Muellerius capillaris is a species of parasitic roundwormsThin section of a lung with Muellerius capillaris. © J. Kaufmann / Birkhäuser Verlag that infects sheep and goats as well as other wild ruminants. It is also called the goat lungworm, or the hair lungworm.

It is found almost worldwide. Incidence in endemic regions can be very high and up to 100% of all goats in a herd may be infected. Surveys in slaughtehouses in Germany showed up to 75% of sheep to be infected. It is often found together with other pulmonary roundworms (e.g. Dictyocaulus filariaProtostrongylus rufescens, etc).

These worms do not affect cattle, pigs, dogs or cats.

The disease caused by Muellerius capillaris is called muelleriosis or muelleriasis.

Is livestock infected with Muellerius capillaris contagious for humans?

  • NO: The reason is that these worms are not human parasites.

You can find additional information in this site on the general biology of parasitic worms and/or roundworms.

Final location of Muellerius capillaris

Predilection sites of adult Muellerius capillaris are the bronchi, bronchioles, alveoli and surrounding lung tissues.

Anatomy of Muellerius capillaris

Larva of Muellerius capillaris. Picture from

Adult Muellerius capillaris are medium-sized (not longer than 3 cm) and thin worms. Males are shorter than females. They have a whitish to brownish color.

As in other roundworms, the body of these worms is covered with a cuticle, which is flexible but rather tough. Typical for males of this species is that the posterior end is coiled like a corkscrew. The worms have a tubular digestive system with two openings. They also have a nervous system but no excretory organs and no circulatory system, i.e. neither a heart nor blood vessels.

Males have a copulatory bursa with two spicules for attaching to the female during copulation.

L1-larvae, not eggs are shed in the feces of the infected host.

Life cycle of Muellerius capillaris

Muellerius capillaris has an indirect life cycle. Goats, sheep, and other wild ruminants (e.g. moufflons, deer, chamois) are final hosts. Intermediate hosts are several snails (Helix, Helicella, Theba, Abida, Zebrina, etc.) and slugs (Limax, Agriolimax, etc).

Adult worms in the lungs lay eggs where L1-larvae developed that hatch still in the bronchi and trachea. These larvae are coughed to the mouth together with the respiratory secretions and subsequently swallowed and shed with the feces. Once in the environment these larvae penetrate into the snails very quickly and develop to infective L3-larvae in a few weeks to several months, strongly depending on weather conditions and snail species. Such infective larvae can survive up to 2 years inside their intermediate host.

Livestock becomes infected after eating contaminated snails or slugs while grazing. L3-larvae are released after digestion. They cross the gut's wall and migrate to the lungs through the lymphatic system and the blood stream. Once in the lungs the larvae cross the alveolar mucosa to the lumen of the alveoli or remain in the lung tissue, where they complete development to adult worms and begin producing eggs. The host's lungs react building up to 2 cm large nodules that contain necrotic material, eggs masses, worms, etc. surrounded by connective tissue.

The prepatent period (time between infection and first larvae shed in the feces) is about 1 month.

Harm caused by Muellerius capillaris, symptoms and diagnosis

Lung nodule caused by Muellerius cpillaris. © J. Kaufmann / Birkhäuser Verlag

Muellerius capillaris is one of the causative agents of verminous bronchitis in sheep and goats, but not as harmful as Dictyocaulus filaria. Infected animals often show no or only slight clinical signs such as general weakness or mild respiratory disturbances. Goats are often more severely affected than sheep. Animals younger than 6 months are seldom affected. Heavy infections can cause bronchopneumonia, particularly in weak animals (old, sick, undernourished, etc.). Infections with secondary bacteria can also follow. 

Acquired natural resistance of sheep and goats to these worms after repeated exposure seems to be quite low, not enough to prevent worm development in such animals.

Diagnosis is based on clinical symptoms and is confirmed by larvae found in the feces (250 to 300 micrometers long) with a characteristic tapering and a wavy ouline tail and a dorsal spine. At necropsy typical nodules are found in the lungs.

Prevention and control of Muellerius capillaris

Prevention is difficult because snails and slugs that act as intermediate hosts cannot be easily reduced in the pastures. Since the need humidity for development and survival, effective drainage or anything else that keeps the pastures dry will reduce the snail population. Some preventative measures used against gastrointestinal roundworms can be also appropriate against Muellerius capillaris and are explained in a specific article in this site ( click here).

Chemical control of the snails with molluscicides (i.e. snail killers) such as copper sulphatesodium pentachlorophenate, niclosamide, etc. can make sense for very specific purposes, e.g. for treating places where livestock congregates (water holes, feeding areas, salt licks, shade trees, etc) to keep them free of snails. However, trying to eradicate snails from a property is hopeless and useless. It is virtually impossible to treat every place where they can survive and they reproduce extremely quickly. Cleaned pastures would become re-infested very fast. In addition it would be also very harmful for the environment. In fact, such molluscicides (mainlyniclosamide) are approved only in a few countries as an aid in the prevention of human schistosomiasis (also called bilharziosis or snail fever).

Chemical control is difficult. Some usual anthelmintics such as broad spectrum benzimidazoles (albendazolefebantel, fenbendazole, oxfendazole, etc.) or levamisole are not or only partially effective against these worms. Macrocyclic lactones (e.g. abamectin, doramectin, eprinomectin, ivermectin, moxidectin) seem to be effective against adult worms at the usual therapeutic dose, but not or only partially effective against immature larvae.

So far no vaccine is available against Muellerius capillaris. To learn more about vaccines against parasites of livestock and pets click here.

Biological control of Muellerius capillaris (i.e. using its natural enemies) is so far not feasible. Learn more about biological control of worms.

You may be interested in an article in this site on medicinal plants against external and internal parasites.

Resistance of Muellerius capillaris to anthelmintics

There are a no reports on confirmed resistance of Muellerius capillaris to anthelmintics.

This means that if an anthelmintic fails to achieve the expected efficacy, chance is very high that it was not due to resistance but to incorrect use, or the product was unsuited for the control of these parasites. Incorrect use is the most frequent cause of failure of antiparasitic drugs.

Learn more about parasite resistance and how it develops.

Ask your veterinary doctor! If available, follow more specific national or regional recommendations for Muellerius capillaris control.