Understanding the transmission ecology of parasites involves the challenge of studying the complexity of life-cycles at multiple levels of biological organisation and at various space-time scales. We think that a single field of science alone cannot fully address this issue and that a way to understand such complexity is to connect various fields of science, to consider the whole transmission system, and to identify which are the variables reasonably accessible to measurement and the relevant scales at which they may provide information about transmission processes and indicate a higher risk of transmission⁄emergence. Based on ongoing studies carried out in Europe and in China, the aim of the present paper is to discuss this approach and to show how results obtained from mass-screening of human populations may be combined to those obtained from small mammal and landscape ecology studies and modelling to promote an understanding of Echinococcus multilocularis transmission and to determine how differences in the time-space scales at which human infection and small mammal population dynamic processes occur may complicate the analysis.

BACKGROUNDOvergrazing was assumed to increase the population density of small mammals that are the intermediate hosts of Echinococcus multilocularis, the pathogen of alveolar echinococcosis in the Qinghai Tibet Plateau. This research tested the hypothesis that overgrazing might promote Echinococcus multilocularis transmission through increasing populations of small mammal, intermediate hosts in Tibetan pastoral communities.

METHODSGrazing practices, small mammal indices and dog Echinococcus multilocularis infection data were collected to analyze the relation between overgrazing and Echinococcus multilocularis transmission using nonparametric tests and multiple stepwise logistic regression.

RESULTSIn the investigated area, raising livestock was a key industry. The communal pastures existed and the available forage was deficient for grazing. Open (common) pastures were overgrazed and had higher burrow density of small mammals compared with neighboring fenced (private) pastures; this high overgrazing pressure on the open pastures measured by neighboring fenced area led to higher burrow density of small mammals in open pastures. The median burrow density of small mammals in open pastures was independently associated with nearby canine Echinococcus multilocularis infection (P = 0.003, OR = 1.048).

CONCLUSIONOvergrazing may promote the transmission of Echinococcus multilocularis through increasing the population density of small mammals.

Animals ; Dog Diseases ; transmission ; Dogs ; Echinococcosis ; transmission ; veterinary ; Echinococcus multilocularis ; Humans ; Population Density ; Tibet

Since the first 2 cases observed in southern Germany and the correct identification of a parasite at the origin of the disease by the famous scientist Rudolf Virchow in 1855, the borders of the endemic area of alveolar echinococcosis (AE) have never stopped to expand. The parasite was successively recognized in Switzerland, then in Russia, Austria and France which were long considered as the only endemic areas for the disease. Cases were disclosed in Turkey in 1939; then much attention was paid to Alaska and to Hokkaido, in Japan. The situation totally changed in 1991 after the recognition of the Chinese endemic areas by the international community of scientists. The world map was completed in the beginning of the 21st century by the identification of AE in most of the countries of central/eastern Europe and Baltic States, and by the recognition of cases in central Asia. Up to now, the disease has however never been reported in the South hemisphere and in the United Kingdom. In the mid-1950s, demonstration by Rausch and Schiller in Alaska, and by Vogel in Germany, of the distinction between 2 parasite species responsible respectively for cystic echinococcosis (“hydatid disease”) and AE put an end to the long-lasting debate between the "dualists", who believed in that theory which eventually proved to be true, and the "unicists", who believed in a single species responsible for both diseases. At the end of the 20th century, molecular biology fully confirmed the "dualist" theory while adding several new species to the initially described E. granulosus; within the past decade, it also confirmed that little variation existed within Echinococcus (E.) multilocularis species, and that AE-looking infection in some intermediate animal hosts on the Tibetan plateau was indeed due to a new species, distinct from E. multilocularis, named E. shiquicus. Since the 1970s, the unique ecological interactions between the landscape, the hosts, and E. multilocularis have progressively been delineated. The important role of the rodent/lagomorph reservoir size for the maintenance of the parasite cycle has been recognized within the last 2 decades of the 20th century. And the discovery of a close relationship between high densities of small mammals and particularities in land use by agriculture/forestry has stressed the responsibility of political/economic decisions on the contamination pressure. Urbanization of foxes in Europe and Japan and the major role of dogs in China represent the new deals at the beginning of the 21st century regarding definitive hosts and prevention measures.
Animals ; China ; epidemiology ; Echinococcosis, Hepatic ; epidemiology ; parasitology ; Echinococcus ; pathogenicity ; Humans

BACKGROUNDAlveolar echinococcosis is a major zoonosis of public health significance in western China. Overgrazing was recently assumed as a potential risk factor for transmission of alveolar echinococcosis. The research was designed to further test the overgrazing hypothesis by investigating how overgrazing influenced the burrow density of intermediate host small mammals and how the burrow density of small mammals was associated with dog Echinococcus multilocularis infection.

METHODSThe study sites were chosen by previous studies which found areas where the alveolar echinococcosis was prevalent. The data, including grass height, burrow density of intermediate host small mammals, dog and fox fecal samples as well as Global Positioning System (GPS) position, were collected from field investigations in Shiqu County, Sichuan Province, China. The fecal samples were analyzed using copro-PCR. The worms, teeth, bones and hairs in the fecal samples were visually examined. Single factor and multifactor analyses tools including chi square and generalized linear models were applied to these data.

RESULTSBy using grass height as a proxy of grazing pressure in the homogenous pasture, this study found that taller grass in the pasture led to lower small mammals' burrow density (chi(2) = 4.670, P = 0.031, coefficient = -1.570). The Echinococcus multilocularis worm burden in dogs was statistically significantly related to the maximum density of the intermediate host Ochotona spp. (chi(2) = 5.250, P = 0.022, coefficient = 0.028). The prevalence in owned dogs was positively correlated to the number of stray dogs seen within a 200 meter radius (Wald chi(2) = 8.375, P = 0.004, odds ratio = 1.198).

CONCLUSIONSOur findings support the hypothesis that overgrazing promotes transmission of alveolar echinococcosis and confirm the role of stray dogs in the transmission of alveolar echinococcosis.

Animals ; China ; Dog Diseases ; parasitology ; transmission ; Dogs ; Echinococcosis ; parasitology ; transmission ; Echinococcus multilocularis ; physiology ; Ecology ; Poaceae ; growth & development ; parasitology ; Tibet