Modern poultry housed indoors are essentially free of flukes, because all flukes require a snail as an intermediate host and often require a third invertebrate host. However, these parasites might persist in backyard poultry, which may have contact with snails or other hosts and wild birds. Flukes are sometimes reported in free range poultry, especially those raised in warmer and wet climates, and they are less host specific. They appear mainly in wild birds with low prevalence.
Prosthogonimus macrorchis, the oviduct fluke of poultry, infects birds after they consume infective metacercariae in larval or mature dragonflies, the secondary host. Postharmostomum commutatum (synonym P gallinum) can be found in the caeca and Philophthalmus gralli in the eye of birds.
Linking fluke infections with clinical signs is difficult, because experimental data are sparse, and diseased birds might have other diseases as well. Consequently, light infections appearing without signs are most common in birds with a functional bursa. In gallinaceous birds, heavy infections with Prosthogonimus macrorchis in the oviduct cause inappetence, droopiness, weight loss, calcareous cloacal discharge, depressed egg production, and an increase in soft-shelled eggs. Lesions range from mild inflammation to distention or rupture of the oviduct; death may result. Infection with Philophthalmus gralli might lead to blindness with consequences on feed uptake. Diagnosis of flukes by fecal examination is unreliable, because fluke eggs are not consistently present. Adult flukes can be noticed at the site of lesions.
To prevent fluke transmission, birds must be kept from feeding on dragonflies. There is no effective treatment approved for use in poultry. Elimination of P gralli from infected turkeys with praziquantel or fenbendazole was not successful. Carbon tetrachloride, a common remedy, is highly toxic to chickens and other birds.
Collyriclum faba, another common fluke in birds, appear as subcutaneous cysts 4–6 mm in diameter (usually containing two adults) anywhere on the body but more frequently near the vent in turkeys, chickens, and other birds. The cysts ooze an exudate, which attracts flies and predisposes to bacterial infection. Signs in young birds include locomotor difficulty and inappetence; heavy infections may cause death. The parasites can be removed surgically. The life cycle is unknown but probably involves snails and insects such as dragonflies or mayflies. Prevention of infection requires restricting birds from bodies of water and areas frequented by aquatic insects.
Key Points
Fluke infections are rare in commercial poultry because housing indoors limits exposure to intermediate hosts.
Lightly infected birds show no clinical signs, but heavy infections with some species lead to anorexia, weight loss, cloacal discharge, and decreased egg production.
There are no effective treatments, so control relies on limiting exposure to intermediate hosts, such as snails and dragonflies.
