Lecture 23 Diseases of the Lung Parenchyma 2

Question 1

Why is the right cranial lung lobe of ruminants and pigs predisposed to inflammation?

Answer 1

right cranial lung lobe in ruminants and pigs arises from the trachea
predisposes the right cranial lobe in these species to inhalation of foreign materials (especially liquids) and to accumulation of inflammatory exudate

Question 2

Which of the domestic animals have poor collateral ventilation? To what pulmonary conditions
does this anatomical feature predispose?

Answer 2

cattle and pigs, the well-developed interlobular septa and hence poor collateral ventilation
predisposes the lungs of these species (especially cattle) to obstructive atelectasis and interstitial emphysema and chronic supprative bronchopneumonia

Question 3

Why are type I pneumocytes so vulnerable to injury? How are they replaced following irreversible injury (necrosis)?

Answer 3

vulnerable to oxidant injury because of their large surface area and low concentration of anti-oxidants
type II pneumocytes act as progenitor cells during repair of alveolar injury

Question 4

Which cell type plays the most important role in defence of the deep alveolar parenchyma of the lungs?

Answer 4

pulmonary alveolar macrophages are the principal defenders of the delicate alveoli

Question 5

What are the normal functions of pulmonary alveolar macrophages? How are they replaced over time? What factors can compromise their phagocytic function?

Answer 5

short lifespan (only a few days) so the population is constantly replenished by
recruitment of monocytes from the circulation
 rapid phagocytosis (within 2-4 hours) and intracellular destruction of inhaled bacteria by means of reactive oxygen and nitrogen species and lysosomal enzymes
hypoxia and pulmonary oedema also compromise their phagocytic function

Question 6

Where else in the lungs are macrophages normally found? What role do they play in defending the lung?

Answer 6

(intravascular and interstitial)
within alveolar capillaries
they are responsible for phagocytosis of circulating bacteria and particulates

Question 7

What is meant by the term pneumonia? What are the characteristic gross general features of pneumonia?

Answer 7

inflammation of the lung parenchyma

increased firmness of the affected lung parenchyma on gentle palpation

Question 8

What microscopic events characterise acute versus chronic pneumonia? In other words, outline the differences between the acute red phase and the chronic grey phase of pneumonia.

Answer 8

Acute: dominated by hyperaemia, oedema, exudation of neutrophils, and
degeneration and necrosis of type I pneumocytes
Chronic: within 7 days of onset, exudate is slowly cleared by phagocytosis, epithelial repair continues and fibrosis may develop

Question 9

What is meant by the term bronchopneumonia (lobular bronchopneumonia)? What are its typical gross features?

Answer 9

suppurative bronchopneumonia caused by inhalation of bacteria
insult is aerogenous and inflammation is centred on the junction of the distal bronchioles and alveoli
cranioventral parts of the lungs

Question 10

What are some examples of causes of bronchopneumonia in domestic animals?

Answer 10

Streptococcus spp.
Staphylococcus spp.
Bordetella bronchiseptica
E coli`

Question 11

Why does bacterial bronchopneumonia often persist in pigs and cattle?

Answer 11

the poor collateral ventilation in pigs and cattle compromises clearance of exudates from the alveoli and predisposes them to chronic suppurative bronchopneumonia

Question 12

What is meant by the term lobar pneumonia (fibrinous pneumonia)? What are its typical gross features?

Answer 12

lobar pneumonias are essentially fulminant (severe and rapidly progressive) bronchopneumonias ->
consolidation of large areas of lung parenchyma (one or more entire lobes)
bacterial and inhaled and inflammation initially commences at the junction of distal bronchioles and alveoli, especially in cranioventral parts of the lungs

Question 13

What are some examples of causes of lobar pneumonia in domestic animals?

Answer 13

Mannheimia haemolytica (“shipping fever”) - ruminants
Pasteurella multocida - cattle and sheep

Question 14

Why do many animals affected by a lobar pneumonia often die despite the fact that the
inflammatory process may only involve less than 50% of the lung parenchyma?

Answer 14

death is often referable to toxaemia (i.e. absorption of bacterial toxins into the general circulation)

Question 15

What is a pulmonary sequestrum?

Answer 15

if animals survive, the necrotic tissue (sequestrum) becomes separated from viable tissue by a rim of exudate and eventually becomes walled off by scar tissue

Question 16

What is meant by the term bronchointerstitial pneumonia? What are its typical gross features? How is this type of pneumonia distinguished from a bronchopneumonia?

Answer 16

inflammation is typically restricted to cranioventral areas of the lungs and is induced by inhalation of pathogens that localise to the junction of the distal bronchioles and alveoli
-extensive injury not only to the distal bronchioles but also to the alveolar walls

Question 17

What are some examples of causes of bronchointerstitial pneumonia in domestic animals?

Answer 17

parainfluenza viruses - cattle and sheep
influenza viruses - pigs and horses
herpesviruses - cattle, horses, pigs, dogs, cats
Mycoplasma species - cattle, sheep, pigs

Question 18

What is enzootic pneumonia of calves, lambs and pigs? What are the characteristic features of
chronic enzootic pneumonia?

Answer 18

in most animals, the pneumonia is chronic, bronchointerstitial in pattern, and either subclinical or
responsible for illthrift and coughing
intensively farmed lambs, calves and young pigs world-wide
- infection typically develops at the waning of maternal immunity
-classic lesion of chronic enzootic pneumonia is a bronchointerstitial pneumonia with homogeneous grey consolidation and atelectasis of cranioventral areas of the lungs

Question 19

Enzootic pneumonia

• calves
• lambs
• pigs

Answer 19

• calves - pneumonia is usually initiated by viral infection
• lambs - often a synergistic infection with Mycoplasma ovipneumoniae
• young pigs - especially Mycoplasma hyopneumoniae

Question 20

What is meant by the term interstitial pneumonia? Which cells in the lungs may be targeted in an interstitial pneumonia and what is the most common route of injury?

Answer 20

characterised by diffuse or patchy injury to the walls of the alveoli
- the primary insult may be to the vascular endothelium of alveolar capillaries, to type I pneumocytes
most interstitial pneumonias are haematogenous in origin

Question 21

What are the typical gross features of an interstitial pneumonia?

Answer 21

difficult to recognise grossly(in acute phase)
lungs are heavy, wet and rubbery due to pulmonary oedema rather than firmly consolidated
-entire lungs are involved to some extent, although lesions may be more pronounced in dorsocaudal areas
-lungs may be more ‘meaty’

Question 22

What are some examples of causes of acute interstitial pneumonia in domestic animals?* Why
do many animals die in the acute phase of interstitial pneumonia?

Answer 22

Infectious agents in circulation - bacteraemias, septicaemias, endotoxaemias
Parasites - e.g. Toxoplasma gondii
Inhaled toxins- smoke
-affected animals often die in the acute stage of interstitial pneumonia (acute respiratory distress syndrome (ARDS)) due to pulmonary oedema and hypoxaemia

Question 23

What are some examples of causes of chronic interstitial pneumonia in domestic animals?*

Answer 23

Infectious agents (either in circulation or inhaled ) - viraemias - e.g. feline infectious peritonitis virus - inhaled fungi - e.g. Pneumocystis carinii
- inhaled bacteria - e.g. Mycobacterium bovis in bovine tuberculosis (exotic)
Parasites - e.g. Dirofilaria immitis (heartworm) microfilariae in dogs
Chronic hypersensitivity reactions - e.g. inhaled fungal spores in cattle and horses

Question 24

What is fog fever (acute interstitial pneumonia) of cattle? Briefly outline its aetiopathogenesis.

Answer 24

• sudden onset of severe dyspnoea within 4-10 days of pasture access
• L-tryptophan in the pasture is metabolised in the rumen to 3-methylindole (3-MI) -> haematogenous
  spread to the lungs -> metabolism by type II pneumocytes +/- bronchiolar Clara cells to a highly toxic metabolite->necrosis of bronchiolar epithelium and type I pneumocytes->acute interstitial pneumonia, with usually severe pulmonary oedema and interstitial emphysema

Question 25

What are some examples of causes of multifocal pneumonia in domestic animals?* How do the causal agents reach the lungs?

Answer 25

Suppurative - usually due to bacteraemia
- e.g. Corynebacterium pseudotuberculosis (caseous lymphadenitis) in small ruminants - e.g. Arcanobacterium pyogenes in cattle
Granulomatous or Pyogranulomatous - usually due to inhalation of fungi or bacteria
- e.g. Aspergillus spp.
Haematogenous Parasitism
- cestodes (tapeworms)

Question 26

What is meant by the term aspiration pneumonia? What are some conditions that can predispose to aspiration pneumonia?

Answer 26

aspiration pneumonia = pneumonia resulting from inhalation of foreign material, often liquids
-predisposed to by force feeding, pail feeding of milk, vomiting, regurgitation, dysphagia, anaesthesia, cleft palate or laryngeal dysfunction/paralysis

Question 27

What are the possible adverse consequences of aspiration of gastric contents in a monogastric animal?

Answer 27

aspiration of vomitus in monogastric animals often ->sudden death due to laryngeal spasm, acute diffuse pulmonary oedema

Question 28

What is the likely outcome in a herbivore of inhalation of ingesta (or aspiration of a drench intended for the stomach/rumen)?

Answer 28

in herbivores, aspiration of ingesta usually -> a severe and usually fatal gangrenous lobar pneumonia because of the presence of putrefactive bacteria

Question 29

What is exogenous lipid pneumonia? In what circumstances is it likely to develop?

Answer 29

aspiration of oil (administered as a laxative for constipation or for furballs) -> exogenous lipid pneumonia with a cranioventral or multifocal distribution in the lungs
mineral oils (e.g. paraffin) (the usual cause)  more intense granulomatous inflammation and fibrosis

Question 30

What is endogenous lipid pneumonia? What is the source of the lipid?

Answer 30

lipid is derived from surfactant and is always intra-cellular within foamy macrophages and multinucleated giant cells
-usually idiopathic

Question 31

What is meant by the term pneumonoconiosis?

Answer 31

pneumonoconiosis = significant lung disease induced by inhalation of inorganic particles

Question 32

What are some examples of pneumonoconioses in domestic animals? What lesions do they provoke?

Answer 32

Carbon and silica inhalation

• inhaled carbon is relatively non-toxic and is phagocytosed readily by alveolar macrophages
• silicate crystals->activation of pulmonary macrophages and fibroblasts->multifocal pulmonary granuloma formation and fibrosis respectively