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

In Sheep

CAR bacillus

• As in cattle

In Pigs

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