Syngamus trachea

This is the gapeworm of poultry, found in the trachea of chickens, turkeys, guinea fowl and many species of wild birds. It is of particular importance in farm-raised pheasants. Although Syngamus is found throughout the world,  conversion of domestic poultry raising from outdoors to indoors has significantly reduced its prevalence  in the United States.


cj033sm.gif (7338 bytes)
The most distinctive feature of this nematode is that males and females are joined together in a state of permanent copulation forming a Y shape as seen in the image on the right. Females are much larger (up to 20mm long) than males (up to 6mm long).

Life cycle

The life cycle is complicated in both its preparasitic and parasitic phases. In the preparasitic phase L3s develop inside the eggs at which time they may hatch. Earthworms play an important role in the life cycle, serving as transport (paratenic) hosts. Larvae have been shown to remain viable for more than three years   encapsulated in earthworm muscles. Other invertebrates may also serve as paratenic hosts and these include terrestrial snails and slugs as well as the larvae of Musca domestica (the common house fly) and Lucilia sericata (the greenbottle fly responsible for cutaneous myiasis). The parasitic phase involves substantial migration in the definitive host to reach the predilection site.


Young birds are most severely affected with migration of larvae and adults through the lungs causing a severe pneumonia. Lymphoid nodules form at the point of attachment of the worms in the bronchi and trachea. Adult worms appear also to be blood suckers. Worms in the bronchi and trachea provoke a hemorrhagic tracheitis and bronchitis with formation of large quantities of mucus, plugging the air passages and, in severe cases, causing asphyxiation.

Pheasants appear to be particularly susceptible to Syngamus infections resulting in mortality rates as high as 25% during outbreaks.


Earthworm transport hosts are important factors in the transmission of Syngamus trachea where poultry and game birds are reared on soil. The longevity of L3s in earthworms (up to 3 years) is particularly important in perpetuating the infection from year to year.

Wild birds may serve as reservoirs of infection and have been implicated as the sources of infections in outbreaks on game-bird farms as well as poultry farms. Wild reservoir hosts may include pheasants, ruffed grouse, partridges, turkeys, magpies, meadowlarks, robins, grackles, jays, jackdaws, rooks, starlings and crows.

There is also evidence to suggest that strains of Syngamus trachea from wild bird reservoir hosts may be more infective for domestic birds if they first pass through an earthworm transport host rather than by direct infections via ingestion of L3s or eggs containing L3s.

Clinical signs

Blockage of the bronchi and trachea with worms and mucus will cause infected birds to gasp for air. They stretch out their necks, open their mouths and gasp for air producing a hissing noise as they do so. This "gaping" posture has given rise to the common term "gapeworm" to describe Syngamus trachea. These clinical signs first appear approximately 1-2 weeks after infection. Severely affected birds, particularly young ones, will deteriorate rapidly; they stop drinking and  become anorexic. At this stage, death is the usual outcome. Adult birds are usually less severely affected and may only show an occasional cough or even no obvious clinical signs.


A diagnosis is usually made on the basis of the classical clinical signs of   "gaping".  Subclinical infections with few worms  may be confirmed at necropsy by finding copulating  worms in the trachea and also by finding the characteristic eggs in the feces of infected birds.

Syngov1.gif (21923 bytes)

GlIVasm.gif (21369 bytes)

Syngamus trachea - bioperculate egg
Syngamus trachea - adult worms  in the trachea of  an infected turkey
Image courtesy of Professor Max Murray








Parasites and Parasitic Diseases of Domestic Animals
Dr. Colin Johnstone (principal author)
Copyright 1998 University of Pennsylvania
This page was last modified on January 24, 2000