Objective: To analyze the changing rules of schistosomiasis endemic situation in the area of transmission that has been interrupted before and after they reach the criteria of transmission interruption, so as to offer the basis of amending to the criteria of schistosomiasis transmission interruption and a more scientific, standardized assessment and evaluation of the effects of schistosomiasis control in the future.
Methods: Nineteen counties of transmission that has been interrupted in 9 provinces nationwide were selected and investigated with the retrospective research method to collect and record the endemic detailed data 10 years before they reach the criteria of transmission interruption and several years later (ended in 2008 or 2009) and then a database was established. The changing rules of various disease indices in different endemic areas before and after reaching the criteria of transmission interruption were analyzed and compared.
Results: The average time from the transmission control to the transmission interruption was 17 years in the 17 counties. After reaching the criteria of transmission interruption, the infection rates of people turned down to a minimum level in various endemic areas, the infection rates in a few numbers of lake endemic areas and hilly endemic areas increased slightly after the transmission interruption 4-9 years later, but all of them were below 1%. The densities of living Oncomelania snails in lake endemic areas and water-network endemic areas were high and the changes were great each year, and the densities of living snails were much lower in hilly endemic areas than in the above two types of areas and they came to the lowest 4 years before and after the transmission interruption. The infected snails appeared occasionally in lake endemic areas, and they recurred 6 years and 10 years after the transmission interruption in water-network endemic areas and hilly endemic areas, respectively. The continued time without infected snails found before reaching transmission interruption was 2.71 +/- 1.10 years averagely in transmission-interrupted counties with endemic stable, and was 3. 80 +/- 1.43 years in lake endemic areas.
Conclusions: It is possible to maintain a low level of population schistosome infection, and the endemic rebound is shown as snail rebound after the endemic areas reach the criteria of transmission interruption, The infected snails could be the comprehensive index reflecting the control achievement and the risk of schistosomiasis transmission. So the persistent control of infected snails is the fundament of schistosomiasis transmission interruption. It is suggested that in our current social and economic development and science and technology capacity conditions, the status of no infected snails found continuously for 5 years would be one of the criteria of schistosomiasis transmission interruption.