Dictyocaulosis - Cattle

Clinical

• Dictyocaulus viviparus causes parasitic bronchitis

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)
    • Egg-producing mature worms
    • Bronchitis - due to mature worms
    • Parasitic pneumonia - due to aspiration of eggs and larvae -> cellular infiltration of neutrophils, macrophages, giant cells
  • 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