Detection and distribution of toxigenic Pasteurella multocida in pig herds with different degrees of atrophic rhinitis

Four herds of pigs were selected which had different degrees of clinical atrophic rhinitis and used different specific counter-measures. In two of them, the clinical signs occurred spasmodically and were slight. The sows, suckling pigs and growing pigs in all the herds were sampled for toxigenic Pasteurella multocida. In one of the slightly affected herds (herd D), the weaners were moved to a second farm for finishing. No toxigenic P multocida were found at the breeding farm, but 50 per cent of the large growing pigs were positive. It seemed that the organism had entered only at the finishing farm and that the mild clinical signs were due to the infection starting in older pigs than usual. In the second mildly affected herd, 47 per cent of the sows and 42 per cent of the growers were infected. Three toxigenic isolates from this herd produced as severe turbinate damage experimentally in specific-pathogen-free pigs as a stock pathogenic strain. Except in herd D, toxigenic P multocida were found in all the age groups of pigs sampled. However, the pattern of distribution of the organism within the herds was not obviously correlated with the severity of the disease. In a fifth herd there were obvious cases of clinical atrophic rhinitis, with marked turbinate atrophy, from which toxi-genic P multocida were recovered in abundance. Subsequently, the clinical disease disappeared and, despite extensive and repeated sampling, the organism was not found again.     

Comparison of methods for the sampling and isolation of toxigenic Pasteurella multocida from the nasal cavity of pigs

The efficacy of detecting toxigenic Pasteurella multocida from nasal swabs of slaughtered and live pigs was assessed. The isolation of toxigenic P multocida from nasal cavities of slaughtered bacon pigs from two herds with atrophic rhinitis was reduced by immersion in the hot water tank by 25 per cent and 75 per cent. Individual sows from one of the infected herds were repeatedly swabbed to find the best method of isolating toxigenic P multocida. Toxigenic P multocida were isolated from 50 per cent of cotton swabs inoculated on to selective medium the same day. After 24 hours in the post, 45 per cent of cotton swabs placed in transport medium, 38 per cent of alginate swabs dissolved in transport medium and inoculated into mice, and 36 per cent of the dissolved swabs inoculated directly on to selective medium yielded toxigenic P multocida. These bacteria were isolated from only 25 per cent of cotton swabs held in transport medium at 10 degrees C for 48 hours to simulate prolonged postage times; from slaughtered pigs a similar reduction in isolation was seen with swabs kept for 24 or 48 hours. The reduced isolation caused by a delay before culture was associated with an overgrowth of other flora. The development of this flora was prevented by storage of swabs at 4 degrees C in the laboratory or by the use of cool boxes for postage.     

Interactions between Bordetella bronchiseptica and toxigenic Pasteurella multocida in atrophic rhinitis of pigs

Three strains of Bordetella bronchiseptica were compared for their ability to assist colonisation of the nasal cavity of gnotobiotic pigs by toxigenic Pasteurella multocida. Toxigenic P multocida (counted in nasal washings) colonised the cavity in large numbers in pigs previously infected with a cytotoxic phase I strain of B bronchiseptica (B58), whereas it colonised only in small numbers in those previously infected with B65, a phenotypic phase III variant of B58. Toxigenic P multocida colonised pigs infected with a non-cytotoxic phase I strain of B bronchiseptica (PV6) in fewer numbers than were seen in pigs infected with the cytotoxic phase I strain but in greater numbers than in pigs infected with the phase III strain. The turbinates of pigs infected with the cytotoxic phase I strain of B bronchiseptica and toxigenic P multocida were most severely affected and those in pigs infected with the non-cytotoxic phase I strain and toxigenic P multocida were moderately reduced in size. The turbinates of pigs infected with the phase III strain and toxigenic P multocida were slightly reduced in size except for one piglet whose turbinates were severely affected. Pigs infected with the non-cytotoxic phase I strain of B bronchiseptica alone showed no signs of atrophy and their turbinates were used to calculate reductions (per cent) in those infected with P multocida. The reduction (per cent) in size of turbinates and total numbers of P multocida isolated from the nasal washings of each pig were linearly related.(ABSTRACT TRUNCATED AT 250 WORDS)     

Identification of toxigenic Pasteurella multocida in atrophic rhinitis of pigs by in vitro characterisation

Toxigenic strains of Pasteurella multocida were readily differentiated from non-toxigenic strains by an agarose overlay method using bovine turbinate cells or bovine lung cells. Cells which were young and densely confluent were best suited to this assay. The incubation period required to distinguish toxigenic strains was dependent on the confluence of the monolayers, which was affected by the seeding rate, cell passage level and growth time prior to overlay. The agarose overlay method correctly identified 11 of 11 reference strains of Pasteurella multocida, and visible cytotoxic changes were present in the monolayers after 48 to 65 h. Outbreaks of the enzootic form of atrophic rhinitis in 2 New South Wales piggeries were associated with the isolation of toxigenic type D strains of P. multocida.     

Epidemiology of Pasteurella multocida in a farrow-to-finish swine herd.

Thirty-eight clinical isolates of Pasteurella multocida, recovered from a continuous flow, farrow-to-finish swine herd, were characterized by capsular serotyping and restriction endonuclease analysis (REA) in order to study the epidemiology of P. multocida pneumonia. Twenty-three of the 38 isolates obtained in the study belonged to serotype A. They displayed three REA patterns after digestion with HpaII, of which one designated A-3 represented 70% of the samples. The remaining 15 isolates were serotype D. Four different REA patterns were observed in the type D isolates. The REA type D-1 was most prevalent and accounted for 47% of the serotype D isolates. All serotype A isolates were nontoxigenic, whereas five (33%) of the serotype D isolates were toxigenic. Vertical transmission of P. multocida could not be demonstrated, and was probably not a major route of infection. The results of this study suggest that strains of P. multocida virulent for pigs exist and cause swine pneumonic pasteurellosis in continuous flow herds by horizontal transmission.     

Development of turbinate lesions and nasal colonization by Bordetella bronchiseptica and Pasteurella multocida during long-term exposure of healthy pigs to pigs affected by atrophic rhinitis.

Natural transmission of atrophic rhinitis from pigs from a herd with an endemic atrophic rhinitis problem to pigs from a herd free of atrophic rhinitis was demonstrated. Six replicates each with five pigs from the endemic atrophic rhinitis herd (Group A) and five pigs from the atrophic rhinitis-free herd (Group B) were housed together from 5 wk of age, with each replicate kept in isolation rooms maintained at optimal and controlled environmental conditions. Three replicates each with six pigs/room from the atrophic rhinitis-free herd (Group C), served as nonexposed controls. Group C pigs remained healthy and had no turbinate atrophy at either 10 or 17 wk of study (atrophic rhinitis score = 0 on a 0 to 3 scale). Group A pigs had a mean atrophic rhinitis score of 1.85 +/- 0.84, and group B pigs developed atrophic rhinitis to a mean score of 1.57 +/- 0.70. The isolation rate and quantity of Pasteurella multocida found on nasal swabs was directly related to lesions while those for Bordetella bronchiseptica were inversely related to turbinate atrophy. Of the various types of P. multocida evaluated, nontoxigenic type A and toxigenic type D were both directly related to atrophic rhinitis while nontoxigenic type D strains were not. No toxigenic type A P. multocida strains were isolated.     

Detection of neutralizing antibodies against Pasteurella multocida toxin in swine with atrophic rhinitis

Blood sera of 1171 pigs, not vaccinated against PAR, were tested for antibodies against P. multocida toxin in a neutralization test with EBL cell cultures. 277 sera were from 18 herds with clinical PAR; 104 of them (37.5%) had neutralizing antibody titres from 1:2 to 1:1024. No antitoxin was detected in the sera of 866 pigs in 25 PAR nonsuspicious herds. In one nonsuspicious herd, however, 11 of 28 sera were neutralizing in the 1:2 or 1:4 dilution. 30 sows had been vaccinated with inactivated toxigenic P. multocida and/or with the P. multocida toxoid. 21 of these sows had neutralizing sera with titres between 1:8 and 1:4096. The neutralization test presented can be applied for herd diagnosis of PAR and for demonstration of vaccination effects.     

Bordetella bronchiseptica and toxigenic type D Pasteurella multocida as agents of severe atrophic rhinitis of swine

Bordetella bronchiseptica and toxigenic type-D Pasteurella multocida were cultured from pigs in each of five herds diagnosed as having severe atrophic rhinitis (AR). B. bronchiseptica alone, P. multocida alone, or both organisms isolated from four herds were inoculated intranasally into 1-week-old gnotobiotic pigs which were necropsied 4 weeks post-inoculation (PI). Nasal turbinate atrophy in B. bronchiseptica-inoculated pigs was moderate to severe, while P. multocida-inoculated pigs had slight to severe atrophy. Pigs inoculated with both organisms had moderate to complete turbinate atrophy. P. multocida was reisolated at necropsy from all pigs receiving the organism except those having no turbinate damage. B. bronchiseptica and P. multocida from a fifth herd were simultaneously inoculated into six naturally farrowed 6-day-old SPF pigs. Necropsy performed 4 weeks PI revealed severe to complete turbinate atrophy. Nasal turbinates were normal for control pigs in both experiments.     

Toxigenic type A Pasteurella multocida as a causative agent of nasal turbinate atrophy in swine.

Although no clinical signs of atrophic rhinitis (AR) were recognized in 2- and 5-week-old pigs, approximately 60% of 2- to 6-month-old pigs showed clinical signs of AR in an affected pig farm. None of the pigs had normal turbinate at slaughter. Bordetella bronchiseptica was not isolated from any of the pigs before onset and incipient stage of the outbreak (2-week to 2-month-old). Pasteurella multocida of capsular type D was not isolated from any of those pigs. However, toxigenic P. multocida of capsular type A was isolated from a number of the pigs immediately before onset and incipient stage of the outbreak. Thirty-six-day-old primary specific-pathogen-free pigs were inoculated intranasally with a toxigenic type A P. multocida isolated from a 5-week-old pig. Severe nasal turbinate atrophy was observed in those pigs which were necropsied at 3 weeks post-inoculation. This is the first report on outbreak of severe nasal turbinate atrophy induced by toxigenic type A P. multocida in Japan.     

Pasteurella multocida and Bordetella bronchiseptica in atrophic rhinitis and pneumonia in swine.

A total of 163 pigs from nine farrow-to-finish herds representing various levels of atrophic rhinitis (AR) were selected for postslaughter examination of AR and pneumonia. Nasal swabs and lungs were cultured for detection of Bordetella bronchiseptica and Pasteurella multocida. Seventy-three pigs were examined at eight weeks of age and 90 contemporaries at six months of age. Mean AR scores were 1.21 and 1.11 for the eight week and six month old pigs, respectively (0 = normal, 3 = severe). In individual pigs increasing AR score was related to increasing pneumonia score in eight week old pigs but not in six month old hogs. In eight week old pigs, B. bronchiseptica and P. multocida were isolated more frequently from pigs with higher AR scores. From nasal swabs of six month old hogs, Bordetella was almost never recovered while Pasteurella was frequently isolated score. Toxigenic type DP. multocida was isolated from nasal cultures of only seven (4%) pigs and from lung cultures of only one pig. Pasteurella was never isolated from lungs of the eight week old pigs and Bordetella never from the six month old hogs. The isolation rate of P. multocida, predominantly type A, from lungs of six month old pigs increased from 11% in grossly normal lungs to 86% in lungs with severe pneumonia. Pigs from one herd free from lesions of AR and pneumonia were also examined; type AP. multocida was isolated from nasal cultures of one of six eight week old pigs. Somatic antigens of P. multocida were determined for 94 nasal and 20 lung isolates. Somatic serovar 3 was found in 93% of the nasal isolates and in all lung isolates.(ABSTRACT TRUNCATED AT 250 WORDS)     

Screening pig herds for toxigenic Pasteurella multocida and turbinate damage in a health scheme for atrophic rhinitis

The Pig Health Control Association launched a health scheme for atrophic rhinitis in 1978. For several years pig herds were monitored by scoring the degree of turbinate damage and by clinical inspections. When laboratory facilities became available for detecting toxigenic Pasteurella multocida, nasal swabs were taken from pigs in Association herds during 1988 and 1989 to determine whether the organism was present. Sows were screened routinely and in the worst affected herds, sucklers and weaners were also swabbed. In 12 of 19 herds with consistently low snout scores toxigenic P multocida were not isolated, and in 15 herds which developed higher snout scores with time toxigenic P multocida were also not found. Eleven herds had never been listed by the Association, either because their snout scores were consistently high or because they had received importations of stock from herds with high snout scores; of six of these herds with the most persistently high snout scores five showed varying degrees of the clinical signs of atrophic rhinitis, but none of the six showed evidence of infection with toxigenic P multocida, and the organism was not found in the other five herds in the group. There seems to be an overlap between the clinical and gross pathological signs of atrophic rhinitis seen in some herds not infected with toxigenic P multocida and the mild and spasmodic signs of atrophic rhinitis seen in some herds which are substantially infected with the organism.     

Prevalence of Actinobacillus pleuropneumoniae, Actinobacillus suis, Haemophilus parasuis, Pasteurella multocida, and Streptococcus suis in representative Ontario swine herds

Tonsillar and nasal swabs were collected from weanling pigs in 50 representative Ontario swine herds and tested for the presence of 5 important bacterial upper respiratory tract pathogens. All but 1 herd (2%) tested positive for Streptococcus suis by polymerase chain reaction (PCR); 48% of herds were S. suis serovar 2, 1/2 positive. In all but 2 herds there was evidence of Haemophilus parasuis infection. In contrast, toxigenic strains of Pasteurella multocida were detected by a P. multocida--enzyme-linked immunosorbant assay (PMT-ELISA) in only one herd. Seventy-eight percent of the herds were diagnosed positive for Actinobacillus pleuropneumoniae by apxIV PCR. Sera from finishing pigs on the same farms were also collected and tested by ELISA for the presence of A. pleuropneumoniae antibodies. Seventy percent of the herds tested had evidence of antibodies to A. pleuropneumoniae including serovars 1-9-11 (2%), 2 (4%), 3-6-8-15 (15%), 5 (6%), 4-7 (26%), and 12 (17%). This likely represents a shift from previous years when infection with A. pleuropneumoniae serovars 1, 5, and 7 predominated. At least 16% and possibly as many as 94% of the herds tested were Actinobacillus suis positive; only 3 of the 50 herds were both A. pleuropneumoniae and A. suis negative as judged by the absence of a positive PCR test for apxII. Taken together, these data suggest that over the past 10 years, there has been a shift in the presence of pathogenic bacteria carried by healthy Ontario swine with the virtual elimination of toxigenic strains of P. multocida and a move to less virulent A. pleuropneumoniae serovars. As well, there appears to be an increase in prevalence of S. suis serovar 2, 1/2, but this may be a reflection of the use of a more sensitive detection method.     

An abattoir survey of pneumonia and pleuritis in slaughter weight swine from 9 selected herds. II. Enzootic pneumonia of pigs: microbiological findings and their relationship to pathomorphology

Lungs from 191 slaughter pigs with gross lesions indicative of enzootic pneumonia of pigs (EPP) and 80 grossly normal lungs, all originating from 9 different herds, were subjected to microbiological and pathological examinations. The microbiological studies included both bacterial and mycoplasmal culture and also testing for Mycoplasma hyopneumoniae antigen in tissue by indirect immunofluorescent technique. M. hyopneumoniae, Pasteurella multocida and Mycoplasma hyorhinis were detected in 83%, 43% and 37% of the pneumonic lungs, respectively. Mycoplasma flocculare was the most frequently isolated organism in the non-pneumonic lungs. The greatest amounts of macroscopic pneumonia (25.2%) were recorded in lungs with all the three agents M. hyopneumoniae, P. multocida and M. hyorhinis present. The amounts of pneumonia in lungs with M. hyopneumoniae alone and in concurrence with P. multocida, were 9.3% and 15.6%, respectively. M. hyorhinis was also, in this study, associated with higher frequency of diffuse pleuritis. These findings indicate that M. hyorhinis might be involved in the pathogenesis of pneumonia in slaughter pigs. Ninety-six per cent of the isolates of P. multocida from pneumonic lungs could be characterized as type A. In the herds which had the most severe pneumonia problems, toxin production was detected in 83% of the P. multocida strains while only 28% were toxigenic in herds with subclinical to moderate pneumonia problems.     

Colonisation by Pasteurella multocida in atrophic rhinitis of pigs and immunity to the osteolytic toxin

Gnotobiotic pig antisera to purified toxoid from a capsule type A or D strain of Pasteurella multocida contained large quantities of antitoxin but comparatively little antibody to a crude lysate of P. multocida. These sera given intraperitoneally to further pigs were almost completely protective against turbinate atrophy after intranasal inoculation of dilute acetic acid and infection with type D toxigenic P. multocida. In contrast, antisera to a crude lysate or bacterin of toxigenic P. multocida which contained large titres of antibody to P. multocida lysate, but no detectable antitoxin, were not protective. Colonisation by toxigenic P. multocida was significantly reduced in protected pigs and was similar to colonisation by nontoxigenic P. multocida in pigs untreated or treated with dilute acetic acid. These results indicated (1) that antitoxin was protective and cross protective between toxins from different capsule types; and (2) that the toxin was the main colonisation factor produced by toxigenic bacteria in the acetic acid model of infection and that immunity to it did not eliminate infection.     

Development of a typing system for epidemiological studies of porcine toxin-producing Pasteurella multocida ssp. multocida in Denmark

The aim of the present study was to evaluate capsular-typing, plasmid-profiling, phage-typing and ribotyping for epidemiological studies of toxin-producing Pasteurella multocida ssp. multocida in Denmark. The evaluation of methods was based on 68 strains from nasal swabs and 14 strains from pneumonic lungs. Strains from lungs were all of capsular Type A, whereas strains from nasal swabs were of both capsular Types A and D. Only 9% of the strains contained plasmids, which could not be associated with antibiotic resistance. Phage-typing divided 61% of strains into 10 groups, while 39% were non-typable. CfoI ribotyping divided strains into four groups of which one type contained 94% of isolates. HindIII ribotyping divided strains into 18 types. A total of 18 strains from The Netherlands, UK and USA were subjected to HindIII ribotyping, resulting in 13 types of which six were identical to ribotypes of Danish strains. Phage-typing of isolates from an outbreak of atrophic rhinitis involving six herds in 1985 showed the existence of an epidemic strain. This type was recognised in the herd suspected of being the source of the infections and in four of the five infected herds. These findings were supported by HindIII ribotyping, as 85% of isolates from all herds were assigned to one ribotype. In conclusion, HindIII ribotyping seems to represent a useful tool for epidemiological studies of toxigenic P. multocida ssp. multocida.     

Effect of aerial ammonia on porcine infection of the respiratory tract with toxigenic Pasteurella multocida

The objective of the experimental study was to examine whether aerial ammonia alone could predispose the respiratory system of pigs to infection with toxigenic Pasteurella multocida type A. Two groups of 5 pigs each were continuously exposed to 50 ppm ammonia and less than 5 ppm ammonia, respectively, for a 59-day period (from 37 kg to 90 kg bodyweight) followed by necropsy. In an aerosol chamber all pigs were exposed to an aerosol of toxigenic P. multocida type A (mean bacterial concentration in the aerosol-exposure chamber: 10(5) colony forming units/m3; exposure period: 25 min) at day 10, 21, 35 and 49 after the onset of ammonia exposure. During the experiment none of the pigs showed clinical signs of pneumonia nor did they develop visible distortion of the snout. None of the pigs had gross lesions in the lungs at necropsy and toxigenic P. multocida was not detected by culture from the lungs from any of the pigs. The chance of recovering toxigenic P. multocida from nasal swabs (collected during experiment) was 2-4 times greater in the test group compared to the control group. The average daily weight gain was lower for the ammonia exposed pigs compared to the control group. In conclusion the results from this study suggest that ammonia in concentrations of 50 ppm is unlikely to predispose growing pigs to pulmonary infection with toxigenic P. multocida.     

Lack of effect of aerial ammonia on atrophic rhinitis and pneumonia induced by Mycoplasma hyopneumoniae and toxigenic Pasteurella multocida

The objective of this experimental study was to determine the effects of aerial ammonia on disease development and bacterial colonization in weaned pigs inoculated with toxigenic Pasteurella multocida and Mycoplasma hyopneumoniae. Two groups of 10 pigs each were continuously exposed to 50 and 100 p.p.m. ammonia, respectively, and compared to a non-exposed control group of 20 pigs. Following aerosol inoculation with M. hyopneumoniae at day 9, all pigs were aerosol-inoculated with toxigenic P. multocida type A at days 28, 42 and 56. At day 63 they were euthanized. Clinical signs including coughing and respiratory distress were present in all groups following inoculation. No significant differences could be established in the extent or frequency of pneumonia between ammonia-exposed pigs and controls, or in the extent of conchal atrophy, the frequency of isolation of toxigenic P. multocida from conchae, tonsils, lungs and kidneys, or the average daily weight gain. The recovery of toxigenic P. multocida from nasal swabs following inoculation was significantly greater in pigs exposed to 50 p.p.m. ammonia or more as compared to the control group. In conclusion, high levels of ammonia combined with inoculations with M. hyopneumoniae and toxigenic P. multocida had no significant effect on disease development, but may have enhanced colonization by toxigenic P. multocida on the nasal turbinates.     

Serum haptoglobin concentration in growing swine after intranasal challenge with Bordetella bronchiseptica and toxigenic Pasteurella multocida type D.

The acute phase reaction, in association with progressive atrophic rhinitis (AR), was monitored for 3 wk using serum haptoglobin (HPT) quantification in thirty-six, 15 kg swine after intranasal challenge with varying doses of Pasteurella multocida type D (toxigenic strain) and Bordetella bronchiseptica. The challenge doses were administered alone or in combination with pigs divided into 9 isolated treatment groups. Increasing doses of B. bronchiseptica were associated with lower serum HPT (P < 0.05), whereas increasing doses of P. multocida tended to increase serum HPT (0.05 < P < 0.10). Significant and positive correlation of mean HPT and AR score was found in these pigs; increased AR scores were associated with elevated mean HPT concentration (r = 0.41, P < 0.01). A significant interaction between P. multocida and B. bronchiseptica dose indicated that increasing the dose of B. bronchiseptica, for a fixed P. multocida dose, was associated with less AR (P < 0.05). The AR scores were greater in pigs given P. multocida, than B. bronchiseptica alone. These results indicate that a complex interaction between Pasteurella multocida and Bordetella bronchiseptica causes progressive atrophic rhinitis and alters serum HPT concentration in swine.     

Isolation of toxigenic strains of Pasteurella multocida from lungs of pneumonic swine

Lungs from 113 pneumonic pigs were examined for Pasteurella multocida. The lungs were smeared directly onto blood agar and homogenized in brain-heart infusion broth and then inoculated intraperitoneally in mice. Pasteurella multocida isolates were typed for serotypes A (by hyaluronidase inhibition of capsule) and D (by acriflavine autoagglutination). Strains were tested for toxin production by intradermal injection of 0.2 ml of filtered 24-hour culture supernatants into guinea pigs. Most lungs (70.8%) yielded isolations. Most isolants (87.5%) were type A and 12.5% were type D. Of the type D strains, 80% were toxigenic. Of the type A isolants, 18.2% were toxigenic.     

Experimental atrophic rhinitis in 2 and 4 month old pigs infected sequentially with Bordetella bronchiseptica and toxigenic type D Pasteurella multocida.

Experimental infections with Bordetella bronchiseptica and/or toxigenic type D Pasteurella multocida were studied in 2- and 4-month-old primary specific-pathogen-free pigs. None of the 2-month-old pigs inoculated with B. bronchiseptica or P. multocida alone developed turbinate atrophy. All the pigs inoculated with B. bronchiseptica (10(7) CFU/head) and P. multocida (10(9) CFU/head for 5 consecutive days) together, however, developed clinical and post-mortem signs of atrophic rhinitis (AR) similar to the naturally occurring disease. Slight to severe turbinate atrophy was observed in the 4-month-old pigs inoculated with B. bronchiseptica and P. multocida (at the same concentration as above) at necropsy.