Birds are infected with the parasite when they consume the eggs found in the feces, or by consuming a transport host such as earthworms, snails (Planorbarius corneus, Bithynia tentaculata and others) Males and females are joined in a state of permanent copulation forming, a Y shape (forked worms).

The life cycle of the gapeworm is peculiar in that transmission from bird to bird may be successfully accomplished either directly (by ingesting embryonated eggs or infective larvae) or indirectly (by ingestion of earthworms containing free or encysted gapeworm larvae they had obtained by feeding on contaminated soil).

Worms in the bronchi and trachea provoke a hemorrhagic tracheitis and bronchitis, forming large quantities of mucus, plugging the air passages and, in severe cases, causing asphyxiation.

Turkey poults usually develop gapeworm signs earlier and begin to die sooner after infection than young chickens.

The male worm, in the form of lesions, remains permanently attached to the tracheal wall throughout the duration of its life.

Earthworm transport hosts are important factors in the transmission of Syngamus trachea when poultry and game birds are reared on soil.

Birds infected with gapeworms show signs of weakness and emaciation, usually spending much of their time with eyes closed and head drawn back against the body.

An infected bird may give its head a convulsive shake in an attempt to remove the obstruction from the trachea so that normal breathing may be resumed.

Adult birds are usually less severely affected and may only show an occasional cough or even no obvious clinical signs.

Confinement rearing of broilers/pullets and caging of laying hens, have significantly influenced the quantity and variety of nematode infections in poultry.

Confinement rearing on litter largely prevents infections with nematodes using intermediate hosts such as earthworms or grasshoppers, which are not normally found in poultry houses.

Conversely, nematodes with direct life cycles or those that utilize intermediate hosts such as beetles, which are common in poultry houses, may prosper.

Adult turkeys, which are carriers of gapeworms, can transmit the disease to young chicks or pheasants, although older chickens are almost resistant to infection.