Laboratory diagnostics: Atrophic rhinitis

Assays available:

Bacterial culture

• Isolation of live organisms
  • Pasteurella multocida Type D (not always present)
  • Bordetella bronchiseptica (primary concern)
• Sample types: Lungs, nasal swab
• Pros:
  • Bacteria is easy to grow in 1 day.
  • Easy to do in any lab (including in-house).
  • Relative low cost.
• Cons:
  • Often find other secondary bacterial infections
  • Target lung only for cases with pneumonia.
  • Pigs previously treated with antibiotics can prevent bacterial growth.

Antimicrobial susceptibility

• Tests in vitro ability of live organism to grow under specific concentrations of different antimicrobials.
• Sample types: Lungs, nasal swab
• Pros:
  • Identification of susceptibility or resistance of each specific isolate to common antimicrobials.
• Cons:
  • Requires bacterial isolates
  • In vitro testing may be slightly different than in vivo results.
  • Some specific antimicrobials may not be tested or require separate, special testing.
  • Moderate cost.

Gross necropsy of snouts

• Evaluate nasal turbinates
  • Transverse section of snout
  • At level of 1st or 2nd premolar
  • Score space between turbinate and wall
  • Score deviations of septum
• Sample types: nose from skull
• Pros:
  • Associate bacterial presence with tissue damage.
  • Evaluation of severity of disease and chronicity of infection.
• Cons:
  • Unable to confirm B. bronchiseptica as only causative agent.

Result interpretation:

Bacterial culture

• Purity:
  • Pure growth: highly suggestive of disease contributor (especially with B. bronchiseptica)
  • Mixed growth: questionable value.
• Amount:
  • High: highly suggestive of disease contributor.
  • Moderate: variable interpretation.
  • Low: questionable value (could be contaminant).
  • No growth: Animal possibly previously treated with antibiotics or not significant contributor.

Antimicrobial susceptibility:

• Susceptible: possible good choice for treatment if antimicrobial can reach target tissue.
• Resistant: select different antimicrobial.
• MIC: MICs are done to ensure antimicrobial selected achieves the listed MIC value in the target organ.

Gross necropsy of snout:

• European Pharmacopoeia
  • Turbinate scores for each of 4 scrolls (16 points maximum)
    • 0 = No atrophy
    • 1 = Mild atrophy (< 50% scroll lost)
    • 2 = Moderate atrophy (> 50% scroll lost)
    • 3 = Severe atrophy (Scroll bone is straight)
    • 4 = Very severe atrophy (No scroll left)
  • Septal deviation (2 points maximum)
    • 0 = No deviation
    • 1 = Mild deviation
    • 2 = Severe deviation
  • Total score (turbinates + septal = 18 points maximum)
    • Grade 1 = 0-4 points
    • Grade 2 = 4-8 points
    • Grade 3 = >8 points

Scenarios:

Routine slaughter check:

• Obtain 30 snouts from pigs gone to slaughter and evaluate nasal turbinates and septums for atrophic rhinitis
  • Use European Pharmacopoeia approach (most clinically relevant result)
  • Do nasal swabs to culture for B. bronchiseptica

6-week-old piglets with sneezing:

• Collect 10 nasal swabs from sneezing pigs
• Culture swabs for B. bronchiseptica and P. multocida type D

20-week-old pigs with deviated septum

• Collect 10 nasal swabs from affected 20-week-old pigs
• Collect 20 nasal swabs from 6–8-week-old pigs to try to identify earlier infection
• Culture all swabs for B. bronchiseptica and P. multocida type D