Atlas of livestock parasites
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Dictyocaulus viviparus



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Cattle lungworm

General Description:

Adults are up to 8 cm long, thin, and milky white. Females are longer than males.

Life Cycle:
Adults living in the airways lay eggs containing larvae. As respiratory secretions carry these toward the mouth, they are coughed up and swallowed. Hatching occurs in the intestine. First-stage larvae are passed in feces and molt twice on pasture before becoming infective third-stage larvae, about 7 days after leaving the host. Dictyocaulus larvae are less mobile than those of other parasites. This characteristic, in some cases, prevents their ingestion by cattle, which do not graze in areas contaminated by feces. However, lungworm larvae frequently live on the Pilobolus fungus, common in cattle feces. When the ripe sporangium of Pilobolus explodes to release spores, the larvae living on the fungus are deposited on pasture as far as 10 feet from the fecal pat, improving their chance of being ingested by grazing cattle. When swallowed, the larvae penetrate the bowel wall and are carried to local lymph nodes, where they molt to become fourth-stage larvae. They then travel via the thoracic duct to the jugular vein to the right side of the heart, which pumps them to the lungs. Here they complete their final molt some 14 days after ingestion. Sexually mature adults can be found about 8 days later. Larval stages may remain inhibited in the lungs for up to 150 days. However, the prepatent period is about 29 days.

Airways: trachea, bronchi, and bronchioles.

Geographical Distribution:
Worldwide; more important in temperate climates and with intensive management conditions.


In severe infections, complications may result in the death of 20 percent or more of the infected animals.

Effect on Host:

Larval lungworms irritate the bronchioles before eggs can be seen in nasal secretions or larvae appear in feces. Later, the adult worms irritate the trachea and bronchi. in both stages, increased respiratory secretions cause lung congestion. The disease caused by lungworm is parasitic bronchitis, also called "husk" or "hoose," characterized by rapid shallow breathing and severe coughing. Severe cases lead to emphysema and pneumonia. Heavy infections may cause death.

Diagnostic Information:
Nasal discharges may contain embryonated eggs or larvae, and larvae may be found in feces. Coughing may occur in the prepatent period, before adults develop and lay eggs. Lungworms are found in the airways on postmortem examination.

Dictyocaulus viviparus larvae

Length 390-450 µm
Larva often curved
Sluggish movement
Note: Dictyocaulus viviparus does not have a protruding protoplasmic knob on the head unlike Dictyocaulus filaria*.
The features shown are used to confirm diagnosis and to distinguish from free-living and other nematodes that might be present.


Pasture management - keep pasture well drained. Separate young and adult animals, as older cattle may carry lungworms after becoming resistant to further infection. These older animals may continue to shed larvae and thus endanger the young.


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