The Condition

The Capillaria species of nematode, or roundworm, are intestinal worms that can cause severe symptoms such as diarrhoea, weakness, weight loss and a drop in egg production. The condition is sometimes referred to as capillariasis. There are several species of Capillaria, and they cause paralysis of different parts of the alimentary tract, including the crop, oesophagus and the intestinal tract. Commonly, the Capillaria species are referred to as the threadworm or hairworm, and they can be highly pathogenic, causing severe disease.

The Capillaria are a small species of worms, and some tend to be restricted to free-range birds, as the intermediate host is the earthworm. Others have a more direct life cycle. Capillaria bursata is found only in chickens and its life cycle is dependent on the earthworm as an intermediate host. Capillaria caudinflata has a similar life cycle and can be found in a number of domestic poultry species. Capillaria obsignata can be a problem in deep-litter systems. This worm does not have an intermediate host and can be found in a number of poultry species.

The main site of infection of C. bursata, C. caudinflata and C. obsignata is the small intestine. Capillaria anatis is a parasite of the caecum and is found mainly in ducks. The main species afflicting turkeys and game birds are C. annulata and C. contorta. Capillaria obsignata (53.6%), Capillaria anatis (31.9%) and Capillaria caudinflata (1.5%) have been found in organic/free range systems in Denmark (Permin et al, 1999). Amongst Dutch organic poultry farms, Capillaria, along with coccidiosis, was the second most prevalent internal parasite, being present in 30% of the faeces samples examined (Iepema et al.,2006)..

Capillaria obsignata has a direct development. Freshly deposited eggs require 6-8 days to develop completely formed embryos. The eggs remain infective for a period of up to 14 days. Following the ingestion of the worm eggs from the pasture, the embryo escapes from the egg and completes its development in the duodenum of the host bird. Birds infected with C. obsignata spend much of their time apart from the rest of the flock, huddled on the ground or corner of the house. They develop diarrhoea and the feathers are ruffled. These first clinical symptoms are noted at approximately 12 days after infection.

Capillaria annulata occurs in the crop and oesophagus. These worms are long and thread-like. The developmental cycle involves the earthworm. Eggs passed in bird faeces develop slowly to produce larvae which are infective to earthworms. At normal temperatures, this can take 3-4 weeks. The infective stage in the earthworm is reached 2-3 weeks after ingestion. The worm develops to maturity in a bird approximately 1-2 months after the earthworm has been ingested.

Capillaria contorta, which occurs in the oesophagus, crop and mouth of a number of bird species, has a direct life-cycle. Eggs become infective to birds 4-6 weeks after they have been passed in faeces.

Poor drainage and ventilation and the feeding of birds off the ground have been associated with infections of Capillaria species. The nematode eggs are markedly resistant to adverse conditions and they may survive on pasture or in deep-litter houses for a considerable period. The larval stages of those that pass through the earthworm probably survive as long as the earthworms survive.

Capillaria caudinflata, which occurs in the small intestine, also has the earthworm as a secondary host.

The presence of Capillaria can be detected by post-mortem microscopic examination of mucosal washings.