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Fauna Series No. 7







Study Area

Isle Royale Mammal History

Methods and Extent of Present Research


Wolf-Moose Coaction




Fauna of the National Parks — No. 7
The Wolves of Isle Royale
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Parasites and Diseases

Wolves are susceptible to several diseases and physical disorders, and are hosts to many helminth parasites; mange also infests them. Stenlund (1955) has reviewed the literature on the subject. Since his work, Rausch (1958) reported on 43 rabid canids from Alaska, including two wolves. Rausch and Williamson (1959) examined 200 wolf carcasses and listed the helminths found therein.

No wolf carcass was handled during the present study, so little information on parasites and diseases was obtained. However, intermediate stages of two species of helminths, for which the wolf is the definitive host, were found in Isle Royale moose. Taenia hydatigena occurred in two of four adults examined, and Echinococcus granulosus was found in three of them. Adults of both worms have been reported from wolves in several areas (table 12).


Species Location Number

Echinococcus granulosus: Minnesota  8   563 Riley (1939)
Minnesota 18   528 Erickson (1944)
British Columbia  5   120 Cowan (1947)
N. Ontario 58  3662 Sweatman (1952)
Minnesota 18   422 Stenlund (1955)
Alaska200  6030 Rausch & Williamson (1959)
Ontario520 10320 Freeman et al. (1961)

Taemia hydatigena: Minnesota 18  8 44 Erickson (1944)
British Columbia  5  4 80 Cowan (1947)
Minnesota 18 15 83 Stenlund (1955)
N. Ontario 10 10100 Sweatman & Plummer (1957)
Alaska 78 56 72 Rausch & Williamson (1959)
Ontario520 39  8 Freeman et al. (1961)

An adult Taenia sp. was found by D. L. Allen soon after it had been passed by an animal (presumably a wolf, from the sign). This could have been T. hydatigena, or even T. krabbei, the larvae of which encyst in the muscles of big game. Moose were not examined for this parasite, so it is not known whether the species occurs on Isle Royale. Rausch and Williamson (1959) found the adults in 48 of 78 wolves from Alaska, and Erickson (1944) and Stenlund (1955) reported Taenia sp., which may have been this species, from Minnesota wolves. Peterson (1955) reported that cysticerci occurred in muscles of an Ontario moose.

The effect of these parasites on the wolf is unknown. Erickson (1944) noted that some wolves harbored so many Taenia hydatigena that their intestines appeared blocked. Adults of Echinococcus granulosus are only 2 to 8 mm. long (Chandler, 1955), but according to Rausch (1952:159) heavy infections of Echinococcus granulosus in the final hosts are usual; "in some cases the cestodes cover nearly the entire mucosal surface of the host intestine." According to Monnig (1938:103), "varying degrees of enteritis may be present [in dogs and cats] from a catarrh to a croupous or haemorrhagic enteritis, especially in heavy infections. . . ."

Choquette (1956) experimentally infected dogs with Echinococcus granulosus cysts (as many as seven cysts, from 3 to 10 cm. in diameter, to an individual). He writes (p. 191) that "while it is agreed that dogs can harbor a great number of adult worms without apparent ill effects there are reports of pathogenicity." Haemorrhagic enteritis and rabiform symptoms, diarrhea, asthenia, cachexia, catarrhal inflammation, and death in heavily infected individuals, are listed as effects in dogs. Three of the eight dogs infected by Choquette showed severe diarrhea, weight loss, and asthenia. "Death occurred within a few days of the appearance of symptoms and a month after initial infection. Post-mortem examination showed a severe haemorrhagic enteritis and a very large number of immature worms" (Choquette, 1956:192).

Wolves probably have a greater resistance to these worms than do domestic animals, since the former certainly have evolved with the parasites. Although eight of Choquette's nine experimental dogs became infected, only five passed eggs and segments in their feces, so even all dogs are not equally susceptible. Apparently, the adults of Echinococcus are short-lived. One of Choquette's dogs passed eggs for 8 months and then stopped. Autopsy showed it was worm-free. A second dog, still eliminating eggs, was autopsied 6 months after infection, and senile worms were found. Thus, infections probably do not accumulate for more than 8 months, but in this period, a wolf could become reinfected several times. Wolves probably can support high cestode populations without significant effects, although young, ailing, or old individuals may be affected adversely.

moose femur
Figure 66—Author checking femur marrow of wolf-killed moose.

moose femur
Figure 67—Comparison of normal femur marrow (left) with fat-depleted marrow.

moose lung
Figure 68—Lung with hydatid cysts from wolf-killed moose. Photo by D. L. Allen.

Figure 69—Hydatid cysts from wolf-killed moose. Photo by D. L. Allen.

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