Intestinal parasites consist of helminths (worms) and protozoa. They live inside the chicken's gastrointestinal tract and interfere with digestion and absorption of nutrients from food. They can cause significant tissue damage, weaken their immune system, predispose the birds to bacterial infections and kill the chicken.
There are several internal parasites that infect chickens:
Worms
- Nematodes (roundworms): Nematodes are unsegmented worms with a cylindrical or elongated shape that live in the digestive tract. The most common nematodes of chickens include:
- Large roundworms (Ascaridia galli) are the most prevalent and pathogenic worm species that infects chickens worldwide. It lives in the small intestine and occasionally found in the eggs or feces of infected chickens. It a large, cylindrical, semitransparent, creamy-white worm that can grow up to 16 cm (6.3 inches) in length.
- Capillariasis is caused by infection with Capillaria. They are thin, "threadlike" nematodes that invade different regions of the gastrointestinal tract depending on the species.
- Cecal worms (Heterakis gallinarum) are small white worms that live in the ceca. They don't typically cause problems in chickens but the worms are frequent carriers of the protozoa Histomonas meleagridis. H. meleagridis invade and damage the ceca and liver. Infection with H. meleagridis causes Histomoniasis (Blackhead disease).
- Tapeworms (cestodes): Tapeworms are flat intestinal worms that are made up of several small segments. They attach themselves to the bird's small intestine using their hook-like mouthparts. There are several species of tapeworms that infect chickens.
Protozoa
- Coccidiosis is the disease caused by infection with Eimeria (coccidia). They are species-specific protozoan organisms that live and reproduce in the chicken's digestive tract where they cause tissue damage, reduce nutrient and fluid absorption and blood loss.
- Cryptosporidiosis is an infection caused by the protozoa Cryptosporidium spp (cryptosporidia), a parasite that infects many different species, including humans.
- Giardiasis is an intestinal disease caused by the Giardia protozoa. Giardia invade the intestine which can damage the tissue and impact the absorption of nutrients. Chickens may lose weight despite having a good appetite.
