Pneumonia Overview

Pneumonia - Introduction and Classification

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

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

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

Pneumonia
- Inflammation that takes place in the alveoli and their walls
- Can be grouped either according to
  - Nature of the inflammatory process
  - Aetiological agent
  - Pattern of the lesion

Patterns of lung inflammation vary depending on the aetiology, route and method of exposure and multiple host factors including age, general health, and immune status
- There are five general patterns of pneumonia:

Bronchopneumonia

Bronchointerstitial Pneumonia

Lobar Pneumonia

Interstitial Pneumonia

Embolic Pneumonia

Granulomatous Pneumonia

Verminous Pneumonia

Stages of pneumonia

Regardless of the pattern, all pneumonias pass through three stages:
- Exudative phase
  - In this initial stage inflammatory exudate pours into alveolar spaces and alveolar capillaries are congested
  - Type I alveolar epithelial cells are highly sensitive to injury and cannot proliferate in response to injury
  - Necrosis and sloughing of injured type I cells, denuding alveolar spaces of lining epithelium
  - Neutrophils begin to enter alveolar spaces distended with inflammatory oedema
- Proliferative phase
  - Type II alveolar cells (less sensitive to and can proliferate in response to injury) begin to proliferate within 24 hours and eventually line the alveolar walls denuded of type I cells ***By 6 days cuboidal type II cells can completely line the alveoli
  - Proliferation of type II cells marks the shift from the exudative to the proliferative stage of pneumonia, also heralded by decreased blood flow in alveolar capillaries
  - Because the original squamous type I cells have been replaced by cuboidal type II cells, the microscopic appearance of pneumonic lungs at about 1 week has been described as “alveolar epithelialization”, “alveolar adenomatosis”, or “bronchiolisation of alveoli”
- Repair phase
  - Resolution of pneumonia is accomplished by transformation of type II cells to type I cells

Pulmonary abscesses

Infectious causes of pneumonia

.	VIRAL	BACTERIAL	FUNGAL	PARASITIC
Dogs	Canine distemper	usually secondary	Blastomyces dermatitidis	Angiostrongylus vasorum
.	Infectious canine tracheitis	bronchopneumonia: Bordetella bronchiseptica, Staphylococci, Streptococci, Coliforms	Histoplasma capsulatum	Toxoplasma gondii
.	Herpes virus	.	.	.
Cats	Feline calicivirus	bronchopneumonia: Pasteurella sp., Streptococcus spp.	.	Aelurostrongylus abstrusus
.	.	Feline chlamydiosis	.	.
Horses	Equine rhinopneumonitis	Strangles	Pneumocystis carinii	Parascaris equorum
.	Equine influenza	Glanders	.	.
.	Equine viral arteritis	Rhodococcus equi	.	.
Cattle	Parainfluenza- 3	Necrotic Laryngitis	.	Dictyocaulus viviparus
.	.	Pneumonic pasteurellosis	.	.
.	.	Contagious bovine pleuropneumonia	.	.
.	.	Enzootic pneumonia of calves	.	.
.	.	Acute exudative pneumonia	.	.
.	.	Mycoplasmal pneumonia	.	.
.	.	Mycobacterium bovis - tuberculosis	.	.
.	.	bronchopneumonia: Pasteurella sp., Corynebacterium pyogenes	.	.
Sheep	Maedi Visna	bronchopneumonia: Corynebacterium pyogenes	.	Muellerius capillaris
.	Parainfluenza- 3	Enzootic pneumonia of lambs	.	.
.	Sheep Pulmonary Adenomatosis	Pseudomonas (Malleomyces) pseudomallei	.	.
Pigs	Inclusion body rhinitis	Enzootic pneumonia of pigs	.	Ascaris suum
.	Swine influenza	Actinobacillus pleuropneumoniae	.	.
.	Porcine reproductive and respiratory syndrome	Necrotic Laryngitis	.	.
.	Postweaning multisystemic wasting syndrome	Pasteurella multocida	.	.
.	Porcine respiratory coronavirus	Contagious porcine pleuropneumonia	.	.
.	.	Glasser's disease	.	.
.	.	Bordetella bronchiseptica	.	.
.	.	bronchopneumonia: Pasteurella spp., Corynebacterium pyogenes, also Streptococcus spp., Tuberculosis	.	.