Occurrence: Worldwide.   Species affected: Chicken, turkey, duck goose, grouse, guinea fowl, partridge, pheasant and quail.   Age affected: All.

Causes: Heterakis gallinarium is a small white caecal parasitic nematode worm, 7-15 mm long.

Effects: Unthriftiness. The economic importance of H. gallinarium infection is as a vector of the blackhead organism Histomonas meleagridis.

The small, white worms are found in the lumen of the caecum. The male is 7-13 mm long, the female is 10-15 mm long.

The chief economic importance of the caecal worm lies in its role as a carrier of the blackhead organism Histomonas meleagridis. The protozoan parasite is found incorporated in the worm egg and its presence identified in the gut wall and in the reproductive systems of the male and female and in the developing eggs of this caecal worm.

Eggs pass out in the faeces; within 2 weeks, under favourable conditions of temperature and moisture, they reach the infective stage.

When eggs are swallowed by a susceptible host, the embryos hatch in the upper part of the intestine; at the end of 24 hours most of the young worms have reached the caeca. The larvae are closely associated with or occasionally embedded in the caecal tissue until 12 days post-exposure, with peak association at 3 days.

Tissue association increases with age of birds; nevertheless, a true tissue phase rarely occurs with H. gallinarum. Earthworms may also ingest the eggs of the caecal worms and may be the means of causing infection in poultry.

Heterakis infection results in few clinical signs. On postmortem examination, most of the adult worms are found in the tips or blind ends of the caeca. The caeca of experimentally infected birds show marked inflammation and thickening of the walls. The major economic importance of Heterakis infection is as a carrier of the blackhead organism Histomonas.

At necropsy most of the adult worms are found in the tips or blind ends of the caeca. The caeca of experimentally infected birds show marked inflammation and thickening of the walls. In heavy infections nodules form in the mucosa and submucosa.

Modern poultry practices, especially confinement-rearing of broilers and pullets and caging of laying hens, have significantly influenced the quantity and variety of nematode infections in poultry. Many that caused extensive problems in backyard flocks are seldom seen in commercial operations.

For most nematodes, control measures consist of sanitation and breaking the life cycle rather than chemotherapy. Confinement-rearing on litter largely prevents infections with nematodes using outdoor intermediate hosts such as earthworms or grasshoppers. Conversely, nematodes with direct life cycles or those that utilise indoor intermediate hosts such as beetles may proper. Treatment of the soil or litter to kill intermediate hosts may be beneficial. Insecticides suitable for litter treatment include carbaryl, tetrachlorvinphos (stirofos). Treatment is carried out usually only between grow-outs. Extreme care should be taken to ensure that feed and water are not contaminated.

Treatment of range soil to kill ova is not very effective. After the old litter has been removed, spraying with permethrin a mixture of Rabon and Vapona has proven effective for beetle control.

Raising different species or different ages of birds together or in close proximity is bad practice as regards parasites.

Phenothiazine is highly effective in the control of caecal worms in chickens (0.5 g/bird) when given for 1 day only. Hygromycin B and Coumaphos are also approved for use in chickens.

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