Rabbit pasteurellosis: induced disease and vaccination

Pasteurellosis was induced in rabbits by conjunctival inoculation with 2 strains of Pasteurella multocida. The LD50 of strain P1062 (a bovine isolate) was 10(5.1) colony-forming units and that of strain P1059 (a turkey isolate) was 10(5.5) colony-forming units. Pasteurella-free rabbits were vaccinated IV or mucosally with boiled cells of P multocida or a cross-reactive uridine diphosphogalactose epimerase-deficient mutant of Escherichia coli J5. In rabbits challenge exposed with P multocida strain 1062 or 1059, homologous P multocida strain gave the best protection against fatal bacteremia. Partial protection was provided by J5; mucosal routes of vaccination (aerosol or conjunctival) gave better protection than did the IV route. Serum antibody titers were lower in rabbits vaccinated by mucosal routes than in those vaccinated IV. Cross-reactive IgG and IgM titers to P multocida were demonstrated when rabbits were vaccinated with J5. On the basis of bacteriologic examination of nasal secretions, rabbits that died were considered culture positive sooner than were those that survived. On the basis of bacteriologic examination of blood, rabbits that died were considered culture positive, and those that survived were considered culture negative. Seemingly, heat-stable antigens were protective, the cross-reactive E coli J5 mutant (with only core lipopolysaccharide) provided partial protection against pasteurellosis, and the mucosal route was somewhat useful for cross-protective immunization.     

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.     

The pathology of experimental respiratory infection with Pasteurella multocida and Bordetella bronchiseptica in rabbits

Groups of female New Zealand White rabbits, 8-10 weeks old, were inoculated intranasally with three different Pasteurella multocida serotypes (A:3, A:4 and A:12) or one of three Bordetella bronchiseptica strains of rabbit origin. Seven out of 18 rabbits died of experimental infection with P. multocida. B. bronchiseptica killed 3 out of the 8 animals inoculated with it. Deaths occurred between 3 and 6 days postinoculation (PI). In the rabbits that died of P. multocida inoculation, necropsy and histology revealed severe pleuritis with the accumulation of a remarkable amount of fibrinopurulent exudate in the thoracic cavity, serous rhinitis and tracheitis, acute hepatitis with necrotic foci in the parenchyma, and atrophy of the lymphoid organs and tissues. Rabbits killed 10 days PI developed only subacute serous rhinitis and hyperplasia of the lymphoid tissues. Rabbits that died of B. bronchiseptica inoculation showed acute serous rhinitis, acute catarrhal-fibrinopurulent pneumonia and mild pleuritis. As opposed to P. multocida inoculated animals, hepatitis and atrophy of the lymphoid tissues were not characteristic of these rabbits. Rabbits killed 10 days PI developed subacute purulent and necrotic pneumonia with remarkable macrophage proliferation, involving all lobes, and hyperplasia of the lymphoid tissues.     

Experimental infection of calves with Pasteurella multocida Serovar A: 3 isolated in Japan

Pasteurella multocida, serovar A: 3, selected by pathogenicity in mice from among 10 strains isolated from pneumonic lesions of calves, was adjusted to 10(7), 10(8) and 10(10) colony-forming units (CFU), and inoculated intratracheally into four calves. All calves showed pyrexia and had lungs with congestion and hepatization. Inoculation with 10(10) CFU of bacteria produced respiratory symptoms and abscesses in lungs. This information will aid elucidation of the pathogenicity of P. multocida and the development of vaccines.     

Preliminary studies with a live streptomycin-dependent Pasteurella multocida and Pasteurella haemolytica vaccine for the prevention of bovine pneumonic pasteurellosis.

Twelve Pasteurella-free Holstein-Friesian calves were used in a study to test the efficacy of a live streptomycin-dependent Pasteurella multocida A:3 and streptomycin-dependent Pasteurella haemolytica A1 vaccine. The calves were inoculated intramuscularly twice at 14-day intervals with either the streptomycin-dependent vaccine, containing 1 X 10(6) colony forming units/mL P. multocida and 4 X 10(8) colony forming units/mL P. haemolytica, commercial bacterin, or phosphate buffered saline. Two weeks following the second vaccination, all calves were challenged by intranasal inoculation of 10(8) TCID50/4.0 mL infectious bovine rhinotracheitis virus followed three days later by intratracheal injection with 2.3 X 10(7) colony forming units/mL of a 16 hour culture of P. multocida A:3 and 2.6 X 10(8) colony forming units/mL of an 8 hour culture of P. haemolytica A1. Seven days after challenge with Pasteurella, calves were killed for collection of tissues at necropsy. Each calf was given a score based on macroscopic and microscopic lesions. The scores for the calves receiving live vaccines were significantly lower (p less than 0.025) than those for the controls. Also, the calves receiving live vaccines had a significant (p less than 0.05) increase in the level of serum antibody to P. haemolytica. The results of this preliminary study showed that the streptomycin-dependent vaccine offered better protection than the commercial bacterin against a virulent homologous challenge.     

Seroprevalence of antibodies against gram-negative core antigens in rabbits, using an Escherichia coli J5 antigen-capture enzyme-linked immunosorbent assay

OBJECTIVE: To determine the seroprevalence of antibodies to gram-negative core antigens (GNCA) in specific-pathogen-free (SPF) rabbits (ie, free of Pasteurella multocida) and rabbits of undefined bacterial status (conventional). SAMPLE POPULATION: Serum samples were obtained from 7 groups of rabbits. The SPF rabbits comprised 2 adult groups and 1 immature group, whereas the 4 groups of conventional rabbits were all adults. PROCEDURE: A seroprevalence survey was conducted on rabbit sera for antibodies against GNCA, using an Escherichia coli J5 antigen-capture ELISA. RESULTS: Collective geometric mean titer (GMT) of adult rabbits was 1:6,463. The GMT of each of the 6 groups of adult rabbits was 1:956, 1:1,133, 1:4,525, 1:5,338, 1:7,669, and 1:25,600. Titers of populations differed significantly. CONCLUSION: Data analysis revealed there were anti-GNCA antibodies in rabbits. Similar to other species, the prevalence of IgM and IgG anti-GNCA antibodies increased with age. The IgG response was more marked than the IgM response. The SPF rabbits had lower IgG anti-GNCA titers than conventional rabbits, indicating possible cross-reactive epitopes between P multocida and Enterobacteriaceae. Rabbits with the highest anti-GNCA titers were those used in polyclonal antibody production, possibly stemming from endotoxin contamination of antigen or adjuvant. CLINICAL RELEVANCE: The possible cross-reactive antibodies directed at homologous wall components of Pasteurellaceae and Enterobacteriaceae could prove to be a possible heterotypic vaccination strategy for the protection of rabbits against pasteurellosis. Investigators should determine whether antigen impurity (endotoxin contamination) influences epitope focus during polyclonal antibody production and whether it affects sera variability among rabbits.     

Vaccination of turkeys with cell-free culture filtrate of Pasteurella multocida

Turkeys given cell-free culture filtrate (CCF) of Pasteurella multocida strain R44/6 orally, via air sacs, or subcutaneously mixed 1:1 with incomplete Freund's adjuvant (IFA) at 6 and 9.5 weeks of age were compared with negative controls given bacteriologic medium and positive controls vaccinated with a commercial bacterin. At 13 weeks of age, serum antibody titers to P. multocida were detectable only in turkeys given CCF in IFA (low titers) and positive control turkeys (high titers), at which time turkeys were challenged orally with either the homologous strain or strain P-1059. Protection against challenge with strain R44/6 was provided by the commercial bacterin, CCF in IFA, and CCF given via air sacs. When turkeys were challenged with strain P-1059, protection was superior in turkeys given CCF via air sacs, intermediate in turkeys given commercial bacterin or CCF in IFA, and absent in negative control turkeys and turkeys given CCF orally. These results indicate CCF is an effective immunogen when administered via the lower respiratory tract for protecting turkeys against pasteurellosis.     

Mortality in swine herds endemically infected with Haemophilus pleuropneumoniae: effect of immunization with cross-reacting lipopolysaccharide core antigens of Escherichia coli

The benefit of increased immunity to cross-reacting lipopolysaccharide core antigens of gram-negative bacteria induced by vaccination with an Rc mutant of Escherichia coli 0111:B4 (strain J5) was evaluated in commercial swine herds endemically infected with Haemophilus pleuropneumoniae. Weanling pigs were vaccinated IM with E coli J5 (group 1) before the expected time of H pleuropneumoniae infection. Clinical signs, antibiotic treatment frequency, mortality, growth performance (days to market weight), and serologic responses of the pigs were monitored for approximately 5 months after vaccination. The results were compared with those of pigs vaccinated IM with a commercial H pleuropneumoniae bacterin (group 2) and with those of nonvaccinated control pigs of the same age (group 3). The treatment frequency and growth performance were similar in the 3 groups. However, vaccination with E coli J5 or with the H pleuropneumoniae bacterin lowered mortality, compared with mortality in the controls. Serum titers against E coli J5 increased after vaccination with the E coli J5 bacterin, but were not increased by vaccination with the H pleuropneumoniae. In contrast, serum titer to E coli J5 increased in all treatment groups as a result of H pleuropneumoniae infection or exposure. The protection against lethal H pleuropneumoniae infections in swine that was provided by vaccination with the E coli J5 and the H pleuropneumoniae bacterin appeared to be immunologically distinct on the basis of serologic analysis, indicating the possibility of different mechanisms of protection.     

Evaluation of the effect of heating an oil-emulsion Pasteurella multocida bacterin on tissue reaction and immunity

Killed vaccines in oil emulsions are critical components of breeder and layer vaccination programs. Current vaccination sites are limited, and each has inherent problems. Oil emulsion vaccines are associated with increased condemnations of spent fowl when vaccines are injected intramuscularly into the breast. In an attempt to reduce tissue reaction when injected into the breast muscle, a commercially available Pasteurella multocida bacterin was heated to 41 C (100 F) for 5 hr prior to administration. A second treatment group was injected with the same bacterin at room temperature, 25 C. The vaccine was injected into the breast muscle at 10 and 18 wk of age into white Leghorn hens. Seroconversion was evaluated using P. multocida enzyme-linked immunosorbent assay (ELISA) at 10, 18, and 24 wk. Treatment and control groups were euthanized and lesions scored at 24 wk of age. One replicate was challenged with type 1 P. multocida at 24 wk of age. Lesion scores for the heated vaccine group were significantly lower than the room temperature vaccine. ELISA titers were not significantly different at 24 wk between the two treatment group; however, a significant rise in antibody titer was observed at 18 wk in the group that was injected with the heated vaccine. Survivability to challenge was improved in birds injected with the heated vaccine. Results suggest that heating of a P. multocida bacterin reduces local tissue reaction without having a deleterious effect on immunity as measured by ELISA and challenge.     

Interaction between Bordetella bronchiseptica and toxigenic Pasteurella multocida on the nasal mucosa of SPF piglets.

The interaction between Bordetella bronchiseptica and type D toxigenic Pasteurella multocida was studied in five groups of 4 specific-pathogen-free (SPF) piglets each. At 28 days of age, piglets of groups 3 and 4 were inoculated into both nostrils with 10(8) colony-forming-units (CFU) of a non-dermonecrotic toxin (DNT)-producing, phase I strain of B. bronchiseptica. Piglets of groups 1 and 3 were treated intranasally with a sonic extract of the non-toxic strain of B. bronchiseptica and those of groups 2 and 4 with B. bronchiseptica DNT into the left nostril. Sonic extract and DNT treatment was started at 33 days of age and lasted for 5 days. Piglets of group 5 served as controls. At the age of 37 days, piglets of all groups except group 5 were inoculated into both nostrils with 5 x 10(7) CFU of toxigenic P. multocida. At slaughter at 50 days of age, P. multocida was recovered from the left nasal cavity of 3 piglets of group 2 and all piglets of group 4. In piglets inoculated with B. bronchiseptica DNT the mucosal epithelial cells of the left nasal cavity showed loss of cilia, regressive lesions such as vacuolation, karyopycnosis and necrosis, hypertrophy of the epithelium, infiltration of the epithelium and submucosa by inflammatory cells, could also be seen. The results suggest that action of the B. bronchiseptica DNT on the nasal mucosa is a precondition of the growth of P. multocida in the nasal cavity.(ABSTRACT TRUNCATED AT 250 WORDS)     

Duration of immunity and efficacy of an oil emulsion Escherichia coli bacterin in cattle

An oil emulsion Escherichia coli bacterin administered in 1- and 2-dose vaccination regimens was evaluated in beef cattle. Serologic responses to the K99 pilus antigen were monitored, and suckling offspring from vaccinated and nonvaccinated cows were inoculated with virulent, K99-positive, enterotoxigenic Escherichia coli. The degree of protection and duration of immunity conferred were determined in 2 respective studies. In the first study (study A), titers of pregnant cattle were determined from time of vaccination through calving (a 6- to 20-week period). Titers of 24 cows vaccinated with a single 2-ml dose of bacterin were compared with those of 24 cows given a 2-dose regimen and with those of 23 nonvaccinated cattle (contemporary controls). Inoculum consisting of 1.2 X 10(12) viable enterotoxigenic E coli/dose administered to nursing calves from these dams yielded 0% mortality (0 deaths/20 calves) in calves from 1-dose vaccinates, 6% mortality (1 death/18 calves) in calves from 2-dose vaccinates, and 37% mortality (7 deaths/19 calves) in calves from nonvaccinated dams. Study B was an extended evaluation conducted in cattle that were kept in the study up to 87 weeks from initial vaccination until calving. Serologic titers to the K99 pilus antigen were compared in 1-dose, 2-dose, and nonvaccinated cattle in groups of 8, 6, and 6, respectively. Calves from these dams were inoculated with 8.1 X 10(11) viable enterotoxigenic E coli/dose, which resulted in 0% mortality (0 deaths/5 calves) in calves from 1-dose vaccinates, 0% mortality (0 deaths/5 calves) in calves from 2-dose vaccinates, and 80% mortality (5 deaths/6 calves) in calves from nonvaccinated dams.     

Pasteurella multocida infection in the domestic rabbit: immunization with a streptomycin-dependent mutant.

Fourteen Pasteurella multocida-free rabbits were inoculated intranasally with a streptomycin-dependent mutant of P. multocida serotype 12:A. Vaccinations with approximately 10(8) colony forming units were done on days 0, 14 and 28. Two weeks later the animals were separated into groups, which included 12 rabbits divided into two control groups of six unvaccinated Pasteurella-free animals. Seven vaccinated rabbits were challenged intranasally with the homologous virulent parent strain and the other seven vaccinates were challenged with a virulent strain of serotype 3:A. Rabbits were necropsied two weeks later. The vaccinated group challenged with the parent strain showed a more rapid nasal clearance of the organism than the vaccinated group challenged with the heterologous strain. However, the number of positive cultures of P. multocida recovered from tissues post-challenge were similar in vaccinated and control animals. In a significant number of animals, vaccination with serotype 12:A induced detectable antibody production to somatic antigens of both 12:A and heterologous strain 3:A.     

Effect of endobronchial challenge with Actinobacillus pleuropneumoniae serotype 10 of pigs vaccinated with bacterins consisting of A. pleuropneumoniae serotype 10 grown under NAD-rich and NAD-restricted conditions

The efficacy of two bacterins containing an Actinobacillus pleuropneumoniae serotype 10 strain was evaluated. The bacterial cells constituting bacterin 1 and 2 were grown under nicotinamide adenine dinucleotide (NAD)-rich (low-adherence capacity to alveolar epithelial cell cultures) and NAD-restricted (high-adherence capacity to alveolar epithelial cell cultures) conditions, respectively. Ten pigs were vaccinated twice with the bacterin 1 and nine pigs with the bacterin 2. Ten control animals were injected twice with a saline solution. Three weeks after the second vaccination, all pigs were endobronchially inoculated with 106.5 colony-forming units (CFU) of an A. pleuropneumoniae serotype 10 strain. In the bacterin 1 and 2 group, three and two pigs died after inoculation, respectively. Only two pigs of the control group survived challenge. Surviving pigs were killed at 7 days after challenge. The percentage of pigs with severe lung lesions (> 10% of the lung affected) was 100% in the control group, 70% in the bacterin 1 group and 22% in the bacterin 2 group. Actinobacillus pleuropneumoniae was isolated from the lungs of all animals. The mean bacterial titres of the caudal lung lobes were 7.0 x 10(6) CFU/g in the control group, 6.3 x 10(5) CFU/g in the bacterin 1 group and 1.3 x 10(6) CFU/g in the bacterin 2 group. It was concluded that both bacterins induced partial protection against severe challenge. Furthermore, there are indications that the bacterin 2, containing A. pleuropneumoniae bacteria grown under conditions resulting in high in vitro adhesin, induced better protection than the bacterin 1.     

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.     

Intranasally inoculated Mycoplasma hyorhinis causes eustachitis in pigs

Specific-pathogen-free pigs were experimentally inoculated with Mycoplasma hyorhinis, Pasteurella multocida, or both bacterial isolates to evaluate the role of these bacteria in the pathogenesis of otitis media. Six pigs were inoculated intranasally with 4.4 X 10(8) colony-forming units (CFU) of M. hyorhinis. Twenty-one days later, three of these six pigs were inoculated intranasally with 5.0 X 10(8) CFU of P. multocida. Three additional pigs were also inoculated intranasally at the time with P. multocida alone. Two pigs served as uninoculated controls. Seven days later, all pigs were euthanatized. Histologically, subacute inflammation was found in 10 auditory tubes of six pigs and two tympanic cavities of two pigs inoculated with M. hyorhinis. Immunohistochemically, M. hyorhinis antigens were detected on the luminal surface of eight of 10 inflamed auditory tubes, and ultrastructural examination confirmed mycoplasmal organisms in two pigs. M. hyorhinis was isolated from the inflamed tympanic cavities of two pigs. None of the pigs inoculated only with P. multocida had otitis, and P. multocida was not isolated from the tympanic cavity. These findings indicate that M. hyorhinis can cause eustachitis but rarely otitis media in specific-pathogen-free pigs.     

Ultrastructural pathology of the upper respiratory tract of rabbits experimentally infected with Pasteurella multocida A:3.

Twenty-four 8 to 9 week-old Pasteurella multocida -free rabbits were divided into three equal groups, the first group was pretreated with hydrocortisone and inoculated intranasally with pasteurella multocida serotype A:3. The second group was inoculated intranasally with P. multocida without hydrocortisone treatment. The third group was inoculated with phosphate buffered saline only and used as a control group. Pasteurella multocida was isolated from the nasal cavity of all infected rabbits in group 1 and 2 and from the trachea of seven rabbits in group 1 and five rabbits in group 2. This study was conducted to observe the ultrastructural changes of the upper respiratory tract of hydrocortisone treated and non-treated rabbits infected with P. multocida serotype A:3. The ultrastructural changes detected in infected rabbits were ciliary destruction and deciliation of the ciliated epithelial cells, cellular swelling, goblet cell hyperplasia and endothelial cell damage. Pasteurella multocida was observed attached to the degenerated cilia, microvilli and mucus. Pasteurella multocida infection was associated with inflammatory responses, which may have caused tissue damage. It is possible that hydrocortisone modulates the severity of infection as an immune suppressor and an inhibitor of goblet cell secretion.     

Comparison of vaccination protocols of broiler breeder hens for Pasteurella multocida utilizing enzyme-linked immunosorbent assay and virulent challenge

A commercial enzyme-linked immunosorbent assay (ELISA) to detect serological response to vaccination and virulent challenge with type 1 (X-73) Pasteurella multocida was used to determine the best vaccination protocol for broiler breeders against fowl cholera. Birds vaccinated twice, at 10 and 19 weeks of age, with the avirulent Clemson University (CU) strain both times, with a commercial bacterin first and the CU strain second, or with the CU strain first and bacterin second had the highest survival rates (98-100%) following challenge at 25 weeks. The two groups that received the CU strain and bacterin also produced the highest mean ELISA antibody titers (greater than 10,000). Birds vaccinated once, at 10 weeks, with the CU strain had the same survival rate as birds vaccinated twice with bacterin (90 and 91%). Under the conditions of this experiment, an ELISA titer greater than or equal to 1000 resulted in at least a 92% survival rate after virulent challenge (23% survival in nonvaccinates).     

The influence of growth conditions of Pasteurella multocida on its ability to colonise the nasal mucosa of SPF piglets

Colonisation of type D Pasteurella multocida was studied in five groups of seven SPF piglets each. Piglets of Group 1 were kept together with seven 5-week-old piglets obtained from a large herd infected with toxigenic P. multocida for 16 weeks (contact infection). These piglets were made free from toxigenic Bordetella bronchiseptica by local immunisation. Piglets of Group 2 were inoculated with 5 x 10(7) colony-forming units (cfu) of P. multocida washed from the nasal mucosa of piglets free from toxigenic B. bronchiseptica with fetal calf serum. Piglets of Group 3 were inoculated intranasally with 5 x 10(7) cfu of P. multocida washed from yeast-extract proteose-peptone cystine (YPC)-blood agar with fetal calf serum. Piglets of Group 4 were inoculated with 5 x 10(7) cfu of P. multocida grown in a YPC-based broth without blood. Piglets of Group 5 served as controls. The piglets of Group 1 did not contract P. multocida infection from infected contact piglets. After a single inoculation one of four, while after three inoculations two of three piglets of Group 2 became infected by P. multocida. After a single inoculation none of four, while after three inoculations one of three piglets of Group 3 were colonised by P. multocida. Both single and repeated inoculation failed in piglets of Group 4.     

Immunogenic potency of an oil-emulsified Escherichia coli bacterin

Immunogenicity of an oil-emulsified Escherichia coli (O1:K1) bacterin with an aqueous-phase-to-oil-phase ratio of 1:4 was evaluated in chickens. Chickens were vaccinated subcutaneously with 0.5 ml of the bacterin at 4 and 6 weeks of age. At 8 weeks, the vaccinated chickens and unvaccinated controls were challenged via air sacs with 10(4) colony-forming units (CFU) of homologous E. coli. Vaccinated chickens were protected against active respiratory infection in that they (a) gained body weights comparable to those in unvaccinated, unchallenged chickens, (b) suffered no morbidity or mortality, (c) had gross lesions so mild that the scored values were comparable statistically to the 0 lesion scores of the negative controls, and (d) did not yield E. coli when their heart blood, pericardial sacs, livers, and air sacs were cultured. Unvaccinated challenged chickens had severe respiratory distress, suffered 36% mortality, and had average air sac, pericardial sac, and liver lesion scores significantly (P less than or equal to 0.05) different from both the vaccinated and negative control chickens. Also, the challenge strain of E. coli only was isolated from the affected tissues of 5 of 14 chickens. Protection against active respiratory infection was again demonstrated in a second experiment, though the challenge dose was 1.06 X 10(6) CFU of E. coli. The immunity, however, was partially overcome, as the vaccinated chickens gained less body weight and the scored values for lesions in the air sacs, pericardial sacs, and livers were significantly higher than those of the negative controls (P less than or equal to 0.05).     

Experimental model of swine pneumonic pasteurellosis using crude Actinobacillus pleuropneumoniae cytotoxin and Pasteurella multocida given endobronchially.

This study was designed to develop and characterize a swine pneumonic pasteurellosis model by concurrent introduction of Pasteurella multocida type A and Actinobacillus pleuropneumoniae crude cytotoxin. After a series of preliminary experiments, a combination of 4 x 10(9) P. multocida and 4,000 toxic units of A. pleuropneumoniae crude cytotoxin was determined to produce optimal results. A total of 48 pigs were divided into four groups of 12 pigs each. The control group received buffered saline only. Four pigs from each group were randomly selected for necropsy 3, 7 and 14 days postinoculation (PI). Inoculation of pigs with P. multocida and A. pleuropneumoniae cytotoxin (group 1) resulted in moderate to severe pneumonia. Pasteurella multocida was isolated from pneumonic lesions, grossly normal lung, and bronchial lymph nodes of all group 1 pigs throughout the 14 day experimental period. Pathological changes typical of field cases of swine pneumonic pasteurellosis were produced. Pigs inoculated with P. multocida alone (group 2) had pneumonic lesions and P. multocida was reisolated from lungs at three days PI. Pasteurella multocida was not isolated from these pigs at 7 and 14 days PI, except for one pig in which an abscess developed in the thorax. Pulmonary lesions induced by A. pleuropneumoniae crude cytotoxin alone (group 3) were transient and resolved by seven days PI. Group 1 pigs had significantly greater lung lesion volumes than group 2 and 3 pigs at 3, 7 and 14 days PI. Statistical analysis indicated a significant interactive effect of P. multocida and A. pleuropneumoniae cytotoxin on the development of lung lesion volumes at 7 and 14 days PI (p < 0.05).(ABSTRACT TRUNCATED AT 250 WORDS)