Search

BackgroundSchistosomiasis is one of the most important tropical parasitic diseases worldwide. Biomphalaria straminea, the intermediate host of Schistosoma mansoni, has invaded and spread to Southern China since 1974 and may pose enormous threats to public health. Controlling intermediate host snails is an effective strategy in schistosomiasis intervention. However, the only effective chemical molluscicide, niclosamide, currently recommended by WHO may cause environmental pollution, loss of biodiversity, and high costs. Thus, to counter intermediate hosts, a sustainable and environmentally friendly tool is urgently needed. Here, we conducted field investigations to collect and identify a potential snail competitor rotifer and evaluated its molluscicide effect.ResultsIn this study, we collected two samples of rotifers from Shenzhen. We found both red and black phenotypic B. straminea snails at the sampling sites. We identified the rotifer population as a species of the genus Philodina according to the amplification and phylogenetic analysis results of coxI gene. We found that rotifer exposure did not significantly affect the hatching rate of B. straminea eggs but promoted the killing of juvenile snails. Meanwhile, rotifer exposure did not significantly alter the fecundity of B. straminea quantified by the number of eggs per egg mass, the number of egg masses per snail, and the number of eggs per snail; but the snails exposed to rotifers showed lower fecundity performance than the control snails. Importantly, rotifer exposure could significantly affect the development of juvenile B. straminea, showing a smaller shell diameter of the exposed snails than that of the control snails. In addition, rotifer exposure affected the life span of B. straminea snails, showing a 16.61% decline in the average life span. After rotifer exposure, the S. mansoni-infected B. straminea snails died significantly faster than those without rotifer exposure. Similar findings were observed in S. mansoni-infected Biomphalaria glabrata snails. These results implied that rotifer exposure significantly promoted the mortality of S. mansoni-infected B. straminea and B. glabrata.ConclusionsOur study demonstrated the potential molluscicide effect of rotifers on intermediate hosts under laboratory conditions. Our findings may provide new insights into the development of biocontrol strategies for snail-borne disease transmission.

This article has been retracted: please see Elsevier Policy on Article Withdrawal (https://www.elsevier.com/about/our-business/policies/article-withdrawal) This article has been retracted at the request of the authors: Benjamin Sanogo, Dongjuan Yuan, Xin Zeng, Yanhua Zhang, and Zhongdao Wu. Our article reviews the evolution, geography, diversity, genetics and host-compatibility of human schistosomes and their hosts. It has come to our attention that readers have found some of the content in the article to be confusing or misleading. As authors, we have tried our best to share our scientific discovery and understanding faithfully, but we also agree that scientific reports should stand up to doubt and discussion. After serious consideration, to avoid confusion in the Schistosoma research community, we are retracting the Review. We apologize to the community for any inconvenience we have caused.

Schistosomes infect more than 200 million people worldwide, and globally, over 700 million people are at risk of infection. The snail Biomphalaria straminea, as one of the intermediate hosts of Schistosoma mansoni, consecutively invaded Hong Kong in 1973, raising great concern in China. In this study, a malacological survey was conducted over a period of four years, and investigations were performed on the mechanism of susceptibility of B. straminea to S. mansoni. B. straminea was investigated in China from 2014 to 2018. Out of 185 investigated sites, 61 were positive for stages of black B. straminea (BBS), which shows pigmented spots. Twenty of the 61 sites were positive for red B. straminea (RBS), which is partially albino and red colored. Phylogenetic analyses based on cox1 and 18S rRNA sequences demonstrated that both phenotypes were clustered with Brazilian strains. No S. mansoni infections were detected in field-collected snail. However, in laboratory experiments, 4.17% of RBS were susceptible to a Puerto Rican strain of S. mansoni, while BBS was not susceptible. The highest susceptibility rate (70.83%) was observed in the F2 generation of RBS in lab. The density of RBS has increased from south to north and from west to east in Guangdong since 2014. Five tyrosinase tyrosine metabolism genes were upregulated in BBS. Transcriptome comparisons of RBS and BBS showed that ficolin, C1q, MASP-like, and membrane attack complex (MAC)/perforin models of the complement system were significantly upregulated in BBS. Our study demonstrated that B. straminea is widely distributed in Hong Kong and Guangdong Province, which is expanding northwards very rapidly as a consequence of its adaptation to local environments. Our results suggest that B. straminea from South China is susceptible to S. mansoni, implying the high potential for S. mansoni transmission and increased S. mansoni infection risk in China., Author summary Biomphalaria straminea is an important intermediate host for the blood fluke Schistosoma mansoni. B. straminea has spread in Hong Kong and in mainland China since 1973. However, whether resident snails can transmit intestinal schistosomiasis caused by S. mansoni remains unclear. Our results revealed that different types of B. straminea are widespread in cities such as Hong Kong, Shenzhen, Dongguan, Huizhou and Puning and that the distribution of the species has shifted northwards. The most important finding was that one of the phenotypes (red phenotype of B. straminea, RBS), which is highly susceptible to S. mansoni, has spread into the city of Shenzhen since 2016. The density of RBS in Guangdong Province has increased rapidly since 2014, especially since 2016. Transcriptome analysis showed that the high expression levels of ficolin, C1q, MASP-like, and membrane attack complex (MAC)/perforin models of the complement system might be associated with the mechanism of susceptibility. Our study suggested that B. straminea is susceptible to S. mansoni, implying a high potential risk of S. mansoni transmission in South China. More attention should be paid to the potential transmission of S. mansoni, and control measures should be established to prevent the spread of this snail in South China.