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通过系统观察，认为云南省钉螺仍以壳长划分成、幼螺比较客观。夏季幼螺最多，交替指数0．4516，是云南钉螺螺口交替时期。秋季感染性钉螺最多，上年感染的螺已大部份消亡，当年感染的螺多处于尾蚴发育阶段，交替指数为3．6201，是感染螺主要交替时期。建议每年灭螺2次：5月消灭上年生钉螺和感染螺，防止人畜感染，阻碍其交替：10月消灭当年生钉螺和感染螺，减少下一年的危害。
Through systematic observation, the snails in Yunnan Province are still divided into shell length, snail more objective. Most snails in summer, alternating index 0.4516, is the Yunnan snail screw alternate period. Infectious snails fall most in the past year, most of the infected snails have died, when the infected spiral cercariae more in the developmental stages, the alternate index of 3.6201, is the main alternate phase of infection. It is recommended to kill snails twice a year: in May to eliminate previous year’s snails and snail infestation, to prevent human and animal infections, impeding the alternation: in October to eliminate the year snails and snail infestation, reducing the next year’s harm.