Pneumonia Flashcards
What are the 5 broad classifications (morphologic) of pneumonia?
Bronchopneumonia Lobar pneumonia Bronchointerstitial pneumonia Interstitial pneumonia Multifocal pneumonia
What is the usual route of infection for bronchopneumonia? What is the usual causative agent (i.e bacteria, virus, fungus)
Inhalation of bacteria
Where in the bronchial tree does inflammation localise to in bronchopneumonia? Why?
The junction of the distal bronchioles and alveoli
Because of the sudden reduction in air velocity and multiple points of branching
What is the usual distribution of bronchopneumonia in the lung?
Cranioventral
What is one exception to the usual distribution of bronchopneumonia in the lung? Where is it instead?
Pneumonia caused by parasitic lungworm (verminous) is usually dorsocaudal. e.g Metastrongylus in pigs
In which species is bronchopneumonia less likely to resolve? Why?
Cattle and pigs
Distinct lobular septa inhibiting exudate drainage and inflammatory cell clearance
What histological factor is significant in distinguishing bronchopneumonia from bronchointerstitial pneumonia?
Damage to the pulmonary interstitium
What type of inflammation is typical of bronchopneumonia?
Suppurative
What are three possible consequences of chronic bronchopneumonia?
Atelectasis > degeneration and fibrosis of collapsed parenchyma
Pulmonary abscessation
Alveolar emphysema
What are three common causes of bronchopneumonia? Where might these organisms have come from?
Streptococcus spp.
Staphylococcus spp.
Bordetella bronchiseptica
All are commensal organisms of the URT that take advantage of respiratory tract compromised by viral infection, noxious gas exposure, cold air etc
What are two important distinguishing features of Lobar pneumonia related to bronchopneumonia?
Lobar is more rapidly progressive and severe
Typically lobar involves an entire lobe of lung, or more
What is the usual distribution of lobar pneumonia in the lung?
Cranioventral
What is the exception to the usual distribution of lobar pneumonia? Where is it located?
Pneumonia caused by Actinobacillus pleuropneumoniae in pigs
Usually dorsocaudal
What sort of inflammation is usual for lobar pneumonia? Which other condition commonly occurs at the same time?
Fibronecrotising Fibrinous pleuritis ( = 'pleuropneumonia' )
How much exudate can you squeeze from a lobar pneumonia sample at post mortem?
Not much - airways are mostly blocked by fibrin
How do you get ‘sequestrae’ in lobar pneumonia? What significance might this have for the resolution of the disease?
Erosion of pulmonary artery by inflammation > thrombosis and loss of blood supply > ischaemia and necrosis of dependent tissue > fibrosis. Causative organism can remain in these sequestra
Why does the animal commonly die in lobar pneumonia when only 20 - 40% of lung function is lost?
Because the causative organism toxins are released into the blood > toxaemia
What are three potential causes of lobar pneumonia?
Mannheimia haemolytica (ruminants) Pasteurella multocida (cattle and sheep) Actinobacillus pleuropneumoniae (pigs)
What is the usual distribution of bronchointerstitial pneumonia?
Cranioventral
What is the usual route of infection for bronchointerstitial pneumonia?
Aerogenous (inhaled)
What is the major distinguishing feature of this pneumonia from bronchopneumonia? Can they be differentiated grossly?
No - need histopath to tell them grossly
Bronchointerstitial has damage to the alveolar walls (see lymphocytes accumulate within)
What are three potential causes of bronchointerstitial pneumonia?
Parainfluenza viruses - cattle and sheep
Influenza viruses - horses and pigs
Paramyxovirus such as canine distemper in dogs
What is the most common cause of bronchoninterstitial pneumonia in Australia? Does this come under another category of pneumonia as well?
Mycoplasma infection
- counts as enzootic pneumonia
Which species is enzootic pneumonia an issue in? What age group? When is the risk period?
Calves, lambs and pigs in intensively farmed enterprises
Infection typically occurs as maternal immunity wanes
What is one potential combination of causative organisms for enzootic pneumonia in calves?
Bovine respiratory syncytial virus (primary)
+ Mycobacterium bovis
What is one potential combination of causative organisms for enzootic pneumonia in lambs?
Mycoplasma spp. + Bordetella parapertussis
What is one potential combination of causative organisms for enzootic pneumonia in young pigs?
M. hyopneumoniae (primary)
+ Pasteurella multocida (secondary)
Give three histological features you might expect to see in a sample of enzootic pneumonia
Mucoid metaplasia of the respiratory epithelium
Aggregation of lymphocytes and plasma cells in the alveolar septa
Aggregation of lymphocytes around the pulmonary vessels (cuffing)
What are the three possible cell types that were initially damaged in the development of interstitial pneumonia?
Vascular endothelial cells of alveolar capillaries
Type I pneumocytes
Type II pneumocytes (less common)
What is the usual route of infection for interstitial pneumonia?
Haematogenous
What is the gross appearance of interstitial pneumonia in the early stages?
Lungs oedematous, heavy, wet, rubbery (rather than firm)
If the entire lung isnt involved in interstitial pneumonia, what is the next most common distribution?
Dorsocaudal
What is the significance of a hyaline membrane?
Means the permeability of the local capillaries has been increased enough to permit fibrinogen through.
What is a reasonably common feature of interstitial pneumonia in cattle? What causes it?
Interstitial emphysema due to increased inspiration and expiration pressures
What are three potential causes of acute interstitial pneumonia in specific species?
Hendra virus - horses
Ascaris suum - pigs
Paraquat toxicity - dogs
What are three potential causes of acute interstitial pneumonia in any species?
DIC
Uraemia
Aspiration of gastric acid (mongastrics)
What are three potential causes of chronic interstitial pneumonia?
FIP in cats
Dirofilaria immitis microfilaria infestation in dogs
Aurolostrongylus abstrusus infestation in cats
Pyrrolizidine alkaloid plant consumption (e.g crolataria) in horses
Which sort of pneumonia is ‘fog fever’ classified as?
Acute interstitial pneumonia
Briefly explain the pathogenesis of fog fever
Ingestion of lush green pastures > L-tryptophan in grass is metabolised to 3-methylindole in the rumen > 3-MI travels in the blood to the lung > taken up by type II pneumocytes and metabolised into highly toxic compound > bronchiolar epithelial necrosis and severe pulmonary oedema +/- interstitial emphysema +/- subcutaneous emphysema
In which region of the lung does multifocal pneumonia usually start?
Cranioventral
What is the usual route of infection for multifocal pneumonia?
Haematogenous
What are three potential lesions that multifocal bacterial pneumonia could evolve into?
Granulomas
Pyogranulomas
Abscesses
What is one common cause of suppurative multifocal pneumonia?
Arcanobacterium pyogenes in cattle
What is one potential cause of caeseous multifocal pneumonia?
Corynebacterium pseudotuberculosis
What are three potential causes of granulomatous or pyogranulomatous multifocal pneumonia ?
Aspergillus spp.
Cryptococcus neoformans
Rhodococcus equi
What are two potential causes of parasitic multifocal pneumonia?
E. granulosis (the hydatid cyst stage) esp. in sheep
F. hepatica in cattle
Why can aspirating stomach contents cause sudden death in monogastrics?
Laryngospasm
Acute diffuse pulmonary oedema
Vagal reflex > bradycardia or asystole
What sort of inflammation is typical of aspirating rumenal contents? why?
Severe, gangrenous lobar pneumonia
Due to presence of putrefactive bacteria in the fluid
What is the difference between exogenous and endogenous lipid pneumonia? Are they distinguishable grossly?
Exogenous due to aspiration of supplementary oils. Lipid seen outside the cell only on histopath
Endogenous due defect in surfactant production or clearance; lipid always inside the macrophages and giant cells
The two are not distinguishable grossly
- good history + histopath
Which type of oils are safest for laxative therapy in cats?
vegetable oils - largely non-irritant if aspirated
