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Cyathocotyle bushiensis and Sphaeridiotrema globulus were previously implicated in the annual mortality of wild ducks in southern Quebec. Of 21 snail species collected from nine aquatic communities in southern Quebec and southeastern Ontario, May to October 1989 and 1990, only Bithynia tentaculata was heavily and consistently infected with C. bushiensis metacercariae. Although infection levels varied spatially, a consistent concave seasonal pattern of prevalence and abundance was found which may be due to overwintering metacercariae and the almost simultaneous onset of cercarial transmission and recruitment of new snails in mid-summer. Even though S. globulus metacercariae were found in 18 of 21 snail species, B. tentaculata is believed to contribute most to transmission to ducks. The variety of seasonal patterns and large scale spatial heterogeneity in the prevalence and abundance of S. globulus suggested that cercariae may be from more than one source. Some of the spatial variation in metacercarial levels may be due to small scale processes; extensive spatial heterogeneity at a scale of 10 m was detected in S. globulus cercarial transmission to sentinel snails. This small scale heterogeneity may be due to B. tentaculata having small home ranges as suggested by mark-recapture studies on movement. In aquaria, even though smaller B. tentaculata were more active than larger ones and intraspecific microhabitat preferences were found, preliminary results from ducks (Anas discors) feeding on snail communities in pools suggested that snails are ingested in proportion to their presence. Therefore, the importance of a snail species or size class in the transmission of the two parasites to ducks may depend only on its density and metacercarial abundance. Finally, another mode of transmission is proposed for S. globulus: ducks may become infected by consuming empty snail shells containing viable cysts.

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Cyathocotyle bushiensis (Digenea) and Sphaeridiotrema globulus (Digenea) are gastrointestinal pathogens of waterfowl, and are known to co-occur in salvaged ducks. The intensity and time-dependent pathogenesis induced by single infections of the two digeneans, and concurrent infections were studied in two species of dabbling ducks. Gross tissue pathology by single C. bushiensis infection was found to be a function of both the intensity and the duration of infection. Infection with single species infections of C. bushiensis and S. globulus was associated with decreased weight gain, tendencies for increased body temperatures and increased hematological parameters in Pekin ducklings. The hematological parameters in blue winged teal infected with C. bushiensis were found to decrease. Infection with S. globulus did not induce any significant systemic changes in the blue winged teal. A preliminary study of the effects of concurrent infection on the duck hosts suggests that in general, concurrent infection enhances the detrimental aspects of single infection, decreasing weight gain, increasing body temperatures, and decreasing hematological parameters in both species.

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No description available.

No description available.