Objective   To learn the impact of the routine snail control with niclosamide on the population of snails and infected snails in the main channel in the man-made irrigation area.

  Methods   In the irrigation area o f Diaoyutai reservoir in Anhui, a section of the main channel, which the mullicicide measure was implemented according to the local plan, was selected as a trial spot.A neig hboring branch without no snail was selected as a control spot.Systemic survey of snails was carried out from the Dec of 2002 to the Nov of 2003.All snails were anatomized.The date, method, dosage of Niclosamide and conduction were deicded and completed by the local station of anti-Schistosomiasis.

  Results   Before the snail control, the trend of the death rate in the main channel was generally the same as that in the branch.After mullicicide measure was given to the channel on the 20th of Apr, the death rate in the channel on the 10th day and the 37th day was respectively 24.46% and 43.01%, but it was 1.25% at the end of Aug.Mean while the death rate in the branch didn't change grealty.During the period ahead of the 20th of Apr, there were 3 months in the channel and 1 month in the branch when infected snails were found.During the period from Apr to Jun, infected snails were discovered both in the channel on the 10th day after snail control and in the branch in May.The infection rate of snails and infected snail density in the two spots rose up during the rest time of the year.

  Conclusion   In the main channel of the man-made irrigation area, snail control with Niclosamide, as an ordinary measure, might play an important role in preventing human from infection with Schistosoma, but the role in reducing the population of snails and infected snails in near future was very limited.