Gapeworm Infection

The gapeworm, Syngamus trachea, is a parasitic nematode found in the trachea of domestic and wild birds worldwide. S. trachea are tiny, bright red (caused by ingestion of the host's blood), worms that have a 'y'-shaped appearance (which are actually two worms, the male and female---that are joined together, with the male acting as an anchor for the female). These worms attach themselves to the mucosa of the chicken's trachea, where they feed on blood. This results in the development of lymphoid nodules, catarrhal tracheitis and occasional secondary lobar pneumonia. If enough worms are present, they can cause partial to complete obstruction of the trachea.

Female S. trachea lay their eggs in the bird's trachea, which hatch and are either coughed up or swallowed by the bird, later defecated out into the environment.

Life cycle
Chickens become infected with S. trachea by accidentally eating the larvae that has contaminated the surrounding environment, feed, or water through the presence of feces from an infected bird. Many wild bird species can be infected with S. trachea, which will shed the larvae in their feces. Chickens can also become infected indirectly, by eating earthworms, snails or slugs that are infected. Regardless of how, once chickens ingest the larvae, they will migrate through the gastrointestinal system until they reach the trachea, where they reproduce, lay eggs, feed on blood, and live. The eggs are either coughed up or swallowed by the chicken. When swallowed, they will get passed along with the feces, further contaminating the environment with more eggs for other flock members---or even the same bird to ingest and accumulate more worms or infect others. The prepatent period is between 17 to 20 days.

Clinical signs
Affected chickens are often observed stretching their necks out, while opening their mouths and gasping or gaping for air. The gaping is caused by the presence of multiple worms in the trachea, causing a partial to complete block in airflow. Without treatment, if birds are heavily infested, they often die from suffocation.

Small chicken breeds, such as bantams and younger chickens are more severely affected by gapeworms. This is related to the size of the chicken's trachea, as when there is a larger amount of space available for the worms to attach onto, the less likely they will cause a blockage in the airflow for the chicken not to be able to breath.