Dictyocaulosis - Horse

Introduction

Dictyocaulous arnfieldi is the lungworm of horses. The main sourse of infection is donkeys as these remain infected for years and contminate horses pasture. Infection can cycle in horses.

The prevalence of lungworm in horses is around 10-20% whereas in donkeys it is 75%. There are very few adults worms or eggs in the faeces in horses, whereas in donkeys there are many of both present. In horses the period of patency is around 8months or less, whereas in donkeys it is around 5 years, hence such a problem occurs with donkeys on shared pasture. Also, clinical signs are rarely seen in donkeys, unlike horses where signs can be much more severe.

Clinical Signs

Clinical signs vary from non to chronic and include a chronic cough at rest or during exercise in a single animal or in a group of horses. This is most prevalent in autumn or early winter.

[[Respiratory Parasitic Infections - Pathology#Dictyocaulus_arnfieldi|]]

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