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Thread Worms, Hairworm Infection, Capillara, Small Roundworms

Capillariasis is the name of the disease caused by infection with Capillaria species (referred to often as hairworms or threadworms), which are a type of internal parasite. When chickens are mildly to moderately infected, they can show a variety of nonspecific signs from general poor health, diarrhea, and eventually death. However during heavy infections, it starts to have a significant impact on their overall health. These birds will have a lower resistance against other infections and more severe symptoms, especially in younger poultry. Signs include unthriftiness, slow growth, weight loss, emaciation, reduced egg production, and death.

What are Capillaria species?

Adult Capillaria are very thin, "threadlike" nematodes, that are approximately 1 cm (0.39 in) long. Their eggs, which can only be seen using a microscope, are barrel-shaped and have clear pugs on each pole. There are several different species of Capillaria, each invades a specific region inside the chicken. Some species (C. contorta and C. annulata) will invade the crop and esophagus, causing thickening and inflammation of the mucus membranes. Others (C. bursata, C. caudinflata, and C. obsignata) target the lower intestinal tract, causing inflammation, hemorrhage, and erosion of the intestinal lining. When Capillaria are present in high enough numbers, it can be fatal to the chicken.

Capillaria Life Cycle

The worms live inside infected birds, where they feed on various parts of their body and lay their eggs. Their microscopic eggs get passed through into the chicken's feces, contaminating the surrounding environment. The eggs are so microscopic, that you cannot see them with the naked eye. You need a microscope in order to identify their presence, hence why fecal tests are used as a great preventative tool. Other chickens in the flock will ingest the eggs when forging, eating, or drinking. Once ingested, the eggs hatch in the chicken and develop and feed on their crop, esophagus, small intestines, or ceca. Upon reaching adult age, the worms will then lay their eggs which gets passed through the chicken in their feces.

Nematode speciesWhere FoundIntermediate HostDefinitive Hosts
Capillaria annuataEsophagus, cropEarthwormChicken, turkey, guinea fowl, partridge, pheasant, quail, goose, grouse
C. anatisSmall intestine, cecum, cloacaNoneChicken, turkey, partridge, pheasant, goose, duck
C. bursataSmall intestineEarthwormChicken, turkey, pheasant, goose
C. caudinflataSmall intestineEarthwormChicken, turkey, guinea fowl, partridge, pheasant, quail, goose, grouse, duck, pigeon
C. contortaEsophagus, crop, mouthNone or earthwormChicken, turkey, guinea fowl, partridge, pheasant, quail, duck
C. obsignataSmall intestineNoneChicken, turkey, guinea fowl, quail, pigeon, goose

Clinical Signs

Loss of appetite
Foul odor
Changes in egg shell quality
Decreased egg production
Retarded growth
Weight loss
Poor body condition


  • History
  • Fecal exam
  • Post mortem examination


AlbendazoleAdministered orally, 1/4 cc (mL) per bantam, 1/2 cc (mL) per large breed, repeated in 2 weeks.
Ivermectin (drench or injectable)Administered orally - 1/4 cc (mL) per large breed chicken, 6-7 drops (0.1 cc) per bantam.
Administered in drinking water - 4 cc (mL)/gal of water, for 2 days.
Levamisole (drench)Administered orally - 1/4 cc (mL)/lb body weight.
Administered in drinking water - 10 cc (mL)/gal for 1 day. Repeat in 7 days, and repeat again in 7 days.
Levamisole (injectable)Injected under the skin, 1/4 cc (mL)/s lb body weight (25 mg/kg).
Tetramisole40 mg/kg
Note is not approved in the USA for use in commercial poultry
Khaziev GZ et al., 1975
Mebendazole5-25 mg/kg orally , every 12 hours for 5 daysEnigk K et al., 1973; Gundlach JL et al., 1987
Thiabendazole200-500 mg/kg with feedShang N et al., 2011



  • Allow chickens to dust bath by providing an area with appropriate substrate
  • Frequently change bedding and clean coop area to minimize accumulation of chicken droppings
  • Conduct annual fecal test on flock members

Scientific References

Risk Factors

  • Use of deep-litter systems
  • Unsanitary conditions (fecal build up)