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Publication #PS18

Nematode Parasites of Poultry (and Where to Find Them)1

R. D. Jacobs, J. A. Hogsette, and G.D . Butcher2

Nematodes or roundworms are the most important group of helminth parasites of poultry. This is due to the large number of parasitic species (23) that cause damage to the host, especially in severe infections. Roundworms are elongated, cylindrical and unsegmented. They are covered with a tough, noncellular layer called the cuticle.

Nematode Life Cycle

Each species of roundworm tends to infect a specific area of the intestinal gastro tract. Different species of the same genus may infect several different areas of the tract. In general, the different species of roundworms have very similar life cycles. Adult roundworms lay eggs inside the infected bird. The eggs are voided from the hosts through the feces. The eggs incubate in soil before they become infective. Roundworms may or may not require intermediate hosts. The eggs or intermediate hosts must then be consumed by the avian host. Once the infective agent finds its way back to its infective site, the cycle is complete. An interesting example of this is the eye worm (Oxyspirura mansoni). The eye worm lays eggs on the surface of the eye. These eggs are then washed down the naso-lachrymal duct and pass into the intestinal tract of the host and are voided with feces. The eye worm eggs must then be consumed by a cockroach, the intermediate host. After an incubation period, the worm larvae becomes free inside the body cavity and legs of the cockroach. After the cockroach has been consumed by the avian hosts (chickens, turkeys, peafowl and ducks) the eye worm larvae are released in the crop. They migrate up the esophagus, tear ducts and back to the eye. The time required for the cycle to be completed may be a few days or several weeks depending upon the worm species.

Six infectious groups of roundworms are identified in this fact sheet. The first three groups (large roundworms, cecal worms and capillaria) are the more common, the remaining three groups (eye worms, gapeworms and gizzard worms) are less common.


The best method for controlling roundworms is prevention, which includes sanitation of the area where poultry are kept, controlling secondary hosts, keeping poultry age groups separated and keeping different kinds of poultry separated. Secondary hosts include not only insects such as beetles, roaches and grasshoppers, but also earthworms.

Problems associated with roundworms can be reduced if the hosts are maintained on wire placed above ground level, thus preventing contact with contaminated feces and/or intermediate hosts.


Symptoms of roundworm infections closely resemble symptoms of other types of diseases. The presence of roundworms should be identified prior to using chemical treatment. In all cases if chemical treatments are to be used, manufacturers recommendations should be followed.

Large roundworms

Primary species: Ascarida galli

Location: Lumen of intestines

Symptoms: Large roundworms are found in all ages of chickens, the greatest amount of damage is in young birds under 12 weeks of age. Unthriftiness, drooping of the wings, bleaching of the head and emaciation are described. In adult hens, egg production can be reduced. In heavy infections, large roundworms may move up the oviduct and be found in hens' eggs, and sometimes large roundworms can be found in the birds' feces.

Autopsy: Large numbers of worms can occlude the intestines and penetrate the mucosa during growth causing injury, loss of blood and permitting bacterial infection.

Treatment: Piperazine salts, continuous medication in feed with Hygromycin B.

Cecal Worms

Primary species: Heterakis gallinae

Location: Lumen of cecal pouches

Symptoms: With heavy infection (500), especially in young birds, listlessness, depression and unthriftiness are present. In production birds, heavy infestation of cecal worms can adversely affect production. Cecal worm eggs can be carriers of the blackhead organism Histomonas meleagridis.

Autopsy: Large numbers of worms can cause thickening of the cecal walls, hemorrhages.

Treatment: Phenothiazine as drug of choice, piperazine salts, Hygromycin B in the feed and Levamisole.

Capillaria or Small Roundworms

Primary species: Capillaria amulata

Location: Embedded in the lining or mucosa of the esophagus, crop, duodenum and small intestine.

Symptoms: Droopiness, anemia, muscular weakness, loss of appetite, foul breath, emaciation, twisting of the neck and paralysis of the legs are described.

Autopsy: To identify presence of small roundworms, scrape mucosa of infected area, wash through a fine mesh screen, backwash into a large glass jar. Identify worms suspended in the backwash. Inflammation and thickening of walls are described.

Treatment: Levamasole in drinking water, Hygromyacin B in feed.

Eye Worms

Primary species: Oxyspirura mansoni

Location: Under the nictitating membrane of the eye and in the naso-lachrymal duct.

Symptoms: Scratching of the eyes; can cause blindness.

Treatment: Physical removal of worm using local anaesthetic.


Primary species: Syngamus trachea

Location: Inner lining of trachea

Symptoms: Respiratory distress and death may occur from asphyxiation.

Autopsy: Red worms can be found in trachea causing inflammation, ulceration and accumulation of mucus in the trachea.

Treatment: None

Gizzard Worms

Primary species: Cheilospirura hamulosa

Location: Musculature of gizzard

Symptoms: Dullness, loss of appetite, emaciation, weakness and death are described.

Autopsy: Presence of red worms attached to musculature of gizzard at opening to proventriculus; nodules also may be present.

Treatment: None


Gapeworms: Red, ¼ to 1½ inches* long, worms that infect the inner lining of the trachea. Two species involved.

Large Roundworms: Grey, white worms 1½ to 4 inches* long infecting the lumen ** of the duodenal loop through the small intestines. Several species of roundworms involved.

Cecal Worms: White, ¼- to ½-inch* long worms infecting the lumen** of the cecal pouches. Several species of roundworms involved.

Eye Worms: White, ¼- to ½-inch* long worms infecting the eye, beneath the nictitating membrane. One species of roundworms involved.

Gizzard Worms : Red, ½ to 1 inch* long, worms that infect the musculature of the gizzard.

* Length varies with age and species.

** Lumen is the space inside the specific organ wall occupied by feed that is being digested and/or absorbed.



This document is PS18, one of a series of the Animal Sciences Department, UF/IFAS Extension. Original publication date June 1997. Reviewed June 2015. Visit the EDIS website at


R. D. Jacobs, multi-county poultry Extension agent; J. A. Hogsette, USDA-ARS, Gainesville; and G. D. Butcher, professor, Veterinary Medicine, UF/IFAS Extension, Gainesville, FL 32611.

The Institute of Food and Agricultural Sciences (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and other services only to individuals and institutions that function with non-discrimination with respect to race, creed, color, religion, age, disability, sex, sexual orientation, marital status, national origin, political opinions or affiliations. For more information on obtaining other UF/IFAS Extension publications, contact your county's UF/IFAS Extension office.

U.S. Department of Agriculture, UF/IFAS Extension Service, University of Florida, IFAS, Florida A & M University Cooperative Extension Program, and Boards of County Commissioners Cooperating. Nick T. Place, dean for UF/IFAS Extension.