[Trends in the distribution of Oncomelania hupensis in forestlands in Songjiang District, Shanghai Municipality from 2009 to 2023].

ABSTRACT

OBJECTIVE: To investigate the changes in distribution of Oncomelania hupensis snails in forestlands in Songjiang District, Shanghai Municipality from 2009 to 2023, so as to provide insights into formulation of O. hupensis snail surveillance programs. METHODS: The reports on O. hupensis snail surveillance in Songjiang District, Shanghai Municipality from 2009 to 2023 were collected, and the snail surveillance data in forestlands were extracted. The trends in the proportion of areas with snails in forestlands in total areas with snails, occurrence of frames with living snails and density of living snails were evaluated using a Joinpoint regression model in Songjiang District from 2009 to 2023, and the annual percent change (APC) and average annual percent change (AAPC). RESULTS: A total of 40 sites with snails were found in forestlands in 14 administrative villages of 4 townships, Songjiang District, Shanghai Municipality from 2009 to 2023. A total of 39 065 frames were surveyed for snails in settings covering an area of 609 600 m2, and there were 6 084 frames with snails, covering 151 250 m2 snail habitats. A total of 22 210 snails were captured, with the highest density of 260.00 snails/0.1 m2, and 6 262 snails were dissected, with no Schistosoma japonicum infection identified in snails. The proportion of areas with snails in forestlands in total areas with snails appeared a tendency towards a rise in forestlands in Songjiang District, Shanghai Municipality from 2009 to 2023 (APC = AAPC = 24.9%, P > 0.05); however, there were no turning points in the trend curve, with the highest proportion seen in 2009 (53.81%), the lowest in 2011 and 2023 (both 0) and a mean proportion of 24.81%. The occurrence of frames with living snails appeared a tendency towards a rise from 2009 to 2023 (APC = AAPC = 41.5%, P > 0.05); however, there were no turning points in the trend curve, with the highest occurrence in 2009 (53.81%), the lowest in 2011 and 2013 (both 0), and the mean occurrence of 15.57%. In addition, the density of living snails appeared a tendency towards a rise from 2009 to 2023 (APC = AAPC = 55.0%, P > 0.05); however, there were no turning points in the trend curve, with the highest density in 2023 (0.96 snails/0.1 m2), the lowest in 2011 and 2013 (both 0), and a mean density of 0.57 snails/0.1 m2. CONCLUSIONS: The difficulty in O. hupensis snail control and risk of imported snails appeared a tendency towards a rise in forestlands in Songjiang District, Shanghai Municipality over years from 2009 to 2023. Supervision and assessment prior to seedling transplantation and intensified surveillance post-transplantation are recommended to reduce the risk of O. hupensis snail importation and spread.