Observations on Some Natural-Focal Zoonoses in Alaska

In Alaska, as in arctic and subarctic Eurasia, important natural-focal zoonoses are rabies, brucellosis, tularemia, trichinosis, alveolar hydatid disease, cystic hydatid disease, and diphyllobothriasis. Most frequently affected are aboriginal peoples in villages within biocenoses that include the natural parasite-host assemblages. Pathogens are transmitted to man from wild animals and from dogs, which are important as synanthropic hosts. The prevalence and rate of transmission of certain pathogens in natural foci are related to the numerical density of small mammals, especially rodents, which may themselves be involved as hosts, and on which the numbers of their predators ultimately depend, such as is evident in the natural cycles of Echinococcus multilocularis and of rabies virus. Some pathogens in northern regions exhibit biological Characteristics that separate them from morphologically indistinguishable strains at lower latitudes (e.g., Trichinella spiralis and E. granulosus). Host-parasite relationships may also differ, as in the Arctic where rabies virus is maintained in populations of foxes, without significant involvement of mammals of other groups. Faunal interchanges during and after the Pleistocene period have influenced the distribution of parasite-host assemblages in Alaska.

Studies on Some North American Shrew Cestodes

In spite of the importance of the various species of shrews to the biotic community, several aspects of their ecology remain very incompletely known. The helminths parasitic in the more conspicuous small mammals in North America have been studied more or less completely, but those occurring in shrews have been largely disregarded. This situation is particularly inappropriate when one considers that shrews often constitute the most abundant mammalian group in a given area. We have attempted to secure an adequate amount of shrew helminth material for study, and it is the purpose of this paper to present observations resulting from this work.

On the Ecology and Distribution of Echinococcus spp. (Cestoda: Taeniidae), and Characteristics of Their Development in the Intermediate Host. II. Comparative Studies on the Development of Larval E. multilocularis Leuckart, 1863, in the Intermediate Host

This paper reports the results of a comparative study of the development of the larval Echinococcus multilocularis Leuckart, 1863), and associated tissue reaction in naturally and experimentally infected mammals representing 31 species. The histogenesis of the larval cestode was traced in detail in arvicoline rodents of several species, and interspecific differences were defined. In arvicoline rodents, the developing larva exhibited host-specific characteristics within about a month after infection was established. The tissue reaction in Microtus oeconomus was characterized by the production of a large quantity of detritus around the larva, and by the formation of a thick epithelioid zone. In one subspecies, M. oeconomus innuitus, development of the larva was retarded, and the detrital mass was often calcified; in another, M. oeconomus operarius, the detritus rarely became calcified and the larva proliferated more rapidly. In M. pennsylvanicus, the tissue reaction was minimal, and little detritus was present. The characteristics of the tissue reaction in M. montebelli placed it in an intermediate position between the aforementioned species. In Clethrionomys rutilus, a thin epithelioid zone and an outer zone of loose collagenous fibers composed the adventitial layer; exogenous budding was retarded in this vole. A minimal tissue reaction occurred in Lagurus curtatus. In Lemmus spp., larger cysts were characteristic, but areas of small-cystic proliferation were always present. Similar differences in species or subspecies of Citellus and Dicrostonyx were described. Lesions of alveolar bydatid disease in man also were studied. The invasive growth of the larval cestode in the human liver involves a process comparable to small-cystic proliferation in the natural intermediate hosts. Although the later stages of development of the larval cestode are inhibited in man, exogenous proliferation of vesicles continues for the life of the host. The lesion in man was compared with a morphologically similar formation produced by anomalous development of the larval E. granulosus in the bovine liver. The latter is distinguished by the absence of areas of small-cystic proliferation. Non-echinococcal lesions found in the tissues studied, some of which resembled foci caused by the larval E. multilocularis, were briefly discussed.