Respiratory Bacterial Infections - Pathology

()Map CARDIORESPIRATORY SYSTEM (Map) RESPIRATORY SYSTEM INFLAMMATION

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

Infectious Canine Tracheitis

In Cattle

Necrotic Laryngitis

Cillia-associated Respiratory Bacillus

Enzootic pneumonia of calves

Acute suppurative pneumonia (Image sourced from Bristol Biomed Image Archive with permission)

Calf pneumonia - chronic, with abscesses, fibrosis (Image sourced from Bristol Biomed Image Archive with permission)

• 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
    • Manheimia (Pasteurella) haemolytica serotype A1
    • Pasteurella multocida
    • Arcanobacter pyogenes
    • Haemophilus somnus
• 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

Oedema and chondritis in larynx of sheep (Image sourced from Bristol Biomed Image Archive with permission)

• 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

Severe atrophic rhinitis (Image sourced from Bristol Biomed Image Archive with permission)

• 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
• 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

• Bordetella bronchiseptica also causes bronchopneumonia

Necrotic laryngitis in pigs

• As in cattle
• Caused by infection with Fusobacterium necrophorum

Enzootic pneumonia of pigs

Enzootic pneumonia of pigs(Image sourced from Bristol Biomed Image Archive with permission)

• 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