Assessing cercarial transmission of Cyathocotyle bushiensis and Sphaeridiotrema pseudoglobulus by use of sentinel snails

Sentinel snails (Bithynia tentaculata) were used to assess spatial and temporal variation in cercarial transmission of Cyathocotyle bushiensis and Sphaeridiotrema pseudoglobulus at two field locations in southern Quebec and southeastern Ontario from mid-August to the end of October, 1989. Sentinels acquired infections with both digeneans; however, low levels of metacercariae of C. bushiensis precluded any conclusions regarding transmission of this parasite from being reached. In contrast, extensive spatial heterogeneity existed in the S. pseudoglobulus – snail system. Sentinel snails within 10 m of each other were apparently exposed to vastly different levels of naturally occurring cercariae. All size classes of sentinels were apparently equally susceptible to cercarial infections but no consistent temporal differences in infection levels were found.

Seasonal occurrence of Cyathocotyle bushiensis Khan, 1962 (Digenea: Cyathocotylidae) metacercariae in the intermediate host Bithynia tentaculata L. (Gastropoda: Prosobranchia)

Cyathocotyle bushiensis Khan, 1962 (Digenea) has been associated with late-summer duck mortality in southern Quebec. In an attempt to relate these die-offs with seasonal availability of the infective metacercariae to the ducks, two intermediate host (Bithynia tentaculata L.) populations were regularly sampled in 1984 and 1985. Prevalence varied between 5.3 and 57.3% at the South River, and between 9.1 and 49.7% at Lake St. Francis over the period of the study. Maximum abundances at the two localities were 1.38 and 1.66 metacercariae per snail, respectively. No close link between availability of metacercariae and periods of duck mortality was found, as the total prevalence and abundance of the cysts decreased through the summer, probably as a consequence of snail recruitment and low cercarial transmission rates, and increased in the autumn. Prevalence and abundance of metacercariae increased with snail age, estimated by both size and annual growth lines, and the metacercariae were found to be aggregated in the snail population. Comparison of infection levels reached at the end of the two sampling seasons by two year classes of B. tentaculata suggested that transmission of cercariae was higher in 1984 than in 1985. This was supported by the results of exposure of sentinel snails in an infected area during the 2 years of the study: transmission was detected in 1984 but not in 1985. In addition to C. bushiensis metacercariae, the sentinel snails acquired Sphaeridiotrema globulus (Rudolphi, 1814), another potential duck pathogen, in both years. The peak rate of transmission of S. globulus metacercariae occurred in August.

Hatching and survival characteristics of Cyathocotyle bushiensis Khan 1962 (Digenea) eggs and miracidia

SUMMARYCyathocotyle bushiensis Khan 1962 is a digenean intestinal parasite of ducks that appears to be involved in seasonal mortality of the definitive host. Temperature dependence of egg hatching and miracidial survival at 25%C were experimentally investigated as part of a study on transmission of the larval stages. Maximum percentage of hatching was obtained at a temperature of 25%C, at which the average hatching time was 21·7 days. The average hatching time decreased linearly from 38·9 days to 9·8 days between 18 and 28%C. Eggs exposed to cold (4%C) prior to incubation at 25%C were significantly less successful in hatching than fresh eggs incubated at the same temperature. Their hatching percentage was much reduced and their average hatching time was increased. Similarly, eggs collected in late autumn (as opposed to summer) and incubated at 23%C had significantly lower hatching success and significantly increased average hatching time. At 25%C, the average life-span of the miracidia was 8·8 h. These results are compared with similar data from other digenean species and their significance is discussed in relation to transmission to the first intermediate host in climatic conditions prevalent in endemic areas.

Waterfowl mortality caused by Cyathocotyle bushiensis Khan, 1962 (Trematoda: Cyathocotylidae), St. Lawrence River, Quebec

In St. Lawrence River marshes, fatal sporadic and epizootic typhlitis in breeding populations of black ducks, Anas rubripes; blue-winged teal, A. discors; and migrant green-winged teal, A. carolinensis, is attributed to Cyathocotyle bushiensis Khan, 1962. This is the first report of C. bushiensis in natural definitive hosts, and the first record of the genus Cyathocotyle in North America. Pathogenicity of C. bushiensis was confirmed experimentally by using metacercariae from the most abundant local gastropod, Bythinia tentaculata, to produce cyathocotyliasis in Pekin ducklings.

The host-parasite interface of Cyathocotyle bushiensis Khan, 1962 (Trematoda: Strigeoidea)

A combination of histochemical and electron microscope techniques have demonstrated, in Cyathocotyle bushiensis, alkaline phosphatase activity in the matrix of the tegument, in the distal and basal plasma membranes of the tegument, in the wall of the ducts extending from the adhesive organ gland cells and in the wall of the adhesive organ microvilli. Acid phosphatase activity was much stronger and was present in the tegument matrix and in the granular component of the secretion from the adhesive organ gland cells. Strong acid phosphatase activity was also present in the cisternae of the endoplasmic reticulum of the adhesive organ gland cells.I am greatly indebted to Professor Brough for the excellent facilities available within this department. I also wish to thank Professor J. Sinclair (Department of Mining) for electron microscope facilities extended to me in the early stages of this investigation, and to Mr W. Henderson, Mr T. Davies and Miss M. Williams for their invaluable assistance. The purchase of the Huxley ultramicrotome, coating unit and an AEI EM 6 electron microscope was made possible by a grant from the Science Research Council.