1. As an intermediate host of the hydatid tapeworm in boreal North America, the moose is of relatively greater importance than other indigenous cervids (white-tailed deer, wapiti, barren-ground caribou) primarily because of a higher rate of infection in different individuals and the fertility of the hydatid cysts.2. The European reindeer introduced into north-western Canada is of considerable importance as an intermediate host where it occurs locally.3. Timber wolves are the important definitive hosts; no infections occurred naturally or were produced experimentally in the bobcat, Canada lynx, raccoon, fisher, marten, striped skunk or European ferret.4. A description using biological and morphological criteria is presented forEchinococcus granulosus granulosusin dogs, sheep and other domestic animals,E. g. borealissubsp.nov. in timber wolves, moose and other cervids indigenous to North America, andE. g. canadensisWebster and Cameron, 1961, in dogs and reindeer introduced into north-western Canada from Laplandic Norway.5. The rate of cystic growth, scolex production, infectability of timber wolves and dogs and prepatent period are similar for all three subspecies.6.E. g. borealisreached a gravid state in experimental red foxes (Vulpes fulva).7. Hydatid cysts developed only rarely in sheep fed eggs ofE. g. borealisorE. g. canadensis.8. Eggs ofE. g. granulosusproduced only one viable hydatid cyst in a series of experimental red deer (Cervus elaphus) and fallow deer (Dama dama).9.E. g. granulosus, E. g. borealisandE. g. canadensisare morphologically distinct, the most distinctive characters occur inE. g. canadensis.10. Besides the above andE. multilocularis, other species inEchinococcusare little known. Those recognized as being currently valid areE. lycaontis, E. ortleppi, E. felidis, E. cameroni, E. oligarthrus, E. cruziand possiblyE. patagonicus.The writers wish to thank Sir Charles Hercus and the other members of the Hydatid Research Committee for their interest and encouragement in the present study. Valuable discussion in the early stages of this work was had with Prof. A. M. Fallis, Director, Department of Parasitology, Ontario Research Foundation. Much of the field work was done with various members of the Ontario Research Foundation; Institute of Parasitology, McGill University; Canada Department of Agriculture; and Canada Department of Northern Affairs and Natural Resources, to whom we extend our thanks. Norwegian material was kindly provided by Dr Sven Skjenneberg, Statens Veterinaera Laboratorium for Nord-Norge. Technical assistance was provided by Messrs G. D. Page, D. V. Weston, Miss L. A. Duncan and Mrs B. R. Clarke.
The stages in the life cycle of P. cuniculi and other species or varieties in the genus are described. Host specificity currently attributed to the different types in Psoroptes is disproved, but differences exist in individual susceptibility. The six auricular types of psoroptic mites are reduced to two, and the five kinds of body mites to four. A dendrogram is included which shows the relations between the genera and species in Psoroptidae.
1. A 12·8% incidence of hydatid infections occurred in 709 horses examined in England. By contrast, hydatid cysts do not occur in horses in New Zealand where Echinococcus granulosus granulosus is common in sheep, cattle and swine.2. Experimentally, scolices from hydatid cysts from English horses reached a gravid state in laboratory dogs. It was not possible to infect horses with E. g. granulosus of sheep-dog origin, and only one of two sheep became infected with two cysts following the ingestion of eggs of English horse-dog origin.3. Our observations, together with those of others on secondary hydatid cyst formation, indicate that the two types are not only biologically but morphologically distinct.4. In the horse-dog worms, the cirrus sac tilts anteriorly at an acute angle; the testes (about 35) are distributed throughout the proglottid with two or three rows posterior to the vitelline gland, and persist in proglottids when some mature eggs are present; the average length of the rostellar hooks is greater than in E. g. granulosus.5. It is proposed that the horse-dog material be named E. g. equinus subsp. nov.6. Rostellar hooks from cysts in British cattle resembled morphologically those from horses, while those from a British sheep and from man were like the hooks from hydatid cysts in man and livestock in New Zealand.7. A red deer, hedgehog and European rabbit were not infected artificially following the ingestion of eggs of E. g. equinus.Mr J. T. Briggs, Chief Public Health Inspector, Public Health Department, Bently, Doncaster, England, was responsible for the inspection of the British horses reported in this paper. We are indebted to Mr Briggs for this courtesy and for sending us fresh hydatid cysts from horses for experimental purposes. Mr N. Aitken was responsible for maintaining the experimental horses in an area of New Zealand known to be free of E. granulosus. Our thanks are also due to Messrs G. D. Page, D. V. Weston, Miss L. A. Duncan and Mrs B. R. Clarke for their able technical assistance.
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