Vet on call: Chickens, snails and earthworms

Some seemingly harmless creatures on your farm will often spring surprises when it comes to diseases or even the death of your livestock.

Today, I narrate an enquiry from Moses Were a poultry farmer. He narrated on phone that he has been seeing his mother’s rural free-range chicken happily eat garden snails.

However, the chickens later cough endlessly, sneeze, squeak, gape and die. Sometimes they gape and struggle to breathe before they die.

Chicken feeding on snails

His concern was what could be the relationship between eating snails and the consequent fate of the chickens.

This enquiry took me many years back. I remembered as a small boy growing up on our upcountry farm that we had a lot of free-range chickens that were very tasty when well-cooked.

The chickens fed on snails, dung beetles, insects and earthworms in addition to plant matter. Frogs and toads were also on their menu.

Some of our chicken would develop the same condition Were observed. My father believed that dead animals are toxic to humans and eating them was unreligious. He would quickly slaughter the birds before they made their last kick and we enjoyed eating them. One thing he always insisted was the birds slaughtered because of sickness could only be cooked through boiling.

He believed the birds died of toxins from snails and beetles but those chemicals would be destroyed by boiling.

I only got to understand the mystery of the snails, the earthworms and the gaping chicken when Prof Maingi taught us parasitology in our second year at the university.

“Such chickens will show a symptomatology of open mouth breathing, gaping, difficulties in breathing and often death if not treated. The disease is not known to affect humans,” said the professor with a tone of finality.

I smiled as I took the notes, knowing that my dad’s generosity with sick chicken had not jeopardised our family health. Gaping is the opening of the mouth continuously.

From Were’s description, the symptomatology or group of symptoms observed highly indicate his mother’s chickens suffer from infestation with gape worms.

Inflammation at the attachment site

The worm is scientifically called Syngamus trachea and the disease is commonly called gapes. The gape worm is a roundworm that affects wild birds, chickens and turkeys. It is transmitted mainly by snails, slugs, earthworms, and grasshoppers.

Other invertebrates such as beetles may also transmit it. These are called the worm’s intermediate hosts. Gape worms can remain active as cysts in the muscles of the earthworm for up to three years. Chickens mainly get infected by swallowing the larval stage of the worm carried in the intermediate host. The larva hatch in the chicken intestines, burrow into the body and migrate to the lungs where they settle for the rest of their life in the airways of the bronchi and trachea. The worms live in permanent mating and form a characteristic Y shape visible without the use of instruments. This earns them the pseudonym, “the forked worm”.

The male worm is permanently attached in one location of the trachea and bronchi while the female detaches from time to time to select good feeding locations. The gape worm has a characteristic red colour and is thus also called the red tracheal worm.

Once settled in the airways, the worms feed on mucous and blood and lay eggs that are coughed up and swallowed by the bird.

The eggs come out in the bird’s droppings and are eaten by the intermediate host such as an earthworm or snail. The larva of the worm hatch in the host, burrow into the muscles and form cysts awaiting consumption by the chickens to continue with the life cycle. It takes about one to two weeks after infection for the signs of gapes to start showing. Gape worms in the airways cause direct blockage to breathing and the production of lots of mucous due to inflammation on the attachment site.

As the number of worms increase, the airways get clogged making it difficult for the bird to breathe. This is the cause of the coughing, gaping, gasping and head shaking seen in affected birds.

Among free-range chicken

Worms migrating through the lungs may also cause severe pneumonia. The chickens in most cases suffocate and die.

Birds with fewer worms will show long-standing coughing, weight loss and poor growth. Young birds are more affected than the older ones.

Older birds may live with the worms without symptoms but keep contaminating the environment and infecting other birds. Turkeys are more resistant to the worms but when raised among chicken, can be the worm reservoir. Gapes is diagnosed by clinical examination and confirmed by a postmortem. The doctor will find the Y-shaped red worms in the trachea and bronchi.

Examining the droppings of affected birds under the microscope may also show presence of the characteristic worm eggs. Should you slaughter a chicken at home, always slit the trachea open down to the bronchi and see if there are red Y-shaped worms attached to the tracheal lining.

The common practice of rearing chicken in confinement has greatly reduced the occurrence of gape worm in poultry.

However, in chicken houses where wild birds and the intermediate hosts have access, gape worms may still be found in confined poultry.

There are a number of dewormers available for treatment of gape worm in its early stages before the physical blockage of the trachea and bronchi occurs.

DISEASE

Gapes

Gapes is diagnosed by clinical examination and confirmed by a post-mortem