Liang Ys

A novel molluscicidal formulation of niclosamide

Snail control by molluscicides is an important strategy for schistosomiasis control in China. Currently, only one chemical molluscicide, niclosamide, which is used as 50% wettable powder of niclosamide ethanolamine salt (WPN), is commercially available for field snail control in China. However, WPN is costly, toxic, and has a lower dispersibility and precipitates rapidly. In this paper, we describe the development of a novel formulation of niclosamide, a suspension concentrate of niclosamide (SCN). The efficacy of SCN was evaluated both in the laboratory and field. SCN showed better molluscicidal effects than conventional formulation of WPN, as determined by LC50 for adult snails, young snails, and snail eggs. The acute toxicity of SCN to Brachdanio rerio hamiton was less than WPN. In conclusion, the novel formulation of SCN suspension is physically more stable, more effective, and less toxic. Therefore, it can be more useful for controlling snails in endemic areas of schistosomiasis in China.

Is there reduced susceptibility to praziquantel in Schistosoma japonicum? Evidence from China.

Praziquantel is widely used for the treatment of human schistosomiasis. However, in recent years, there has been increasing concern about the resistance of Schistosoma species to praziquantel. The study described here was designed to evaluate the current susceptibility to praziquantel in S. japonicum in China. During the non-transmission period of schistosomiasis, a random sample of 4760 subjects from the main endemic foci of China were examined using parasitological stool examination. In total, 584 subjects were identified as being infected with S. japonicum, with a prevalence rate of 12.27%. Among them, 565 stool-egg-positive subjects were treated with praziquantel in a single oral dose of 40 mg/kg. Six weeks post-treatment, among the 505 villagers re-examined, 480 (95.05%) had no detectable S. japonicum eggs. Twenty-one subjects still excreting eggs after the first treatment were treated with praziquantel for the second time. All stool samples, including those from those participants with second treatment were re-examined 6 weeks after the second treatment, and no stool-egg-positives were found. The results indicate that the current efficacy of praziquantel against S. japonicum is still high and has not changed after more than 2 decades of repeated, expanded chemotherapy in the main endemic areas of China. It is suggested that no evidence of tolerance or resistance to praziquantel in S. japonicum was detected in China.

Spatio-temporal analysis to identify determinants of Oncomelania hupensis infection with Schistosoma japonicum in Jiangsu province, China

BackgroundWith the successful implementation of integrated measures for schistosomiasis japonica control, Jiangsu province has reached low-endemicity status. However, infected Oncomelania hupensis snails could still be found in certain locations along the Yangtze river until 2009, and there is concern that they might spread again, resulting in the possible re-emergence of infections among people and domestic animals alike. In order to establish a robust surveillance system that is able to detect the spread of infected snails at an early stage, sensitive and reliable methods to identify risk factors for the establishment of infected snails need to be developed.MethodsA total of 107 villages reporting the persistent presence of infected snails were selected. Relevant data on the distribution of infected snails, and human and livestock infection status information for the years 2003 to 2008 were collected. Spatio-temporal pattern analysis including spatial autocorrelation, directional distribution and spatial error models were carried out to explore spatial correlations between infected snails and selected explanatory factors.ResultsThe area where infected snails were found, as well as their density, decreased significantly between 2003 and 2008. Changes in human and livestock prevalences were less pronounced. Three statistically significant spatial autocorrelations for infected snails were identified. (i) The Moran’s I of infected snails increased from 2004 to 2007, with the snail density increasing and the area with infected snails decreasing. (ii) The standard deviations of ellipses around infected snails were decreasing and the central points of the ellipses moved from West to East. (iii) The spatial error models indicated no significant correlation between the density of infected snails and selected risk factors.ConclusionsWe conclude that the contribution of local infection sources including humans and livestock to the distribution of infected snails might be relatively small and that snail control may limit infected snails to increasingly small areas ecologically most suitable for transmission. We provide a method to identify these areas and risk factors for persistent infected snail presence through spatio-temporal analysis, and a suggested framework, which could assist in designing evidence based control strategies for schistosomiasis japonica elimination.

Effect of an integrated control strategy for schistosomiasis japonica in the lower reaches of the Yangtze River, China: an evaluation from 2005 to 2008

BackgroundSchistosomiasis japonica remains a major public health concern in China. There are many interventions implemented to control the transmission of the disease. The purpose of the present study was to investigate the effects of an integrated control strategy for schistosomiasis control.MethodsAn integrated control strategy for schistosomiasis japonica with emphasis on removing cattle from snail-infested grasslands, providing farmers with mechanized farm equipment, improving sanitation by supplying tap water and building lavatories and latrines and providing boats with fecal-matter containers was implemented in 107 villages of the lower reaches of the Yangtze River, Jiangsu Province, China, during a 32-month period from May 2005 to 2008, and the effectiveness was investigated.ResultsFollowing the effects of the comprehensive control, the snail habitat, infected snail habitat, snail infection rate, and S. japonicum prevalence in both humans and livestock all appeared a declining trend year by year, with reductions of 47.88%, 94.29%, 92.55%, 96.94%, and 100% compared with those before the comprehensive control. In addition, all of the 17 counties achieved the infection control in 2007, and 7 reached the criteria of transmission control in 2008. The confirmed snail habitats reduced from 107 to 20, and the acute infections have also been controlled for 2 successive years since 2007.ConclusionsThe integrated control strategy for schistosomiasis japonica is effective to control the transmission of S. japonicum.

The South-to-North Water Diversion Project: effect of the water diversion pattern on transmission of Oncomelania hupensis, the intermediate host of Schistosoma japonicum in China

BackgroundThe South-to-North Water Diversion Project (SNWDP) is the largest national water conservancy project in China. However, the Eastern Route Project (ERP) of SNWDP will refer to the habitats of Oncomelania hupensis, the intermediate host of Schistosoma japonicum. The present study was aimed at investigating the effects of some factors relating to the water diversion pattern on the spread north of O. hupensi s and transmission of S. japonicum.MethodsMarked snails were attached to the floating debris, and then placed on the water surface, the passage of snails through water pumps was observed. Some marked living adult snails were placed under water in the 5 spots, 15, 30, 60, 90 and 120 days later, their survival and transfer under water were investigated. 2, 4, 8, 16, 32, 64 and 128 juvenile snails, with a male: female ratio of about 1, were caged, 1 year later, their reproductions were calculated.ResultsThe snails attached on the floating debris at 100-, 50- and 20-cm-distance from the inlet pipe of the big pump (with a diameter of 80 cm), could be absorbed into the pumps, with passing rates of 2.45%, 3.93% and 43.46%, respectively, compared with 72.07% and 91.00% for the snails at 20 cm and 10 cm-distance from the inlet pipe of the small pump (with a diameter of 20 cm). A total of 36,600 marked living snails were put into 5 ponds and ditches, with the water depths of 1-1.6 m, 15-120 days later, no marked ones were found along the ponds and ditches or in the straw packages. The juvenile snails did not reproduce until their density reached up to 8 snails (ratio of male: female of 1)/0.16 m2.ConclusionsDuring the construction of ERP of SNWDP, the risk of northward spread of schistosomiasis japonica will be decreased or eliminated as long as long-term reliable interventions for snail control are implemented.

African schistosomiasis in mainland China: risk of transmission and countermeasures to tackle the risk

Schistosomiasis is a major disease of public health importance in humans occurring in 76 countries of the tropics and sub-tropics. In China, schistosomiasis japonica is one of the highest priorities in communicable disease control defined by the central government. Since 1970s, the habitats of Biomphalaria straminea, an intermediate host of Schistosoma mansoni in South America, have been identified in Hong Kong Special Administrative Region and Shenzhen city, Guangdong province of China. With the sharp growth in the China-aided projects in Africa and labor services export to Africa, a gradual rise in the cases infected with S. haematobium or S. mansoni is reported in those returning from Africa to China. The existence of intermediate snail hosts and import of infectious source of schistosomiasis results in concern about the transmission of African schistosomiasis in mainland China in the context of global climate change. This paper evaluates the risk of transmission of African schistosomiasis in China, and proposes countermeasures and research priorities to tackle the risk.

A Google Earth-based surveillance system for schistosomiasis japonica implemented in the lower reaches of the Yangtze River, China

BackgroundDue to the success of the national schistosomiasis control programme in China, transmission has been sufficiently reduced in many areas to severely limit identification of areas at risk by conventional snail surveys only. In this study, we imported Google Earth technology and a Global Positioning System (GPS) into the monitoring system for schistosomiasis surveillance of the banks of the Yangtze River in Jiangsu Province, China.MethodsA total of 45 sites were selected and the risk was assessed monthly by water exposure of sentinel mice at these sites from May to September in 2009 and 2010. The results were assembled and broadcast via the Google Earth platform.ResultsThe intensity of schistosomiasis transmission showed peaks of risk in June and September of 2009, while there was only one small peak in June in 2010 as the number of detected positive transmission sites dropped dramatically that year thanks to improved mollusciciding. River ports were found to be areas of particular risk, but ferry terminals and other centres of river-related activities were also problematic.ConclusionsThe results confirm that the surveillance system can be rapidly updated and easily maintained, which proves the Google Earth approach to be a user-friendly, inexpensive warning system for schistosomiasis risk.

The Sensitivity of Schistosoma japonicum to Praziquantel: A Field Evaluation in Areas with Low Endemicity of China

The purpose of the current study was to investigate the susceptibility of Schistosoma japonicum to praziquantel in low endemic foci of China. During the non-transmission period of schistosomiasis, a total of 43 of 1,242 subjects were identified as being infected with the parasite using parasitological stool examinations in two low-endemicity areas of China, with a prevalence rate of 3.46%. All stool-egg-positive subjects were treated with praziquantel in a single oral dose of 40 mg/kg or 30 mg/kg for two successive days. Six weeks post-treatment, no S. japonicum eggs were detected in the 43 treated villagers. The results indicate that the current efficacy of praziquantel against S. japonicum seems satisfactory and has not changed over the past three decades in the low endemic areas of China. It is also suggested that no evidence of tolerance or resistance to praziquantel in S. japonicum is detected in areas with low endemicity in China.

Resistance to niclosamide in Oncomelania hupensis , the intermediate host of Schistosoma japonicum : should we be worried?

As the currently only available molluscicide, niclosamide has been widely used for snail control for over 2 decades in China. There is therefore a concern about the emergence of niclosamide-resistant snail populations following repeated, extensive use of the chemical. The purpose of this study was to investigate the likelihood of niclosamide resistance in Oncomelania hupensis in China. Active adult O. hupensis snails derived from 20 counties of 10 schistosomiasis-endemic provinces of China, of 10 snails in each drug concentration, were immersed in solutions of 1, 0.5, 0.25, 0.125, 0.063, 0.032, 0.016 and 0.008 mg L-1 of a 50% wettable powder of niclosamide ethanolamine salt (WPN) for 24 and 48 h at 25 °C, and the median lethal concentration (LC50) was estimated. Then, the 24- and 48-h WPN LC50 values were compared with those determined in the same sampling sites in 2002. The results indicated that the 24- and 48-h WPN LC50 values for O. hupensis were not significantly different from those determined in 2002 (P = 0.202 and 0.796, respectively). It is concluded that the current sensitivity of O. hupensis to niclosamide has not changed after more than 2 decades of repeated, extensive application in the main endemic foci of China, and there is no evidence of resistance to niclosamide detected in O. hupensis.

A strategy for emergency treatment of Schistosoma japonicum-infested water

BackgroundSchistosomiasis japonica, caused by contact with Schistosoma japonicum cercaria-infested water when washing, bathing or production, remains a major public-health concern in China. The purpose of the present study was to investigate the effect of a suspension concentrate of niclosamide (SCN) on killing cercaria of S. japonicum that float on the water surface, and its toxicity to fish, so as to establish an emergency-treatment intervention for rapidly killing cercaria and eliminating water infectivity.ResultsAt 30 min after spraying 100 mg/L SCN, with niclosamide dosages of 0.01, 0.02, 0.03, 0.04 g/m2, the water infectivity reduced significantly and no infectivity was found at 60 min after spraying SCN. The surface of static water was sprayed with 100 mg/L SCN, the peak concentration was found at 0 min, and the solution diffused to site with a water depth of 10 cm after 10 min. 30 min later, SCN diffused to the whole water body, and distributed evenly. After spraying 100 mg/L SCN onto the surface of the water with a volume of(3.14 × 202×50)cm3, with niclosamide dosages of 0.02 g/m2, 96 h later, no death of zebra fish was observed.ConclusionsBy spraying 100 mg/L SCN, with a niclosamide dosage of 0.02 g/m2 onto the surface of S. japonicum-infested water, infectivity of the water can be eliminated after 30-60 min, and there is no evident toxicity to fish. This cercaria-killing method, as an emergency-treatment intervention for infested water, can be applied in those forecasting and early warning systems for schistosomiasis.