Atlas of livestock parasites
digitized collection of microscopical preparations

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Dictyocaulus filaria



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General Description:
Long nematodes, white in colour, with a dark line, representing the intestine, which runs the length of the worm. Males are 3 to 8 cm long and females 5 to 10 cm.

Life Cycle:
Direct life cycle. Females in airways of lungs lay eggs containing larvae. These are coughed up and swallowed, usually hatching in the intestine. First-stage larvae are passed in feces and reach the infective third stage in about 6 to 7 days after leaving the host. Cool temperatures may prolong this to 20 days. Infection occurs by ingestion with grass. Larvae penetrate the intestinal wall and eventually are carried to the lungs in the lymph. Fourth-stage larvae emerge in the lungs and develop into adults, which travel to the small bronchi and begin to lay eggs some 4 to 5 weeks after ingestion.

Small airways (bronchi and bronchioles) of lung.

Geographical Distribution:
Worldwide, especially in warm, moist areas.

Serious losses occur from lungworm damage in sheep.

Effect on Host:
Adults and eggs deposited by them irritate the airways, causing exudates to occur. Accumulation of this along with the worms and eggs obstructs the airways, and all lung tissue beyond no longer receives inspired air. The tissue is functionless and collapses. When this is extensive enough, the animal may suffocate. Also, pneumonia may develop from secondary bacterial infections, making sheep very sick, coughing and breathing with difficulty.

Diagnostic Information:
Larvae must be identified in feces. Eggs may be found in nasal exudates, but this is unreliable.

Dictyocaulus filaria larvae

Length 550-585 µm
Larvae often curved
Sluggish movement
The features shown are used to confirm diagnosis and to distinguish from free-living and other nematodes that might be present.

Pasture management, avoiding wet pastures, is effective. Animals must be kept off areas where infected sheep have been; old and young stock should be separated. Infected animals may be treated with anthelmintics.


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