Retrospective investigation and analysis of endemic situation of schistosomiasis in hilly regions of Sichuan Province

Objective: To explore the rules of the changes of schistosomiasis infection and Oncomelania snails in areas where schistosomiasis transmission was controlled or interrupted or rebounded after interruption.

Methods: Qingbaijiang District, Longquanyi District and Xide County were selected and investigated retrospectively to collect schistosomiasis epidemiological information 10 years before they reached the criterion of transmission control and the subsequent years until 2008. The database of retrospective investigation was established for analyzing the trends and rules of changes of snail status and human infection status.

Results: In Qingbaijiang District, there was a positive correlation between density of living snails and snail area (r = 0.74, P < 0.01), and the infection rate of population was declining. In Longquanyi District, the snail area presented a declining trend. In Xide County, the human infection rate was positively correlated with snail area (R = 0.53, P < 0.01) and the density of living snails (r = 0.42, P < 0.05) respectively.

Conclusions: The rebound of snail situation is always prior to the emerging of human infection, and it prompts that the rebound of snail situation can be considered one of the important indicators of early warning of the rebound of human infection situation in those places where schistosomiasis transmission was controlled or interrupted. Implementing comprehensive control of the snail habitat, as well as eliminating the potential infectious source is an important measure to consolidate the achievement of schistosomiasis control.