The Classification Of Endemic Areas Of Cystic Echinococcosis In Rangtang County, Sichuan Province

Cystic echinococcosis is a severe zoonitic disease caused by the metacestode Echinococcus granulosus.The parasite has a world-wide geographic distribution and occurs in all continents including circumpolar, temperate, subtropical and tropical zones. Within the endemic zones, the prevalence of the parasite varies from sporadic to high whereas. The endemicity degree of echinococcosis is influenced by various factors including biological, environmental and social factors. If we could know how these factors influence the levels of it endemicity, it may help a better understanding of the transmission and support the echinococcosis control work.The study was conducted in Rangtang County, Sichuan Province. Data related to cystic echinococcosis were collected, including the prevalence of Echinococcus granulosus in yaks died during the spring, livestock production, dog number and other related material. Administrative villages were divided into different classes according to the prevalence of cystic echinococcosis infected yaks died during the spring. Altitude and mean land surface temperature of the study sites were extracted from remote sensing images. The relation between the prevalence of cystic echinococcosis and potential influencing factors including environment and livestock was analyzed with cumulative logistic regression analysis. A prediction model was developed.The highest prevalence in yaks died during the spring was 71% among the 35 administrative villages surveyed. The mean prevalence in the 15 villages with highest prevalences was (32.49±23.24)%. The 35 administrative villages were classfied into the following 4 categories according to the prevalence in yaks died during the spring and information from local people:Class 1, highly endemic; Class 2, moderately endemic; Class 3, endemic; Class 4, sporadic or suspected.Statistical analysis of the survey data by the univariate analysis demonstrated that mean livestock number per family was significantly different in statistics between the 4 classes(F=5.834, P=0.003).There was no significant difference in mean dog number per family, altitude and mean land surface temperature, however there was a downtrend following the descent of endemic intensity.Cumulative logistic regression was used to determine factors that combine best to provide favorable conditions for the endemicity degree of echinococcosis. The mean livestock number per family, mean dog number per family and altitude were found to be positively correlated with endemic intensity. Mean land surface temperature was negatively correlated with endemic intensity. The interaction between mean land surface temperature and altitude was also found to be related to endemic intensity. Max-rescaled R-square and rank correlation index of the prediction model was 59% and 82%, respectively.This study showed that the transmission of Echinococcus granulosus was a complicated process, influenced by the biological, environmental and social factors. The prediction model in ever study suggested that the pattern how these factors influence the transmission of Echinococcus granulosus could be demonstrated by using an appropriate interdisciplinary approach, and may proved a new clue and scientific basis for selecting a suitable strategy for echinococcosis control.