Abstract:

Objective To analyze the changes of schistosomiasis epidemic situation before and after reaching the criteria of schistosomiasis transmission control or transmission interruption in endemic rebounded areas, so as to offer the information for modifying the criteria of schistosomiasis control and elimination, and consolidating achievements of schistosomiasis control in People’s Republic of China. Methods Twelve counties with endemic rebound were selected from seven endemic provinces and investigated with the retrospective research method. The data including the epidemic information and relative materials 10 years before the counties reached the criteria of transmission control and several years later (until 2008 or 2009) were collected. The changes of epidemic situation of these counties before and after the transmission was under control or interrupted, and the factors causing the endemic rebound were analyzed. Results Counties consolidated the endemic situations with an average time of 5±3 years after the transmission control, with endemic rebound normally caused by single factor. The ratio of Oncomelania snail areas to historically accumulative snail areas increased over 10% in hilly endemic regions and lake endemic regions in 7 and 12 years separately, while it was stabilized in a low level in water-network endemic areas. The rebound peak time of infected snail densities was consistent with or later than that of densities of living snails. The prevalence of schistosome infection in humans in lake endemic regions rebounded 2 years after transmission under control. The transmission interruption counties consolidated the endemic situations with an average time of 7±4 years. The human prevalence of schistosome infection decreased to a very low level after the counties reaching the criteria of transmission interruption. The snail areas increased to over 2% of historically accumulative snail areas 3－6 years after transmission interruption in lake, water-network endemic areas successively, while densities of living snails and infected snails were increased at the same year or 2－3 years later. Conclusions The endemic rebound in regions after the transmission under control or interrupted is caused by biological, natural and social factors and mainly presents as the rebound of snail status. The modification of criteria for schistosomiasis control and elimination should consider the influence of variation of snails, snail areas and density of infected snails on endemic situations in different endemic areas comprehensively. Sensitive and valid surveillance and forewarning system should be established to strengthen the monitoring and consolidating endemic situation in endemic areas after the transmission under control or interrupted.

Key words: Schistosomiasis, Transmission control, Transmission interruption, Endemic rebound

摘要：

目的 分析我国血吸虫病流行区达到传播控制（传控）和传播阻断（传阻）后疫情回升地区的疫情变化情况，为修订血吸虫病控制和消灭标准、巩固达标地区防治成果提供参考。 方法 选择全国7个血吸虫病流行省中的12个疫情回升县（市、区），采用回顾性调查法，收集各县达传控前10年和以后各年（至2008年或2009）的疫情数据及相关资料，分析其疫情变化情况及达标后疫情回升因素。结果达传控后疫情回升县的疫情巩固时间平均为5±3年。山丘型和湖沼型流行区钉螺面积分别在达标后第7年和第12年回升至历史累计有螺面积10%以上，水网型流行区钉螺面积相对稳定在较低水平；感染性钉螺密度的回升时间与活螺密度的回升高峰基本一致；湖沼型流行区在达传控后2年居民感染率即回升至>10%。达传阻后疫情回升县的疫情巩固时间平均为7±4年。达传阻后湖沼型、水网型和山丘型流行区的人群感染率均稳定在较低水平，但钉螺面积在达传阻后的3～6年先后回升至历史累计有螺面积的2%以上，而活螺密度和感染性螺密度则在钉螺面积回升的当年或随后２~3年相继出现回升。结论受生物、自然、社会等诸多因素的影响，传控和传阻达标地区疫情回升主要表现为螺情回升。建议修订我国血吸虫病控制和消灭标准时，应综合考虑不同类型流行区的螺情变化规律、钉螺面积或感染性钉螺密度等因素对疫情的影响。传控和传阻地区应建立敏感而有效的监测预警体系，加强达标后的疫情监测和巩固工作。

关键词: 血吸虫病, 传播控制, 传播阻断, 疫情回升