The risk surveillance of schistosomiasis in Yunnan, 2021 / 中国热带医学

@#Abstract: Objective　To evaluate the potential transmission risk of schistosomiasis in Yunnan Province, and to provide strategic basis for the prevention and control. Methods　Based on the prevalence of schistosomiasis, the social and environmental factors that may lead to the epidemic, 1-3 villages from 3 provincial-level and 15 county-level counties (cities and districts) were selected as the evaluated villages in 2021. The risk of schistosomiasis spread was analyzed comprehensively by consulting, reviewing and collecting routine surveillance data of schistosomiasis in the villages, combined with snail and wild feces survey. The risk level was evaluated for the positive snails, positive wild feces, resident infection, average density of live snails and snail frame occurrence rate. Results　Totally 7 snail counties schistosomiasis transmission was blocked of 18 epidemic counties and the rest were eliminated counties. A total of 152 447 snail frames were investigated and 3 043 frames with snails, 15 895 snails were captured and included 15 727 live snails in the 32 evaluated villages. The total area of snail was 58.87 hm2 and the area of reoccurrence was 34.19 hm2 with snail frame occurrence rate of 2.00% and average density of live snails 0.103 2/0.11 m2, and no positive snails were found by loop-mediated isothermal amplification (LAMP) assay. A total of 1 374 wild feces were collected in 27 evaluated villages of 14 epidemic counties, mainly from cattle, dogs, sheep, equine animals, pigs and so on, all of which were negative. According to the risk assessment of epidemic spread, Yongle Village and Yongsheng Village in Eryuan County, Zhiming Village in Chuxiong City were Ⅱ risk, and the rest were Ⅲ risk. Conclusions　Although the risk of transmission is low in Yunnan Province, the risk of transmission and spread still exists. It is necessary to strengthen the risk monitoring, control of snail and effective management of livestock to prevent the rebound of the epidemic.

[Analysis of Oncomelania hupensis status in schistosomiasis surveillance sites of Yunnan Province in 2015].

OBJECTIVE: To understand the Oncomelania hupensis distribution and infection status in the schistosomiasis surveillance sites of Yunnan Province, so as to provide the evidence for making the control and prevention measures. METHODS: Eighteen administrative villages were selected as the surveillance sites where the schistosomiasis endemic was serious in 18 epidemic counties, one village for one county. The snail status was investigated with the systematic sampling and environmental sampling methods, and the infection status of the snails was detected by a microscope and loop-mediated isothermal amplification (LAMP). The surveillance database was established and descriptively analyzed. RESULTS: In 2015, the total surveillance area was 1826.55 hm², and the area with snails was 55.03 hm², that was reduced by 57.70% as compared to that in 2013, and by 40.63% as compared to that in 2014. No new snail area was discovered, and also no schistosome infected snails were discovered. Totally 718,532 frames were surveyed, and the occurrence rate of frames with snails was 0.45% and the density of living snails was 0.013 9 snail/0.1 m². In the endemic controlled areas, the snail area and density of living snails were both the highest. The snails concentrated on the environments of paddy field, ditch, bottomland, small reservoir, and dry land, and the vegetations of rice, dry crop, weed and wood. The snail area, occurrence rate of frames with snails, total number of snails and number of living snails all showed a downward trend. No infected snails were found for three years. CONCLUSIONS: The Oncomelania hupensis snails have been effectively controlled in the national schistosomiasis surveillance sites of Yunnan Province. However, the comprehensive snail control measures still should be continually strengthened in order to consolidate the achivements.

[Evaluation of effectiveness of comprehensive schistosomiasis control project in Yunnan Province from 2004 to 2013].

OBJECTIVES: To evaluate the effect of comprehensive schistosomiasis control project in Yunnan Province after its implementation for ten years, so as to provide the evidence for formulating the future prevention and control strategy. METHODS: The data of the schistosomiasis comprehensive control project and the endemic situation were collected and analyzed to evaluate the control effect of the project in Yunnan Province from 2004 to 2013. RESULTS: After the comprehensive control project implementation for ten years, the Oncomelania hupensis snail area in Yunnan Province decreased from 4,364.79 hm2 in 2004 to 1,528.50 hm2 in 2013, with a reduction rate of 64.98%, and the occurrence rate of frames with snails and the density of living snails decreased from 4.71% and 0.26 snails/0.1 m2 in 2004 to 1.35% and 0.04 snails/0.1 m2 in 2013, with the reduction rates of 71.34% and 84.62%, respectively. The schistosome infected snails were found only in 2011 and 2013 since 2008. In 2013, the infection rates of human (0.0021%) and cattle (0.0209%) decreased by 99.84% and 99.44%, respectively, compared to those in 2004, and no acute schistosome infection cases were found since 2008. The 212 villages with relatively serious endemic situation (Type One, Type Two and Type Three) all declined to the slight endemic villages (Type Four and Type Five), therefore, they reached the criteria of schistosomiasis transmission controlled or interrupted. The awareness rates of schistosomiasis control among villagers and students in endemic areas were above 90% and 98%, respectively. CONCLUSION: The effect of the comprehensive schistosomiasis control project is significant in Yunnan Province, but the task to consolidate and enlarge the control results still remains a challenge.

[Molluscicidal effect of 5% powder of niclosamide ethanolamine salt granules (NEG) in field of mountainous areas in Yunnan Province].

OBJECTIVE: To evaluate the molluscicidal effect of 5% powder of niclosamide ethanolamine salt granules (NEG) in the field of mountainous areas in Yunnan Province. METHODS: The grasslands with Oncomelania hupensis snail habitats were chosen in Beideng Village, Heqing County, Yunnan Province, and were divided into 7 groups (groups of NEG 30 g/m2, NEG 40 g/m2, NEG 50 g/m2, NEG 40 g/m2 plus obstacle clearing, 50% niclosamide ethanolamine salt wettable powder (WPN) 6 g/m2, WPN 6 g/m2 plus obstacle clearing, and fresh water). The snail death rates and the densities of living snails were investigated and the results were compared in the different groups 7 d, 15 d, and 30 d after the implementation. RESULTS: Seven d, 15 d, and 30 d after the implementation, the snail death rates of the groups of NEG 30 g/m2, 40 g/m2, and 50 g/m2 were from 72.75 % to 95.83%, and the average descent rates of living snail densities were from 72.26% to 95.54%. Seven d, 15 d, and 30 d after the implementation, in the NEG 40 g/m2 group, the snail death rates were from 81.69% to 87.19%, and the average descent rates of living snail densities were from 81.42% to 87.91% ; in the NEG 40 g/m2 plus obstacle clearing group, the snail death rates were from 84.89% to 88.24% and the average descent rates of living snail densities were from 85.63% ~ 88.22%; in the WPN 6 g/m2 group, the snail death rates were from 85.23% to 86.17% and the average descent rates of living snail densities were from 85.76% to 86.05%; in the WPN 6 g/m2 plus obstacle clearing group, the snail death rates were from 88.89% to 92.10% and the average descent rates of living snail densities were from 86.71% to 92.20%. The obstacle clearing improved the molluscicidal effect. CONCLUSION: NEG has a good molluscicidal effect in the field of mountainous areas in Yunnan Province.

[Monitoring of sentinel mice and risk assessment of schistosomiasis transmission in key regions of Yunnan Province in 2014].

OBJECTIVE: To establish and perfect the surveillance and forecast system of schistosomiasis, and timely discover the suspicious high risk environments for preventing the human and livestock from schistosomiasis. METHODS: Eight villages of three counties were selected as survey points. Then, the surveillance and forecast of sentinel mice were carried out in the key water regions. The recovered sentinel mice were dissected in laboratory. The sentinel mouse serum antibodies against schistosome were detected by ELISA, the suspicious water contacts of residents and livestock were investigated and the results were analyzed, and the epidemic risk was assessed. RESULTS: Totally 300 sentinel mice were placed, the recovery rate was 94.67%, and the mortality rate was 8.80%. There were no mice with positive serum antibodies against schistosome, and the results of the dissection of all the sentinel mice were negative. The humans who contacted with the suspicious water were mainly villagers, students, children and fishermen by washing hands and feet, washing vegetables, harvesting, fishing and swimming. The Oncomelania hupensis snail areas, human infection rates, and cattle infection rates were obviously declined in recent 3 years. However, the epidemic risks still existed. CONCLUSION: Although schistosomiasis transmission was effectively controlled in the three counties, the comprehensive control measures still should be strengthened.

[Analysis of schistosomiasis endemic status of national surveillance sites in Yunnan Province, 2014].

OBJECTIVE: To master the dynamic endemic status and influencing factors of schistosomiasis in Yunnan Province, so as to provide the evidence for making the control and prevention measures. METHODS: Four villages of four schistosomiasis heavy endemic counties were selected as survey sites. Then, the serological screening and etiological tests were carried out in the residents, and the basic situations of the survey sites were investigated. The infection status of the livestock and relevant information of Oncomelania hupensis snails were surveyed. All the results were analyzed statistically. RESULTS: Totally 4310 residents were surveyed by the indirect hemagglutination assay with the examination rate of 79.68% and serum positive rate of 8.40%. The positive rate reached upwards 12.53% in Qiandian Village of Eryuan County. The serum positive rate of the female was higher than that of the male, and the positive rates of the 30 years and older age groups were higher than those of the other age groups. The serum positive rates of the peasants, migrant labourers and residents with the junior high school education level were higher. No positive feces were found. A total of 24 advanced cases were reported. No positive livestock and snails were found, and the average density of living snails was 0.023 3-0.056 6/0.1 m2. CONCLUSION: Right now, the schistosomiasis is at a low prevalence status in Yunnan Province, and the endemic situation has been effectively controlled.

[Current prevalence situation and control strategy of schistosomiasis in Yunnan Province].

OBJECTIVE: To evaluate the current prevalence situation of schistosomiasis in Yunnan Province, so as to provide the evidence for making further control strategy. METHODS: The data of schistosomiasis were collected and analyzed statistically in Yunnan Province in 2014. RESULTS: There were 7 transmission controlled counties and 11 interrupted counties in Yunnan Province in 2014, and Oncomelania hupensis snails were not found in 5 of the 11 interrupted counties for at least 5 years. In the transmission controlled areas, the schistosomiasis endemic villages, population, farm cattle, and snail areas accounted for 80.94%, 83.72%, 79.32% and 82.00% of whole schistosomiasis endemic areas in Yunnan Province, respectively. The infection source was not completely eliminated. CONCLUSION: In the transmission controlled areas, the elimination of infection source should still be strengthened; in the transmission interrupted areas, the import infection sources should be prevented.

[Current situation and effect of non-hazardous treatment of excrement of sanitary latrines in rural schistosomiasis endemic areas of Eryuan County, Yunnan Province].

OBJECTIVE: To understand the condition of the construction and management of sanitary latrines, and assess the effect of disposal of the excrement in rural schistosomiasis endemic areas in Yunnan Province. METHODS: Three villages with schistosomiasis endemic were selected from Eryuan County and 30 households per village were sampled randomly for the field survey. The stool samples were sampled and tested according to the national standard. RESULTS: Totally 90 latrines were surveyed. The popularity rates of sanitary latrines in Yongle, Qiandian and Xinzhuang villages were 83.19%, 83.12% and 81.63% respectively. In the 90 household latrines, only 32.22% located inside the courtyard, and 91.67% of sanitary latrines and 70.00% of non-sanitary latrines had integrated buildings. Maggots or pupae or adult flies were found in 33.33% of sanitary latrines and all of non-sanitary latrines with the average amounts of 1.05 and 3.40 per latrine respectively. The removal rate of fecal coliform, the sedimentation rate of parasitic eggs and the mortality rate of Ascaris eggs were 90.00%, 80.61% and 95.20% on average respectively. The qualified rate of the fecal coliform of the outlet of the sanitary latrines was 41.67%, and the qualified rate of the mortality rate of Ascaris eggs was 78.13%. No living schistosome eggs were found at the outlets of latrines. For the effect of non-hazardous treatment, there was a statistically significant difference between the sanitary latrines and non-sanitary latrines. CONCLUSIONS: The latrine improvement has a good effect on non-hazardous treatment of the excrement in Yunnan Province, but the construction, application and management of sanitary latrines still need to be strengthened.

[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.

[Investigation of wild feces pollution in schistosomiasis endemic areas in Yunnan Province].

OBJECTIVES: To understand the status of wild feces distribution and pollution in schistosomiasis endemic areas in Yunnan Province. METHODS: According to the distribution of Oncomelania hupensis snails and characteristics of human and animal activities in recent five years, 6 schistosomiasis endemic villages in Weishan, Nanjian and Midu counties (2 villages each county) were selected as the investigated areas and. more than 4 hm2 area with snails around each village were investigated for the types and densities of wild feces. The schistosome infested feces was detected with the hatching method. RESULTS: Totally 63 hm2 were investigated and 420 wild feces were found in all kinds of environments. The densities of wild feces were 0.066 7 piles/100 nm2, and the densities of wild feces of the road and the hillside were the highest (0.098 7 piles/100 m2 and 0.088 0 piles/100 m2 respectively). Totally 260 fresh wild feces were collected, including the feces of human being, cattle, horse, dog, sheep and pig, and the feces of cattle and dog was the most (37.38% and 30.71%, respectively). No schistosome positive feces was found. CONCLUSIONS: There are a lot of wild feces in snail areas in Yunnan Province, and the risk of schistosomiasis transmission is still high. Therefore, we should strengthen the banning grazing measures and the investigation of dogs.

[Analysis of schistosomiasis endemic situation in Yunnan Province from 2009 to 2012].

OBJECTIVE: To evaluate the effect of schistosomiasis control in Yunnan Province since achieving the transmission control standards, so as to provide the evidence for formulating the next prevention and control strategy. METHODS: The schistosomiasis epidemic monitoring reports, annual reports, relevant information about Oncomrnelania hupensis snails, and schistosomiasis patient conditions were collected and analyzed for epidemic condition and characteristics of schistosomiasis in Yunnan Province from 2009 to 2012. RESULTS: The various epidemic monitoring indicators all decreased. In 2012, compared with 2009, the prevalence reduced by 33.33% after correction; the number of villages with schistosomiasis patients reduced by 55.56%; the adjusted positive rate of livestock stool tests reduced by 45.45%; the number of villages with infected cow reduced by 42.25%; the actual area with snails reduced by 13.58%; the density of living snails reduced by 25.66%, and no schistosome infected snails were found in 2012. CONCLUSION: There still exist schistosome infections in human and animals in some local areas of Yunnan Province, and it is difficult to achieve the standard of schistosomiasis transmission interrupted in a short period.

[Effect of water- saving irrigation engineering on schistosomiasis control in Eryuan County of Yunnan Province].

OBJECTIVE: To evaluate the effect of a water-saving irrigation project on schistosomiasis control. METHODS: The Oncomelania snail situation before and after the water-saving irrigation project was investigated, and the data of snails and schistosomiasis of people in the area of the water-saving irrigation engineering were collected and analyzed statistically. RESULTS: The incidence of frames with snails declined from 10.70% to 2.27% after actualized water-saving irrigation project, and the snail density declined from 0.42 snails/0.1 m(2) to 0.10 snails/0.1 m(2). The snails were eliminated in 57% of the ditches. The snail area and schistosome infection rate of residents declined obviously. CONCLUSION: The water-saving irrigation project is effective in schistosomiasis control and has good social and economic benefits.

[Evolution of schistosomiasis control and prevention strategies in hilly regions with schistosomiasis endemic in China].

This article expatiates the epidemiological characteristics, the evolution process of control and prevention strategies and measures in hilly regions with schistosomiasis endemic, especially the research progress and obstacle factors existed in the implementation process of the comprehensive strategy focused on controlling infection source, aiming at providing references for the hilly regions to reach transmission interrupted standard.

[Effect of a novel plant molluscicide "Luo-wei" against Oncomelania hupensis in plateau mountain areas].

OBJECTIVE: To evaluate the effect of a novel plant molluscicide, 4%"Luo-wei" (Tea-seed distilled saponins, TDS) against Oncomelania hupensis snails in plateau mountain areas in Yunnan Province. METHODS: The immersing and spraying experiments were carried out in the ditches and grassland of Xiaolian Administrative Village in Heqing County, Yunnan Province, to assess the molluscicidal effect of 4% TDS comparing with 50% wettable powder of niclosamide ethanolamine salt (WPN) in different environments and time. RESULTS: After immersion for 24, 48 h and 72 h, the snail death rates were 70.67%, 87.33% and 98.67% in the TDS group, whereas being 77.33%, 96.67% and 100.00% in the WPN group, respectively. The differences of the death rates between the two groups 24 h and 72 h after immersing were not statistically significant ( chi2(24h) =1.73, chi2(72h) = 2.01, both P values > 0.05). Seven days after the immersing experiments, the occurrence rate of frames with living snails and the death rate of snails were 20.00% and 93.03% in the TDS group, while those were 13.33% and 95.76% in the WPN group, and there were no significant differences of the 2 indexes between the 2 groups ( chi(2)(Occurrence rate) = 2.27, chi(2)(Death rate) = 0.94, all P values > 0.05). After spraying for 1, 3, 7 d and 15 d, in both groups, the occurrence rates of frames with living snails and the average densities of living snails gradually declined, while the death rates of snails gradually increased with the extension of time. There were no statistically significant differences of the above 3 indexes between the 2 groups (all P values > 0.05). Fifteen days after the spraying experiment, the occurrence rate of frames with living snails and the adjusted death rate of snails were 15.00% and 87.39% in the TDS group and those were 16.67% and 89.32% in the WPN group, respectively. CONCLUSION: The molluscicidal effect of TDS is satisfying in plateau mountain areas, and the molluscicide is worthy of further extension and application.

[Investigation on infection sources of schistosomiasis in mountainous regions, Nanjian County, Yunnan Province].

OBJECTIVE: To understand the types of schisotsome infection sources and their roles in schistosomiasis transmission in mountainous endemic regions in Yunnan Province, so as to provide the evidence for implementing the comprehensive control measures based on infection source control. METHODS: Two villages of typical mountainous regions in Nanjian County were chosen for field investigation. The Oncomelania hupensis snail status was surveyed by the methods of systematic and environmental sampling. The infections of schistosomiasis were surveyed in residents with the indirect haemagglutination and the hatching method, in livestock with the hatching method and in wild animals with the anatomical method and the hatching method. The distribution and pollution status of wild faeces were investigated in the snail environments nearby villages or with livestock frequent activities. The positives of schistosomiasis in wild faeces were tested with the hatching method. The pollution index of wild feces was calculated. RESULTS: A total of 533.56 hm2 were investigated in two villages, and the area with snails was 16.52 hm2. The rate of frame with snails was 1.03%, the average density of snails was 0.07 snails/0.1 m2, and no positive snails were found. The positive rate of blood examinations of population was 1.61%, but no persons were positive with the hatching method. The infection rates were 0.90%, and 0.62% in cattle and equus, respectively, and there were no positives in other livestock. Totally 472 piles of wild feces of 6 species (human, cattle, equus, goat, pig and dog) distributed in the investigation areas, and among them, the densities of wild feces of cattle, equus, and dog were 7.2, 4.3 piles/hm2, and 2.1 piles/hm2 respectively, being relatively higher than others. The hatching positive rates of wild faeces of cattle, equus, and dog were 2.27% (3/132), 2.63% (2/76), and 3.70% (1/27), respectively. The relative pollution indexes of wild faeces of cattle, equus, and dog were 80.68%, 15.89%, and 3.43%, respectively. CONCLUSIONS: After schistosomiasis transmission is controlled, the potential epidemic factors still remain in the mountainous endemic regions of schistosomiasis in Yunnan Province. The cattle are still the most infection source of schistosomiasis, but equus and dog as infection sources should be not neglected. We should extend the investigation and monitor scope of the infection sources, and carry out scientific and feasible control technique and management measures.

[Surveilance and response for Schistosomiasis japonica based on sentinel mice examination for cercariae-infested water in risk region, 2012].

OBJECTIVE: To monitor water body infestation in schistosomiasis high-risk areas with sentinel mouse technique. METHODS: A total of 72 surveillance sites from 47 counties were selected in Hunan, Hubei, Jiangxi, Anhui, Jiangsu, Yunnan, and Sichuan. The water infectivity of Schistosoma japonicum was determined in the surveillance sites by using sentinel mice during June-July and September, 2012. RESULTS: Among the 3,283 sentinel mice which were placed in 72 sites, 3,062 (93.3%) were recovered and dissected. Infected sentinel mice were found in six sites accounting for 8.3% (6/72) of the total surveillance sites, with an occurrence rate of sites with infected mice of 8.3% in June-July and 2.8% in September. 33 infected mice were discovered with a total infection rate of 1.08% (33/3,062). 1,085 adult worms were collected, with a mean worm burden of 32.9 worms per mouse in infected sentinel mice. 4 positive sites were in Hunan and 2 were in Jiangxi. Local acute schistosomiasis or suspected local acute cases which detected elsewhere were reported in 2 positive sites. Some follow-up activities were conducted in the 6 positive sites. CONCLUSION: Compared with those in 2010, the schistosomiasis risk areas are shrinking in 2012. However, some regions are still the schistosomiasis high-risk areas.

[Surveillance and forecast of Schistosoma japonicum-infected sentinel mice in key water regions of China in 2010].

OBJECTIVE: To explore the approach and tool for surveillance and forecast of schistosomiasis, so as to provide scientific evidence for improving the sensitivity of the surveillance and forecast system of schistosomiasis. METHODS: Two field detections were carried out in June and September by using the determination of sentinel mice in key high-risk water regions of 7 provinces of Hunan, Hubei, Jiangxi, Anhui, Jiangsu, Yunnan and Sichuan, and the sentinel mice were raised in laboratory and dissected for observation of schistosome infections. The database regarding schisosome infections in key water regions of China was established, and the tempo-spatial distribution and environmental features of the national surveillance and forecast sites with positive sentinel mice were analyzed. RESULTS: A total of 72 surveillance and forecast sites were detected in 34 counties (cities, districts) of 7 provinces. Of the 2 667 sentinel mice placed, 2 613 were recovered, with a recovery rate of 97.98%. Among the 72 sites detected, 17 were detected with positive sentinel mice, and the occurrence rate of positive sites was 23.61%. The occurrence rate was 17.24% (10/58) in June and 14.71% (10/68) in September, and no significant difference was observed between two batches (chi2 = 0.151, P = 0.698). Of the 2 436 sentinel mice dissected, 90 were positive, and 459 schistosome worms were collected, with a total infection rate of 3.69%, and the mean worm burdens of positive mice were 5.10 worms per mouse. The infection rate of sentinel mice was 2.82% (31/1 099) in June and 4.41% (58/1 337) in September, the infection rate of sentinel mice was significantly higher in September than that in Juen (chi2 = 14.681, P < 0.01), and the mean worm burdens of infected sentinel mice were 2.45 worms per mouse in June and 6.49 worms per mouse in September. The occurrence rates of the positive sites with infected snails detected in the study year, last year and without infected snails detected in recent 3 years were 29.63%, 41.67% and 12.12%, respectively, and no significant differences were detected (chi2 = 5.227, P = 0.071). The infection rates of sentinel mice in the aforementioned 3 settings were 9.38%, 3.98% and 0.59%, respectively, and there was significant difference observed (chi2 = 20.489, P < 0.01). CONCLUSIONS: The monitoring results of sentinel mice infections in key water regions can almost reflect the endemic situation of schistosomiasis in local areas. Notably, many infections are detected in settings without infected snails detected in recent years. The monitoring of sentinel mice infections could significantly improve the sensitivity of the surveillance and forecast system of schistosomiasis.

[Effects of three kinds of molluscicides in fields of mountainous areas of Yunnan Province].

The molluscicidal effects of 10% salt of quinoid- 2' ,5-dichloro-4'-nitrosalicylanilide (LDS) with dusting method, 26% amine molluscicide (MNSC) and 50% niclosamide (WPN) with insufflation method were tested in the fields of mountainous areas of Yunnan Province. After 7, 15 and 30 days of the tests, the death rates of snails, decline rates of living snail densities, and occurrence rates of frames with living snails of the 10% LDS group were 72.69%-87.16%, 74.10%-88.84%, and 20.00%-30.00%, respectively; those of the 26% MNSC group were 66.21%-91.06%, 69.55%-91.36%, and 19.44%-27.78% respectively; those of the 50% WPN group were 78.10%-90.18%, 82.44%-91.60%, 17.50%-20.00%, respectively. The results showed that the molluscicidal effects of 10% LDS, 26% MNSC and 50% WPN were basically equal.

[Molluscicidal effect of suspension concentrate of metaldehyde and niclosamide in fields of mountainous areas in Yunnan Province].

OBJECTIVE: To evaluate the molluscicidal effect of 26% suspension concentrate of metaldehyde and niclosamide (MNSC) in the fields of mountainous areas in Yunnan Province. METHODS: Some representative Oncomelania snail environments of schistosomiasis endemic regions were selected as study areas in Heqing County, Yunnan Province and 26% MNSC and 50% wettable powder of niclosamide ethanolamine salt (WPN) were used to kill the snails with the mechanical spraying and sprinkler spraying methods respectively. RESULTS: Seven, 15, 30 days after the spraying with the mechanical spraying method, in corn fields, the snail mortality rates were from 88.68% to 92.88% in the MNSC group, and from 89.86% to 90.32% in the WPN group respectively, and in the ditch, the snail mortality rates were from 89.97% to 94.46% in the MNSC group and from 90.08% to 96.74% in the WPN group respectively, and there was no significant difference between the 2 groups (P > 0.05); 7, 15, 30 days after the spraying with the sprinkler spraying method, in corn fields, the snail mortality rates were from 66.14% to 89.11% in the MNSC group, and from 78.40% to 91.22% in the WPN group, respectively, in the ditch, the snail mortality rates were from 84.13% to 94.27% in the MNSC group, and from 85.81% to 95.26% in the WPN group respectively, and there was no significant difference between the 2 groups (P > 0.05). CONCLUSION: 26% MNSC has good molluscicidal effect in the fields of mountainous areas in Yunnan Province

[Relationship between environmental remote sensing alternate indexes and Oncomelania snail distribution in hilly and mountainous areas].

OBJECTIVE: To analyze the relationship between Oncomelania snail distribution and environmental remote sensing indexes in hilly and mountainous areas. METHOD: The normalized different vegetation index (NDVI), land surface temperature (LST), humidity index (Wetness) of 85 snail spots in Dali City were extracted for statistical analysis by TM image, and the land-use types were classified. LST, NDVI, Wetness, snail density and land-use types were overlaid and analyzed by using a weight of suitability model of ArcGIS 9.2, and snail appropriate distribution range in Dali City was calculated. RESULTS: The distribution of LST, NDVI, Wetness values of the investigated snail points were approximately normal, and most of the snail points distributed nearby the average values of the remote sensing alternate indexes, then gradually reduced to the ends. More than 90% of the snail spots were distributed in the land type with crops and grassland. The environments in Dali City were divided into unsuitable snail environment (0-14 points), suitable snail environment (15-21 points), and optimum snail environment (22-26 points) by the weight suitability mode. CONCLUSIONS: Environmental remote sensing indicators can reflect the environmental factors affecting snail distribution directly. Combining remote sensing with GIS and field survey can describe, judge and forecast the distribution of snails.