due to edema disease." The serological response to vaccination was evaluated by an indirect ELISA. Vaccination had a statistically significant effect on the level of antibodies specific for VT2e in both herds. Vaccination resulted in a statistically significant increase in ADG in the nursery period but not in the grower-finishing period. Vaccination had a statistically significant effect on mortality due to edema disease with an odds ratio of 0.039, indicating that there was almost total elimination of mortality due to the disease in the vaccine groups.

Prevention of edema disease in pigs by passive immunization.

The effect of treatment with verotoxin 2e (VT2e) specific antiserum was evaluated in 3 Danish pig herds with edema disease (ED). The antiserum was prepared by immunizing horses with a VT2e toxoid. The study was performed as a randomized blind field trial with parallel treatment and control groups. There were approximately 50 piglets in each group in each of the 3 herds and 741 piglets were included in the study (244 from herd A, 249 from herd B, and 247 from herd C). Treatment groups received 2, 4, or 6 mL anti-VT2e serum intramuscularly the day before weaning. Control groups were treated with 6 mL normal horse serum or 6 mL RPMI 1640 medium as placebo. All pigs that died in the trial period (1 d before weaning to 44 d after weaning) were examined pathologically and microbiologically. Mortality due to ED, mortality due to other causes, and adverse effects due to treatment were recorded. As there was no mortality due to ED, herd B was excluded from statistical calculations on mortality. The content of horse antibodies specific to VT2e in serum from pigs was analyzed in an indirect ELISA. A higher dose of anti-VT2e serum was reflected in higher optical density values in the indirect ELISA. Transient adverse reactions, seen as vomiting, ataxia, and cyanosis, occurred shortly after the injection of horse serum in 1.5% of the pigs, and one pig died. There were no statistically significant differences in mortality due to other causes among the 3 treatment groups in herds A and C. Only pigs from which F18+, VT2e+, ST-, LT- hemolytic E. coli (0139 or O-rough) was isolated were diagnosed as dead due to ED. Deaths due to ED in the control groups were 8.1% and 12.0% in herds A and C, respectively, compared with 0% and 0.7% in the corresponding serum groups. The difference between treatment and control groups was statistically significant (P<0.0001). It was not possible to establish an effect of dose (2, 4, or 6 mL) of anti-VT2e serum, because only one pig died of ED in the treatment groups. It was concluded that passive immunization by intramuscular injection of a VT2e-specific antiserum can be used for protecting piglets against ED.

Protection against progressive atrophic rhinitis by vaccination with Pasteurella multocida toxin purified by monoclonal antibodies.

Pasteurella multocida toxin was purified by affinity chromatography and inactivated by treatment with formaldehyde before use as a single component vaccine against progressive atrophic rhinitis in pigs. Twenty pregnant gilts which were vaccinated twice before farrowing with either low or high doses of the purified toxoid, developed dose-dependent positive serum and colostrum titres to the toxin and, unlike the progeny of 10 untreated control gilts, the offspring of the vaccinated gilts also had serum titres. These titres could be measured in blood samples taken for more than eight weeks from birth for most pigs born to gilts vaccinated with low doses and more than 12 weeks for pigs born to gilts vaccinated with high doses of the vaccine. All the piglets were inoculated intranasally with Bordetella bronchiseptica and toxigenic P multocida. The clinical and post mortem examinations of snouts revealed a significant reduction in the frequency and degree of conchal atrophy in the two groups of pigs from the vaccinated gilts compared with the pigs from control gilts. Clinically 90 per cent of the snouts of pigs born to vaccinated gilts appeared normal whereas only 28 per cent of the snouts of control pigs were not shortened or deviated at eight weeks of age. At slaughter 11 per cent of the pigs born to vaccinated gilts and 81 per cent of the control pigs had severe turbinate atrophy.(ABSTRACT TRUNCATED AT 250 WORDS)