Pathology and Microbiology of Respiratory Infections - Small Animals

Question 1

Normal flora in the lower respiratory tract (LRT)

Answer 1

normally sterile

Question 2

Normal flora in the upper respiratory tract (URT)

Answer 2

Streptococci - α-haemolytic/non-haemolytic 
Streptococci - β-haemolytic 
Pasteurella 
Staphylococci coagulase-negative 
Staphylococci coagulase-positive 
E. coli 
Actinobacillus 
Proteus 
Bordetella 
Pseudomonas 
Neisseria 
Lactobacillus 
Clostridium 
Bacillus 
Mycoplasmas 
Chlamydophila

Question 3

Viral infections of the lower respiratory

tract

Answer 3

viruses that cause infections of the URT frequently spread down the respiratory tract and may cause bronchitis + bronchiolitis
all viruses that cause infections of the URT or LRT can predispose to bacterial infections

Question 4

primary vs secondary infection

Answer 4

Secondary infections more clinically important

affects previously damaged lung tissue due to viral or parasitic involvement, or is facilitated by environmental stress

Question 5

pure vs mixed infection

Answer 5

some bacteria important as pure infections

others are involved in mixed infections where initial damage by one species allows invasion by more pathogenic species

Question 6

Respiratory disease: Small animals

Answer 6

Bordetella 
Pasteurella 
β-haemolytic Streptococci 
Actinomyces & Nocardia 
Chlamydophila 
Mycoplasmas

Question 7

bordetella bronchiseptica

Answer 7

Strict aerobe, Gram-negative rod, Slow growing (48 hours)
Normal inhabitant of upper resp. tract in animals
Exogenous or endogenous infection: survival outside the host is poor.
Associated with tracheobronchitis (kennel cough) bronchopneumonia following distemper.
vaccine available (not v.good)

Question 8

bordetella bronchiseptica in cats

Answer 8

Serological evidence for early exposure
to B. bronchiseptica in kittens
Respiratory disease common
Involvement of B. bronchiseptica unclear
Cultured from 11% of cats; none from household pets
Vaccination with NobivacBb (Intervet)

Question 9

B.bronchiseptica - Pathogenesis & Pathology

Answer 9

Initial trauma? viral infection
adhers to respiratory epithelium (cilia) of trachea
proliferation of B. bronchiseptica in the airway
release of toxins irritation & coughing
epithelial necrosis
peribronchial inflammation & interstitial pneumonia
severe pneumonia due to secondary invaders eg. β-h strep

Question 10

b.bronchiseptica - pathogenicity

Answer 10

Adherence to resp. ciliated epitheliu - FHA, fimbriae, pertactin (OMP)
Toxins - Adenylate cyclase (leucocyte toxin), tracheal cytotoxin (inhibits DNA synth in ciliated cells), dermonecrotic toxin (ADP-ribosylation)

Question 11

Pasteurella multocida

Answer 11

Gram-negative rod, Large grey mucoid colonies, Oxidase-positive
No growth on MacConkey
Strong catarrhal smell
Normal oral bacteria in the dog & other animals
Secondary infection - URT infections
Common bacteria infecting dog bite wounds
Capsular serotypes A and D
Vaccines inappropriate - too few opportunities to intervene

Question 12

Pathology of Pasteurella multocida in dogs and cats

Answer 12

Severe suppurative pneumonia and pleuritis (empyaema)
Important in cats following bites or other infected wounds
Often part of mixed infections

Question 13

enzoonotic pasteurellosis URT

Answer 13

purulent material filling sinuses

Question 14

enzoonotic pasteurellosis - control

Answer 14

Bacterin vaccines fail to protect.

Long-term antimicrobial therapy (enrofloxacin) may be needed to control & even eliminate the infection.

Question 15

enzoonotic pasteurellosis - LRT

Answer 15

multifocal pulmonary abscesses - foci of radiopacity

Question 16

streptococcus

Answer 16

Found in normal URT
β-haemolytic streptococci highly virulent in the lung: S. zooepidemicus (also S. canis)
Lancefield grouping Groups C and G
M protein, toxins, capsule, superantigen
Simple vaccines not effective

Question 17

Actinomyces viscosus

Answer 17

Gram-positive, filamentous, branching, Aerobic growth
Commensal in canine oral cavity
Cause of granulomatous thoracic infection in dogs
Localised granulomatous abscesses of skin
Chronic & progressive

Question 18

nocardia spp.

Answer 18

Gram-positive rods, thin, short filaments, Partially acid fast (wax-like mycolic acid)
Growth within, and destruction of, macrophage
Chronic, progressive, suppurating, thoracic granulomas
Resistant to Penicillin and some other antimicrobials
Prolonged use of TMP, Tetracyclines, Ampicillin

Question 19

pathology of norcardiosis

Answer 19

red-brown exudate in pleural cavity (strawberry milkshake appearance)
may become chronic with adhesion formation
exudate has sulphur granules

Question 20

Chlamydophila felis

Answer 20

intracellular Gram-negative rods (no growth on lab media)
Conjunctivitis in cats, nasal discharge progress to interstitial bronchopneumonia
Detect by ELISA for antigen, PCR, Kosters or fluorescein-labelled antibody
Not seen in the dog (?)
Vaccination in the cat

Question 21

mycoplasma spp.

Answer 21

Several mycoplasmas of the dog resp. tract are known.

M. cynos increasingly implicated in some KC infections.

Question 22

canine nasal aspergillosis

Answer 22

Aetiology - Aspergillus fumigatus
Diagnosis - Radiology, Endoscopy, Serology, Culture, Microscopy
Treatment - Surgical delivery of antifungal

Question 23

nasal aspergillosis - pathology

Answer 23

Nasal turbinates progressively destroyed by chronic granulomatous (and eosinophilic) infl
may be yellow-green mycotic exudate in caudal nasal cavity
Numerous fungal hyphae (filaments) on histopathological examination