Dictyocaulosis - Horse

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.

• Dictyocaulus arnfieldi causes cough in horses

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.

• Found in smaller bronchi
• Cause of chronic cough
• Donkeys are a reservoir mostly without any clinical signs
• Gross pathology:
  • Raised areas of over-inflated pulmonary tissue surrounding small bronchus, containing worms and mucopurulent exudate
  • Hyperplastic bronchial epithelium
  • Coiled worms in small bronchi
  • Peribronchial cuffing
  • In caudal lung lobes
• Histologically
  • Central coiled parasites and associated chronic catharral bronchitis
  • Goblet cell hyperplasia
  • Lymphoid cell infiltration
• In horses, the worms usually fail to achieve sexual maturity