[A sampling survey on the distribution of Oncomelania snails in Zhejiang Province].

ABSTRACT

OBJECTIVE: To find out current distribution of Oncomelania snails and Schistosoma infection in snails in Zhejiang Province, so as to improve the project of schistosomiasis control. METHODS: Investigation spots were selected by stratified cluster sampling method, 100 villages of 34 counties were selected from 7106 villages of 55 counties as survey spots. Synchronously systematic and environmental samplings were used for the survey. Snails were dissected to determine the infection status and spots with sham snails were set to assess the quality of the survey. RESULTS: The result showed that snails were found in 223 strips, 1572 frames and 73,300 m2 area in 32 villages of 21 counties. Snails were found in an area covering 72,640 m2 in 29 villages of 18 counties in hilly region, which accounted for 99.1% of total snail habitats. The significantly larger area with snails was revealed in hilly region than that in water network region (t = 3.04, P < 0.01). 1st, 2nd strata occupied 71,680 m2 snail area, which accounted for 97.8% of total snail area, much higher than that in the 3rd stratum (t = 3.71 , P < 0.01). Snail habitats in the irrigation ditches and canals accounted for 62.6% of total snail area, significantly higher than that of farmland (t = 3.02, P < 0.01). No snails were found infected among 7892 living snails by dissection. The theory value of snail area in Zhejiang Province was 1,361,940 m2. CONCLUSION: It is estimated that the snail-ridden area is about 1,500,000-2,000,000 m2 in the Province, mostly found in the villages of hilly region with a record of snail habitats during the recent 4 years and the primary environment of the snail areas were ditches and canals. No infected snails were found from the survey.