Dictyocaulus arnfieldi

Lungworm

DICTYOCAULUS ARNFIELDI

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.