- Rarely causes primary disease
- Exception: immune-compromised Arab foals (showing both B/T cell deficiencies), causing necrotising bronchiolitis
- Adenoviridae
- May cause necrotising bronchiolitis in immune-deficient foals (Arabian foals)
- Grossly:
- Atelectasis and consolidation of lobules in cranioventral region
- Mucopurulent exudate in airways
- Histologically:
- Severe bronchiolitis, necrotising -> proliferative
- Bronchiolar obstruction by sloughed debri and neutrophils -> alveolar atelectasis
- May lead to secondary bacterial infections