title: [Retrospective investigation on national endemic situation of schistosomiasis. II. Analysis of changes of endemic situation in transmission-controlled counties].
abstract: OBJECTIVE
  To summarize and analyze the process of the changes of schistosomiasis infection and Oncomelania snails in schistosomiasis transmission-controlled areas to explore the rules of the impact of changes of snail indexes on human infection before and after the stage of transmission control, so as to provide the evidence for editing snail indexes in the schistosomiasis controlled criterion and a more scientific, standardized control assessment and evaluation.
  
  
  METHODS
  Twenty-one schistosomiasis transmission-controlled or transmission-interrupted counties in lake endemic areas and hilly endemic areas in 8 provinces were selected and investigated retrospectively to collect schistosomiasis epidemiological information 10 years before these counties reached the criterion of transmission control and the subsequent years until 2008 or 2009. A " Standard county schistosomiasis epidemic survey data review software" was developed to establish a national epidemic retrospectively database; the trends of changes of snail status, infected snail status and human infection status were analyzed in different years. The trends and rules of the changes of snail areas, emerging snail areas, living snail densities, infected snail densities, snail infection rates and human infection rates were analyzed and compared before and after the counties reached the schistosomiasis transmission-controlled criterion in different types of endemic areas.
  
  
  RESULTS
  Before the transmission control, the human infection rate presented a declining trend in endemic areas. In lake endemic areas, the human infection rate declined to below 5% 4 years before the transmission control; in hilly endemic areas, the human infection rate declined to below 3% 8 years before the transmission control, and the human infection rates of the lake and hilly endemic areas declined to 2.10% and 1.45%, respectively, at the year of transmission control. However, 3 to 4 years after transmission control, the disease began to rebound, especially in lake endemic areas. The snail areas and snail densities declined year by year 10 years before the transmission control in the lake and hilly endemic areas, and the proportion of snail areas occupying the historic snail areas declined the lowest, being 2.75% and 0.55%, respectively, at the year of transmission control. The average densities of living snails kept a low level from 3-4 years before the transmission control to 9-10 years after the transmission control, and then rebounded. The new snail areas appeared 6-7 years after the transmission control and the snail areas and densities of living snails rebounded 9-12 years after the transmission control.
  
  
  CONCLUSIONS
  The snail status can maintain a relatively low level during about 10 years after the transmission control in the lake and hilly schistosomiasis endemic areas, but the schistosomiasis status rebounded 5 years after the transmission control. While the comprehensive measures mainly including infectious source controlled are implemented, the snail surveillance and control should be still strengthened, and it is recommended that "the proportion of snail areas decreased" and "the control of infected snails" would be the indicators of the criterion of schistosomiasis transmission control.
authors.affiliation: National Institute of Parasitic Diseases, Chinese Center for Disease Control and Prevention, Shanghai 200025, China.
authors.forename: Rong
authors.initials: R
authors.lastname: Zhu
authors.forename: Dan-Dan
authors.initials: DD
authors.lastname: Lin
authors.forename: Xiao-Hua
authors.initials: XH
authors.lastname: Wu
authors.forename: Qi-Zhi
authors.initials: QZ
authors.lastname: Wang
authors.forename: Shang-Biao
authors.initials: SB
authors.lastname: Lv
authors.forename: Guo-Jing
authors.initials: GJ
authors.lastname: Yang
authors.forename: Yang-Qing
authors.initials: YQ
authors.lastname: Han
authors.forename: Ying
authors.initials: Y
authors.lastname: Xiao
authors.forename: Yi
authors.initials: Y
authors.lastname: Zhang
authors.forename: Wen
authors.initials: W
authors.lastname: Chen
authors.forename: Meng-Tao
authors.initials: MT
authors.lastname: Xiong
authors.forename: Rui
authors.initials: R
authors.lastname: Lin
authors.forename: Jing
authors.initials: J
authors.lastname: Xu
authors.forename: Li-Juan
authors.initials: LJ
authors.lastname: Zhang
authors.forename: Jun-Fang
authors.initials: JF
authors.lastname: Xu
authors.forename: Shi-Qing
authors.initials: SQ
authors.lastname: Zhang
authors.forename: Tian-Ping
authors.initials: TP
authors.lastname: Wang
authors.forename: Li-Yong
authors.initials: LY
authors.lastname: Wen
authors.forename: Xiao-Nong
authors.initials: XN
authors.lastname: Zhou
mesh_terms: D000818:Animals; D002681:China / Q000453:epidemiology; D004197:Disease Reservoirs / Q000469:parasitology*; D019353:Endemic Diseases / Q000517:prevention & control*; D005843:Geography; D006801:Humans; D010571:Pest Control; D012189:Retrospective Studies; D012547:Schistosoma / Q000502:physiology; D012552:Schistosomiasis / Q000453:epidemiology* / Q000469:parasitology / Q000517:prevention & control* / Q000635:transmission; D012908:Snails / Q000254:growth & development* / Q000469:parasitology