Western
Meeting of Poultry
Clinicians and Pathologists
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Clinicians and Pathologists
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Parasitic Enteritis in a Muscovy Duck Caused by Polymorphus minutus Choon Yong Provincial Veterinary & Diary Diagnostic Laboratory
History and Clinical Signs A farmer in the Regina area had hatched and raised Muscovy ducklings on a farm. For a while, one to two ducklings were dying per week. Initially they showed signs of losing body control, flipping over on their backs and dying within 12 to 24 hours. At the time of submission, the farmer had lost 15 out of 18 in the flock. The ducks had access to the farm dugout, which was inhabited with abundant fresh water shrimp. Necropsy Examination The duck submitted for necropsy examination was 1.5 months old and was small in size. It was also anemic and emaciated. The tissues of the carcass were wet and pale. There was some white flaky material scattered on the peritoneum and on the serosal surface of the digestive tract. The small intestine was contracted. Inside the lumen abundant tiny light yellow to pink parasites were present. These worms were small in size and measured less than 1 cm in length. When pulled from the gut, they broke into two pieces with the anterior portion remaining embedded in the intestinal mucosa. No gross lesions were noted in any other organs. Histopathology The intestinal mucosa had severe granulomatous inflammation. All layers of the gut wall were affected. Fragments of parasites were found in the suberosal and muscular layers. Some parasites were also embedded in the mucosa.
Parasitology The Worm The enteric parasite infesting the duck was identified as Polymorphus minutus, which is also known as a thorny-headed worm. The live worms are very small. The male is 3 mm long while the female can be up to 1 cm in length. Characteristically, their proboscis has 16 longitudinal rows of hooks and each row has about 7 to 10 hooks. The identifying features of Polymorphus minutus are:
The life cycle of Polymorphus minutus is shown in the diagram. Basically, feces containing the worm eggs are shed into the water. The eggs are taken up by the shrimp, and develop into infective larvae. When the waterfowl eat the shrimp, the infective larvae are released, infest the intestine and become mature. The cycle repeats itself as more eggs are passed in the feces. The Intermediate Hosts In order for the worms to survive, they require an intermediate host such as crayfish and freshwater shrimp. Many types of freshwater shrimp, the Amphipods, are capable of transmitting the infestation. In the Prairie Provinces, many lakes, ponds, springs and dugouts are inhabited by freshwater shrimp and crayfish. Gammarus lacustris predominates in southern Saskatchewan while the northern Saskatchewan waters are colonized by Hyalella azteca and Pontoporeia assinis. The Final Hosts Waterfowl, including ducks, are the final hosts.
Discussion This was an unusual and rare case. It shows however, that domestic ducks and free-flying waterfowl are at risk on the prairies if exposed to fresh water containing the crayfish or shrimp intermediate hosts. Emaciation is regarded as the cause of death following infestation. It is uncertain whether an effective dewormer is available. However, it has been reported that a dose of carbon tetrachloride at 0.5 mL/kg body weight was 98% effective. Ivermectin could also be tried. |
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Absence of digestive tract