Pulmonary Expression of Tumor Necrosis Factor Alpha, Interleukin-1 Beta, and Interleukin-8 in the Acute Phase of Bovine Pneumonic Pasteurellosis

Inflammatory cytokines are suspected to contribute to the pathogenesis of bovine pneumonic pasteurellosis (BPP) through neutrophil recruitment, leukocyte activation, and the induction of a broad array of soluble inflammatory mediators. An in vivo experimental model of BPP was used to characterize the pulmonary expression kinetics of tumor necrosis factor alpha (TNFα), interleukin-1 beta (IL-1β), and interleukin-8 (IL-8) genes and proteins during the acute phase of disease development. Cytokine expression in bronchoalveolar lavage (BAL) fluid, BAL cells, and pneumonic lung parenchyma was quantitated by northern blot analysis, enzyme-linked immunosorbent assay (ELISA), and in situ hybridization at 2, 4, 8, 16, and 24 hours after endobronchial inoculation of Pasteurella (Mannheimia) haemolytica. Expression of TNFα, IL-1β, and IL-8 was significantly increased in the airways and lung lesions of infected calves as compared with mock-infected controls. Although kinetic patterns varied, peak levels of cytokine mRNA occurred within 8 hours postinfection (PI), and peak cytokine concentrations occurred within 16 hours PI. In all samples, IL-8 was expressed to the greatest extent and TNFα was least expressed. Expression of TNFα was restricted to alveolar macrophages. Alveolar and interstitial macrophages produced IL-1β and IL-8 in the first 4 hours; bronchial and bronchiolar epithelial cells were also significant sources of IL-8 during this period. By 8 hours PI, neutrophils were the dominant source of both IL-1β and IL-8. These findings demonstrate a spatial and temporal association between pulmonary expression of inflammatory cytokines and acute lung pathology, supporting the hypothesis that cytokines contribute to inflammatory lung injury in BPP.

Clinicopathological observations in experimental peste des petit ruminants virus and Mannheimia haemolytica A:2 co-infection in goats

The experiment describes for the first time the clinicopathological features of the co-infection of Peste des petit Ruminants (PPR) virus and Mannheimia haemolytica,in goats. Twenty clinically healthy goats, six months of age were used. 15 goats were infected by intratracheal inoculation of 1ml of pure cultured 106.5 TCID50 PPR virus grown in Baby hamster kidney cell lines, and a week later,1 ml of pure culture (109 CFU) of Mannheimia haemolytica (MH)A2 to study its clinico-pathological features and five goats served as controls. The clinical signs were observed and two goats were euthanized at predetermined intervals for gross examinations, bacteriological, virological and histopathological investigations on tissues collected using standard techniques. The clinical signs were severe and the order of manifestation was anorexia, pyrexia, dyspnea, oculo-nasal discharge, recumbency and death. The lesions observed were severe fibrinous bronchointerstitial pneumonia and pleurisy with thickened alveolar septa, edema and neutrophilic infiltrations of the interstitium with giant cells. There was also marked erosive stomatitis and acute enteritis. The average percentage lung consolidation for the infection was 7.01% and the right lung was more affected (p<0.05) while the overall mortality was 33.3%. MHA:2 and PPR virus were re-isolated from the lungs. The clinicopathological features observed showed that goats were susceptible to co- infection of PPR and Mannheimiosis which was severe and fatal. The data should help veterinarians and other medical experts to recognize cases of bacterial complicated viral infection and be informed of the approach to the treatment of such conditions.

Meta-analysis of treatment of cattle with bovine respiratory disease with tulathromycin

The objective of this study was to evaluate the comparative efficacy of tulathromycin at resolving bovine respiratory disease in North American feedlot cattle. This study was a systematic review of published literature. A search was conducted to identify all manuscripts relating to antibiotic treatment of cattle with respiratory disease. Relevant studies reported treatment with tulathromycin of naturally occurring respiratory disease in beef cattle in North America. Studies which failed to use randomization to minimize bias were excluded from the review. The relative risk of retreatment for bovine respiratory disease was calculated for each study included in the final review. Initially, 782 potential manuscripts were identified. After relevance screening and quality assessment, 21 high quality manuscripts were available for analysis. Two peer reviewed publications and two technical reports describing 14 trials compared tulathramycin with tilmicosin or florfenicol. In the meta-analysis of studies comparing tilmicosin with tulathromycin, the summary Mantel-Haenszel relative risk was 0.51 (95% confidence interval 0.45-0.57). It was not possible to calculate a summary Mantel-Haenszel relative risk comparing florfenicol with tulathromycin as the only three studies reported this comparison. When using a meta-analysis to combined data from randomized clinical trials reporting treatment with tulathromycin or either florfenicol or tilmicosin, tulathromycin was associated with an approximately 50% reduction in the risk of re-treatment for bovine respiratory disease compared with treatment with tilmicosin.

An aetiopathological study of chronic bronchopneumonia in lambs in Ireland

Chronic bronchopneumonia in lambs, also known as 'atypical' or 'chronic, non-progressive' pneumonia is a common, frequently sub-clinical disease affecting animals under 12-months-old in intensive production systems. Infection with both Mycoplasma ovipneumoniae and Mannheimia haemolytica have been implicated in the aetiology of this condition and a variety of pulmonary lesions can result. In this study, detailed laboratory examination of 30 abattoir-derived lungs with the characteristic gross features of atypical pneumonia (AP) was carried out with a view to refining and correlating the histopathological and microbiological criteria required for the diagnosis of this disease. For the first time a broad range of laboratory detection techniques including bacterial and virus isolation, fluorescent antibody tests and immunohistochemistry were used in parallel to identify potential causative pathogens such as M. ovipneumoniae, M. haemolytica, parainfluenza type-3 (PI3) virus and respiratory syncytial virus (RSV) in AP lesions. The most consistent finding was the association of gross AP lesions with M. ovipneumoniae, identified by either culture or immunohistochemistry in 27 (90%) of the 30 cases. However the presence M. ovipneumoniae organisms or antigen did not consistently correlate with particular histopathological changes. Furthermore, peri-airway lymphoid hyperplasia, intra-alveolar exudation and nodular 'hyaline scars', which are all previously reported microscopic lesions of AP, were not identified in 12 (40%) of the cases and isolation of M. haemolytica was over-represented in lungs exhibiting suppurative lesions. These findings illustrate the complex aetiopathogenesis of this disease and highlight the requirement to use a combination of diagnostic criteria in its laboratory diagnosis.

Efficacy of tulathromycin compared with tilmicosin and florfenicol for the control of respiratory disease in cattle at high risk of developing bovine respiratory disease

Three studies conducted at feedlots in Colorado, Idaho, and Texas examined the comparative efficacy of tulathromycin injectable solution for the treatment of cattle at high risk of developing undifferentiated bovine respiratory disease (BRD). Each study randomly allocated 250 calves to receive tulathromycin at 2.5 mg/kg and 250 calves to receive either tilmicosin at 10 mg/kg (Colorado site) or florfenicol at 40 mg/kg (Idaho and Texas sites) on arrival at the feedlot. Calves were housed by treatment group in pens with 50 calves/pen. Beginning 3 days after antimicrobial treatment, cattle were observed for signs of BRD daily until harvest. In all three studies, the treatment success rates at 28 days after treatment and at harvest were significantly higher (P < or = .013) for cattle treated with tulathromycin than for cattle treated with either tilmicosin or florfenicol. Fewer tulathromycin-treated cattle were removed from the group as "chronics" or "mortalities" at 28 days posttreatment (P < or = .014) in all three studies. Tulathromycin demonstrated superior efficacy compared with tilmicosin and florfenicol when treating groups of high-risk cattle before the onset of signs of BRD.

Comparative efficacy of tulathromycin, tilmicosin, and florfenicol in the treatment of bovine respiratory disease in stocker cattle

The therapeutic efficacy and field safety of tulathromycin were evaluated in stocker calves with undifferentiated bovine respiratory disease (BRD) in three field studies conducted over two consecutive grazing seasons in Nebraska. Eight hundred calves exhibiting clinical signs of BRD and with rectal temperatures of 104 degrees F or higher were treated with tulathromycin (n = 340), florfenicol (n = 240), or tilmicosin (n = 220) and evaluated for approximately 60 days. Florfenicol and tilmicosin were administered as single SC injections according to labeled dosage. Tulathromycin was administered as a single SC injection of 2.5 mg/kg. In all three studies, the cure rate of calves 60 days after treatment with tulathromycin was significantly higher (P < or = .05) than that of calves treated with florfenicol or tilmicosin. Suspected adverse reactions were not reported for any of the study drugs. Tulathromycin proved to be significantly more effective than either florfenicol or tilmicosin in the treatment of BRD in stocker calves.

Evaluation of the therapeutic activity of tulathromycin against swine respiratory disease on farms in Europe

The clinical efficacy of tulathromycin in the treatment of natural outbreaks of swine respiratory disease (SRD) was evaluated at five European sites. Pigs (1 to 6 months of age) exhibiting clinical signs of SRD were treated intramuscularly with tulathromycin (n = 247) at 2.5 mg/kg on day 0 versus either tiamulin (n = 102) at 15 mg/kg on days 0, 1, and 2 (Germany, the Netherlands, and the United Kingdom) or florfenicol (n = 20) at 15 mg/kg on days 0 and 2 (France). Actinobacillus pleuropneumoniae, Pasteurella multocida, and Mycoplasma hyopneumoniae infections were the most frequently diagnosed pathogens. For both tulathromycin-treated animals and those treated with tiamulin or florfenicol, there were significant (P = .0001) reductions in mean rectal temperature and the severity of abnormal clinical signs on days 2 and 10 compared with day 0. There were no significant differences (P > .05) between treatments in average daily weight gain. Tulathromycin was found to be safe and highly effective in the treatment of natural outbreaks of SRD.

Efficacy of tulathromycin injectable solution for the treatment of naturally occurring Swine respiratory disease

Tulathromycin, a novel triamilide antimicrobial, was evaluated for treatment of swine respiratory disease (SRD) in field efficacy studies involving 720 pigs in six North American swine herds. In each study, feeder pigs with clinical SRD were randomly assigned in equal numbers to a group treated with tulathromycin given as a single injection at 2.5 mg/kg of body weight or to a saline-treated control group. Four of the studies included a third group treated with ceftiofur sodium for 3 consecutive days at 3 mg/kg of body weight. Pigs were treated on day 0 and evaluated for treatment response on day 7. In each study, 10 or more nontreated pigs and saline-treated pigs that did not respond to treatment underwent necropsies to obtain lung samples that were evaluated for SRD pathogens. The overall cure rate was 46.4% for saline-treated pigs, 71.1% for tulathromycin-treated pigs, and 63.1% for ceftiofur-treated pigs. The cure rate for tulathromycin-treated pigs was significantly higher than for saline-treated pigs (P = .0116). Mortality from SRD occurred in 24 control pigs, seven tulathromycin-treated pigs, and one ceftiofur-treated pig. The mortality rate was significantly lower for both the tulathromycin- and ceftiofur-treated pigs compared with those treated with saline (P = .0148 and P = .0195, respectively). Actinobacillus pleuropneumoniae, Pasteurella multocida, Haemophilus parasuis, and Mycoplasma hyopneumoniae, bacteria commonly associated with SRD, were isolated from SRD-affected pigs. Under field conditions, tulathromycin injectable solution given as a single IM dose of 2.5 mg/kg of body weight was safe and effective in the treatment of SRD.

Therapeutic efficacy of tulathromycin, a novel triamilide antimicrobial, against bovine respiratory disease in feeder calves

Efficacy and field safety of tulathromycin administered as a single-dose treatment to crossbreed beef calves with undifferentiated bovine respiratory disease (BRD) were evaluated in a multicenter field study conducted at four US feedlots. Two hundred castrated male calves were enrolled at each study site. The treatment groups were physiologic saline (n = 160) given SC at 0.02 ml/kg, tulathromycin (n = 320) given SC at 2.5 mg/kg, and tilmicosin (n = 320) given SC at 10 mg/kg. Nasopharyngeal swabs for bacterial culture were obtained before treatment. The cure rate for calves treated with tulathromycin (78%) and tilmicosin (65%) was significantly (P < or = .0001) higher than that of calves treated with saline (23.8%). The cure rate of calves treated with tulathromycin (78.4%) was significantly (P = .0007) higher than that of calves treated with tilmicosin (64.9%). No adverse events related to tulathromycin were reported. Under the conditions of this study, tulathromycin administered as a single-dose treatment was efficacious in the treatment of undifferentiated BRD.

Comparative efficacy of tulathromycin versus florfenicol and tilmicosin against undifferentiated bovine respiratory disease in feedlot cattle

Four studies conducted at feedlots in Greeley and Wellington, Colorado; Nebraska; and Texas compared the efficacy of tulathromycin to florfenicol or tilmicosin for the treatment of cattle with undifferentiated bovine respiratory disease (BRD) and subsequent feedlot performance and carcass characteristics. In each study, 100 calves with BRD were treated with tulathromycin given SC at 2.5 mg/kg body weight. At the Greeley, CO, and Nebraska study locations, 100 calves were treated with florfenicol given SC at 40 mg/kg body weight, and at the Wellington, CO, and Texas study locations, tilmicosin was given SC at 10 mg/kg body weight. Cure rate, a derived variable that included assessments of mortality, rectal temperature, and attitude and respiratory scores from day 3 to day 28 and day 3 through harvest, was the primary assessment of BRD efficacy. Cure rates of calves treated with tulathromycin were significantly (P < or = .009) higher than those calves treated with florfenicol. At Wellington, CO, the cure rate of calves treated with tulathromycin was significantly higher (P < or = .018) compared with tilmicosin-treated calves. The differences in cure rates between tulathromycin and tilmicosin treatment groups in the Texas study were not significantly different (P > .05). Tulathromycin was more efficacious in the treatment of undifferentiated BRD compared with florfenicol and, in one study, compared with tilmicosin.

The comparative pathogenicity of strains of eight serovars and untypable strains of Mannheimia haemolytica in experimental pneumonia of sheep

The experimental induction of pneumonic pasteurellosis in groups of conventionally reared lambs by 8 serovars (A1, A2, A6, A7, A8, A9, T10, and A11) and untypable (UT) strains of Mannheimia haemolytica (Mh) were examined and compared. The groups of lambs were inoculated intratracheally with 1.4 x 10(8) +/- 0.6 x 10(8) (mean +/- SD) colony-forming units of the Mh serovars or UT isolates in the 6-hour log phase of growth. The variables measured as indicators of disease severity were clinical score, percentage lung consolidation and microbiological re-isolation. The clinical parameters for each group were computed daily for 6 days post infection and the lambs which died were necropsied while the remaining lambs were killed on day 7 pi and the extent of lung consolidation was measured. Clinically, the mean scores for the M. haemolytica serovars were A1 (6.1), A2 (18.8), A6 (0.5), A7 (17.4) and A9 (8.5). The mean percent lung lesion scores for M. haemolytica serovars were A1 (12.5), A2 (66.3), A6 (5.0), A7 (51.3), A9 (33.8) and A11 (2.5). The percent mean pneumonic lung lesions recorded for groups inoculated with A2, A7 and A9 were significantly (P < 0.05) higher than the extent of lung lesions in the other groups. A statistically significant correlation was observed between clinical scores and the severity of the lung lesions (r = 0.96, P < 0.01). High titres of M. haemolytica were recovered from lung lesions, with 10 to 100 times the number of organisms inoculated being present in the lung lesions of lambs inoculated with serovars A2 and A7. These data indicate that although M. haemolytica serovars A1, A2, A6, A7, A9 and A11 are important primary lung pathogens of lambs, serovars A2, A7, and A9 are to be regarded as highly virulent strains that have a greater predilection than the other serovars for causing pneumonia in lambs.

Surfactant protein D expression in normal and pneumonic ovine lung

Surfactant protein D (SP-D) is a collagenous calcium-dependent lectin constitutively expressed by alveolar type II pneumocytes and non-ciliated bronchiolar epithelial (Clara) cells. It binds to surface glycoconjugates expressed by a wide variety of microorganisms such as Gram-negative bacteria, influenza A virus, and various fungi, leading to pathogen inactivation or enhanced neutrophil and macrophage activity. Since a hallmark of bronchopneumonia is the initiation of inflammation in the bronchi and bronchoalveolar junction, we chose a classic ruminant model of bronchopneumonia caused by Mannheimia haemolytica to study the expression of SP-D within the bronchioles of infected lambs. Healthy weaned lambs were inoculated with either pyrogen-free saline (controls) or M. haemolytica intrabronchially using a fiber-optic bronchoscope. SP-D protein and mRNA expression in lung was detected by immunohistochemistry (IHC) and fluorogenic real-time relative quantitative reverse transcriptase polymerase chain reaction (real-time RT-PCR), respectively, during acute (1 day), subacute (15 days), and chronic (45 days) bronchopneumonia. At 15 and 45 days post-inoculation, areas of lung had peribronchiolar inflammatory cell infiltrate, epithelial cell hyperplasia, tortuosity of the airway lumens, and decreased intensity of SP-D protein staining and number of positive cells. The levels of SP-D mRNA were not increased or significantly altered by M. haemolytica infection when compared to control animals. In conclusion, cell-associated SP-D protein expression significantly decreases within hyperplastic epithelium of lungs from infected animals during chronic bronchopneumonia. Exhaustion of SP-D protein reserves and absence of SP-D gene upregulation during the progression of bacterial pneumonia into chronicity may result in failure to clear the pathogen from the lung and/or cause animals to be more susceptible to re-infection.

Pathophysiological and immune cell responses in calves prior to and following lung challenge with formalin-killed Pasteurella multocida biotype A:3 and protection studies involving subsequent homologous live challenge

Pneumonic pasteurellosis is a common respiratory infection in cattle that has major economic and welfare implications world-wide and the incidence in the UK due to Pasteurella multocida, currently the same as that associated with Mannheimia haemolytica, is increasing. Whereas much is known regarding the pathogenesis of M. haemolytica infections little information is available on the pathogenic process of pasteurellosis initiated by P. multocida. In the present work calf systemic and innate immune responses to intratracheal challenge with formalin-killed P. multocida biotype A:3 and to subsequent experimental lung infection with live P. multocida were investigated. Eight-week-old calves were challenged intratracheally on day 0 with either 10(9) colony forming units (cfu) of formalin-killed P. multocida biotype A:3 in 300 ml saline (n = 10) or 300 ml saline alone (n = 10), followed, at day 21, by challenge with 10(9) cfu live P. multocida. Pathophysiological and lung phagocyte responses were assessed by clinical monitoring, sequential lung lavage and blood sampling. Results for samples obtained before, during and after challenge showed clinical and acute phase protein responses to both bacterial culture and saline control treatments, although higher responses were associated with bacterial challenge. Phagocytosis of P. multocida during 1h incubation periods with lavaged cells in vitro was unaffected by exposure in vivo to killed P. multocida and there was evidence that P. multocida was able to survive intracellularly during this assay. There was no indication that lung exposure to formalin-killed P. multocida conferred protection against subsequent homologous live challenge.

Protective effect of dexamethasone in experimental bovine pneumonic mannheimiosis

Clinical and experimental studies provide unequivocal evidence that neutrophils participate in the pathogenesis of lung injury in bovine pneumonic mannheimiosis (BPM). Since the inflammatory cytokines tumor necrosis factor-alpha, interleukin-1 beta, and interleukin-8 play a central role in the recruitment and activation of neutrophils, we hypothesize that pharmacological inhibition of their expression may prevent or reduce the inflammatory lung injury that is characteristic of the disease. The purpose of this study was to determine whether systemic therapy with dexamethasone sodium phosphate (DEX), a potent inhibitor of inflammatory cytokine synthesis, ameliorates disease development in an in vivo experimental model of BPM. Four experimental calves were treated intravenously with DEX (2 mg/kg 6 h prior to infection, 2 mg/kg immediately prior to infection, and 1 mg/kg every 12 h thereafter), while two placebo-treated control calves received dose-matched volumes of sterile saline. Disease was induced in the left lungs of the six calves by endobronchial administration of Mannheimia haemolytica. Clinical disease was characterized using a non-parametric scoring system, and the extent of gross pulmonary pathology affecting the left lung 48 h post-infection (PI) was determined using morphometric methods. Disease scores for DEX-treated calves were significantly lower than those for placebo-treated controls at all time points beyond 2 h PI (P<0.05) and the percent volume of the left lung exhibiting gross pneumonic lesions was significantly lower in DEX-treated calves (6.0+/-1.1%) as compared to controls (68.9+/-13.3%), P<0.05. In addition, histopathological lesions were less severe and extensive in DEX-treated calves. These findings indicate that pharmacological modulation of pulmonary inflammation may represent an alternative approach to control this disease. Successful implementation of this strategy will require additional research to identify drug agents that target the expression of cytokines and other inflammatory mediators without compromising host immune responses.

The effects of danofloxacin and tilmicosin on neutrophil function and lung consolidation in beef heifer calves with induced Pasteurella (Mannheimia) haemolytica pneumonia

Pneumonia caused by Pasteurella (Mannheimia) haemolytica was induced in weaned beef heifer calves, approximately 6 months of age. Calves were treated at 20 h after challenge with therapeutic doses of danofloxacin or tilmicosin. Peripheral blood neutrophils were collected at 3, 24 and 48 h after treatment. The ex vivo effects on neutrophil function, neutrophil apoptosis, and hematological parameters were examined, as was the effect on percentage lung consolidation. Neutrophil function assays included random migration under agarose, cytochrome C reduction, iodination, Staphylococcus aureus ingestion, chemotaxis, and antibody-dependent and antibody-independent cell-mediated cytotoxicity. Apoptosis was determined using a cell death detection kit. Killing was performed at 72 h after treatment. Statistical comparisons were made among the three groups of challenged-treated animals: saline, danofloxacin, and tilmicosin. Comparisons were also made between nonchallenged nontreated animals (NCH) and challenged saline-treated animals. There were no significant differences for any of the neutrophil function assays or neutrophil apoptosis among the challenged-treated groups. This suggests that danofloxacin and tilmicosin have no clinically significant effects on neutrophil function or apoptosis. There were also no significant differences in percentage lung consolidation among the challenged-treated groups. Significant differences were found between the NCH calves and the challenged saline-treated calves in several neutrophil assays, which were attributed to effects of P. haemolytica infection.

Novel protease produced by a Pasteurella trehalosi serotype 10 isolate from a pneumonic bighorn sheep: characteristics and potential relevance to protection

A strain of Pasteurella trehalosi serotype 10, E(CO)-100, isolated from a bighorn sheep that had succumbed to pneumonic pasteurellosis during an epizootic, was compared to well-characterized strains of P. trehalosi serotype 10 and Mannheimia haemolytica serotype 1. The gene for leukotoxin A (lktA) from E(CO)-100 was sequenced and found to be identical on an amino acid basis to a published sequence for lktA from P. trehalosi serotype 10. However, the toxic activity in culture supernatant measured over time for E(CO)-100 was quite different from reference strains. Typically, the ability of the supernatant to lyse target cells increases over time corresponding to the logarithmic growth of the organism, peaks at mid to late phase, then declines gradually. Supernatant from E(CO)-100 exhibited a sharp decline in toxicity after mid-logarithmic growth to undetectable levels. Investigation of this anomaly using a commercial kit with a porcine gelatin/bovine albumin substrate matrix revealed high protease activity in the supernatant of this strain compared to another P. trehalosi serotype 10 and to a M. haemolytica serotype 1. Protease activity was also visualized using gelatin based zymogram gels. This protease was not substrate specific as it was shown to degrade leukotoxin. Activity was neutralized by bighorn sera in a titratable manner. There was an association between the ability to neutralize protease and low pneumonic lung scores in bighorn sheep experimentally challenged with E(CO)-100 (r=0.5, P=0.1). This previously unidentified protease may be an important protective antigen in vaccines designed to prevent pneumonic pasteurellosis resulting from P. trehalosi in bighorn sheep.

The importance of interleukin-8 as a neutrophil chemoattractant in the lungs of cattle with pneumonic pasteurellosis

Interleukin-8 (IL-8), an in vitro and in vivo neutrophil chemoattractant, is expressed at high levels in the lesions observed in bovine pneumonic pasteurellosis. Because of the role of neutrophils in the pathogenesis of pneumonic pasteurellosis, we investigated the relative importance of IL-8 as a neutrophil chemoattractant in this disease. Bronchoalveolar lavage (BAL) fluid was harvested from calves experimentally infected with bovine herpesvirus-1 and challenged with Mannheimia haemolytica. Neutrophil chemotactic activity was measured in pneumonic BAL fluid samples treated with a neutralizing monoclonal antibody to ovine IL-8, and compared to the activity in samples treated with an isotype-matched control antibody. Bronchoalveolar lavage fluid was analyzed at a dilution which induced a half-maximal response, and the concentrations of antibody were optimized in a preliminary experiment. Following incubation of replicate samples of diluted pneumonic bovine BAL fluid with 70 microg/mL of IL-8-neutralizing antibody or control antibody, the neutrophil chemotactic activities of the samples were determined using an in vitro microchemotaxis assay. Overall, pretreatment of BAL fluid samples with neutralizing anti-IL-8 antibody reduced neutrophil chemotactic activity by 15% to 60%, compared to pretreatment with control antibody. This effect was highly significant (P < 0.001), and was present in 5 of 5 samples. These data indicate that IL-8 is an important neutrophil chemoattractant in calves with pneumonic pasteurellosis, but that mediators with actions redundant to those of IL-8 must also be present in the lesions.

The effect of Pasteurella haemolytica A2 infection on phagocytosis efficiency of caprine broncho-alveolar macrophages

An experiment was designed to study the in vivo effect of Pasteurella haemolytica A2 infection on the phagocytosis activity of caprine broncho-alveolar macrophages and the extent of pneumonic lesions. Twelve healthy local Kacang goats, about 7 months of age, were divided into two groups of six. Goats in group 1 were inoculated intratracheally with 4 ml inoculum containing 2.8 x 10(9) colony-forming units (CFU)/ml of Staphylococcus aureus. Goats in group 2 were inoculated intratracheally with 4 ml of inoculum containing 9.5 x 10(8) CFU/ml of Pasteurella haemolytica A2 isolated earlier from pneumonic lungs of goat. At intervals of 3 and 7 days post-challenge five goats from each group were killed and the lungs were washed with sterile phosphate-buffered saline. Smears were prepared from the lung washing fluid and the number of macrophages with phagocytic activity was determined. At day 3 post-infection, goats of both groups showed a similar pattern of pneumonic lesion. The lung washing fluid of goats in group 2 was found to contain numerous neutrophils and macrophages. Goats in group 2 showed significantly (P < 0.05) higher extent of lung lesions than group 1. Similarly, the average extent of lung lesions was significantly (P < 0.05) more severe in group 2 at day 7 post-infection. The lung washing fluid contained mostly macrophages. The phagocytic activity following S. aureus infection was more efficient and significantly (P < 0.01) higher compared with infection by P. haemolytica A2. There were weak correlations between the extent of pneumonic lesion and the phagocytic activity. Thus, goats with poor phagocytic activity were likely to develop more extensive lung lesions.

Ultrastructural study of ovine pulmonary pasteurellosis: involvement of neutrophils and macrophages

Pasteurellosis is a common infectious disease characterised by fibrinous pneumonia and involving neutrophils and macrophages. This study aimed to determine the timing and extent of the pathogenic involvement of these cell elements in lesions induced in experimentally-infected lambs. A concentration of approximately 3x10(8) bacteria/ml. was inoculated into 30 two-month-old disease-free Merino lambs. Five lambs were assigned to each of five experimental batches, slaughtered on days 1, 3, 7, 11 and 15 following intratracheal inoculation, and to one control batch inoculated with a sterile solution. One control animal was slaughtered at the same time as each experimental batch. More characteristic lesions occur in bronchioles, peribronchial tissue and alveoli and are characterised by fibrinous processes. From the start of the experiment, epithelial-cell disruption and loss of microvilli were apparent; cell debris, desquamate cells and bacterial elements were observed in bronchiolar lumina, embedded in a fibrillar granular material. Alveolar structures displayed fewer neutrophils and macrophages, containing phagocytic vacuoles. Laminar bodies were apparent in type II pneumocytes. The interseptal area contained similar cell types, as well as abundant edema. In the course of the experiment, macrophage numbers increased in all the areas involved, with signs of intense phagocytic activity. The final phase of the experiment was characterised by a mild interseptal infiltrate and by clear alveolar lumina.

Mast cell density and substance P-like immunoreactivity during the initiation and progression of lung lesions in ovine Mannheimia (Pasteurella) haemolytica pneumonia

To determine the density of mast cells (MCs) and the extent of substance P (SP) immunoreactivity during initiation and progression of pneumonic pasteurellosis (PP), 18 lambs were inoculated intrabronchially with Mannheimia (Pasteurella) haemolytica or saline, and lung tissue was collected at 1, 15 and 45 days post-inoculation (n=3, each group). Additionally, the left (non-inoculated) contralateral lungs in bacteria-inoculated animals were collected as controls. At 1 day after bacterial inoculation the lungs had typical M. haemolytica lesions. These pneumonic lesions had fewer numbers of MCs and reduced histamine content. Macrophages infiltrating some of the inflamed areas were strongly immunoreactive for SP. At 15 days, MCs remained scarce at sites where lung damage persisted, i.e. pyogranulomatous foci, but were increased in number in areas of interstitial damage. Pulmonary ganglion neurons were strongly immunoreactive for SP. By 45 days the fibrosing changes became more defined as pleural fibrosis, fibrosing alveolitis, alveolar epithelial hyperplasia and bronchiolitis obliterans. These lungs had increased numbers of MCs, but histamine content was not different from saline- and non-inoculated left lungs. Substance P immunoreactivity occurred only in nerves and was scarce and mild. This work demonstrates that MC density decreases initially with PP, but increases with progression of PP. SP fibres tend to be decreased during the initiation and at 45 days of PP, but other cells, such as macrophages and neuronal ganglion cells, produce substance P during progression of PP and thereby constitute an additional source of substance P.

Development of an ex vivo model to study adherence of Mannheimia haemolytica serovar 1 to mucosal tissues of the respiratory tract of cattle

OBJECTIVE

To develop and validate an ex vivo model for study of adherence of Mannheimia haemolytica (formerly Pasteurella haemolytica) to respiratory tract mucosa of cattle and to use this model to confirm adherence of M haemolytica serovar 1 (Mh1) to several relevant respiratory mucosal surfaces.

SAMPLE POPULATION

Excised nasal, nasopharyngeal, turbinate, and tonsillar mucosal tissue from the bovine upper respiratory tract.

PROCEDURE

Mh1 was radiolabeled by use of tritiated leucine. Various concentrations of labeled bacteria were incubated with bovine upper respiratory tract tissues for various times. Tissue was washed to remove nonadherent bacteria, and percentage of bacteria adhered (percentage of adherence) was estimated using radioactivity. Using an optimal inoculum concentration and incubation time, percentage of Mh1 adherence was compared on nasal, nasopharyngeal, turbinate, and tonsillar mucosal tissue, and adherence to nasopharyngeal tissue was confirmed by scanning and transmission electron microscopy.

RESULTS

The optimal Mh1 inoculum concentration was 1 X 10(7) colony forming units/ml and incubation time was 3 hours. Percentage of adherence of Mh1 to nasopharyngeal tissue was greater than adherence to other tissue types.

CONCLUSIONS AND CLINICAL RELEVANCE

The ex vivo model maintained the functional and structural integrity of bovine upper respiratory tract mucosa, as confirmed by light and electron microscopy. Electron microscopy revealed participation of epithelial cell cilia and surface mucus in adherence of Mh1 to nasopharyngeal tissue. Adherence of Mh1 was confirmed in repeated assays, indicating that this organism adheres to upper respiratory tract mucosa of cattle.

Effects of the synthetic selectin inhibitor TBC1269 on tissue damage during acute Mannheimia haemolytica-induced pneumonia in neonatal calves

OBJECTIVE

To determine effects of the selectin inhibitor TBC1269 on neutrophil-mediated pulmonary damage during acute Mannheimia haemolytica-induced pneumonia in newborn calves.

ANIMALS

Eighteen 1- to 3-day-old colostrum-deprived calves.

PROCEDURE

Mannheimia haemolytica or saline (0.9% NaCl) solution was inoculated in both cranial lung lobes of 12 and 6 calves, respectively. Calves were euthanatized 2 (saline, n = 3; M haemolytica, n = 4) or 6 hours (saline, n = 3; M haemolytica, n = 8) after inoculation. Four M haemolytica-inoculated calves euthanatized at 6 hours also received TBC1269 (25 mg/kg, IV) 30 minutes before and 2 hours after inoculation. Conjugated diene (CD) concentrations, inducible nitric oxide synthase (iNOS) expression, and apoptotic cell counts were determined in lung specimens collected during necropsy.

RESULTS

Conjugated diene concentrations were significantly increased in all M haemolytica-inoculated groups, compared with saline-inoculated groups. Calves treated with TBC1269 had decreased concentrations of CD, compared with untreated calves, although the difference was not significant. Number of apoptotic neutrophils and macrophages increased significantly inTBC1269-treated calves, compared with untreated calves. Inducible nitric oxide synthase was expressed by epithelial cells and leukocytes. However, iNOS was less abundant in airway epithelial cells associated with inflammatory exudates. Degree of iNOS expression was similar between TBC1269-treated and untreated calves.

CONCLUSIONS

Mannheimia haemolytica infection in neonatal calves resulted in pulmonary tissue damage and decreased epithelial cell iNOS expression. The selectin inhibitor TCB1269 altered, but did not completely inhibit, neutrophil-mediated pulmonary damage.

Toxoplasmic encephalitis in a free-ranging Rocky Mountain bighorn sheep from Washington

A 4-mo-old free-ranging Rocky Mountain bighorn sheep (Ovis canadensis canadensis) from the Hells Canyon area (Washington, USA) was diagnosed with encephalitis associated with Toxoplasma gondii infection. The sheep had concurrent pneumonic pasteurellosis and resided in a geographic area with endemic Pasteurella-associated pneumonia and mortality in bighorn sheep. The brain had multifocal necrotizing and nonsuppurative encephalitis with intralesional protozoa. The protozoa were identified as T. gondii by immunohistochemistry. To our knowledge, this is the first report of T. gondii infection in a Rocky Mountain bighorn sheep.

Immunohistochemical characterization of calf pneumonia produced by the combined endobronchial administration of bovine herpesvirus 1 and Pasteurella haemolytica

Ten calves ("group 4") were inoculated endobronchially with Pasteurella haemolytica 4 days after inoculation with bovine herpesvirus 1 (BHV-1). Four calves (group 3) were similarly inoculated with P. haemolytica alone, and three (group 2) with BHV-1 alone. All group 4 animals showed severe respiratory signs and had bilateral lobar pneumonia; one died 6 days after inoculation with P. haemolytica. Two types of pneumonic lesion were observed. One was characterized by interlobular and interstitial lymphatic thrombosis, fibrinous pleuritis and coagulative necrosis, and the other by necrotizing bronchiolitis with intranuclear inclusion bodies. The former type of lesion was associated with the presence of P. haemolytica antigen and the latter with the presence of BHV-1 antigen. The weight of infection of BHV-1 and P. haemolytica in bronchoalveolar (BAL) fluid was clearly reflected in the immunohistochemical demonstration of the corresponding antigens in BAL fluid cells. Group 4 calves differed from the calves of groups 1-3 in showing 10-1530 times more endotoxin in BAL fluid. These findings suggested that BHV-1 infection partly destroyed the clearance mechanisms of the respiratory tract epithelium and exacerbated the subsequent P. haemolytica infection.

Reduction of pulmonary mast cells in areas of acute inflammation in calves with Mannheimia (Pasteurella) haemolytica pneumonia

Mast cells in the left cranial pulmonary lobe of colostrum-deprived neonatal calves were quantified 2 and 6 h after intrabronchial inoculation with Mannheimia (Pasteurella) haemolytica A1. The mast cells were detected (1) immunohistochemically with a mouse anti-human mast cell tryptase monoclonal antibody, and (2) by metachromatic staining with low pH toluidine blue. A greater number of mast cells was demonstrated by the second method than by the first. At 6 h after inoculation, but not at 2 h, the number of mast cells was significantly reduced at the site of the main lesions. Treatment of calves with a sialyl Lewis mimetic (TBC1269) did not appreciably affect the results at 6 h.

Role of platelet-activating factor in alveolar septal injury associated with experimentally induced pneumonic pasteurellosis in calves

OBJECTIVE

To determine whether platelet-activating factor (PAF) is involved in acute lung microvascular injury associated with pneumonic pasteurellosis in calves.

ANIMALS

15 healthy 2- to 4-week-old male Holstein calves.

PROCEDURE

Calves were anesthetized and inoculated intrabronchially with saline (0.9% NaCl) solution (n = 5) or 1x10(9) Pasteurella haemolytica organisms (n = 10). Of the 10 calves inoculated with P haemolytica, 5 also were treated with WEB 2086, a potent inhibitor of PAF, and 5 were treated with vehicle. Blood and bronchoalveolar lavage samples were collected before and 1, 2, 4, and 6 hours after inoculation of P. haemolytica. Blood samples were analyzed to evaluate total number and differential counts of leukocytes, dilute whole-blood leukocyte deformability, size of neutrophils, and neutrophil CD11b expression. Bronchoalveolar lavage samples were analyzed for total number and differential counts of nucleated cells, total protein concentration, and hemoglobin concentration. Size and gross and histologic appearance of lung lesions also was determined.

RESULTS

Treatment of calves with WEB 2086 reduced size of lung lesions, attenuated the increase in microvascular permeability, and reduced neutrophil infiltration in the first 4 hours after inoculation. Treatment with WEB 2086 also attenuated a decrease in leukocyte deformability, increase in size of neutrophils, and CD11b expression by circulating neutrophils.

CONCLUSIONS AND CLINICAL RELEVANCE

It appears that PAF is a major mediator for altered lung microvascular permeability and activation of circulating neutrophils in the first 4 hours after onset of pneumonic pasteurellosis in calves.

The potential role of the Arthus and Shwartzman reactions in the pathogenesis of pneumonic pasteurellosis

Pneumonic pasteurellosis (PP) is an economically important disease in cattle, sheep, and goats. Pasteurella haemolytica is commonly isolated from the severe fibrinopurulent pneumonia that characterize this respiratory syndrome. During infection, the bacteria produce leukotoxin (LKT) and lipopolysaccharide (LPS), both potent inducers of inflammation. Nonetheless, it has also been demonstrated that an exacerbated host's inflammatory response is responsible for the severe lung damage. Despite research in this field, the pathogenesis of PP is still incomplete. Two classical models of acute inflammatory response induced in laboratory animals, the Arthus and Shwartzman reactions, could explain the pathogenesis of the severe lung lesions that characterize PP.

Interalveolar septal changes with Pasteurella haemolytica-induced pneumonia in exertion-stressed calves

This study compared the effects of exertion stress and exertion stress combined with P. haemolytica infection on cells in the pulmonary capillaries and interalveolar septa adjacent to pneumonic lung. Two calves stood on an Anamill treadmill to serve as nonexercised controls and four calves were run to exhaustion (exertion-stressed) on the treadmill. Two of these four calves were inoculated endobronchially with 5 x 10(9) CFU of virulent Pasteurella haemolytica immediately following treadmill exercise. All calves were euthanized 24 h later and lung tissue was collected from the right mid-caudal lung lobe, next to the area of the gross lesion in inoculated calves. Ultrastructural evidence of increased metabolic activity of pulmonary intravascular macrophages (PIMs) and slight alveolar edema were present after exertion stress, but no changes in numbers of PIMs and platelets were observed between exertion-stressed and control calves. Lungs of calves that were subjected to stress and experimental infection had increases in size, number, and metabolic activity of PIMs, and numerous platelets that were interspersed among the PIMs. These findings suggest that exercise has minimal effect on the cellular changes in interalveolar septa after 24 h. However, exercise with P. haemolytica infection can stimulate PIM activity at short distances (<2.5 mm) from the gross pneumonic lesion. It is possible that the alterations in PIMs are stimulated by cytotoxic products arising from a nearby lesion in which bacteria and infiltrated cells are present.

In situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in calves with acute Pasteurella haemolytica pneumonia

The in situ expression of intercellular adhesion molecule-1 (ICAM-1) mRNA in normal and pneumonic lung tissues of Holstein calves with bovine leukocyte adhesion deficiency (BLAD) was compared with that of age-matched non-BLAD Holstein calves by in situ hybridization. Twenty-four Holstein calves (both BLAD and non-BLAD) were randomly assigned to one of two experimental groups and inoculated intrabronchially with Pasteurella haemolytica or pyrogen-free saline. Lung tissues were collected and fixed in 10% neutral formalin at 2 or 4 hours postinoculation (PI). The expression and distribution of ICAM-1 mRNA in the different cell types of the lung tissue was detected by in situ hybridization with a 307-base-pair bovine ICAM-1 riboprobe. In lungs of both non-BLAD and BLAD saline-inoculated calves, ICAM-1 expression was present in epithelial cells but occurred in <30% of cells in bronchi, bronchioles, and alveoli. ICAM-1 expression in vascular endothelial cells was present in <30% of cells in pulmonary arteries and veins. The expression of ICAM-1 was significantly greater (>60% of cells) in bronchiolar and alveolar epithelial cells and pulmonary endothelial cells of arteries and veins in both BLAD and non-BLAD calves inoculated with P. haemolytica. Bronchiolar epithelium had the highest intensity of mRNA expression and highest percentage of cells that were stained, whereas bronchial epithelium had the lowest intensity and percentage of cells stained. Most alveolar macrophages and neutrophils in infected lungs also expressed ICAM-1. ICAM-1 expression was generally increased in infected BLAD calves at 2 hours PI as compared with non-BLAD calves but not at 4 hours PI. The increased expression of ICAM-1 during acute P. haemolytica pneumonia in calves suggests that ICAM-1 is upregulated and may play a role in leukocyte infiltration. The extent of ICAM-1 expression in P. haemolytica-inoculated calves with BLAD was initially enhanced but otherwise similar to that in non-BLAD calves.

[Mechanisms of pathogenicity and adhesion in Pasteurella haemolytica]

Pasteurella haemolytica is one of the bacteria most commonly isolated from pneumonic cases in ruminants. Some of the mechanisms and factors involved in the pathogenesis of the disease are partially documented; and the early stages of bacterial colonization have not been totally clarified. Therefore a review is presented in this paper, particularly related with the mechanisms of bacterial pathogenicity responsible of pulmonary damage to ruminants, as well as a detailed analysis of the adherence process.

Evidence of Pasteurella haemolytica linked immune complex disease in natural and experimental models

The pathogenesis of bovine pneumonic pasteurellosis is not completely understood, and studies have not established that Pasteurella haemolytica A1 (Ph1) virulence is exclusively responsible for the development of acute pulmonary lesions. The purpose of this investigation was to determine if immune complex disease is involved in the pathogenesis of bovine pneumonic pasteurellosis. A retrospective immunohistologic study of lung tissue from natural cases of bovine pneumonic pasteurellosis (44) as performed, and immune complexes were observed in alveloar spaces and walls in 88% of these cases. To study this pathologic mechanism experimentally, groups of mice were immunized with purified Ph1 outer membranes (OMs) or sham immunized on days 0 and 14. Mice were challenged intratracheally on day 24 with either live Ph1 or Ph1 OMs, and pulmonary lesions were assessed 24 h after challenge. Placebo immunized mice developed focal infiltrates of neutrophils and macrophages centered around large caliber bronchi. Mice immunized with Ph1 OMs and challenged with live Ph1 or OMs developed severe bronchointerstitial pneumonia with diffuse neutrophilic infiltration, focal necrosis, hemorrhage and edema, that is histologically similar to bovine pneumonic pasteurellosis. Immunohistology revealed flocculent aggregates of IgG and complement positive material within alveolar spaces and walls from mice challenged with live Ph1, and fine granular deposits of IgG and complement positive material were observed lining the alveolar walls from mice challenged with Ph1 OMs. Immunized mice exhibited high serum IgG antibody titers to Ph1 outer membrane proteins (OMPs). Results of this study suggest that immune complex disease plays a role in the pathogenesis of bovine pneumonic pasteurellosis.

The clinical efficacy of enrofloxacin in the treatment of experimental bovine pneumonic pasteurellosis

The clinical efficacy of enrofloxacin was tested in calves with experimentally induced pneumonic pasteurellosis. A strain of Pasteurella haemolytica, biotype A, serotype 1 (P. haemolytica A1), which had been isolated from an outbreak of pneumonic pasteurellosis in feedlot calves, was used to induce the disease in 24 eight-month-old calves. Each animal received, by intratracheal injection, 6 x 10(11) colony forming units of P. haemolytica A1 in a four-hour log phase culture. Twelve similar animals were kept as non-infected controls (Negative Control group). Treatment of the infected animals commenced 40 h after infection and was as follows: 12 animals each received 2.5 mg/kg enrofloxacin subcutaneously and 12 animals each received 5 ml sterile saline intramuscularly (Positive Control group). All treatments were given once daily for three consecutive days. Clinical examinations were performed on all animals once daily, starting prior to infection and continuing until 12 d post-infection. The parameters evaluated were rectal temperature, habitus (attitude), ocular mucous membrane congestion and abnormal sounds on lung auscultation. On day 14 post-infection, all animals were killed and their lung lesions (if any) estimated as the percentage involvement of each pair of lungs. The only statistically significant (P > or = 0.05) differences observed were between the Negative Control group and the Positive Control group. Noticeable differences were seen between the enrofloxacin-treated group and the Positive Control group, but they were not statistically significant (P > 0.05). The average lung lesion score (pneumonic lesions as a percentage of total lung volume) for the Positive Control group was 12.1% and that of the enrofloxacin-treated group, 8.4%. This difference was not statistically significant (P > 0.05).

In vivo effect of Pasteurella haemolytica infection on bovine neutrophil morphology

OBJECTIVE

To determine whether characteristic changes in neutrophil morphology caused in vitro by Pasteurella haemolytica leukotoxin (LKT) can be observed in vivo by electron microscopic examination of infected tissue chamber fluids and pneumonic lungs.

ANIMALS

7 mixed-breed beef calves.

PROCEDURE

Tissue chambers were implanted subcutaneously in 3 calves and were inoculated with P haemolytica or phosphate-buffered saline solution. Chamber fluid samples, obtained at 8 and 32 hours after inoculation, were examined, using electron microscopy. Experimental pneumonia was induced in an additional 4 calves by transthoracic inoculation with P haemolytica. These calves were euthanatized at 6, 12, 24, and 36 hours after inoculation and lung sections were examined, using transmission electron microscopy.

RESULTS

On examination, using transmission electron microscopy, neutrophils in lung sections and tissue chamber fluids had cytoplasmic and nuclear changes indicative of irreversible cell injury, including cell swelling, loss of plasma membrane ruffling, mitochondrial swelling, autolytic vacuolation, disruption of plasma membrane, nuclear pyknosis, karyolysis, and karyorrhexis. On examination, using scanning electron microscopy, leukocytes obtained from tissue chambers did not have their typical convoluted surfaces, but appeared rounded and swollen or shrunken with pitted surfaces.

CONCLUSIONS

Pasteurella haemolytica-induced changes in neutrophil morphology in vivo were similar to those previously induced by in vitro exposure of neutrophils to LKT. Changes were suggestive of injury initiated by damage to the plasma membrane, which is consistent with the mechanism of action of pore-forming cytolysins.

CLINICAL RELEVANCE

Pasteurella haemolytica LKT appears to be an important virulence factor in vivo; a fact that should be addressed in the development of vaccines.

Expression of the neutrophil chemoattractant interleukin-8 in the lesions of bovine pneumonic pasteurellosis

We investigated the expression of interleukin-8 (IL-8) in pneumonic pasteurellosis of cattle because neutrophils are important mediators of tissue injury in this disease and because IL-8 is a major neutrophil chemoattractant in other species. We also compared IL-8 expression in bacterial and viral pneumonia, since the latter lacks the severe neutrophil exudation typical of pneumonic pasteurellosis. IL-8 expression was assessed by northern analysis, in situ hybridization, enzyme-linked immunosorbent assay, and in vivo bioassay. IL-8 mRNA expression was elevated dramatically in lesions of pneumonic pasteurellosis compared to unaffected lung from the same calves. In situ hybridization revealed intense expression of IL-8 mRNA in alveolar macrophages and neutrophils and milder expression in bronchiolar and alveolar epithelium, interstitial cells, and pleural mesothelium. Bronchoalveolar lavage fluid from lesional lung contained 16.06+/-4.00 ng/ml IL-8, whereas those from nonlesional and normal lung contained 0.34+/-0.11 and 0.01+/-0.002 ng/ml, respectively. We detected IL-8 expression at only minimal levels in bovine respiratory syncytial viral pneumonia. Lung extracts from lesions of pneumonic pasteurellosis induced vigorous neutrophil infiltration following injection into bovine skin, and 89% depletion of IL-8 from the extract reduced this neutrophil influx by 60%. These results demonstrate consistent upregulation of IL-8 expression in lesions of pneumonic pasteurellosis, implying a role for IL-8 in the ongoing recruitment of neutrophils to established lesions of pneumonic pasteurellosis. Because neutrophil-mediated tissue injury is critical to the pathogenesis of pneumonic pasteurellosis, these data suggest that neutralization of IL-8 activity could ameliorate the severe clinical signs and lesions of this disease.

Changes in the lungs of lambs after intratracheal injection of lipopolysaccharide from Pasteurella haemolytica A1

Ten lambs aged 8 weeks were inoculated intratracheally through the tracheal wall with lipopolysaccharide from Pasteurella haemolytica A1 and examined in chronological sequence by light and electron microscopy for pulmonary lesions. An acute fibrinopurulent pneumonia was produced, which resolved within 72 h but bore many resemblances to field cases of pneumonic pasteurellosis. Sequestration of neutrophils in the capillaries of the lungs and aggregation of surfactant in the alveoli occurred rapidly, followed by swelling of the alveolar and capillary endothelia, oedema, haemorrhage, and emigration of neutrophils into the interstitium and small air spaces of the lungs. Necrosis of isolated neutrophils was a constant feature. Alveolar, interstitial and intravascular macrophages and lymphoid cells increased slowly to become the predominant inflammatory cells at 72 h. A surprising feature was the transient appearance of multinucleated cells in the lungs at 2 and 6 h after inoculation. It is concluded that lipopolysaccharide makes a major contribution to the pathogenesis of P. haemolytica infection in the lungs of sheep.

Construction of an isogenic leukotoxin deletion mutant of Pasteurella haemolytica serotype 1: characterization and virulence

Allelic replacement was used to generate two isogenic lktA deletion mutants of Pasteurella haemolytica serotype 1 that were incapable of synthesizing leukotoxin (Lkt). Southern blot data confirmed that lktA sequences were absent in the two P. haemolytica deletion mutants. Culture supernatants and whole cell lysates from the wild type P. haemolytica, D153 parent strain, but not the lktA deletion mutants, contained immunoreactive and bioactive leukotoxic protein. In addition, only the parent strain was haemolytic when grown on bovine and sheep blood agar plates. Virulence of the lktA deletion mutant, lktA 77, was compared with the parent in an experimentally infected calf model of pneumonic pasteurellosis. Results revealed significant reduction in virulence in the lktA mutant as measured by clinical and lung lesion scores. Notable differences in histological changes such as markedly reduced necrosis and lack of leukocyte degeneration occurred in calves infected with the lktA mutant in comparison with those infected with the parent wild-type strain. Thus, it appears that leukotoxin plays a important role in the pathogenesis of lung injury in bovine pneumonic pasteurellosis.

Treatment of experimentally induced pneumonic pasteurellosis of young calves with tilmicosin

Twenty four (24) healthy male Holstein calves (< 70 kg) were each experimentally infected by intrabronchial inoculation of 4.0 x 10(9) viable cells of Pasteurella haemolytica-AI (B122) at Time = 0 h. At 1 h following inoculation animals received either: 1) Sham treatment with sterile 0.85% saline SC (n = 12); or 2) a single injection of 10 mg tilmicosin per kg body weight (n = 12). Calves that were non-infected and tilmicosin-treated were also included for determining tilmicosin concentrations in serum and lung tissue at 1, 2, 4, 6, 8, 24, 48, and 72 h (n = 3-per time). In the infected calves, response to therapy was monitored clinically. Serum samples were collected for determination of tilmicosin concentrations using HPLC. Any animal becoming seriously ill was humanely killed. Complete necropsy examinations were performed on all animals and included gross pathologic changes, bacteriologic analysis, histopathology, and determination of pulmonary concentrations of tilmicosin. Tilmicosin treated animals responded significantly better to therapy than saline-treated control calves. Clinical assessment of calves during the study indicated that tilmicosin-treated calves had significantly improved by T = 8 h compared to satine-treated animals (P < 0.05). At necropsy tilmicosin-treated calves had significantly less severe gross and histological lesions (P < 0.05) of the pulmonary tissue. Of the 12 saline-treated calves, 92% (11/12) had Pasteurella haemolytica-A1 in lung tissue, while of the tilmicosin-treated calves 0% (0/12) cultured positive for P. haemolytica. Mean (+/- standard error) serum tilmicosin concentrations in infected calves peaked at 1 h post-injection (1.10 +/- 0.06 micrograms/mL) and rapidly decreased to 0.20 +/- 0.03 microgram/mL, well below the MIC of 0.50 microgram/mL for P. haemolytica-A1 (B122), by 12 h. These serum concentrations were very similar to serum concentrations of tilmicosin in non-infected tilmicosin-treated calves. Lung tissue concentrations of the antibiotic were comparatively high, even at 72 h post-infection (6.50 +/- 0.75 ppm). Lung tissue concentrations at 72 h were significantly higher in experimentally infected calves than in non-infected tilmicosin-treated animals (P < 0.05). These data demonstrate that tilmicosin was effective in treating experimentally-induced pneumonic pasteurellosis as determined by alleviation of clinical signs, pathological findings at post mortem, and presence of viable bacteria from the lung. Concentrations substantially above MIC for P. haemolytica were present in lung tissue even at 72 h following a single subcutaneous injection of 10 mg tilmicosin per kg body weight.

Pulmonary venous thrombosis in caprine Pasteurella pneumonia

A 3-year-old Angora goat that developed acute fibrinous pleuropneumonia associated with Pasteurella haemolytica infection had thrombotic occlusion of a large pulmonary vein. Thrombosis of pulmonary capillaries occurs in pneumonic pasteurellosis, but large vessels are not commonly affected. This unusual lesion may reflect the procoagulant effect of pasteurella endotoxin on vascular endothelium. An incidental observation was the presence of myocardial-type muscle fibres in the tunica media of the pulmonary vein.

Pasteurella haemolytica leukotoxin induces bovine leukocytes to undergo morphologic changes consistent with apoptosis in vitro

Infection of the bovine lung with Pasteurella haemolytica results in an acute respiratory disorder known as pneumonic pasteurellosis. One of the key virulence determinants used by this bacterium is secretion of an exotoxin that is specific for ruminant leukocytes (leukotoxin). At low concentrations, the leukotoxin can activate ruminant leukocytes, whereas at higher concentrations, it inhibits leukocyte functions and is cytolytic, presumably as a result of pore formation and subsequent membrane permeabilization. We have investigated the possibility that the activation-inhibition paradox is explained in part by leukotoxin-mediated apoptosis (i.e., activation-induced cell death) of bovine leukocytes. Incubation of bovine leukocytes with P. haemolytica leukotoxin caused marked cytoplasmic membrane blebbing (zeiosis) and chromatin condensation and margination, both of which are hallmarks of apoptosis. The observed morphologic changes in bovine leukocytes were leukotoxin dependent, because they were significantly diminished in the presence of an anti-leukotoxin monoclonal antibody. In addition, bovine leukocytes incubated with culture supernatant from a mutant strain of P. haemolytica that does not produce any detectable leukotoxin failed to exhibit the morphologic changes characteristic of cells undergoing apoptosis. These observations may represent an important mechanism by which P. haemolytica overwhelms host defenses, contributing to the fibrinous pleuropneumonia characteristic of bovine pasteurellosis.

The goat as a model for studies of pneumonic pasteurellosis caused by Pasteurella multocida

A model of pneumonic pasteurellosis has been established in goats using Pasteurella multocida harvested from pneumonic lungs of goats (types A and D), rabbits (type A) and sheep (type D). The resultant infections were acute, subacute or chronic. The gross and histological lesions of the subacute and chronic infections were typical of pneumonic pasteurellosis. P. multocida type D produced significantly (P < 0.01) more severe lesions when compared with other isolates. There were strong correlations between the clinical signs and the severity of lesions.

Induction of nitric oxide production by bovine alveolar macrophages in response to Pasteurella haemolytica A1

We assessed the kinetics of inducible nitric oxide synthase (iNOS) mRNA expression and production of nitric oxide (NO) in bovine alveolar macrophages (AMs) stimulated with purified lipopolysaccharide (LPS) from Pasteurella haemolytica strain 12296. The effect of LPS on iNOS gene expression was dose-dependent and was expressed maximally at 24 h after stimulation with 10 micrograms/ml of LPS. Production of NO measured as secreted nitrite in supernatants took place in a time and dose-dependent manner with peak production at 24 h after LPS stimulation. Recombinant bovine gamma interferon (rb gamma IFN) augmented the LPS-induced iNOS gene expression and production of NO. The ability of LPS to induce iNOS gene expression and NO production either alone or in combination with rb gamma IFN was significantly abrogated by polymyxin B. In addition, the iNOS inhibitor NG-monomethyl-Larginine (L-NMMA) significantly inhibited LPS and rb gamma IFN + LPS induced NO production. Our results also demonstrated that NO produced from an exogenous NO donor sodium nitroprusside (SNP), and NO generated from LPS-stimulated AMs (endogenous) caused cytotoxic injury to bovine pulmonary artery endothelial cells in a dose-dependent manner. The cytotoxic injury caused by NO generated from LPS stimulated AMs was inhibited by polymyxin B or L-NMMA. There was a markedly increased concentration of nitrite in the lung lavage fluids of calves following P. haemolytica infection. These findings support a role for NO in the pathogenesis of lung injury in bovine pneumonic pasteurellosis.

Development of bronchus-associated lymphoid tissue in goats

Development of bronchus-associated lymphoid tissue (BALT) was studied in clinically healthy and diseased Assam local goats. Animals were sacrificed before term as well as at different postnatal periods to screen lung sections for the presence of BALT. In a retrospective study sections prepared from pneumonic lungs were examined for any alteration of BALT. No BALT-like structure was found in neonatal goats. Bronchial lymphoid structures appeared in half of the animals from 1 month of age onward. The frequency of the BALT/4.5 cm2 of lung section ranged from one to two in 1-month-old and three to six in 1-year-old goats. In pneumonic lungs BALT became hyperplastic, and the size was also increased. The incidence of BALT was increased in lungs with fibrotic pneumonia. The number of BALT/section was high (five to eight/4.5-cm2 area) in mesenchymal cell proliferation. The present study shows that BALT did not develop in prenatal periods. But in the presence of potent antigens lymphoid aggregates appeared in the bronchial lamina propria of normal and diseased lungs.

Protection of ruminants by Pasteurella haemolytica A1 capsular polysaccharide vaccines containing muramyl dipeptide analogs

The capsular polysaccharide (CP) of Pasteurella haemolytica serotype A1 is a poor immunogen for the prevention of pneumonic pasteurellosis of ruminants. To improve CP immunogenicity, vaccines were prepared with 1.0 mg CP dose-1 with and without the synthetic adjuvant, muramyl dipeptide (MDP; range 0.2-1.0 mg) or a lipophilic derivative, MDP-sn-glyceryl-dipalmitoyl (MDP-GDP; range 0.1-1.0 mg). The optimum effective concentration of adjuvant was first determined in lambs and calves and then the efficacy of CP +0.5 mg MDP and CP +1.0 mg MDP-GDP was compared with that of two commercial vaccines in calves. After immunization with CP, antibody titers in lambs and calves were typical of that seen with polysaccharide immunogens and characterized by an early IgM response followed by later IgG1 and IgG2 responses. CP + MDP or MDP-GDP vaccines induced significantly higher IgM, IgG1, and IgG2 titers. After transtracheal challenge of immunity with P. haemolytica serotype A1, extensive pulmonary consolidation containing P. haemolytica (10(6)-10(8) c.f.u. g-1) was seen in all lambs and calves vaccinated with CP alone and was not significantly different (P < 0.05) from the consolidation and concentrations of organisms in nonvaccinated challenge controls. In lambs, vaccines containing 1.0 mg CP +0.05 mg MDP or MDP-GDP significantly reduced pulmonary consolidation and concentrations of P. haemolytica in lung lesions. In calves, vaccines containing 0.2 mg MDP, 0.5 mg MDP, or 1.0 mg MDP-GDP also significantly reduced pulmonary consolidation and concentrations of P. haemolytica in lung lesions. Vaccines containing CP +0.5 mg MDP and CP +1.0 mg MDP-GDP induced high titer bactericidal antibodies by 7 days and were more efficacious than two commercial vaccines. Potentiation of CP with MDP or MDP-GDP has great promise in furthering the potential of CP as a vaccine immunogen for the prevention of pneumonic pasteurellosis.

Increased tumor necrosis factor-alpha and interleukin-1 beta expression in the lungs of calves with experimental pneumonic pasteurellosis

We used a well characterized pneumonic pasteurellosis model in calves to determine whether increased proinflammatory cytokines, tumor necrosis factor-alpha (TNF-alpha) and interleukin-1 beta (IL-1 beta) expression and secretion were associated with pneumonic lesions. Bronchoalveolar lavage fluids, lavage cells consisting of alveolar macrophages and neutrophils with degenerative changes, and lung tissues were analyzed for the presence of TNF-alpha and IL-1 beta approximately 48 h following endobronchial inoculation of logarithmic phase Pasteurella haemolytica 12296 organisms. Levels of TNF-alpha and IL-1 beta mRNA were significantly increased in lavage cells of P. haemolytica-infected animals but not in cells from phosphate buffered saline (PBS) inoculated controls based on in situ hybridization analysis. Significantly increased levels of TNF-alpha, and IL-1 beta mRNA were also expressed within the pneumonic lesions from P. haemolytica-infected calves. In contrast, lung tissues from PBS-inoculated control calves had cytokine mRNAs expressed at extremely low levels. Increased levels of bioactive IL-1 and immunoreactive (not bioactive) TNF-alpha were found in lavage fluids from P. haemolytica-infected calves compared with lavage fluids from PBS-inoculated calves. These findings indicate that the proinflammatory cytokines TNF-alpha and IL-1, may be associated with pathogenesis of lung injury in bovine pneumonic pasteurellosis.

[Pathogenesis of lung damage caused by Pasteurella haemolytica]

Pneumonic pasteurellosis is the major economic problem of the cattle industry in North America. This disease is characterized by an acute, severe, fibrinonecrotic pleuropneumonia. Pasteurella haemolytica A1 is commonly isolated from these pneumonic lesions. It has been demonstrated that stress or viral infection compromises defense mechanisms of the upper respiratory tract and lung, predisposing to an initial multiplication of bacteria in the nasopharynx and, subsequently, lungs are deluged with large numbers of bacteria. Once multiplication in the alveoli has begun, virulence factors exert their influence to induce an excessive host inflammatory response that results in severe tissue damage. Despite a large number of studies conducted to explore the complex interaction between P. haemolytica and the host response, there still remains a lack of detailed understanding. This review discusses evidence of the role of the main virulence factors of P. haemolytica on the pathogenesis of pulmonary damage.

Pulmonary ventilation, mechanics, gas exchange and haemodynamics in calves following intratracheal inoculation of Pasteurella haemolytica

A Pasteurella haemolytica A1 broth was injected intratracheally in eight calves and measurements of pulmonary function values (PFV) were made once before and hourly post inoculation (p.i.). Changes in PFVs, included increased respiratory rate and minute ventilation (up to 158% of baseline 2 h p.i.) and decreased tidal volume and lung dynamic compliance (up to 33% of baseline 3 h p.i.). Total pulmonary resistance was not affected. At and after 3 h p.i. there was a progressive impairement of gas exchange, as judged from arterial O2 tension which decreased up to 65% of baseline. In contrast, arterial CO2 tension was not affected. Pulmonary hypertension was observed during the 3 last h of the study and was attributable to an increased pulmonary vascular resistance. Severe neutropenia was observed at 3 h p.i. and post-mortem histological findings were consistent with an acute fibrinohemorragic bronchopneumonia. In conclusion, P. haemolytica airway challenge unequiovocally resulted in acute pneumonia, providing a reproducible pathophysiological model for investigations regarding new therapeutic strategies.

Serotypes of Pasteurella multocida and Pasteurella haemolytica isolated from pneumonic lesions in cattle and sheep from México

A total of 13,000 pairs of lungs were examined at Mexico's City abbatoir, where 8,000 corresponded to sheep and 5,000 to cattle. From those, 224 pneumonic lesions were observed, obtaining 97 positive isolates, which yielded 112 strains of Pasteurella sp. Forty isolates were identified as P. haemolytica and 72 as P. multocida. One-hundred percent of P. haemolytica belonged to biotype A. Serotypes were determined by indirect haemagglutination. P. multocida isolates were classified according to the acriflavine and hyaluronidase techniques, 61% belonged to type A, 25% to type D and 14% were untypified. Somatic serotypes were determined by gel immunodiffusion; serotype 3 was more frequent, in sheep 72% and in cattle 77%.

Fatal pneumonia following inoculation of healthy bighorn sheep with Pasteurella haemolytica from healthy domestic sheep

In a series of three experiments, isolates of Pasteurella haemolytica biotype A, serotype 2, ribotype reference WSU-1, from healthy domestic sheep, were inoculated intratracheally into eight bighorn sheep (Ovis canadensis canadensis) and seven domestic sheep with doses of bacteria ranging from 5.3 x 10(8) to 8.6 x 10(11) colony forming units. Seven of eight inoculated bighorn sheep died from acute pneumonia within 48 hr of inoculation, whereas all seven domestic sheep inoculated with comparable or greater doses of bacteria remained healthy. One contact control bighorn sheep also died 6 days after its penmates received P. haemolytica. Three other noncontact control bighorn sheep remained healthy during the experiments. Pasteurella haemolytica biotype A, serotype 2, ribotype reference WSU-1 in the inocula was recovered from one or more tissues from all bighorns that died; whereas, it was not detected in any bighorn sheep before inoculation. Three different ribotypes of P. haemolytica A2 were recovered from bighorn sheep; however, only the ribotype reference WSU-1 in the domestic sheep-origin inoculum was recovered from all dead bighorn sheep, and was not recovered from bighorn sheep that survived the experiments. Thus, a relatively nonpathogenic and common isolate of P. haemolytica from healthy domestic sheep was lethal in bighorn sheep under experimental conditions.