[Longitudinal observation on a schistosome-infected snail spot as a source of infection in a mountainous village of Dali city].

AIM

To observe longitudinally the changes in survival and infection rate of Oncomelania snails in a positive snail spot in Yunnan.

METHODS

A positive snail spot in a ditch in Shalimuzhuang Village, Dali City, was continually observed on the changes in the density of snail population and natural infection rate of the snails by random environmental sampling for 8 times in 4 successive years.

RESULTS

During the 8 times of snail survey, living snails were found relatively stable in the ditch, in which positive snails were obtained in 6 occasions, the average infection rate being 3.99%.

CONCLUSION

The density and the positive rate of snails in the mountain region remains relatively stable as a source of human infection. Elimination of the positive snail spots is necessary for controlling schistosomiasis.