| Schistosomiasis is one of the most serious parasitic diseases,it is widely prevalent in many countries and regions like Asia,Africa and South America and so on.China is a schistosomiasis endemic area of Schistosomiasis japonicum.At present,many regions have reached the level of transmission blocking.However,with the acceleration of the global integration process,the number of imported schistosomiasis cases in China has shown an upward trend.If it is not taken seriously,it is likely to cause outbreak of imported schistosomiasis in our country.Schistosomiasis mansoni is mainly prevalent in many regions such as the tropical and subtropical regions of Africa,the Middle East and the Americas.It is a zoonotic disease that seriously endangers the health of people in the affected areas and hinders social and economic development.Many species of snails in the Biomphalaria genus can naturally infect one or more strains of Schistosoma mansoni,but their susceptibility varies.Among them,Biomphalaria straminea is one of the intermediate hosts of Schistosoma mansoni,and it is an important transmission link in many areas of schistosomiasis.The Biomphalaria straminea is a special freshwater aquatic snail,mainly distributed in many regions such as Africa and Americas.However,there have been cases of spread out of the domain.Since the first discovery of Biomphalaria straminea in Hong Kong in the 1970s,it has spread to many waters in Guangzhou and Shenzhen.In view of its use as an intermediate host for the transmission of schistosomiasis mansoni,and the current increase in the number of floating population in China,especially a large number of people traveling to and from the endemic area of schistosomiasis,it may carry the source of disease into the Biomphalaria straminea habitat,There is a potential risk of an outbreak of schistosomiasis mansoni.Therefore,this paper studies the ecological characteristics of Biomphalaria straminea and its spread in southern China,predicts the risk of disease transmission,and studies the sensitivity of Biomphalaria straminea to niclosamide.The prevention and control of Biomphalaria straminea provides ideas and technical reserves.Objective:1.To study the hatching rules of Biomphalaria straminea,compare the differences of autologous and allogeneic reproduction of the snails,and observe the differences in the effects of light and temperature on the snails lay eggs,Survival rate anout snails in the environment of lack of food and water shortage.designed to provide a scientific reference for on-site prevention and control.2.Predict the trend and risk of the spread of Biomphalaria straminea from the southern coastal provinces to the inland and other provinces.3.To study the killing effect of niclosamide on Biomphalaria straminea,and provide scientific guidance and technical reserve for the prevention of Biomphalaria straminea.Methods:1.Observe and record the hatching process of the snail eggs at 25°C,understand the hatching cycle and regularity,and study the development time from the growth of the snail eggs to the adult snails.Under laboratory conditions,a single snail egg was separately hatched and raised separately to cultivate the self-fertilized Biomphalaria straminea;the multiple-egg collective hatching and concentrated feeding method was used to cultivate the all-natural reproductive snail.Compare the differences in spawning conditions between the two and the differences in the hatching of snail eggs.The snails were placed in 24 hours of continuous illumination;avoid light for 24h;12 hours of nighttime illumination and 12 hours of nighttime illumination（25℃）.Observe and record the number of eggs laid in one week.Number of eggs,explore the influence of lighting factors on their spawning.Place 30 adult snails into a constant temperature incubator at different temperatures,observe and record the spawning situation within 15 days.Exploring the temperature range at which snails can lay eggs。The snail was placed on a dry sponge,observe and record the survival number with time at 25℃.2.Biological methods were used to determine the extreme temperature and average generational effective accumulated temperature of the adult snail、the young snail and the snail eggs,and collect meteorological data of Hainan,Guangdong,Guangxi,Fujian,Zhejiang,Shanghai,Jiangsu.,Anhui,Hubei,Hunan,Jiangxi,Chongqing,Guizhou,Yunnan,Sichuan,all 15 provinces,380 meteorological monitoring points in 2010-2016,established a database,using GIS software to analyze the areas where Biomphalaria straminea may spread.3.The 25%niclosamide suspension was formulated into a solution with effective concentrations of 0.125 mg/L,0.063 mg/L,0.032 mg/L,0.016 mg/L,and 0.008 mg/L.The young snails and adult snails were placed in the corresponding concentration of liquid for 24h,48h,and 72h（the control group was set,the control solution was dechlorinated water）,and then washed with dechlorinated water for 3 times.After 24hours of resuscitation,the life and death were identified by clear water resuscitation.LC50 and LC95 were calculated according to Linear weighted regression.The effective concentration of 25%niclosamide suspension is 0.030 mg/L,0.025 mg/L,0.020 mg/L,0.015 mg/L,0.010 mg/L,0.005 mg/L,respectively.The snail egg was immersed in the drug solution（the control group was set,the control solution was dechlorinated water）,and placed in a 25℃incubator for 24h,48h,and 72h,then rinsed with dechlorinated water for 3 times,and then placed in a 25℃incubator for incubation.Observe and record the number of hatching,the total number minus the number of hatching is the number of deaths,and calculate LC50 and LC95 according to linear weighted regression.Results:1.It takes 9 days for the snail to hatch from the snail to the young snail.The snail is developed from the snail to the spawning snail.The average developmental duration is129.27±14.21 days.Compared with autologous and allogeneic fertilization of snails,the peak number of eggs and the total number of eggs produced by snails under allogeneic conditions were 13.03±3.91 and 268.07±71.36,both of which were higher than the peak of autologous reproduction（9.13±3.10,170.83±53.48）is large,and the peak duration of spawning is also significantly higher than that of autologous reproduction.In the hatching rate of snail eggs,the hatching rate of snail eggs in allogeneic group is 69.40%,and the hatching rate of snail eggs in autologous reproductive group Compared with62.16%,the statistical analysis showed that P>0.05,which was not statistically significant,that is,there was no difference in hatching rate between the two groups.The number of eggs laid by snails under light conditions was greater than that aviod light conditions.The 24h light group,the 24h light group and the 12h light group were compared.The statistical analysis showed p<0.01.that is statistically significance,there is a significant difference between the groups,which proves that the light has a promoting effect on the spawning of Biomphalaria straminea.The temperature range of adult snail laying is 9.6432.21℃.In the laboratory,snails can survive for up to 67 days in the absence of water and food in the laboratory.Within two months,15%of the snails can recover and carry out life activities.2.The half-lethal hypothermia and lethal low temperature of the survival of the snails were 5.33℃and 4.23℃,and the half-lethal high temperature and lethal high temperature were 36.31℃and 38.04℃.The half-lethal low temperature and lethal low temperature of the young snail survival were respectively At 5.44℃and 3.45℃,the half lethal high temperature and lethal high temperature were 31.69℃and 33.52℃;the half lethal low temperature and lethal low temperature of the snail survival were 4.01℃and 2.96℃,and the half lethal high temperature and lethal high temperature were 32.47℃and 33.32℃.The average accumulated effective temperature of the generation is2684.94±295.14（day·degree）.Combined with the half-lethal low temperature and high temperature data and the average daily temperature in January and July of 2016,the data of the study area was interpolated by the inverse distance weighted interpolation method,and the map was displayed by ArcGIS software to predict and analyze the snail in In some parts of Hainan,Guangxi,Guangdong,Fujian,and Yunnan have high survival risks.It is likely to spread to the above areas from the breeding areas of Guangzhou and Shenzhen,and parts of Hunan,Jiangxi,Zhejiang,and Guizhou provinces.The spread risk is medium,and the risk of spread in other areas is low.According to the laboratory conditions,the effective accumulated temperature of the average generation of the double-umbilical snails of the mast and the average monthly temperature of the2010-2016 estimated the number of generations of the double-umbilical snails after the diffusion of the snails,the analysis shows that in Hainan Province,Guangxi Province,In the small parts of Guangdong Province and Fujian Province and Yunnan Province,the number of snail generations is 2 generations or more,there is a risk of colonization of reproduction.3.The sensitivity of the snail to niclosamide was higher.The median lethal dose of25%niclosamide suspension to the snails of the double umbilical snail for 24h,48h and72h was 0.013mg/L,respectively.The median lethal doses of 0.014mg/L and 0.010mg/L for 24h,48h and 72h of young snails were 0.014mg/L,0.013mg/L and 0.013mg/L,respectively,and the snail eggs were immersed for 24h,48h,72h,The median lethal doses at were 0.013mg/L,0.013mg/L,and 0.011mg/L.Conclusion:1.Biomphalaria straminea has a shorter incubation time.The snail can reproduce the offspring through autologous fertilization and allogeneic fertilization.The fertility of the two snails is significantly different with time.The snail fertility of allogeneic reproduction is slightly better than autologous reproduction.The existence of adult snail,young snail and snail egg alone may promote the snail population by autogenous reproduction under suitable environmental conditions.Illumination factors can promote the increase of egg production in the snail.At 25°C,the snails can survive for 67 days without leaving the water,suggesting that the snails will not die in a short period of time due to drought and lack of food,and should cope with drought,lack of food,etc.The ability to condition environmental conditions is strong,easy to spread,colonize,and pose a potential risk to the spread of schistosomiasis.2.The snail has been invaded and colonized in Hong Kong,Guangzhou and other places in China,and it has further spread to other parts of Guangdong Province,Hainan Province,Guangxi Province,Yunnan Province and Fujian Province.The risk degree is from south.A downward trend is presented to the north.3.The snail is more sensitive to niclosamide,and the 25%niclosamide suspension has better killing effect on the snail,young snail and snail egg（the half-lethal dose in 72h is0.013mg/L,0.013mg/L,0.011mg/L）.At its effective median lethal dose,toxic doses affecting mollusks,fish,aquatic crustaceans,and aquatic plants in water have not been reached[1].It can be used as a reserve snail-killing drug for controlling the snail... |
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