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 persist in backyard poultry, which allows contact with snails or other hosts and wild birds. The trend toward free-range rearing of poultry may increase the exposure of poultry to this type of parasite, but flukes are mainly reported 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. The fluke matures in ~2 wk in the bursa of Fabricius or, in gallinaceous birds without a functional bursa (eg, chickens, turkeys, pheasants), in the oviduct.
Light infections without signs appear in ducks and other birds with a functional bursa. In gallinaceous birds, heavy infections 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. Diagnosis by fecal examination is unreliable, because fluke eggs are not consistently present. Adult flukes may appear in the bird's eggs or be found in the oviduct on necropsy.
To prevent fluke transmission, birds must be kept from feeding on dragonflies. There is no effective treatment approved for use in poultry. 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.
Last full review/revision March 2014 by Michael Hess, DMV