[Effect of ditching for drain on control of Oncomelania hupensis snail in beaches of Dongting Lake].

OBJECTIVE: To evaluate the effect of ditching for drain on the control of the breed of Oncomelania hupensis snails in beaches of Dongting Lake. METHODS: From November, 2009 to November, 2012, an 0. hupensis snail infested beach of the Yueyang jail and an O. hupensis snail infested beach of Junshan District were selected as research fields in the eastern Dongting Lake area, and the former, as the intervention field, was performed with the ditching for drain by excavators and the latter, as the control field, was not. RESULTS: Before the project implemented, the average soil moisture contents on the beaches in dry seasons of the two fields were both about 35.56%. After the project implemented, in the intervention field, the average soil moisture content was 26.53% which was significantly lower than that (35.56%) in the control field (F = 6.53, P < 0.05). The underground water levels in different heights in the intervention field were lower than those in the control field (χ2 = 33.33, P < 0.05). Before the project implemented, the natural death rates of the snails were 0.98% and 0.89% in the two research fields respectively (P > 0.05), and after the project implemented (in 2012), no adult and young snails were found in the interventional field, but in the control field, the average densities of living snails and young snails were 29.37 snails/0.1 m2 and 213 ± 108.45 snails/0.1 m2 respectively. CONCLUSION: The intervention of ditching for drain can decrease the soil moisture contents quickly and change the ecological condition, therefore, can control the breed of O. hupensis snails in the beaches of Dongting Lake.

[Effect of calcium cyanamid synthetic drug on Schistosoma japonicum egg morphology].

OBJECTIVE: To study the morphological change of Schistosoma japonicum eggs processed by calcium cyanamide synthetic drug, so as to provide the basis for further study of the mechanism that calcium cyanamide synthetic drug to schistosome eggs. METHODS: The calcium cyanamide synthetic drug was added to the cattle feces containing schistosome eggs and mixed up, and then the cattle feces was stacked as original shape on the marshland. Blank controls were set at the same time. The cattle feces samples were collected and.the schistosome eggs were observed under a microscope on the 1st, 2nd, 3rd, 7th day after the experiment. RESULTS: By the effect of calcium cyanamide synthetic drug, the color of eggs was deepening gradually, the miracidia were atrophied, and the shells of eggs were thickened. The embryonic membrane of miracidia was no longer completed 3 days later, and the miracidia were deformed severely 7 days later. The atrophy of miracidia was not obvious in the blank controls. CONCLUSION: The schistosome miracidia and embryonic membrane can be damaged by the calcium cyanamide synthetic drug, and worse damaged with time extending.

Schistosomiasis in a migrating population in the lake region of China and its potential impact on control operation.

Coverage of migrating people in schistosomiasis control program is a growing concern in China. Schistosomiasis caused by Schistosoma japonicum is still one of the major infectious diseases of public health importance in China though tremendous efforts have been made to control the transmission over the past decades. Along with the rapid social-economic development, migrant population has been remarkably increasing across the country. The infected migrants may introduce a new souse of infection to endemic areas or the areas where the transmission had been controlled or interrupted but the intermediate host Oncomelania snail is still present. Preliminary studies for surveillance on schistosomiasis prevalence in migrants were reported, but there is little basic information provided. We carried out an investigation on the prevalence in immigrants, emigrants and permanent residents in three villages of Hunan province located in the main endemic area of lake region, and analyzed the potential impact of migration on control practice. In the study villages, the migrant population accounts for 53.6% of the total. Schistosoma infection was detected by modified Kato-Katz method and miracidium hatching test. Questionnaire survey was conducted comprising knowledge of disease and its transmission, water contact, personal protective measures, and whether examined and treated after water contact. The survey indicated that the migrants and permanent residents had similar life style, and the majority of them experienced water contact in agricultural work or routine life activities. However, the infection rate in immigrants was significantly higher than that in permanent residents. It was also found that the migrants had significantly less knowledge about the disease than the permanent residents, and took no personal protective measures. This is due to that the control program could not cover the migrants when they were absent at the time the program being implemented. The present study suggested that the surveillance and intervention for migrants, immigrants in particular, should be included and strengthened in schistosomiasis control program and a feasible scheme be developed.

[Evaluation on molluscicidal effect of chlorosalicylicamide on Oncomelania hupensis in schistosomiaisis endemic areas of eight provinces in China].

OBJECTIVE: To evaluate the effects of a novel molluscicide, the salt quinoid-2', 5-dichloro-4'-nitrosalicylanilide from niclosamide (LDS), with 10% wettable powder, in main schistosomiasis epidemic areas of China, including Hunan, Jiangxi, Hubei, Anhui, Jiangsu, Sichuan, Yunnan and Zhejiang Province. METHODS: In the immersion test, 6 effective concentrations of 10% LDS were tested respectively: 0.1, 0.2, 0.4, 0.6, 0.8, 1.0 g/m3 in the field; at the same time, 50% wettable powder of niclosamide ethanolamine salt (WPN) with effective concentrations of 1.0 g/m was used as the molluscicide control, and the fresh water as the blank control, then the mortality rates of 0. hupensis snails were recorded at 24 h, 48 h and 72 h after the immersion. In the spraying test and powder-spraying test, 5 effective dosages of 10% LDS were tested respectively: 0.2, 0.4, 0.6, 0.8, 1.0 g/m2, while 50% WPN 1.0 g/m2 was used as the molluscicide control, and the fresh water as the blank control in the field for 1 d, 3 d and 7 d, then the mortality rates of O. hupensis snails were recorded at 1 d, 3 d and 7 d after the spraying and powder-spraying. RESULTS: The snail mortality rates of LDS using the immersion test for 72 h were more than 95% in the field of eight provinces (0.1 g/m in Sichuan, Jiangxi, Jiangsu and Zhejiang provinces, 0.2 g/m3 in Yunnan, Hunan and Hubei provinces, and 0.4 g/min Anhui Province); the snail mortality rates of LDS using the spraying test for 7 d were more than 85% (0.2 g/m2 in Hunan, Hubei, Jiangxi and Zhejiang provinces, 0.4 g/m2 in Sichuan and Anhui provinces, 0.6 g/m2 in Yunnan and Jiangsu provinces). The snail mortality rates of LDS the powder-spraying test for 7 d were more than 85% (0.6 g/m2 in Yunnan, Sichuan, Hubei, Jiangxi, Anhui, Jiangsu and Zhejiang provinces). According to the standards of "Efficacy test methods and evaluation of molluscicide for pesticide registration (NY/T 1617-2008)", LDS is a qualified molluscicide. CONCLUSIONS: LDS has good molluscicidal effects through the immersion, spraying and powder-spraying test in the fields. It is suitable for a variety of environments to control O. hupensis snails of schistosomiasis endemic areas in China. The recommended dosages of LDS are 0.1-0.2 g/m3 by the immersion method, 0.2-0.4 g/m2 by the spraying method, and 0.4-0.6 g/m2 by the powder-spraying method in the fields.

[Impact of environmental changes on Oncomelania snail distribution in Dongting Lake beach].

OBJECTIVE: To study the impact of environmental changes on the distribution and the growth and decline of Oncomelania snails in Dongting Lake beaches after the implementation of Three Gorges Project. METHODS: T-embankment of Junshan District where there was a greater human factor related to the snail spread and a lake beach named Dongkou of Junshan District where there was a less human factor related to the snail spread were selected as study areas. The various ground elevations were measured and the high points were marked with GPS. The height of vegetation was surveyed regularly, soil moisture content and micro-environment temperature and humidity at different elevations in the lake beaches were detected, and the snail distribution was investigated. Both the longitudinal and retrospective studies were conducted. RESULTS: In 1993, the soil was taken from the lake beach at the elevation of 25 m to build an isolated canal, and this made snail density decline year by year, and no snails have been found since 1998. The elevation of the vegetation in the T-embankment was significantly lower than that in Dongkou, and there was no high rod plant growth. The snails were found in the elevation from 23.5 to 26.5 m where the vegetation was mainly Cyperus spp. The growth of the vegetation was 16.0 to 54.0 cm 30 days after flood withdrew, and the vegetation reached the highest density 60 days after flood withdrew. The snail density was highest at the elevation from 24.5 to 25.5 m, and the elevation of snails and their eggs was lower than that in 1980s. In the dry season, the water content of the soil in Dongkou was from 46.80% to 52.20%, which was more than that in T-embankment, while at the elevation over 26.0 m, the water content was from 21.36% to 29.77%, which was equal to that in T-embankment. CONCLUSION: Three Gorges Project plays an important role in the control of water level of Dongting Lake, but there is no impact on the snail reproduction and density.

[Toxicity test of Luokuwei on mice].

The result of toxicity test of Luokuwei to mice showed that, when the dose of the drug was 400-1 200 times of molluscicidal dosage, the mortality rate of mice was only 10%-20% in 24 h, and in 14 d, only the mortality rate in high doasage group was above 50%. It is suggested that Luoweiku is a molluscicide with low toxicity.