Lungworm (dictyocaulus arnfieldi)
Lungworm can cause severe coughing in horses, although it is relatively uncommon and seldom seen. Horses become infected by eating the worm larvae from the pasture. These larvae then travel to the lungs where they become adult. It is when they are in the airways that severe coughing can be seen. The adults lay eggs which are coughed up and swallowed to then be passed out in the droppings to continue the cycle. Donkeys are a prime source of contamination of the pasture as they often have large numbers of lungworm without showing any clinical signs.
Signs
The clinical signs of lungworm infection range from moderate coughing, with slightly increased respiratory rate, to severe persistent coughing and respiratory distress.
Diagnosis
Diagnosis is based on clinical signs and the presence of larvae in feces.
Treatment
Lungworm can be treated with most wormers. The best form of treatment is prevention. Horses should be wormed regularly, see worming section, and good pasture management should be employed. It is also advisable not to graze horses with donkeys.