Common poultry worms - Veterinary Practice
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Common poultry worms

SUSAN McKAY reviews the major parasitic worms that affect both commercial and back-yard flocks

ROUTINE poultry worming is important to producers of commercial flocks and keepers of back-yard poultry.

With the number of free-range flocks increasing, parasitic worms have potentially become more of a threat in commercial flocks in recent years.

Enthusiasts and hobbyists are often well-educated about the need to worm but conversely, some small-scale keepers may not know how often to worm or are using “natural remedies” that do not have proven efficacy, potentially storing up future problems as the immediate environment where the birds are kept becomes more and more contaminated.

Route of infection

Birds may become infected directly, ingesting worm eggs or larvae direct from the ground. Worm eggs can be very resistant, often surviving for months in soil. Both worm eggs and larvae may be introduced on footwear, clothing, feedbags, other animals, or equipment. Wild birds can also introduce contamination and infected wild or domestic birds can excrete thousands of parasitic worm eggs every day.

Worm eggs need warmth and moisture to embryonate, so they can be more problematic in spring and summer months but deep litter systems can provide equally as favourable conditions all year round. Indirect infections can occur as a result of the bird ingesting an intermediate host – such as an earthworm – infected by the parasite’s larvae, or simply carrying their eggs.

Signs of worms

The signs can be difficult to identify due to the chronic nature of infection and some birds show no obvious signs of illness at all. Non-specific signs include ill thrift, reduced appetite, weight loss, pale combs due to anaemia and intermittent diarrhoea.

Egg production may drop, with smaller eggs, pale yolks and fragile shells. More specific signs may be seen with some worm species, such as snicking with Gapeworm, but birds can carry multiple worm species simultaneously.

  • Ascaridia galli (large roundworm, prepatent period 35-42 days in young birds or 50-56 days in older birds)

Roundworms are common and are the largest worms affecting poultry. In appearance they are thick and white and up to 12cm in length. These intestinal worms can cause intestinal impaction and fatalities in severe cases.

  • Capillaria obsignata (hair worm, prepatent period 20-26 days)

Hairworms are small, thread-like and barely visible to the naked eye. Even small burdens can be pathogenic and can be fatal quite quickly. Clinical signs are diarrhoea, depression and wasting.

  • Heterakis gallinarum (caecal worm, prepatent period 24-30 days)

Heterakis worms are white, 1.5cm long with a pointed tail. Worm eggs may be ingested directly, or infected earthworms may transport eggs or host partially developed larvae. Heterakis worm eggs may remain viable for months in the environment.

There are few pathogenic lesions as a result of Heterakis infection, other than caecal thickening and petechiae, and infection is generally asymptomatic, although large numbers of birds can be affected.

The caecal worm can carry a protozoan organism, Histomonas meleagridis, also known as blackhead, which can cause turkey flocks to experience mortality rates of up to 90%.

Although all poultry can be affected by blackhead, turkeys, pheasants, partridges and peacocks are particularly susceptible and regular worming becomes much more important when the species are kept in close vicinity with chickens.

  • Trichostrongylus tenuris

These worms live in the gut and can cause severe enteritis and weight loss, particularly in game birds.

  • Amidostomum anseris (gizzard worm, pre-patent period 14-22 days)

The gizzard worm is slim and reddish in colour. The parasite mainly affects ducks and geese and infection results in depression, anaemia, weight loss and stunted growth.

  • Syngamus trachea (gapeworm, pre-patent period 18-20 days)

Gapeworm is a particular problem in pheasant and turkey poults, but other birds can be affected, especially when young. Larvae are ingested, and travel via the liver and lungs to the windpipe.

The bright red y-shaped adult worms (the male and female adults are almost always found attached) are found here, and are between 1-2cm long. Worm eggs are coughed up, swallowed and passed out in the faeces. Migration through the lungs and attachment to the tracheal mucosa cause most of the clinical signs.

Signs of infection include dyspnoea, head shaking, extension of the neck, coughing and “snicking”. Anaemia, weakness and emaciation may be noticed and some birds die of asphyxiation.

Infective larvae can live for months or years in intermediate hosts such as slugs, snails or earthworms. Passage through an earthworm may increase infectivity to the end host as large numbers of larvae can be found in one earthworm. Wild birds, especially rooks and blackbirds, are a common source of infection.

Tapeworm species

There are a number of tapeworm species that can affect poultry. Tapeworm do not generally present a hazard to health, unless there are significant numbers present. Young birds may show slower growth.

The various species include Davainea proglottina (microscopic adults) and Raillietina cesticullus (adults 4-15cm long). Beetles and snails can act as intermediate hosts. Tapeworms are difficult to treat and control may be more easily achieved in intensive systems by controlling the intermediate hosts.

Strategic worming

The presence of worm eggs in the environment on an ongoing basis can mean that irregular treatment for worms can be ineffective in reducing the infection pressure, and strategic approaches are likely to be much more useful for long-term control.

As with many parasitic diseases, increasing infection pressure can increase the number of birds affected and also the severity of clinical signs, due to the higher worm burdens being carried.

In situations with high infection pressure, due to greater stocking density and higher levels of environmental contamination, treatment intervals should be reduced to within the prepatent period for the worm in question – at around 3-4 week intervals. This prevents eggs from being shed and recontaminating the environment, gradually reducing the infection pressure.

Once the infection pressure is reduced, as measured by a reduction in faecal egg counts, treatment intervals can be extended. In medium pressure situations, treatment every 6-8 weeks is advocated, and in low infection pressures, every 8-10 weeks. Control can generally be achieved by treating every 10-12 weeks, or quarterly.

When taking a history from backyard poultry keepers, it is worth asking what preparation has been used for routine worming. A recent study found that a leading natural “wormer” had no demonstrable effect on worm burdens.

Advantages of worming

There are obvious health benefits to regular worming but worming may also improve productivity too. A commercial free-range facility with 32,000 hens looked at two different dosing regimes, worming every 10 weeks or every five weeks. The trial ran for six months and resulted in an impressive improvement with an increase of approximately 10 additional eggs per hen over the standard production levels in this unit in the more frequently wormed group.

These observations highlight the need to be aware of faecal worm egg counts within flocks and suggest that a 4-5 week worming regime can significantly improve egg production where there is a history of parasitic worms and high infection pressure.


  • Flubendazole (Flubenvet) is the only licensed treatment for worms in poultry and game birds – available as a Flubenvet 1% Medicated Premixture in a 60g pack to treat 20 chickens for backyard users, or Flubenvet 2.5% Medicated Premixture (as a 2.4kg bag or 240g tub) for larger flocks, or the 5% Premix can be incorporated in foodstuff by a registered feed manufacturer.

The wormer is supplied in feed for seven days; larger birds consume more feed so ingest a higher dose. Clients should be advised to use the correct dosage in feed and to ensure adequate mixing.

When used at the recommended dose rate in chickens, flubendazole has a zero day egg withdrawal period. A water soluble oral emulsion, Solubenol, is available for commercial use. Flubenvet is not licensed for the treatment of tapeworms.

Preventive action

Although it is not possible to completely eradicate worms under normal husbandry systems, there are steps that can be taken to help reduce worm burdens:

  • Keep muddy areas dry (use gravel round pop holes) to expose worm eggs to dessication.
  • Always use feeders, don’t feed from the ground.
  • Follow good hygiene practices.
  • Rotate pastures.
  • Keep grass short to expose worm eggs to sunlight.
  • Worm new birds and keep in isolation for 24-48 hours before providing access to pasture and the rest of the flock.
  1. Squires, S. et al (2010) Comparative efficacy of flubendazole and a commercially available herbal wormer against natural infection of Ascaridia galli, Heterakis gallinarum and intestinal Capillaria spp in chickens. Janssen Animal Health: awaiting publication.

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