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Other Names: 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

Head flicking
Difficulty swallowing
Loss of appetite
Weight loss
Poor body condition


  • History
  • Fecal exam
  • Post mortem examination

Reported Cases

  • Case 1: Threadworms in a Chukar partridges A flock of approximately 3000 Chukar partridges, aged five months and older, were experiencing a decrease in performance and a slight increase in mortality. The birds continued to eat but many lost weight and eventually died. No overt respiratory or digestive clinical signs were observed. Six live, 5-month-old Chukar partridges were presented to the Texas A&M Veterinary Medical Diagnostic Laboratory (TVMDL) in Gonzales for necropsy. At the time of examination, all birds were alert, but most were very thin with prominent keels. All birds were similar in necropsy findings with mild to severe breast muscle atrophy. Feed was present in both the crop and gizzard. The small intestines were slightly reddened and the mucosa of the duodenum and jejunum in some birds was mildly thickened while in others the intestinal tract appeared within normal limits. Intestinal scrapings of the duodenum and jejunum demonstrated large numbers of long, thin, thread-like worms consistent with Capillaria obsignata. Many of these worms contain numerous double operculated eggs. Ref


Albendazole (Valbazen)Given to each bird orally. Measure out ¼ mL (per bantam) or ½ mL (per regular-sized breed). Repeat in 2 weeks.G Damerow
Safeguard 10% Liquid Dewormer for GoatsFenbendazole is used off-label in poultry. Add to the flock's drinking water source at a rate of 3 mL per gallon of water.G Damerow
Panacur or Safeguard Equine Dewormer 25 g Paste 10%Fenbendazole is used off-label in poultry. Given individually to each chicken orally, squeezed out in a pea-size portion and placed inside their mouth. Repeat in 10 days.G Damerow
(1% Ivermectin) Injectable for Cattle and SwineIvermectin is used off-label in poultry. The drug is given to each chicken orally or added to the flock’s water source.

If given by mouth - 0.25 mL per large size, 0.1 mL per bantam size.

If added to flock water source- 4 mL per gallon of water. Made fresh daily for 2 consecutive days.
G Damerow
Pour-on for Cattle and Swine (5 mg/mL Ivermectin)Ivermectin is used off-label in poultry. Should not be given internally to the bird. Should be used only externally.

Apply to each chicken topically - Use an eye dropper to apply to the skin at the back of the bird’s neck. Bantam size birds should get 3 drops, normal-sized 4-5 drops, and large breeds 6 drops. Repeat in 2 weeks.
G Damerow
Levamisole Soluble Drench Powder (46.8g)Levamisole is used off label in poultry. It's added to the flock’s water source.

Note- Chickens who are severely debilitated should not receive this medication, because it will impact their ability to fight infections.

Add to the flock’s drinking water source - at a rate of 10 mL per gallon of water for only 1 day.
G Damerow
Diatomaceous earthAdded as 2% of overall dietD Bennett; R Isabirye et al., 2019



  • 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)