云南大山区阳性钉螺转阴的观察

STUDIES ON NEGATIVE CONVERSION OF SCHISTOSOME-INFECTED SNAILS IN MOUNTAINOUS REGION OF YUNNAN

在云南省巍山县石头地村现场饲养条件下,观察了90个人工感染的阳性钉螺逐月逸蚴的情况。每月均能逸蚴的阳性钉螺占20％,间断性逸蚴的阳性钉螺占42.2％。37.8％的阳性钉螺逸放尾蚴数次后不再逸放尾蚴。对此类钉螺的解剖发现,有的已无尾蚴和胞蚴存在。 对304个自然感染的阳性钉螺也进行了逐月逸蚴观察。各月未逸出尾蚴者作抽样解剖。结果,第1次逸蚴后2个月估计转阴的钉螺约占36.1％,3个月占50％,4个月占41％,5个月占39.8％,6个月占2.6％。

The monthly cercaria shedding of 90 artificially infected Oncomelania snails was observed under a field condition in mountainous region,Shitoudi Village,Weishan County,Yunnan Province.The results showed that 20% of the snails shed cercaria monthly,42.2% could shed irregularly and 37.8% stopped releasing cercariae after several times of shedding.Final disvection of the snails showed that none cercaria or sporocyst could be found in part of the snails.A total of 304 naturally infected snails were observed individually every month.Samples were taken each month from the snails which did not shed cercaria,then dissecled and examined.The negative conversion rate was calculated in the second,third,fourth,fifth and sixth month after the first shedding,which were 36.1,50.0,41.0,39.8 and 2.6% respectively.