Dictyocaulus arnfieldi

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Lungworm

DICTYOCAULUS ARNFIELDI

Dictyocaulus arnfieldi from horse faeces - Joaquim Castellà Veterinary Parasitology Universitat Autònoma de Barcelona

General

  • Lungworm of equidae; adult worms found in smaller bronchi. Frequently incriminated as the cause of a chronic cough.

Morphology and Life-Cycle

  • Similar to lungworm in cattle, except:
    • embryonated eggs (80-100µm) passed in fresh faeces; and
    • prepatent period = 12weeks.

Epidemiology

  • Main source of infection = donkeys (remain infected for years) - contaminate horse pasture.
  • Infection can cycle in horses.


Horses Donkeys
Prevalence 10-20% 75%
Adult worms Few Many
Eggs in faeces Often zero Many
Period of patency <8months 5+ years
Clinical signs Sometimes Rarely


NOTE: Clinical signs - chronic cough at rest or during exercise, single animal or group of horses, autumn or early winter.

Pathogenicity

  • Raised areas of over-inflated pulmonary tissue (several cms in diameter) surrounding small bronchus containing worms and mucopurulent exudate.
  • Hyperplastic bronchial epithelium.
  • Peribronchial "cuffing".

Diagnosis

  • Clinical signs.
  • Grazing history (donkey contact or shared grazing).
  • Faecal examination (only detects patent infections = small proportion of lungworm infections in horses):
    • process sample immediately = McMaster method, embryonated eggs
    • process sample later = Baerman technique, larvae with tail spine.
  • Tracheobronchial washings (large eosinophils).
  • Response to anthelmintic treatment (e.g. resolution of clinical signs = retrospective diagnosis).

Control

  • Do not keep horses on pastures grazed by donkeys (potential carriers).
  • Treat donkeys with appropriate anthelmintic in spring if grazed with horses.