Study On The Relation Of Distribution Of Intermediate Host Of Echinococcus Multilocularis To The Environmental Factors In Southern Qinghai Plateau

Alveolar echinococcosis(AE) is a severe parasitic zoonosis caused by the metacestode Echinococcus multilocularis with a high mortality,which is distributed in different geographic regions in western China,and has a great impact on the public health and social economy.The geographic distribution of Echinococcus multilocularis is determined by the existence of its natural definitive host and intermediate host. Rodential and lagomorpha animals are the main intermediate hosts.The study conducted in the southern Qinghai Plateau proved that the two species of small mammals-Ochotona curzoniae and Microtus fuscus are the main rodential and Lagomorpha animals and are abundant in this area.The burrow density of both Ochotona curzoniae(40.4/100 square meter) and Microtus fuscus(47.8/100 square meter) is 88.2/100 square meter.Ochotona curzoniae and Microtus fuscus are proved to be the main intermediate hosts through field mousing and parasitological investigation. The total infection rate was 2.46%,while the infection rate of Ochotona curzoniae (4.36%) was higher than that of Microtus fuscus(1%)(X~2=9.41,P＜0.05).The research results showed that Echinococcus multilocularis was prevalent in the Southern Qinghai Plateau,the abundance of Ochotona curzoniae and Microtus fuscus may increase the spread pressure and epidemic risk.Statistic analysis of the survey data by univariate analysis demonstrated that the distribution of Ochotona curzoniae and Microtus fuscus may be related to the edaphic type and vegetation.Ochotona curzoniae was mainly distributed in the alpine meadow soil and alpine steppe soil,where the burrow density was significantly higher than that in alpine cold bush soil and meadow swamp soil(P＜0.05).However,Microtus fuscus was mainly distributed in the meadow swamp soil,the burrow density was significantly higher than that in other soil types.As to the distribution in different vegetation types,Ochotona curzoniae was mainly found in the alpine meadow,where the burrow density was significantly higher than that in alpine cold bush(P＜0.05);the burrow density in the swamp meadow land was mediate while the burrow density in the alpine cold bush was at the lowest.In the case of Microtus fuscus,which was mainly distributed in swamp meadow vegetation,the burrow density was significantly higher than that in alpine meadow and alpine cold bush(P＜0.05).Furthermore,the result revealed that the aggregation and spatial autocorrelation in the distribution of Ochotona curzoniae and Microtus fuscus,and verified that their distribution conformed to the negative binomial distribution.We investigated the environmental factors influencing the distribution of Ochotona curzoniae and Microtus fuscus by field survey and collection of RS/GIS information,and established a regression model of negative binomial distribution. Multivariate analysis was used to determine environmental factors that combine best to provide favorable conditions for Ochotona curzoniae and Microtus fuscus.The type of soil and the pasture(penned or open),and the height of grass were found to be related to the distribution of Ochotona curzoniae.The topographic feature,edaphic type, vegetation type,pasture type(winter pasture or summer pasture) and vegetation coverage were found to be related to Microtus fuscus distribution.The common environment factors for the two species of intermediate hosts were the topographic feature,edaphic type,vegetation type,pasture type,vegetation coverage and the time period of NDVI.We developed a discriminatory model by using stepwise discrimination method and evaluated its efficacy.The test samples were analyzed by the back substitution,and the coincidence rate of extrapolated discrimination was examined on the randomly selected samples.The evaluation test indicated that the discriminatory model we developed displayed the discrimination coincidence rate by back substitution(DCRBS) and extrapolation(DCRE) being 84.8%and 85%for Ochotona curzoniae respectively. The DCRBS and the DCRE for Microtus fuscus was 71.4%and 75%respectively.A high discriminatory coincidence rate was recorded as the overall DCRBS and DCRE for both species were 89.3%and 90%.The negative binominal regression model and the discrimination model developed through this study provided a useful tool for the estimation of distribution of the intermediate hosts for alveolar echinococcosis according to the geographic environment,and for the rodent and Lagomorpha control by the sectors involved.The result of this research may provide a new clue and scientific basis for making suitable control strategy for alveolar echinococcosis.