{'fraction_non_alphanumeric': 0.016931216931216932, 'fraction_numerical': 0.007407407407407408, 'mean_word_length': 4.803680981595092, 'pattern_counts': {'":': 0, '<': 0, '<?xml version=': 0, '>': 0, 'https://': 0, 'lorem ipsum': 0, 'www.': 0, 'xml': 0}, 'pii_count': 0, 'substrings_counts': 0, 'word_list_counts': {'cursed_substrings.json': 0, 'profanity_word_list.json': 0, 'sexual_word_list.json': 0, 'zh_pornsignals.json': 0}}
[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.