Commonly called the giant kidney worm, Dioctophyma renale has been found most frequently in mustelids and in wild and domestic carnivores in practically all parts of the world. Infrequent occurrences of the parasite have been recorded in pigs, horses, cattle and man.
In a survey carried out in Ontario, the parasite was recovered in two (1.5%) of 126 weasels, two (2.2%) of 90 otters, 11 (1%) of 1,102 timber wolves, nine (0.9%) of 854 coyotes, and 700 (18%) of 3,741 mink. From the Parry Sound area 37% of 1,431 mink collected during 1960-69 were infected with D. renale. The parasite is also common in the Sudbury area having been found in 44% of 261 mink examined from 1960-64. These data and other available information strongly suggest that the mink is the main definitive host of D. renale in North America.
The kidney worm is blood-red in colour and is one of the largest of the parasitic roundworms. In mink, the adult female worm may measure up to 60 centimetres in length and up to six or seven milhmetres in diameter. The adult male worm is considerably smaller in length and diameter, varying in lengths up to 30 centimetres. In wolves and dogs, the adult female worms are reported to reach a length of 100 centimetres and are as large around as the small finger. The adult male worms, in these species as in mink, are correspondingly smaller than female worms.
As their name implies, kidney worms usually occur in the kidneys and more frequently in the right organ than in the left. They may also on occasion be found lying free, in the abdominal cavity. In a sample of approximately 400 Ontario mink infected with D. renale, 86% had parasites in the right kidney only, 6% in the abdominal cavity only, 7% in both the right kidney and the abdominal cavity, 0.5% in both the right and left kidney, and 0.3 % in the liver. In a considerably smaller sample of 19 infected wolves and coyotes in Ontario, D. renale was present only in the abdominal cavity of 17 (89%) of the animals and in both the right kidney and the abdominal cavity of the remaining two specimens.
The presence of the worms in the kidney results in the destruction of the functional tissue of the organ, leaving only a greatly distended and thickened kidney capsule containing worms, fluid and a speculated, bony plate. The kidney becomes, in fact, a hollow sac. To compensate for the loss of one functioning kidney the other kidney enlarges to about twice its normal size. If both kidneys become parasitized the animal dies.
There has been some confusion about the life history of D. renale but research by Karmanova (1959, 1960) and Mace (1974) indicates that only one intermediate host-an oligochaete (earthworms and related aquatic forms) -- is required to complete the life cycle of the worm. Briefly, in the life history of D. renale, eggs from the adult worms situated within the kidney of the final host are passed to the outside in the urine. The eggs are ingested by the oligochaete where development into larvae, infective to the final host, takes place. If these infective larvae are eaten by some species of fish or frogs, the latter serve only as reservoir or transport hosts (Mace, 1974). Mink, wolves and other species become parasitized by eating oligochaetes, fish or frogs containing the infective larvae. When the parasite develops in the abdominal cavity or when only one sex of worm is present in the kidney the life cycle is interrupted.
Currently, studies are being completed at the Maple laboratory to determine if the presence of D. renale in mink influences the quality of the animal's pelt.
Selected References:
Karmanova, E.M. 1959. The life-cycle of the nematode. Dioctophyme renale. Dokl. Akad. Nauk. SSSR 127:1317-1319.
Karmanova, E.M. 1960. The life-cycle of the nematode Dioctophyme renale (Goeze, 1782), parasitic in the kidneys of carnivorous animals and man. Dokl. Akad. Nauk. SSSR 132:1219-1221.
Mace, T.F.A. 1974. Studies on the biology of the giant kidney worm, Dioctophyma renale (Goeze, 1782) (Nematoda:Dioctophymoidea). Ph.D. Thesis, University of Guelph, Guelph.
