Toxic substance pneumonia revisited

What is atypical interstitial pneumonia of cattle?
- necrosis of type I pneumocytes
- edema, respiratory distress
- replacement of type I pneumocytes by type II pneumocytes
- septal fibrosis and eventually emphysema

How do cattle get atypical interstitial pneumonia?
- if they eat feed rich in L-tryptophan
- L-tryptophan is converted to 3-methyl indole in the rumen
- Clara cells convert 3-methyl indole to a cytotoxin, resulting in necrosis of type I pneumocytes

Certain plants can be pneumotoxic to cattle: for example, the sweet potato vine, which produces a mycotoxin called ipomeanol. Results are similar to atypical interstitial pneumonia.


There are toxic gases.
What type of toxic gases are we talking?

• nitrogen dioxide
• hydrogen sulfate (derived from bacterial growth on manure)
• ammonia (derived from bacterial growth on urine, manure; causes ciliostasis and loss of cilia, a.k.a. ciliocyophthoria)
• ozone (irritant)
• sulfur dioxide (irritant)
• carbon monoxide (not a pneumotoxin, but causes formation of carboxyhemoglobin, which results in hypoxia)
• volatile fluoropolymers (e.g. overheated Teflon; cause death by peracute pulmonary hemorrhage)

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2 types of emphysema

- emphysema involves trapped air (either in alveoli or lymphatic vessels)
- alveolar emphysema has a bubble wrap appearance (bullae). It involves destruction of alveolar septa. It is uncommon in animals, but is common in humans due to chronic smoking or elastase induction.
- interstitial emphysema involves distended lymphatics between lobules. It is common in cattle with pneumonia; can occur due to gasping while dying. : (
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COPD: an allergic phenomenon

- chronic obstructive pulmonary disease is a chronic bronchiolitis that involves airway constriction and expiratory effort. It involves:

• hyperplasia and hypertrophy of bronchiolar epithelium
• goblet cell metaplasia and increased airway secretions
• excessive mucus retention in airways

- another allergic phenomenon is extrinsic allergic alveolitis; it is uncommon in animals.
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Pulmonary cytology

- tracheobronchial lavage, bronchoalveolar lavage can be used to recover mucus, cells and debris from the respiratory tract. Fluid is centrifuged, smeared onto a slide and examined. Components of normal washes:

• mucus. Inspissated mucus indicates poor ventilation of alveoli; granular mucus has been altered by neutrophil enzymes.
• epithelial cells. Some are present. Squamous epithelium coated with bacteria is from the oropharynx.
• leukocytes. Activated pulmonary alveolar macrophages are normal. More than 20% neutrophils is excessive. Eosinophils, lymphocytes and multinucleated giant cells indicate pathology.
• debris. Should be a small component. If excessive, may indicate aspiration pneumonia.

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Neoplasms of the respiratory tract

- primary pulmonary neoplasms:

• uncommon in animals
• examples: bronchiolar-alveolar adenoma, carcinoma, carcinoid, pulmonary adenomatosis of sheep

- remember that granulomatous pneumonias can look like pulmonary neoplasms
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Pneumonia, pneumonia and more pneumonia

- bronchopneumonia occurs when an animal inhales aerosols that then leave bacteria or particles in the airways.

• inflammatory exudates start in the airways and spill into the alveoli. Inflammation centers are on the bronchi and bronchioles.
• produces a cranioventral pattern of lung injury
• affected areas are consolidated, firm
• diagnosis made by gross exam

- interstitial pneumonia happens via hematogenous delivery of bacteria, viruses, allergens, toxins

• inflammation of insterstitium, alveolus
• type I cells are destroyed! type II cells proliferate
• alveolar septa become thickened
• diagnosis made by histological exam

- embolic pneumonia occurs when bacteria or septic emboli travel via the blood.

• can usually be diagnosed by gross exam

- granulomatous pneumonia can be due to varying agents, including fungi, mycobacteria, foreign body response, etc.

• nodular pattern
• chronic by definition
• grossly, similar to neoplasia

- bronchointerstitial pneumonia is caused by viruses; diagnosis must be confirmed by histological exam.

- aspiration (inhalation) pneumonia is a bronchopneumonia that can occur due to various reasons, including chemical or bacterial injury, sedation, anesthesia, gastric intubation, ingestion of petroleum products, or cleft palate.

• grossly, resembles bronchopneumonia
• histological proof: particles from diet in terminal airways (tertiary bronchi and bronchioles)

- toxic substance pneumonia can occur because type I pneumocytes have few defenses. Clara cells may produce toxic metabolites in certain circumstances.

- lipid "pneumonia" is probably caused by a mixture of surfactants and cell debris. Foamy macrophages and cholesterol crystals are visible in alveoli on histological exam. Grossly, white subpleural spots can be seen. Lipid pneumonia is an incidental finding.

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Let's break down respiratory to make it less scary

Broad overview of the respiratory tract:
- form and function
- special anatomic considerations
- diseases

PLAN:
- skim through first 2 sections without taking notes
- read through diseases, taking brief notes
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