[Development and application of Jingcen DY-1 spraying tanker for Oncomelania hupensis snail control].

OBJECTIVE: To develop a Jingcen DY-1 type spraying tanker for Oncomelania hupensis snail control and evaluate its effect of field application as well as the cost. METHODS: The currently available tractor was used as a vector, and the mechanical and electrical equipments and containers were integrated with shafts, pipelines and electric lines to produce a spraying tanker for snail control, with the functions of carrying people and molluscicides, generating electric power and getting water, mixing stocking solutions, adjusting molluscicide solutions evenly, and spraying drugs. The volume of the molluscicide solution, flow rate of water injection, and the flow rate, range and advance speed of the spray gun were tested, and the solution concentrations of molluscicide in the tanker and at the muzzle of the spray gun at different time were detected. Meanwhile, the molluscicidal effect and cost of the spraying tanker were analyzed by the field test. RESULTS: The volume of the liquid storage pot of the Jingcen DY-1 type spraying tanker was 1 800 L, the flow rate of water injection was 400 L/min, the flow rate and the spray range of the standard spray gun were 110-200 L/min and 19.70-23.50 m, respectively, the efficiency of drug spraying of the spraying tanker was 6 000 m/h, and the ratio of spray width (m) to march speed (m/min) was 1:200. When 5 min post mother liquid recirculating, the average concentration of the molluscicide at the upper-, middle- and lower-layers of the liquid storage pot was (1030.39 ± 43.00) mg/L, with a variation coefficient of 4.17%. The average concentration of the molluscicide in the spraying process (spraying for 2, 4, 6, 8, 9 min) was (953.00 ± 68.87)mg/L, with a variation coefficient of 7.22%. The concentration of the residual drug in the liquid storage pot post spraying was 1 000.43 mg/L, which reached the effect concentration for snail control. After spraying for 7 days in the field, the average density of living snails reduced by 88.20% as compared to that before spraying, and the adjusted mortality of snails was 87.65%. The unit cost of Jingcen DY-1 spraying tanker was 0.086 7 Yuan/m². which reduced by 58.20% as compared to that of the conventional spraying tanker. CONCLUSIONS: Jingcen DY-1 type spraying tanker for snail control which integrates various equipments together can effectively control the concentration and dose of the molluscicide, and the machine is labor-saving, efficient, economic and well adapted, and is worthy to be widely applied.

[Classification and grading of environments with Oncomelania hupensis snails inside embankment of marshland and lake areas].

OBJECTIVE: To classify and grade the environments with Oncomelania hupensis snails inside embankment in marshland and lake areas, so as to improve the work efficiency and realize the systematic management. METHODS: The schistosomiasis endemic area Liaodi and Xiongdi villages in Jiangling County, Hubei Province were selected as the experiment villages, and the environments with snails in the two villages were divided into sections with a length of 500 m, then the snail situation were surveyed by the systematic sampling method with 10 m and 50 m a frame respectively. The environments were classified according to the discovery of infected snails and wild fecal contamination, and the numbers of sites with snails and their areas in different classes were recorded. Meanwhile, the data of sites with infected snails in Jingzhou City during the recent 5 years were collected and graded according to the average density of snails, so as to discuss the correlativity between the grades of environments with snails and the numbers of sites with infected snails and the occurrence rate of frames with snails. RESULTS: There were 1 967 sites with infected snails in Jingzhou City during the recent 5 years, and there was a positive correlation between the grades of environments with snails and the occurrence rate of frames with snails (r(s) = 0.77, P < 0.01), when the grade was 5, the constituent ratio of numbers of sites with infected snails was 3.1%, and when the grade was 2-3, the ratio raised to 56.3%. There were 39 sites with snails in the two villages, the Class 1, 2 and 3 environments included 1, 18 and 20 sites, with the areas of 1080, 51,640 m2 and 41,220 m2, respectively. There were no statistically significant difference between the grades divided by snail survey with 10 m and 50 m a frame ( chi2 = 4.667, P > 0.05), but the time-consuming of the former was 3 times of the latter. CONCLUSIONS: The classification and grading of the environments with snails inside embankment in marshland and lake areas can master the key point of the snail survey. The subsection and setting frames at a suitable distance can save time and manpower, improve work efficiency, as well as understand the distribution of snail status of the environment with snails, which can realize the sort management of the snail environments inside embankment.

[Assessment of risk factors of schistosomiasis transmission control in Jingzhou City].

OBJECTIVE: To understand the key risk factors of schistosomiasis transmission in Jingzhou City, so as to provide the evidence for improving the treatment of these risk factors. METHODS: Each village of six counties was investigated and 3 environments were surveyed each village for the distribution of Oncomelania snails and animal stools in the field. The results were analyzed and the risk factors of schistosomiasis transmission were assessed. RESULTS: The density of living snails was 0.43 snails per 0.1 m2, the frequency of the frames with snails was 9.12%, and no schistosome infected snails were found. All of the animal stools collected from the field were from bovines. The schistosome positive rate of animal stools was 37.50% (3/8) among the environments, and the schistosome infection rate of stools was 8.11% (3/37). The schistosome infection rate of animal stools was 0 near the residence living sites, and the positive rates were 12.50% and 8.33% in the ditches and slopes, respectively (chi2 = 0.07, P > 0.05). CONCLUSIONS: Bovine is still the main infectious source of schistosomiasis, i.e. the main risk factor of the disease transmission. Therefore, the strategy of controlling bovine should be strengthened.

[Molluscicidal effect of 10% LDS in fields].

OBJECTIVE: To evaluate the molluscicidal effects of 10% salt of quinoid-2', 5-dichloro-4'-nitrosalicylanilide (LDS) on Oncomelania hupensis in the fields, so as to provide the evidence for the application of LDS in the fields. METHODS: The fields where O. hupensis density was relative high were selected as the experimental area and the different concentrations of LDS were used for molluscicidal effects with the immersion, insufflation and powdering methods, and 50% wettable powder of niclosamide ethanolamine salt (WPN) was used as the control. RESULTS: With the immersion method for 3 days, the snail death rates of LDS (0.1, 0.2 g/m3) were lower than those of WPN (2 g/m3, P < 0.01), but the snail death rates of LDS (0.4, 0.6, 0.8 g/m3) were similar with those of WPN (2 g/m3, P > 0.05). With the insufflation and powdering methods for 7 days, the snail death rates of LDS (0.2, 0.4 g/m2) were lower than those of WPN (2 g/m2, P < 0.01), but the snail death rates of LDS (0.6, 0.8, 1.0 g/m2) were similar with those of WPN (2 g/mI2, P > 0.05). CONCLUSION: LDS has some molluscicidal effect.

[Relationship of schistosome infection with environment and behavioral characteristics of residents in Jingzhou area].

OBJECTIVE: To understand the relationship of schistosome infection with environment and the behavioral characteristics of residents in Jingzhou area. METHODS: The schistosomiasis patients (positive in stool examinations) were investigated with the questionnaire at home. The content of questionnaire included the hygienic and environmental situation, the behavioral characteristics of the residents, and the treatment of schistosomiasis patients. RESULTS: A total of 1 552 schistosomiasis patients were investigated, and the proportion of the patients aged from 45 to 60 years was 81.0% and the proportion of the patients aged more than 65 years was 9.7%. In Gong'an County and Jianli County, in daily life, the water contact included ditch water (0.7%), running water (43.0%), and well water (56.3%). In product activities, the water contact included farming (48.3%), fishing, and fighting flood. The peak period of water contact was from May to July. Totally 91.24% of the residents knew whether there were Oncomelania snails in their fields, and the snails could be detected in 18.6% of their fields or 10 meters around. There were 8.14% of schistosomiasis patients did not take the medicine last year, and 1 007 persons (64.88%) who took the medicine last year were re-infected in next year. CONCLUSIONS: Productive activities are the main water contact ways in the 2 counties researched. It is the key measures to change the environment and the pattern of agricultural production in rural areas for schistosomiasis control.

[Effect of modified crushing-cercariae escaping method on detection of infected Oncomelania snails in field].

OBJECTIVE: To evaluate the effect of a modified crushing-cercariae escaping method on the detection of infected Oncomelania snails in the field. METHODS: A snail survey was carried out in Jingzhou City in the spring of 2011, and the villages were randomly divided into several groups, the coincidence rates, detection rates and the labour cost of the modified crushing-cercariae escaping method and crushing method were compared. RESULTS: A total of 14 snail spots were surveyed, and the coincidence rate of the two methods was 100%. In the spring snail survey, 539 villages and 3 536 spots with snails were detected by the modified crushing-cercariae escaping method, and 671 villages and 11 375 spots with snails were detected by the crushing method. The detection rates of villages with infected snails of the two methods were 25.79% and 28.46%, respectively, the difference between them was not statistically significant (chi2 = 1.079 5, P > 0.05); and those of spots with infected snails were 5.57% and 3.66%, respectively, which had no significant difference between them (chi2 = 95.464 1, P < 0.01). Compared with the crushing method, the modified crushing-cercariae escaping method reduced labour cost by 87.86%, and saved 12.95 person-days per township. CONCLUSION: The modified crushing-cercaria escaping method can identify the spots with infected snails quickly and accurately with less labour cost, therefore, it is suitable for detecting environments with infected snails in batch in endemic areas.

[Environmental distribution and disposal measures of infected Oncomelania snails in Jingzhou City].

A survey of Oncomelania snail distribution was carried out with the systematic sampling method in combination with the environmental sampling method. A questionnaire survey was performed to find out the sites where stool examination-positive patients were infected. The results showed that there were 1 721 infected snail spots in Jingzhou City. Most of infected snail spots (94.1%) were only 500 m far away from the nearest residential areas from 2004 to 2010. About 97% of patients considered that the sites where they were infected with schistosome were only 400 meters far away from their residential areas. In conclusion, the survey with a questionnaire method in patients with positive stool examinations can quickly identify the environments with infected snails.

[Comparative evaluation of models for infectious source control of schistosomiasis in lake and marshland regions].

OBJECTIVE: To compare the effect of different models for the control of infectious source of schistosomiasis, so as to explore the control models suitable for lake and marshland regions. METHODS: The models of "replacement of cattle with machine" and "grazing prohibition and establishing fixed pasture" were implemented in 2 towns of Gong'an and Jianli counties, Hubei Province, respectively, and the data of infection situation of human and livestock, Oncomelania hupensis snail situation and the contamination status of wild faeces were collected and analyzed from 2008 to 2010. RESULTS: In 2010, for the model of "replacement of cattle with machine", the infection rate of residents in the observation group decreased by 56.82% comparing to that in 2008, the difference had a statistical significance (chi2 = 78.197, P < 0.01), and the decrease extent in the observation group was larger than that in the control group; the infection rates of cattle and snails, and the density of infected snails of the former were all decreased to 0. No wild faeces were discovered in the observation group, while 58 pieces of wild faeces were discovered but no schistosome eggs were found in these faeces in the control group. In 2010, for the model of "grazing prohibition and establishing fixed pasture", the infection rate of residents in the observation group decreased by 39.00% without a statistic significance (chi2 = 1.594, P > 0.05), and the infection rate of cattle decreased by 43.98% without a statistically significant difference (chi2 = 0.751, P > 0.05) comparing to those in 2008. The density of living snails decreased by 89.83% in the observation group, while that in the control group increased by 6.80%. A total of 11 pieces of wild faeces were collected in the observation group, with a positive rate of 18.18%, and 7 pieces were collected in the control group, all of which were negative. During the 2 years, no acute and advanced schistosomiasis patients were newly discovered. CONCLUSIONS: "Replacement of cattle with machine" and "grazing prohibition and establishing fixed pasture" are the main measures for schistosomiasis control in lake and marshland regions, the former is suitable for inner embankment regions, while the latter is suitable for the outer-embankment areas.

[Survey of causes of infected Oncomelania snails and infectious sources of schistosomiasis in marshland and lake region of Jingzhou City].

OBJECTIVE: To explore the causes of infected Oncomelania snails and the sources of infection of schistosomiasis in marshland and lake regions of Jingzhou City, so as to provide the evidence for the establishment of control strategy. METHODS: The snail environments in villages with or without cattle in Gong'an and Jianli counties, Hubei Province were selected, the snail status, infection status of people and livestock and wildlife reservoir host (mice), as well as the contamination status of wild faeces were surveyed, and the infectivity of water in investigated villages without cattle were detected by sentinel mice. The correlation between the densities of infected snails and positive faeces were tested by the rank correlation method. RESULTS: In villages without cattle, there were no positive faeces and infected sentinel mice discovered, while in the villages with cattle, 374 pieces of wild faeces were collected, the densities of wild faeces were 0.02 - 0.29 pieces/100 m2, and those of the positive ones were 0 - 0.01 pieces/100 m2, and the densities of infected snails were 0.001 - 0.040 snails /0.1 m2. The distribution of infected snails was consistent with that of the positive faeces, but the correlation coefficient between their densities had no statistical significance (r(s) = 0.123 5, P > 0.05). The average infection rates of human in villages with cattle inside embankment of Gong'an and Jianli counties were 2.87% and 1.37%, respectively, while that of the villages outside embankment of Gong'an County was 1.23%, and all the infection rates of cattle were 0. No infected wild mice were discovered. CONCLUSIONS: Human and cattle are the main sources of schistosome infection in the local areas, the possibility of wild mice as source of infection is low, and cattle is an important cause of infected snails in marshland and lake regions in Jingzhou City.