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Endoparasites - Dictyocaulus

Dictyocaulus arnfieldi: Equine lungworm

General Description: Slender worm, 25 to 70 mm. long.

Life Cycle: Dictyocaulus has a direct life cycle as described in the overview. The larvae penetrate the wall of the horse´s intestine and are carried by the circulatory system to the lungs, where they break through the blood vessels into the lungs and develop to adults. The prepatent period is 5 to 6 weeks.

Location: Bronchi and bronchioles.

Geographical Distribution: Worldwide, particularly in areas with heavy rainfall.

Significance: Donkeys are a common host and may, in some areas of the world, be the reservoir of infection for horses. Dictyocaulus does no damage if only a few are present, but large numbers of lungworms can cause death. Lungworms are significant only in areas with heavy rainfall.

Effect on Host: Large numbers of larvae breaking into the lungs and many adult worms in the bronchi cause irritation of the mucosa, called parasitic bronchitis. Mucus is produced, causing difficulty in breathing, severe coughing, and loss of appetite. Severe bronchitis is often accompanied by chronic pneumonia, pulmonary edema, and secondary bacterial infection. Heavy infections may cause death, particularly in foals.

Diagnostic Information: Identification of embryonated eggs and larvae in fresh faeces, clinical signs in the infected horse.

Control: Older, resistant horses may harbour mild infections but show no signs, which is why young animals should be maintained separately. Larval lungworms are sensitive to drying, so pasture drainage is an effective management technique.

Dicytocaulus larva   Dicytocaulus– adult anterior end   Lungworms (bovine)