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Dictyocaulus
Dictyocaulus is a lung disease caused by a round, thin, whitish worm, which settles directly in the bronchi of sheep and goats. Adult worms live in the large airways, where they irritate the mucous membrane and trigger a permanent cough. Th...
What is it?
Dictyocaulus is a lung disease caused by a round, thin, whitish worm, which settles directly in the bronchi of sheep and goats. Adult worms live in the large airways, where they irritate the mucous membrane and trigger a permanent cough. The mucus and debris they cause gradually block the small bronchi. It is a disease of wet pasture: it appears after the rains, on lowland plots, around watering troughs and in irrigated areas. A common pitfall keeps coming up: this cough resembles bacterial pneumonia. Many breeders take an antibiotic, notice a partial improvement linked to superinfections, then see the cough start again as soon as they stop. As long as the worms are in the bronchi, the antibiotic alone does not solve anything.
Commonly observed signs
These signs are neither exhaustive nor specific. Only a veterinarian can establish a diagnosis.
Related signs — each one links to its page:
Dry and repeated cough, first after exercise or when moving the lot, then present at rest. She gradually gains several animals from the same group.
Animals that run out of breath quickly: they stay behind when the herd moves, stop on a hill, gasp when they return.
Rapid breathing, sometimes with tense neck and open nostrils in severe forms.
Discharge from the nose, initially clear, which becomes thick and yellowish when a bacterial infection is added.
Decreased growth in lambs, weight loss in adults, dull wool.
Fever appears when the lungs become superinfected; in the absence of superinfection, the temperature can remain normal despite severe coughing.
In severe forms, the animal remains standing, refuses to lie down to breathe better, and can die of asphyxia or bronchopneumonia.
Part of the herd coughs little or not at all while carrying worms: visible coughing never measures the real extent of the problem.
When to consult without delay
This list does not replace veterinary advice. It gathers situations that justify a prompt consultation.
Causes and risk factors
Adult worms live in the bronchi and lay eggs there. The eggs come up with the mucus, are swallowed by the animal and return to the droppings, where they hatch.
On the plot, the larvae leave the droppings and reach the surrounding grass as soon as there is humidity: morning dew, rain, irrigation. Animals swallow them while grazing.
Once swallowed, the larvae cross the wall of the intestine, pass through the lymph nodes and the blood, reach the lungs and ascend into the bronchi, where they become adults.
The cycle is straightforward: no snails or other animals are needed, which explains how quickly a plot loads.
Larvae can pause in the body during the dry season and then leave all together when the rains return, which gives the impression of an illness appearing out of nowhere.
Lesions of the bronchi open the door to bacteria which normally live in the nose and throat: it is this superinfection which most often kills, not the worm itself.
Lambs and young animals in the first grazing season, whose immunity is not yet built.
Periods following the rains, mild autumn and winter, irrigated plots, lowlands, surroundings of water points.
High stocking and low grazing, which forces animals to graze at ground level where the larvae are.
Mixture of age classes on the same plot: adults contaminate the young.
Humid and poorly ventilated sheepfolds, dust, overcrowding, which aggravate respiratory damage.
Animals that are malnourished or already carrying other digestive parasites.
Quarantine-free purchases, fairs and gatherings.
Transmission
Contamination occurs through contaminated grass, never by direct contact from one animal to another, and these worms are not transmitted to humans.
Wet areas, edges of water troughs, lowlands and irrigated plots concentrate the larvae.
Adult animals that cough little are often the carriers who seed the plot for lambs.
An animal purchased without quarantine introduces the disease onto a previously unaffected farm.
The larvae survive poorly in drought and full sun, but do well in mud, packed droppings and damp shaded areas.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian begins with the history of the herd: which animals have been coughing, since when, on which plot, after which episode of rain. This context already guides a lot.
He auscultates the lungs and examines several animals in the group, not just the one coughing the most.
A special scat analysis makes it possible to look for larvae in the feces. Please note: this is not the same technique as searching for digestive worm eggs; you must tell the laboratory that you suspect a lungworm, otherwise the examination will be missed.
A negative result does not rule out the disease: during the phase where the larvae migrate to the lungs, the worms are not yet laying eggs, and this is often the time when animals are the worst.
Examining a dead animal is decisive: by opening the trachea and bronchi, the worms are visible to the naked eye, mixed with abundant foam and mucus. Do not dispose of a dead animal without talking to the veterinarian.
The veterinarian finally rules out other causes of sheep cough, in particular infectious respiratory diseases and chronic lung conditions, which require different behavior.
Treatment
Treatment is based on internal antiparasitics active on lungworms. Several families exist, but not all are equal for this parasite: the choice of family, form and timing falls to the veterinarian.
No dose or rhythm should be decided on your own initiative. Underdosing allows some of the worms to survive and selects the most resistant.
The treatment is based on the scale of the lot: the animals which cough are only the visible part of the problem, the others of the same group graze the same plot.
When a bacterial superinfection is established, with fever and purulent discharge, an antibiotic may be necessary in addition, on prescription. Given alone, without antiparasitic, it only temporarily masks the problem.
The most affected animals need a clean, dry and well-ventilated room, free of dust, unlimited water and quality food. Avoid moving and rough handling, which can be enough to cause an animal in respiratory distress to decompensate.
The death of large numbers of worms in the bronchi can temporarily aggravate respiratory difficulty in massive infestations: this is one more reason for the veterinarian to supervise the treatment rather than treating blindly.
The waiting times for meat and milk appear on the instructions for each product, vary from one molecule to another and must be respected to the letter. Certain products are prohibited for females whose milk is consumed.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Avoid damp plots and lowlands during risky periods, particularly with lambs.
Rotate plots and do not let animals shave the grass.
Reserve the healthiest plots, for example after mowing or cultivation, for young first-season animals.
Separate lambs from adults as much as possible, who are the main sowers of larvae.
Clean up areas around watering troughs: repair leaks, stony or move water points, avoid areas of permanent mud.
Quarantine any purchased animal and seek veterinary advice before releasing it to pasture.
Ensure good ventilation and dry litter in the sheepfold: a lung already damaged by worms tolerates ammonia and dust very poorly.
Feed the herd correctly: an animal in good condition copes much better with the same load of parasites.
Watch for coughing when the herd returns or after the flock has moved: this is the time when it is heard best.
Possible complications
Bronchopneumonia due to bacterial superinfection, the main cause of mortality in this disease.
Long-lasting lung damage: some animals continue to have a cough and shortness of breath during exercise even after the worms have been eliminated.
Delayed growth of lambs, which does not completely catch up.
Weight loss in adults, drop in milk production, poor recovery after lactation.
Worsening of other chronic respiratory diseases in the herd, which accumulate in the same lungs.
Sudden mortality by asphyxiation in massive infestations of lambs.
When to see a veterinarian
Several animals in the same flock cough, especially after a period of rain or on a damp plot.
An animal huffs after a few steps, stays behind the herd or refuses to lie down.
A thick or yellowish discharge appears, with fever.
The lambs are no longer growing even though the diet is correct.
An animal is breathing quickly, with its mouth open or neck stretched: it is an emergency.
The cough returns as soon as antibiotic treatment is stopped: a parasitic cause must be sought.
An animal dies after a few days of coughing: ask for an examination, it will guide the course of action for the whole lot.
Prognosis
Animals treated early, before a secondary infection sets in, recover well and resume growth.
Advanced forms, with bronchopneumonia and respiratory distress, have a guarded prognosis, and some survivors have permanent pulmonary after-effects.
At the herd level, everything depends on grazing management: without change on wet plots, the disease returns each rainy season despite treatments.
Frequently asked questions
My sheep are coughing, I took an antibiotic and it's starting again: why?
Because the antibiotic acts on the bacteria that have settled, not on the worms lodged in the bronchi. As long as the worms are there, the irritation continues and the cough returns. This is the most common confusion about this disease: ask the veterinarian to check for lungworms.
The scat analysis came back negative, does this rule out lungworms?
No. On the one hand, the search for pulmonary larvae requires a specific technique that must be explicitly requested from the laboratory. On the other hand, during the phase where the larvae migrate towards the lungs, the worms are not yet laying eggs: the analysis is then negative even though the animals are doing poorly.
Can I catch this disease from caring for my sheep?
No. This lungworm is specific to ruminants and is not transmitted to humans. Contamination of animals occurs only by swallowing the larvae present on the grass.
Should we treat the whole lot or just those who are coughing?
The animals that cough are only the visible part: the others from the same lot have grazed the same plot. The decision to treat the entire batch, only part of it, and at what time, is made with the veterinarian based on examinations and the season.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
ANSES — Agence nationale de sécurité sanitaire (France)
Content reviewed by the TunisieVet editorial team · Updated 11 August 2026
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