Clinical

Parasitic Bronchitis - Cattle

Dictyocaulus viviparus (Image sourced from Bristol Biomed Image Archive with permission)
Parasitic bronchitis (Image sourced from Bristol Biomed Image Archive with permission)
  • Found in trachea and large bronchi
  • Causes parasitic bronchitis, synonyms: bovine dictyocauliosis, husk, hoose
  • Primary infection:
    • Penetration phase (week 1)
      • Larvae migrate to lungs, no clinical signs
    • Prepatent phase (weeks 1-3)
      • Development and migration of larvae -> bronchiolitis -> eosinophilic exudate -> air passage blocked -> alveolar collapse (distal to blockage) -> clinical signs (tachypnoea, coughing)
    • Patent phase (weeks 4-8)
    • Postpatent phase (weeks 8-12)
      • Majority of worms are expelled
      • In 25% of cases clinical signs may reappear as a result of alveolar epithelialisation
      • May be together with interstitial emphysema and pulmonary oedema, or secondary bacterial infection
  • Reinfection syndrome:
    • Immune cattle show clinical signs only if exposed to large numbers
    • Pathogenesis - large numbers of larvae reach bronchioles where they are killed by immune response
    • Pathology - parasite granulomata (grey-green, 5mm diameter, macrophages, giant cells, eosinophils) and eosinophilic plugs in bronchioles

Above from RVC Parasitology study guide (2005-2006)

  • Preferentially in dorsocaudaland ventrocaudal regions
  • Histologically
    • Bronchial epithelium may show hyperplasia due to the chronic irritation
    • Cross-sections of the parasites
    • Exudate contains many eosinophils
    • Foci of necrosis in the rest of the lung tissue due to aspiration of eggs and larvae fromhese adults
    • In mild infestations, the adults are normally expelled in two months - self cure
  • Repeated infestation and secondary bacterial infection are common
  • Two other types of lesion in lung tissue due to this worm have been reported:
    • Nodules (2-4mm in diameter) with greenish centres in the reinfection of an immune animal - the host mounting a successful defence and preventing larval migration
    • Pulmonary oedema and emphysema - thought to be a hypersensitivity response to a massive invasion of larvae in previously- sensitised animals - the gross and microscopic appearance is similar to that of fog fever