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Members of  the family Dictyocaulidae are unusual among the Trichostrongyloidea in that they parasitize the lungs, especially the bronchi of the diaphragmatic lobes and the trachea. They are found throughout the world but are more common and clinically important in temperate areas particularly when summer rainfall is above average.

They are thin, thread-like worms, from 3 to 8 cm long. The mouth is surrounded by 4   lips and the mouth opening leads into a small buccal capsule. The males have a prominent copulatory bursa.

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Dictyocaulus head end showing the small mouth opening (arrow).

Scanning electron micrograph of Dictyocaulus showing the mouth opening surrounded by lips. Dictyocaulus male bursa showing the short, fat, dark spicules and one dorsal ray with a trilobed tip(arrow)


There are three Dictyocaulus species of importance in domestic anmials.

Nematode Species Host Species Predilection site
Dictyocaulus filaria sheep and goats trachea and bronchi
Dictyocaulus viviparus cattle and deer trachea and bronchi
Dictyocaulus arnfeldi donkeys and horses trachea and bronchi

Dictyocaulus viviparus

Dictyocaulus viviparus is the most pathogenic and will be discussed in detail.

Life cycle

A fuller description of the life cycle may be viewed by clicking here. A summary will be given on this page. Females are ovoviviparus which means that they lay eggs that are already embryonated. These hatch immediately, L1s migrate up the trachea, are coughed up, swallowed and pass out from infected cattle in their feces.

The preparasitic phase of the life cycle is similar to the other Trichostrongyles, with one exception. Because the L3's are not particularly motile, they have evolved a method of facilitating their dispersal from the fecal pad to the surrounding grass where they can be ingested by susceptible grazing animals. Larvae migrate onto the sporangia of the fungus Pilobolus that commonly grows in cattle feces, as shown in the image to the right.

Image courtesy of Merial Inc


When the sporangia explode, releasing their spores into the surrounding environment, the larvae of Dictyocaulus are also released. This is shown in the image cartoon on the right.

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Image courtesy of Merial Inc

Ingested L3s migrate through the intestinal wall to the mesenteric lymph nodes, molt to L4, then continue via the lymphatics and blood to the lungs where they migrate through the capillary walls into the alveoli.  The final molt occurs and the immature adults move up the bronchioles to the bronchi. The prepatent period is 3 to 4 weeks.


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Parásitos y enfermedades parasitarias de los animales domésticos
Dr. Colin Johnstone (autor principal)
Derechos de copia © Universidad de Pennsylvania