Caecal Worm, Capillary Worm, and Gapeworm
Poultry are affected by several important species of internal worms that can significantly impact health, growth, and egg production. Among the most important are caecal worms, capillary (hair) worms, and gapeworms.
While these parasites are small, they can cause major problems – especially in young birds, free-range systems, and flocks kept in crowded or wet conditions. Many infections remain unnoticed until birds begin to lose condition or productivity.
Why These Worms Matter
These parasites damage different parts of the body, including the intestines, caeca, and respiratory tract. This leads to irritation, inflammation, and reduced nutrient or oxygen absorption.
Over time, this can result in:
Weight loss or poor growth
Reduced feed efficiency
Weakness and lethargy
Diarrhoea
Poor feather condition
Reduced egg production
Increased susceptibility to disease
Death in severe cases
Because poultry often hide signs of illness, infections may already be advanced before they are noticed.
Types of Worms in Poultry
Caecal Worm (Heterakis gallinarum)
Caecal worms live in the caeca, two blind-ended pouches attached to the intestines. On their own, they often cause mild or no obvious signs. However, they are extremely important because they can carry and transmit blackhead disease (Histomonas meleagridis), which is deadly in turkeys and can also affect chickens.
Infected birds may show:
Poor growth
Weight loss
Reduced appetite
Diarrhoea
Lethargy
Even low numbers of caecal worms can be dangerous because of their role in spreading blackhead.
Capillary Worms (Hairworms – Capillaria species)
Capillary worms are very thin, hair-like worms that can infect the crop, oesophagus, or intestines, depending on the species.
They embed themselves into the lining of the digestive tract, causing irritation and inflammation.
Signs may include:
Diarrhoea
Weight loss
Poor growth
Reduced appetite
Weakness
Ruffled feathers
In heavy infestations, capillary worms can cause serious digestive damage and even death.
Gapeworm (Syngamus trachea)
Gapeworms live in the trachea (windpipe) of birds. They attach to the lining of the airway, where they interfere with breathing.
This parasite gets its name from the classic sign it causes: birds stretching their necks and gaping for air.
Signs of gapeworm infection include:
Gasping or gaping
Head shaking
Coughing
Laboured breathing
Lethargy
Weight loss
Sudden death in severe cases
Gapeworm is particularly dangerous in young birds.
How These Worms Spread
These parasites have direct or indirect life cycles, depending on the species.
Eggs are passed in droppings and contaminate the environment. Some species are spread directly when birds ingest these eggs from soil, feed, or water.
Others use intermediate hosts such as earthworms, snails, or insects. Birds become infected when they eat these hosts while foraging.
Because of this, free-range systems and wet, muddy environments carry a higher risk.
Signs of Worm Burdens
Worm infections often cause vague, gradual changes rather than sudden illness.
Common signs include:
Weight loss
Poor growth
Reduced egg production
Diarrhoea
Dull or ruffled feathers
Lethargy
Reduced appetite
Breathing difficulties (gapeworm)
Young birds are most vulnerable.
Detection
These parasites are detected using faecal testing, where eggs are identified under a microscope.
Detection helps to:
Confirm which species are present
Guide targeted treatment
Prevent unnecessary medication
Monitor reinfection risk
Protect flock productivity
Gapeworm may also be suspected based on classic breathing signs, especially in young birds.
Treatment & Long-Term Control
Different worms require different treatments, and not all poultry dewormers are effective against all species.
Long-term control involves:
Targeted treatment based on detection
Regular cleaning of housing
Dry bedding
Preventing overcrowding
Rotating outdoor areas
Controlling intermediate hosts where possible
Good biosecurity
Because reinfection can happen quickly, monitoring is essential.