four villages and two villages respectively in counties with a population of more than 100 000 50 000--100 000 10 000--50 000, and below 10 000. In a county, the villages were randomly selected, and the number of different modes villages (or sub districts) were determined based on the proportion of the four types of village modes. At least 200 people in the selected village were examined randomly, with the total participants in the survey accounting for 2.5% of the total population of Tibet.

### Population screening and case diagnosis {#Sec6}

The survey team, with help from the local government, set up diagnostic ultrasound sites in the clinics of the local villages to organize the process of surveying the residents. For residents living in more rural areas, surveys were conducted at their homes. As much asthe performing diagnostic methods to recognize livestock diseases of echinococcosis.

### Determining the surveyed subjects {#Sec12}

For the surveyed villages, if the population of the administrative village was large, a smaller village was selected as the surveyed area. If the population of the administrative village was too small and could not meet the requirement of 200 people in the survey, the people from the adjacent village were added to the survey subjects.

### Case review {#Sec13}

It is determined the diagnosis based on the imaging and result of serological test to confirm a case of echinococcosis by the expert team that is formed by the clinical and imaging experts of echinococcosis in China. A confirmed case was a person who had a typical image of echinococcosis or who had an atypical image