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Capillaria spp.
Kingdom Animalia
Phylum Nematoda
Class Adenophorea
Sub-class Enoplia
Order Trichurida
Super-family Trichuroidea
Family Trichinellidae
Genus Capillaria
Species Many


Capillaria spp. are similar to other members of the Trichuroidea superfamily such as Trichuris but with slight differences in morphology of the anterior and posterior ends. Although they are found in domestic mammals and some reptiles these species are of greatest importance in birds. The predilection sites vary between species and are not restricted to the gastrointestinal system. Important species include; C. annulata, C. anatis and C. contorta.


Capillaria are extremely thin, filamentous worms measuring 15-25mm long (males) and 35-80mm long (females). Males have a single spicule and many have a primitive bursa like structure. The eggs have bipolar plugs and thick shells, the size can vary between species.

Important Species

C. annulata

Also know as: Eucoleus annulata — Hairworms — Threadworms

This species affects many species of wild birds as well as domesticated poultry, turkeys and ducks. Adult worms are thin. The females are around 37-80mm in length, and considerably longer than the male. The eggs have bipolar plugs.

The earthworm is the intermediate host for this species, making the life cycle indirect. The eggs are passed in the host faeces, and are quickly ingested by the intermediate host, in this case the earthworm. The larvae develop and mature into infective larvae. The definitive host then ingest the earthworms, and become infected themselves, where the larvae develop into adults.

Young birds are more susceptible to the disease. Immune adults may be carriers. The predeliction site for this worm is the oesophagus of the bird where it will bury the anterior end into the mucosa causing inflammation. High levels can result in marked thickening of the oesophageal wall and can be fatal. The presence of these worms in low numbers may be a cause of ill thrift in production birds, though in high number emaciation can be seen.

C. contorta

Also known as: Eucoleus contorta

As with C. annulata this species is found in the oesophagus and crop of domestic poultry and many wild birds. Both the adults and the eggs of this species are smaller in size but the general morphology remains the same. The earthworm is normally the intermediate host but it is possible for this species to have a direct life cycle with the L1 embryonated egg as the infective stage. Clinical signs are rare with low levels of infection though they can be associated with a loss in productivity, high parasite burdens will result in emaciation and anaemia and can be fatal. The primary epidemiological concern with this parasite is its ability to have a direct life cycle and so birds kept indoors and away from the intermediate host may still become infected.

C. anatis

Also know as: Capillaria brevicollis — Capillaria colaris — Capillaria anseris — Capillary mergi

Capillaria anatis affects chickens, turkeys, ducks and geese. The adults are filamentous worms and the females are around 30mm in length, and larger than the males. The eggs are colourless and have a thick outer shell.

THe life cycle is direct. L1 develop within the egg. The host is infected through ingestion, and develop into adults. The prepatent period is 3-4 weeks.

C. obsignata

Also known as: Baruscapillaria obsignata — Capillaria columbae

The hosts are chickens, pigeons, turkeys and wilds birds. The worms are of similar appearance to C. annulata, but the adults are slightly smaller at around 10mm in length.

The life cycle is direct. Infection of the host is through ingestion of infective eggs. The eggs then develop into fully reproductive adults within the host, and do not require a migratory phase. The prepatent period is 3 weeks.

C. caudinflata

Also known as: Aonchotheca caudinflata

Definitive hosts are chickens, turkeys, geese, pigeons and wild birds. Worms are morphologically very similar to C. annulata. Females are around 25mm in length, and males around 10mm in length.

Earthworms are intermediate hosts, and the life cycle is indirect.

C. aerophila

Capillaria aerophila is associated with respiratory disease of cats and dogs. The worm can be found in the nasal passages, sinuses, trachea and bronchi. The presence of the worms causes a mild catarrhal inflammation and can cause coughing in dogs but not in all cases. In heavy infestation may cause obstruction of the lumen of airways and may develop into secondary bronchopneumonia

Clinical Signs

Young birds exhibit the most serious clinical signs, including: weight loss, diarrhoea, regurgitation, anaemia and oral necrotic plaques.


Faecal flotation can be carried out to identify the typical barrel-shaped eggs.

However, eggs laid within the gastrointestinal epithelium are only released into the lumen of the digestive tract when the epithelium sloughs. Therefore, severe clinical signs may be associated with negative or low faecal egg counts. Therefore diagnosis is usually made on necropsy examination of the oesophagus and intestines. The worms are small and must be looked for carefully in mucosal washings under a dissecting microscope.


Treatment can be challenging as Capillaria species often demonstrate multiple drug resistance. Fenbendazole, mebendazole and ivermectin have been used and efficacy of therapy should be checked through repeat faecal flotation tests.

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Capillaria publications since 2000


Trees, A. (1987) Parasitic conditions in poultry 2: Helminths and arthropods In Practice; 9:157-161

Lloyd, C. (2003) Avian Practice: Control of nematode infections in captive birds In Practice; 25:198-206

Saif, Y. (2003) Diseases of Poultry Wiley-Blackwell

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