Respiratory Bacterial Infections - Pathology
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In general
- Main clinical expression is as secondary invaders of previously damaged lung tissue due to viral or parasitic involvement or environmental stress
- Some are initial pathogens in their own right while others can damage the tract allowing invasion by more pathogenic types
In Dogs
Tuberculosis - Dogs
Nocardiosis
In Cats
Chlamydiosis, Feline
Mycoplasma felis
In Horses
Strangles
Streptococcus equi subsp. zooepidemicus
Glanders
Rhodococcus equi
In Cattle
Necrotic Laryngitis
Cillia-associated Respiratory Bacillus
Pneumonic Pasteurellosis
Tuberculosis - Cattle
Contagious bovine pleuropneumonia (CBPP)
- Caused by Mycoplasma mycoides, small colony variant
- Causes a fibrinonecrotic pneumonia and fibrinous pleuritis
- Also affects caudodorsal areas
- Bronchopneumonia -> lobar pneumonia
- Sequestra are common
- NB: similarity to pneumonic pasteurellosis but CBPP has more pronounced marbled effect
- Interstitial septa are markedly widened by fibrinous exudate and the necrotic areas may have a fibrous capsule
- Large colony variant will cause a similar disease in goats
Enzootic pneumonia of calves
- Range of infectious agents together with managemental and environmental stress cause damage to the respiratory tract
- Causes unthriftiness in animals < 6 months old
- Usually the primary pathogen is a virus, secondary pathogens are bacteria and mycoplasmas
- Pathogens:
- Mycoplasmas
- Mycoplasmal bronchitis and pneumonia of calves is an important component of the syndrome of enzootic pneumonia
- On its own causes Mycoplasmal ("Cuffing") pneumonia responsible for bronchitis and bronchiolitis and bronchointerstitial pneumonia
- It is thought to pick up host antigens in order to prevent recognition by the body defences as foreign
- In uncomplicated mycoplasma infection, the lesions are generally mild and consist of patchy red/purple areas of atelectasis in the cranio-ventral lung lobes
- More confluent areas can develop with an underlying bronchointestitial pneumonia and resulting atelectasis
- M. bovis
- Most pathogenic
- Widespread lymphofollicular accumulations which contain germinal centres develop more slowly
- These lesions can result in narrowing of the bronchiolar lumina - this is the classical lesion of ‘cuffing pneumonia’
- M. dispar
- Ureaplasma sp.
- Viruses
- Bovine respiratory syncytial virus (BRSV) - can be primary, causes suppression of pulmonary immune response
- Parainfluenza- 3 (PI3) - can be primary, causes suppression of pulmonary immune response
- Bovine viral diarrhoea virus (BVDV) - suppression of pulmonary immune response
- Adenoviruses
- Calf coronavirus
- Bovine herpes viruses
- Bacteria
- Mycoplasmas
- All transmitted by aerosol and direct contact
- Gross pathology:
- Consolidation of the cranioventral areas which increases in volume with duration
- On cut surface, exudate in the main airway of affected lobules with thickening of the surrounding connective tissue
- Micro pathology:
- Substantial lymphoid tissue around the airways
- Even to proper follicle formation, some of which may be large enough to compress the lumen
- Mixed cell exudate in the airway lumen
- Partial alveolar collapse distal to the compression
- Alveolar exudate contains a mixture of inflammatory cells
- Slight thickening of the alveolar walls with lymphocytes
Acute exudative pneumonia
- Pneumonia in very young calves
- Arcanobacter pyogenes is most frequently isolated
- Cranio-ventral distribution
In Sheep
Laryngeal chondritis
- Caused by Fusobacterium necrophorum
- Infection of laryngeal cartilages
- Can be seen in short-necked breed, e.g. Texels, East Friesians and Southdowns
- Leads to extreme respiratory distress
- Laryngeal mucosa is necrotic and ulcerated
- Associated with laryngeal oedema
- Also may occur in young horses and calves
CAR bacillus
- As in cattle
Enzootic pneumonia of lambs
- Caused by Pasteurella (Manheimia) haemolytica, possibly together with Mycoplasma ovipneumoniae
- Mainly in late spring/early summer after environmental stress i.e. handling or moving
- May be acute with producing a fibrinonecrotic bronchopneumonia and associated pleuritis
- Or tending towards chronicity with abscessation and fibrous pleural adhesions
- A septicaemic form (mortality 5%) is reported to follow the stress of movement to new pasture in the autumn in weaned lambs.
- Foci of necrosis containing many bacteria are seen at the site of initial invasion in the pharynx and in the liver
- Meningitis in young lambs and mastitis in ewes are other expressions
Melioidosis (Pseudoglanders)
- Caused by Pseudomonas (Malleomyces) pseudomallei, Closely related to P. mallei in horses
- Causes disease in sheep, goats and pigs, occasionally other species
- Starts as a pyemia and localises in varius tissues, including the lung as abscessation
- Encapsulated abscesses contain yellow, caseous or creamy pus
- Pneumonia and arthritis are the most common presentation
In Pigs
Atrophic Rhinitis
- Atrophy of nasal turbinates and distortion and shortening of the snout
- Caused by co-infection of the nasal mucosa with
- Bordetella bronchiseptica
- Appears to facilitate colonisation of nasal epithelium by the toxigenic Pasteurella
- Toxin-producing strain of Pasteurella multocida capsular type D (or sometimes A)
- Experimental evidence shows that the toxin acts directly on bone cells of the nasal turbinates to cause bone loss, each pathogen can cause atrophy itself but greater damage when together
- Bordetella bronchiseptica
- Exacerbated by adverse dietary and managemental factors
- In rapidly growing young pigs (4-12 weeks old)
- Clinical signs
- Progressive facial deformity with rhinitis, catarrhal nasal discharge
- Sneezing, coughing, can progress to dyspnoea and anorexia
- Gross pathology
- Overlying skin on shortened snout is thrown into folds
- Deviation of the snout to most affected side
- Various loss of turbinate bone, ventral usually more affected
- Deviation of nasal septum away from affected chamber
- Inflammatory, haemorrhagic and ulcerative lesions in the nasal mucosa
- Micro pathology
- Reduction in the amount of bone in the turbinates
- No osteoid laid down between osteoblasts and existing bone
- Increased fibrous tissue
- Non-specific mucosal inflammation
- 2 forms of the disease
- 'Progressive' atrophic rhinitis
- Due to infection of the nasal turbinates by P.multocida strains carrying the toxA gene that encodes for an osteolytic toxin. P.multocida adheres poorly to mucous membranes, and therefore requires a predisposing nasal insult to assist colonisation eg: co-infection with B.bronchiseptica or Porcine cytomegalovirus (inclusion body rhinitis)
- Turbinate bone atrophy is permanent and progressive
- 'Non-progressive' atrophic rhinitis
- Due to infection of the nasal turbinates by Bordetella bronchiseptica strains alone, that carry a gene that encodes for a dermonecrotic toxin.
- Turbinate bone can regenerate by the time of slaughter
- 'Progressive' atrophic rhinitis
- Bordetella bronchiseptica also causes bronchopneumonia
Necrotic laryngitis in pigs
- As in cattle
- Caused by infection with Fusobacterium necrophorum
Enzootic pneumonia of pigs
- Caused by Mycoplasma hyopneumoniae and Mycoplasma hyorhinis
- Also called mycoplasmal pneumonia
- Major cause of unthriftiness in young pigs
- Pneumonia in weaned pigs
- Cough, reduced growth rate
- Attached to cilia - no mucociliary clearance
- Usually non-fatal unless there is secondary infection (e.g. Pasteurella multocida)
- Gross pathology:
- Confluent consolidation of the cranioventral lung lobes
- In other areas there may be small red to grey focal lesions evident which indicate the bronchiolar orientation of the inflammatory process
- Histologically
- Changes result from a catarrhal bronchointerstitial pneumonia
- In chronic cases, prominent accumulations of lymphoid cells can be seen around airways and blood vessels
Actinobacillus pleuropneumoniae
- Causative agent: Actinobacillus pleuropneumoniae
- Expolsive outbreaks of pneumonia
- Spread by direct contact and aerosol
- Lesions
- Largely from toxin produced
- In diphragmatic lobes of the lungs
- Haemorrhage with fibrinous pleuritis
- Usually localised, sometimes generalised
Pasteurellosis in pigs
- Pasteurella multocida can cause a severe acute fibrinous bronchopneumonia in pigs
- The most significant disease here is that caused by P. multocida secondary to underlying mycoplasma pneumonia, see above enzootic pneumonia of pigs
- This results in chronic suppurative bronchopneumonia with abscessation and pleuritis
- If there is considerable pleural involvement, it may be indistinguishable from lesions caused by Haemophilus pleuropneumonia (below)
- Also isolated from cases of meningitis and septicaemia in piglets
Contagious porcine pleuropneumonia
- Caused by Haemophilus (Actinobacillus) pleuropneumonia
- Seen mainly between 6wks-6mths of age but will affect any age
- Highly pathogenic strains are capable of initiating disease on their own with high mortality in young pigs
- A fibrinonecrotic bronchopneumonia with pleurisy
- Foci of haemorrhagic consolidation or necrosis, mainly around major bronchi, tend to sequestrate
- Tending to spread throughout all lung lobes: therefore a cranioventral distribution may not be particularly evident
Glasser's disease
- Caused by Haemophilus parasuis
- May cause suppurative bronchopneumonia and pleuritis (as part of polyserositis)
- Stress of mixing, weaning and adverse environmental conditions are predisposing to the disease
Streptococcal pneumonia
- Caused by Streptococcus suis type II
Tuberculosis in pigs
- Pigs are susceptible to the Mycobacterium spp. causing tuberculosis in cattle
- Rarely extends to lungs after haematogenous spread from ingested bacteria causing tubercles with various degrees of calcification, encapsulation and caseation
In Rabbits
Snuffles
- Caused by Pasteurella multocida, less commonly and/or Bordetella bronchiseptica
- Clinical signs (nasal discharge, sneezing) result from an acute to chronic rhinitis
CAR bacillus
- As in cattle