Impact of overgrazing on the transmission of Echinococcus multilocularis in Tibetan pastoral communities of Sichuan Province,China

Background Overgrazing 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. Methods Grazing 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. Results In 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）. Conclusion Overgrazing may promote the transmission of Echinococcus multilocularis through increasing the population density of small mammals.

Grass height and transmission ecology of Echinococcus multilocularis in Tibetan communities, China

Background Alveolar 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. Methods The 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. Results By using grass height as a proxy of grazing grass in the pasture led to lower small mammals＇ pressure in the homogenous pasture, this study found that taller burrow density （X2=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. （X2=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 X2=8.375, P=-0.004, odds ratio=1.198）. Conclusions Our findings support the hypothesis that overgrazing promotes transmission of alveolar echinococcosis and confirm the role of stray dogs in the transmission of alveolar echinococcosis.