Diagnostic ultrasonography in cattle with thoracic disease

The pleura and lungs were evaluated by means of sonography in 55 bovine patients with diseases of the thoracic cavity. For these ultrasound examinations, a range of transducers was used. As the lung surface was most often involved in cases of pulmonary disease, it was possible to detect ultrasonographically bronchopneumonia, consolidation, pleural effusion, pulmonary emphysema and pleuritis. Determination of the amount of lung tissue affected provided prognostic information. It was not possible to visualise lesions located deeper within the lungs where peripheral tissue was not affected. A diagnosis of thoracic disease was made on the basis of clinical and ultrasonographic findings and confirmed in 33 cases at necropsy.     

ULTRASONOGRAPHIC FINDINGS IN 13 HORSES WITH LYMPHOMA

Ultrasonography and radiography are commonly used for staging of lymphoma in horses, however there is little published information on imaging characteristics for horses with confirmed disease. The purpose of this retrospective, case series study was to describe ultrasonographic and radiographic findings for a group of horses with a confirmed diagnosis of lymphoma. A total of 13 horses were sampled. Lymphadenopathy (8/13), peritoneal effusion (6/13), splenic (6/13), and hepatic (5/13) lesions were the most frequently identified. The predominant splenic and hepatic ultrasonographic lesions were hypoechoic nodules, organomegaly, and changes in echogenicity. Digestive tract lesions were detected in three horses and these included focal thickening and decreased echogenicity of the small (2/13) and large intestinal (2/13) wall. Thoracic lesions were predominantly pleural effusion (4/13), lymphadenopathy (4/13), and lung parenchymal changes (3/13). Enlarged lymph nodes were detected radiographically (4/13) and/or ultrasonographically (2/13) in the thorax and ultrasonographically in the abdomen (7/13) and in the caudal cervical region (4/13). Findings supported the use of abdominal and thoracic ultrasonography for lymphoma staging in horses. Ultrasound landmarks for localizing cecal and caudal deep cervical lymph nodes were also provided.     

LYMPHOMA AFFECTING THE URINARY BLADDER IN THREE DOGS AND A CAT

Three dogs and one cat with lymphoma affecting the urinary bladder are reported and the findings on abdominal radiographs and ultrasound are described. Mural lesions representing lymphoma affecting the urinary bladder were identified ultrasonographically in all animals. The most common complications associated with urinary bladder lymphoma were hydronephrosis and hydroureter. In two patients contrast radiography was necessary to detect leakage of urine in the peritoneal and retroperitoneal space. The radiographic and ultrasonographic signs were similar to those reported with other urinary bladder neoplasms; hence urinary bladder lymphoma could not be distinguished from the more common urinary bladder neoplasms, such as transitional cell carcinoma. It is important to include lymphoma in the differential diagnosis of urinary bladder wall thickening and mural mass in dogs and cats.     

Use of computed tomography and minimum intensity projection in the detection of lobar pneumonia mimicking lung lobe torsion in a dog

A 10‐year‐old female spayed Dachshund was referred with progressive coughing for 1 month. The dog was tentatively diagnosed with right middle lung torsion based on pleural effusion, vesicular emphysema, abruptly ending bronchus in consolidated right middle lung, and no contrast enhancement of the affected lobe on radiography and computed tomography (CT). There was no evidence of torsion upon thoracotomy, and histological examination confirmed lobar pneumonia. The CT images were reevaluated using minimum intensity projection and revealed normal bronchial courses. The minimum intensity projection technique can be to assist in evaluation of the bronchial tree for dogs with suspected lung lobe torsion and other pulmonary diseases.     

RADIOGRAPHIC CHARACTERIZATION OF PRIMARY LUNG TUMORS IN 74 DOGS

Primary pulmonary neoplasia is well recognized in dogs and prognosis depends upon the tumor type. The purpose of this retrospective study was to characterize the radiographic appearance of different primary lung tumors with the goal of establishing imaging criteria to separate the different types. Three‐view thoracic radiographs of 74 dogs with histologically confirmed pulmonary anaplastic carcinoma (n = 2), adenocarcinoma (n = 31), bronchioalveolar carcinoma (n = 19), histiocytic sarcoma (n = 21), and squamous cell carcinoma (n = 1) were evaluated. Radiographs were assessed for tumor volume, affected lobe, location within lobe, overall pulmonary pattern, presence of cavitation, mineralization, air bronchograms, lymphadenomegaly, and pleural fluid. Histiocytic sarcomas were significantly larger than other tumor types (271 cm³; P = 0.009) and most likely to be found in the left cranial (38%; 8/21) and right middle (43%; 9/21) lung lobes, whereas adenocarcinomas were most likely to be found in the left caudal (29%; 9/31) lung lobe. Fifty‐seven percent (12/21) of histiocytic sarcomas had an internal air bronchogram. Findings indicate that a large mass in the periphery or affecting the whole lobe of the right middle or left cranial lung lobe with an internal air bronchogram is likely to be an histiocytic sarcoma.     

Diagnostic challenges: Equine thoracic neoplasia

The diagnosis of thoracic neoplasia in the horse can be difficult due to the nonspecific nature of the clinical signs and their overlap with other pulmonary diseases. Haematological and serum biochemical evaluation, thoracic ultrasonography, radiography, endoscopic examination, and, where appropriate, thoracocentesis and pleural fluid cytology may all be helpful in reaching a diagnosis. Granular cell tumours are the most frequently reported primary pulmonary tumours of horses. They occur as single or multiple masses adjacent to bronchi and bronchioles, and the mass typically extends into the airway, resulting in partial or complete occlusion of the lumen. Thymic tumours are classified as benign or metastatic, based on evidence of tissue invasiveness, even though they uniformly appear benign histologically. These tumours are derived from epithelial reticular cells of the thymus and are rare in horses. Other primary thoracic neoplasms originate from various pulmonary tissues and are primarily reported as single case reports: pulmonary and bronchial carcinoma and adenocarcinoma, bronchogenic squamous cell carcinoma, bronchial myxoma, pulmonary chondrosarcoma, pulmonary leiomyosarcoma and pleuropulmonary blastoma. Clinical signs of these primary pulmonary neoplasms are dependent on the tumour type and location, but commonly include chronic cough, weight loss, anorexia, fever and respiratory difficulty; ventral oedema, pleural effusion and epistaxis are also frequently observed. Mesothelioma is a rare primary pleural tumour arising from the mesothelium of the pleura, pericardium and peritoneum. The clinical presentation in horses includes weight loss, respiratory difficulty and large volume pleural effusion. The tumour appears ultrasonographically as multiple small nodules on a thick serosal surface and pleural biopsy is diagnostic. Lymphoma is the most common haematopoietic neoplasm in horses, which can present with 4 main manifestations of lesions: mediastinal, multicentric, alimentary and cutaneous. Common clinical features include chronic weight loss, lethargy, anorexia, subcutaneous oedema, lymphadenopathy, colic, bleeding tendency and diarrhoea. Coughing and laboured respiratory effort are often apparent in individuals suffering from mediastinal masses. In such instances, pleural effusion may result in severe pulmonary atelectasis and pulmonary function is significantly compromised. Haemangiosarcoma is the second most common metastatic thoracic neoplasm in horses. Disseminated haemangiosarcoma is aggressive and rapidly progressive. The clinical presentation often includes tachypnoea, pale or icteric mucous membranes, respiratory distress, epistaxis, and subcutaneous, cutaneous or intramuscular masses. Other tumour types that metastasise to the thoracic cavity include adenocarcinoma, squamous cell carcinoma, fibrosarcoma, metastatic melanoma, mastocytoma and undifferentiated sarcoma. The clinical features of these tumours are generally nonspecific and often relate more to the primary site of tumour formation.     

Diagnostic contribution of thoracic ultrasonography in 17 foals with Rhodococcus equi pneumonia

The aim of this retrospective study was to determine the clinical usefulness of thoracic ultrasonography compared to thoracic radiography in evaluation of Rhodococcus equi pneumonia. Criteria for patient inclusion in this study were: (1) isolation of R. equi from transtracheal aspirate, (2) radiographic evaluation of the pulmonary parenchyma, and (3) sonographic evaluation of the pulmonary parenchyma. Seventeen foals met this criteria and their medical records were reviewed. Pyogranulomatous pneumonia was identified radiographically in 13 foals. Severe consolidative pneumonia with no detectable abscessation was identified radiographically in three others. Both consolidation and abscessation were identified radiographically in one. In this foal only consolidation was ultrasonographically identified. Ultrasonographically, pulmonary abscessation was identified in 12 foals and pulmonary consolidation with no detectable abscessation was identified in three others. Sonographic examination allowed detection of only pleural irregularities in one foal, which was subsequently found to have pyogranulomatous pneumonia radiographically. Results indicate that ultrasonography may be an accurate alternative imaging modality for detection of pulmonary pathology attributed to R. equi pneumonia in foals when thoracic radiography is not available.     

Lung and pleural lesions of veal calves at slaughter and their relationship with carcass weight

At slaughter the lungs of 2138 veal calves (13 transport groups, mainly from different farms) were examined. Lung and pleural lesions were classified by degree of extension and pathomorphological features, and the accompanying carcass weights were measured. Seventeen percent of the calves had extensive lung lesions, extensive pleural lesions or both, and their mean carcass weight was reduced by 4.3 kg (p less than 0.05). The percentage of calves with extensive lesions varied between transport groups from 4% to 33%. All pleural lesions were adhesive. Most lung lesions (93%) were classified as cuffing/exudative pneumonia. Slaughterhouse inspection of lungs can be used as a non-clinical parameter of respiratory disease in veal calves.     

The first occurrence of demodicosis in cattle in Czechoslovakia

Demodectic lesions were found in 37 per cent out of the total number of seventy-five cows examined by palpation in a large cow-house in South Bohemia, Czechoslovakia. These lesions were intradermal nodules, mostly 2 to 6 mm in diameter, located in the corium in the anterior parts of the body. The animals had 1 to 75 lesions (on the average 11.6). Their age was three to seven years. Their overall health condition was good and their behaviour was not affected. Microscopic examination revealed large numbers of Demodex bovis Stiles, 1892, causative agent of demodicosis, in the contents of nodules in five out of six examined animals. Histopathological changes in two nodules were characterized by inflammatory granulomatous structures containing large numbers of mites, epithelioid cells with rich, pale cytoplasm, giant cells of the foreign body type, and inflammatory infiltrates consisting mostly of lymphocytes. Fibroproduction in the contents of granulomas and along their periphery was markedly low.     

Evaluation of praziquantel for treatment of experimentally induced paragonimiasis in dogs and cats

Praziquantel was used successfully for treatment of a small number of dogs and 1 cat infected with Paragonimus kellicotti. To further evaluate the usefulness of this drug in treating such infections, 7 cats and 7 dogs were inoculated orally with metacercariae (12 and 20 to 22, respectively) obtained from crayfish, then were treated after the infections became patent; 2 cats and 2 dogs served as noninfected controls. Beginning 1 week before infection, and continuing weekly thereafter, physical, hematologic, and fecal examinations were performed on each animal; thoracic radiography was performed every other week. By postinoculation week 6, all dogs given metacercariae had patent infection diagnosed on the basis of positive results of fecal examination. By postinoculation week 7, 5 cats had confirmed patent infection, but 2 cats given metacercariae never had patent infection or had signs of infection. Clinical signs of infection were minor and included increased respiratory tract noise, slight inducible cough, or mild dyspnea. Transient eosinophilia was detected in dogs around postinoculation week 3. Pretreatment radiography revealed cavitated lesions in cats only; pleural lines and patchy infiltrates in cats and dogs; or pneumothorax in dogs only. The treatment regimen consisted of 23 mg of praziquantel/kg of body weight given every 8 hours for 3 days; 1 infected cat and dog were not treated. By 11 days after treatment, eggs had disappeared from the feces of infected animals, and marked resolution of lung lesions was evident radiographically.(ABSTRACT TRUNCATED AT 250 WORDS)     

Lung and pleural lesions of veal calves at slaughter and their relationship with carcass weight

Summary

At slaughter the lungs of 2138 veal calves (13 transport groups, mainly from different farms) were examined. Lung and pleural lesions were classified by degree of extension and pathomorphological features, and the accompanying carcass weights were measured. Seventeen percent of the calves had extensive lung lesions, extensive pleural lesions or both, and their mean carcass weight was reduced by 4.3 kg (p<0.05). The percentage of calves with extensive lesions varied between transport groups from 4% to 33%. All pleural lesions were adhesive. Most lung lesions (93%) were classified as cuffing/exudative pneumonia. Slaughterhouse inspection of lungs can be used as a non‐clinical parameter of respiratory disease in veal calves.     

Efficacy of an Actinobacillus pleuropneumoniae bacterin against serotypes 1, 3, 5 and 9.

A trial was performed in a swine research facility to ascertain the protection provided by a polyvalent Actinobacillus pleuropneumoniae (APP) bacterin containing serotypes 1, 3, 5 and 9. The test animals consisted of 60, eight-week-old, piglets, which were randomly divided into four main groups. The four main groups were further divided into three sub-groups (I, II, III) of five pigs each. Subgroup I was vaccinated intramuscularly, sub-group II was vaccinated subcutaneously, and sub-group III served as the unvaccinated control group. Each main group was challenged with a single APP serotype (1, 3, 5 or 9). Criteria for evaluation of the bacterin efficacy were mortality, lung lesions, pleural adhesions, and isolation of APP from tonsil or lung. Significant effects of vaccination over nonvaccination were reduced mortality, lung lesions, pleural adhesions, and isolations of APP from tonsil and lung. There were no significant differences between the intramuscular and subcutaneous routes of vaccination. It was concluded that the four-way APP bacterin used in this study provided satisfactory protection against homologous challenge. Evidence of protection was lower mortality and lung lesions and increased daily weight gains in vaccinates as compared with controls.     

T-lymphocyte predominance in lesions of canine coccidioidomycosis

Coccidioidomycosis is a systemic fungal infection endemic to the southwestern United States. Although cell-mediated immunity is considered critical in control of the infection, little is known of the cellular population in naturally occurring lesions. To characterize the lymphocytic infiltration, archived formalin-fixed, paraffin-embedded tissues (subcutis, pericardium/heart, lung, bone, and synovium) from 18 dogs with coccidioidomycosis were studied with immunohistochemistry for CD3 and CD79a. In nearly all lesions, T lymphocytes were more numerous than B lymphocytes and were distributed throughout the lesion with concentration in the periphery of granulomas, whereas B lymphocytes were mostly confined to the periphery of granulomas. The predominance of T lymphocytes in lesions of canine coccidioidomycosis was independent of the tissue evaluated, the number of intralesional organisms, and the nature or severity of the inflammatory response.     

Successful treatment of pulmonary aspergillosis in a cat

A 7-year-old, spayed female Domestic Longhair cat was evaluated for a 6-week history of coughing. Thoracic radiography revealed a pleural effusion. Thoracic ultrasound revealed a pleural effusion and a focal lung mass. The cat underwent exploratory thoracotomy and a total left pneumonectomy was performed. Histopathology and cultures revealed fungal pneumonia and pyothorax caused by Aspergillus fumigatus. Abdominal ultrasound, repeat thoracic radiography, urinalysis with culture, and retroviral screening failed to detect evidence of systemic disease. The cat's poorly regulated diabetes mellitus is suspected to be the predisposing factor allowing a fungal pulmonary infection to become established. At 18 months after surgery the cat was still disease-free. To our knowledge this is the first reported case of successful treatment of pulmonary aspergillosis in the cat.     

Rupture of collateral ligaments in metacarpophalangeal and metatarsophalangeal joints in horses: 17 cases (1999--2005)

OBJECTIVE: To characterize ruptures of collateral ligaments (CLs) in metacarpophalangeal and metatarsophalangeal joints in horses. DESIGN: Retrospective case series. ANIMALS: 17 horses with ruptured CLs. PROCEDURES: Data were obtained from medical records, including signalment, history, clinical signs, ultrasonographic and radiographic findings, treatment, and outcome. Additional follow-up information was obtained from owners or referring veterinarians. RESULTS: The lateral CL was ruptured in 11 horses; the medial CL was ruptured in 6 horses. Ultrasonography revealed ipsilateral rupture of the short and long components of the CL in 11 horses and rupture of only 1 component in 6 horses. No biaxial ruptures were detected, but 9 horses had desmitis of the CL on the nonruptured side of the affected joint. All horses were lame (lameness score range, 2/5 to 4/5). Joint instability was palpable in 9 horses; only 4 horses had episodes of joint luxation. Avulsion fractures were identified radiographically in 6 horses and ultrasonographically in another 2 horses. Stress radiography revealed joint instability in 10 horses. Horses were managed by stall confinement, limb immobilization, and gradual return to exercise. Eight horses returned to riding, 2 resumed breeding, 2 were retired, 2 were euthanized, and 3 were doing well 86 to 139 days after injury. CONCLUSIONS AND CLINICAL RELEVANCE: Ultrasonographic examination is indicated in horses with acute lameness and swelling at the metacarpophalangeal or metatarsophalangeal joint, particularly when stress radiography cannot be performed or findings are equivocal. Affected horses can be conservatively managed. Prognosis for athletic use may be better than originally believed.     

Radiography is less sensitive relative to CT for detecting thoracic radiographic changes in dogs affected by blunt trauma secondary to a motor vehicle accident

Thoracic injuries caused by blunt trauma are commonly encountered emergencies in veterinary medicine. However, published studies are lacking that compare radiology to CT in blunt trauma caused by motor vehicle accidents in canine patients. The aim of this prospective diagnostic accuracy, methods comparison study were to estimate the sensitivity (Se) and specificity (Sp) of thoracic radiology relative to CT for detecting lung contusions, pneumothorax, pleural effusion, and rib fractures. The study further aimed to develop a severity scoring system for radiology and CT and to compare the findings between the two modalities. The hypothesis was that radiology would be less sensitive than CT at detecting these injuries and that radiology would underestimate the severity of lung contusions. Fifty‐nine patients met the inclusion criteria. Radiology underestimated the presence of lung contusions (Se = 69%, 95% confidence interval) and overestimated the severity of the contusions relative to CT. There was high interobserver variability in evaluating lung contusion severity (coefficient of variation = 91%). Both the three‐view thoracic and horizontal beam radiography had poor sensitivities for the detecting pneumothorax (Se = 19% and 63%, respectively) and pleural effusions (Se = 43% and 71%, respectively). Similarly, the sensitivity (56%) of radiographs for the detection of rib fractures was poor relative to CT. Findings from the current study indicated that thoracic radiography had low sensitivity for detecting lesions related to blunt thoracic trauma caused by motor vehicle accidents and supported the use of CT as an additional diagnostic imaging modality in these patients.     

Comparison of radiography and ultrasonography to detect osteochondrosis lesions in the tarsocrural joint: A prospective study

Reasons for performing study: Lesions located on the medial malleolus of the tarsocrural joint can be difficult to image radiographically. Ultrasonography allows evaluation of articular cartilage and subchondral bone. Objectives: To compare dorso30° lateral‐plantaromedial‐oblique (DL‐PlMO) and dorso45° views to detect lesions on the medial malleolus, to validate the use of ultrasonography to show lesions in the tarsocrural joint and to compare its sensitivity to radiography. Methods: Tarsocrural joints (n = 111) with osteochondrosis were evaluated ultrasonographically and radiographically prior to arthroscopic lesion debridement. A complete radiographic examination was made and the best view to detect each lesion recorded. Longitudinal and transverse ultrasonography of the dorsal aspect of the joint was performed and the best scan plane to image each lesion recorded. Results: There were 94 joints with lesions on the distal intermediate ridge of tibia, 24 with lesions on the medial malleolus, and 4 with lesions on the lateral trochlear ridge. The sensitivity of radiography to detect lesions on the medial malleolus and distal intermediate ridge of tibia was 71 and 96%, respectively. Eighty‐two percent of lesions on the medial malleolus were better imaged on dorso30° view. The sensitivity of ultrasonography to detect lesions on the medial malleolus and distal intermediate ridge of tibia was 83 and 98%, respectively. Ultrasonography was significantly more sensitive than radiography to detect lesions on the medial malleolus and distal intermediate ridge of tibia. Conclusion: Dorso30° lateral‐plantaromedial‐oblique view was the best to image lesions on the medial malleolus. Ultrasonography was a valuable diagnostic tool to diagnose lesions in the tarsocrural joint and was more sensitive than radiography for lesions located on the medial malleolus and distal intermediate ridge of tibia. Clinical relevance: Radiographic examination should include a dorso30° view for detection of lesions on the medial malleolus and ultrasonography should be considered to diagnose osteochondrosis in the tarsocrural joints.     

Radiographic and radionuclide lung perfusion imaging in healthy calves and calves naturally infected with bovine respiratory syncytial virus.

Nine calves between three and 18 weeks old with serologically confirmed natural bovine respiratory syncytial virus infection were examined clinically, radiographically and by radionuclide lung perfusion imaging. The results were compared with those from seven healthy calves. The diseased calves were euthanased and examined pathologically, virologically and bacteriologically. The clinical signs indicated that the disease was in an acute stage. Radiography of the diseased animals revealed cysts, corresponding morphologically with bullous emphysema, and infiltrations roughly corresponding in distribution with atelectatic and, or, pneumonic areas. Radionuclide lung perfusion imaging revealed no perfusion shifts between the left and right lungs and a normal perfusion pattern in five of the nine diseased calves. The abnormalities in the perfusion patterns of three calves were probably caused by anatomical disorders such as cysts and pleural adhesions, but no cause of the abnormality could be found in one calf. These findings suggest that in calves infected with bovine respiratory syncytial virus, the normal perfusion pattern is maintained until anatomical disorders occur. The pathological examination and radiography revealed that the cranioventral lung fields were particularly poorly ventilated. This finding and the normal perfusion pattern indicate that these parts of the lungs are probably the sites where shuntings and perfusion-ventilation mismatchings occur.     

Severe bilateral fibrosing pleuritis associated with chronic chylothorax in five cats and two dogs.

Severe bilateral fibrosing pleuritis was diagnosed in 5 cats and 2 dogs with chronic chylothorax. All animals were dyspneic on initial examination and remained moderately to severely dyspneic after thoracentesis. Radiographic evidence of fibrosing pleuritis included rounded lung lobes and failure of the lungs to reexpand following effective pleural drainage. Fibrosing pleuritis was also suggested in several animals with radiographic evidence of pleural fluid, in which pleural fluid could not be retrieved. Macroscopically, the lung lobes of all animals were compressed and atelectatic to various degrees, and the pleura appeared to be diffusely thickened and roughened. In several animals, fibrous adhesions were found between the parietal and visceral pleura of some lobes. Lung lobes were markedly constricted and appeared as small, smooth, rounded hilar masses in 4 animals. Mild to moderate pulmonary edema was evident in 3 animals at necropsy. Six of the 7 animals died (2) or were euthanatized (4) within 72 hours after the diagnosis of fibrosing pleuritis. The fibrosing pleuritis developed in 1 animal with lymphoblastic lymphosarcoma and chylothorax after treatment via passive pleuroperitoneal drainage; this animal was euthanatized because of underlying neoplasia. One cat, in which decortication was performed and resulted in marked reexpansion of the lung lobes, died 4 hours after surgery with signs compatible with pulmonary edema. On the basis of our findings, we suggest that animals with chronic chylothorax are at risk to develop fibrosing pleuritis. Furthermore, animals with severe bilateral fibrosing pleuritis should be given extremely guarded prognoses.     

Chronic non-progressive pneumonia of sheep in New Zealand - a review of the role of Mycoplasma ovipneumoniae

Chronic non-progressive pneumonia (CNP) is a common disease which affects lambs in New Zealand during late summer and autumn. Mycoplasma ovipneumoniae can be recovered from a high proportion of lesions but it is also present in some normal lungs. Bacteria, especially Pasteurella haemolytica, can also be recovered from more than half the lungs of affected animals. Isolates of M. ovipneumoniae are genetically heterogeneous, as demonstrated by examination of their DNA or total cellular proteins, and are serologically heterogeneous as shown by metabolic inhibition tests. The number of strains present in New Zealand is large and several distinguishable strains can be recovered from each affected lung. Mycoplasma ovipneumoniae has pathogenic potential as indicated by its ability to produce hydrogen peroxide, cause ciliostasis and by its possession of a capsule. Chronic non-progressive pneumonia can be transmitted consistently to over 50% of lambs by inoculation of pooled pneumonic lung homogenate and transmission can be suppressed by broad spectrum antibiotics. In contrast, penicillin does not prevent the development of lesions but diminishes their severity. Pooled lung homogenate treated with digitonin, which inactivates mycoplasmas, has failed to transmit CNP. Pure cultures of M. ovipneumoniae produce only mild lesions in some animals, whereas inoculation with pooled lung homogenate (from which no viruses were isolated) containing mixed strains of M. ovipneumoniae and free from bacteria, is more effective in producing lesions. Research work to date suggests that CNP may be initiated by colonisation of the lung by M. ovipneumoniae which causes ciliostasis and elicits an exudate allowing colonisation of the lungs by bacteria especially M. haemolytica and by other strains of M. ovipneumoniae. The immune response to the initial strain of M. ovipneumoniae may inhibit its replication but would be less effective in inhibiting heterologous strains of the organism allowing their sequential replication. Eventually production of a broad immune response to M. ovipneumoniae would lead to its elimination which in turn would facilitate the elimination of other microorganisms and the resolution of lesions. As natural immunity to CNP occurs within the first year, it may be possible to develop an effective and useful vaccine. Such a vaccine may need to include multiple strains of M. ovipneumoniae.