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Protostrongylosis
Protostrongylosis brings together several small lung worms which, unlike the verminous bronchitis worm, do not live in the large bronchi but burrow into the deep tissue of the lung. The lung reacts by producing small hard, gray or greenish...
What is it?
Protostrongylosis brings together several small lung worms which, unlike the verminous bronchitis worm, do not live in the large bronchi but burrow into the deep tissue of the lung. The lung reacts by producing small hard, gray or greenish nodules around them, visible under the surface of the lung. These nodules do not resolve: they permanently replace tissue that was used for breathing. It is a discreet disease. It does not cause a spectacular coughing epidemic, but it eats away at the respiratory capacity of animals, year after year. Many farms discover it at the slaughterhouse, on lungs speckled with nodules, even though the animals had never appeared sick. Goats and older animals are often the most burdened.
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:
Most often, there are no visible signs: the animal is grazing normally and the breeder suspects nothing.
When the infestation is significant: discreet, dry cough, which appears especially during exercise, when moving the lot or going uphill.
Abnormal shortness of breath after a trip, animals that lag behind and take a long time to recover.
Faster breathing at rest in the most affected animals.
Slowed growth in young animals, animals which do not take the expected state despite a correct ration.
Dull wool or hair, animals that simply appear less vigorous than the rest of the pack.
In dairy goats, production is plateauing without any other explanation.
The signs worsen when an infectious respiratory disease is added: the already damaged lung defends itself less well.
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 deep tissue of the lungs and lay eggs there. The larvae come up with the mucus, are swallowed and come out in the droppings.
Unlike the verminous bronchitis worm, these larvae cannot directly contaminate another sheep: they must first enter a snail or slug, where they transform.
Animals become contaminated by swallowing, with grass, these small snails or slugs, or the traces they leave on vegetation.
The larvae then reach the lungs through the blood and settle there, surrounded by nodules made by the body.
This obligatory passage by a snail explains the distribution of the disease: wet areas, edges of plots, low walls, piles of stones, undergrowth, surroundings of water points, irrigated plots.
The infestation accumulates with age: an older animal has encountered many more larvae than a lamb, which explains why the heaviest are often the oldest.
Moist, shaded pastures, with low walls, scree, brush and borders rich in snails and slugs.
Irrigated plots, lowlands, areas around springs and watering troughs.
Elderly animals and animals kept on the same routes for a long time, in which the load accumulates.
Goats, more frequently and more heavily affected than sheep.
Herds already affected by other chronic respiratory diseases.
Insufficient food and animals in poor general condition.
Green feeding of fodder mowed in wet areas, which brings the snails directly to the trough.
Transmission
There is no direct contagion from one animal to another: without snails or slugs, the cycle stops.
These worms are not transmitted to humans.
Humid and shaded plots, rich in snails, maintain contamination year after year.
The larvae can survive for a long time in the snail, making a plot infestable long after the sick animals have passed through.
Goats become infected under the same conditions as sheep and often harbor larger loads.
Diagnosis and care
Diagnosis is the veterinarian's responsibility, based on clinical examination and laboratory tests. Care is decided case by case.
The veterinarian looks for coughing on exertion by moving the lot, then examines the most suspicious animals.
An analysis of droppings using the technique adapted to the search for pulmonary larvae makes it possible to highlight them. You must tell the laboratory that you suspect a lungworm: a standard analysis for eggs does not detect them.
The elimination of larvae is irregular from one day to the next; a single, negative examination is not always enough to conclude.
Observation of the lungs at the slaughterhouse or when examining a dead animal is the most direct information: the nodules are characteristic and allow us to assess the extent of the problem in the herd. Slaughterhouse returns are a valuable monitoring tool.
The veterinarian distinguishes between other causes of chronic cough in sheep, in particular slowly evolving infectious pulmonary diseases, which do not require the same treatment at all.
Treatment
Several families of internal antiparasitics act on these worms, but the effectiveness is less complete than on worms lodged in the bronchi, because the parasite is enclosed in a nodule in the heart of the lung.
The choice of product, route and timing belongs to the veterinarian, who takes into account the species, the age of the animals, the milk production and the load observed.
The nodules already formed do not disappear with treatment: destroying the worms prevents worsening, but does not return the lost tissue to the lung. This is why prevention counts more here than curative treatment.
No dose or rhythm should be decided alone: systematically treating the entire herd on a fixed date promotes the appearance of resistant worms and does not provide any demonstrated benefit on this parasite.
In many moderately affected herds, the veterinarian may consider that specific treatment is not justified and favor grazing management and feeding.
Meat and milk withdrawal periods apply and differ from one product to another; certain products are prohibited for dairy females. Ask for them before any treatment.
Treatment depends on the cause and the animal's condition: it must be determined by a veterinarian. No self-medication.
Prevention
Limit access to areas rich in snails and slugs: wet edges, scree slopes, low walls, undergrowth, around springs.
Drain marshy areas when possible, repair leaking water troughs that create permanent puddles.
Avoid mowing green fodder in wet areas for direct distribution.
Rotate the plots and do not keep the animals permanently on the same wet paths.
Reserve the driest plots for young growing animals.
Maintain a good diet: a healthy animal supports without consequence a load that penalizes a thin animal.
Take care of the ventilation and cleanliness of the sheepfold, so as not to add respiratory attack to an already damaged lung.
Use slaughterhouse returns as an indicator: regularly nodular lungs signal strong pressure on the farm.
Reform old animals that are running out of steam and can no longer cope.
Possible complications
Permanent loss of lung tissue, with shortness of breath on exertion which persists throughout the animal's life.
Increased susceptibility to infectious respiratory diseases, which find a weakened lung.
Decreased growth of young and production of dairy females, difficult to pin down to a cause until you think about it.
Seizure or trimming of lungs at the slaughterhouse.
Progressive worsening in animals kept for a long time on infested ranges.
When to see a veterinarian
Many animals cough when the lot is moved, without other signs of illness.
Animals become abnormally out of breath after moving and take a long time to recover.
Lambs or kids do not reach the expected state despite good nutrition.
The slaughterhouse informs you of lungs dotted with nodules: ask for advice even if the herd appears to be in good shape.
Chronic cough sets in in a herd that grazes in wet or bushy areas.
An animal breathes quickly at rest: consult without delay, other serious lung diseases give the same sign.
Prognosis
Moderate infestations do not prevent animals from living and producing normally, especially if they are well fed.
Heavy infestations leave permanent pulmonary after-effects: the animal remains out of breath even after treatment.
At the herd level, the prognosis depends almost entirely on grazing: as long as the animals frequent areas with snails, the contamination recurs.
Frequently asked questions
The slaughterhouse tells me that my sheep's lungs are full of small nodules: is this serious?
This is the typical sign of these little lungworms. In an isolated animal in good condition, the consequences are limited. But if it comes back regularly, this indicates strong pressure on your plots and a loss of performance throughout the herd: talk to the veterinarian.
My goats are more affected than my sheep, is this normal?
Yes. One of these lungworms is particularly common in goats, which often harbor larger loads than sheep living on the same plots.
Why doesn't my usual dewormer seem to change anything?
Because these worms are enclosed in nodules in the heart of the lung, where the products penetrate less well, and because the nodules already formed do not disappear. The treatment prevents worsening, it does not restore to the lung what was lost. The management of damp plots is more effective here than the bottle.
Should I collect snails from my plots?
It's not realistic. What works is to limit the time animals spend in the wet, brushy areas where these snails live, to drain what can be drained, and not to feed mown green fodder into these areas.
References
FAO — Organisation des Nations unies pour l'alimentation et l'agriculture
Content reviewed by the TunisieVet editorial team · Updated 11 August 2026
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