Re-emergence Of Schistosomiasis Research Articles

Construction and characterization of microsatellite markers for the Schistosoma japonicum isolate from a hilly area of China based on whole genome sequencing.

Schistosoma japonicum had once caused the greatest disease burden in China and has still been transmitted in some hilly areas, for example, in Shitai of Anhui province, where rodents are projected to be the main reservoir. This may lead to a critical need of molecular tools with high efficiency in monitoring the dynamic of the rodent-associated S. japonicum, as an appropriate amount of schistosome input can re-establish its life cycle in a place with snails and then result in the re-emergence of schistosomiasis. Therefore, the goal of this study was to develop high polymorphic microsatellites from the whole genome of rodent-associated S. japonicum strain to monitor its transmission dynamic. We sampled the hilly schistosome isolate from Shitai of Anhui in China and sequenced the parasite with the next-generation sequencing technology. The whole genome was assembled with four different approaches. We then developed 71 microsatellite markers at a genome-wide scale throughout two best assembled genomes. Based on their chromosome mapping and the expected length of targeted sequences, we selected 24 markers for the development of multiplex reactions. Two multiplexes composed of 10 loci were finally developed, and their potential was revealed by their successful application on and capturing the genetic diversity of three schistosome populations. The selected 10 markers, each with clear chromosome location and characteristics, will be greatly useful in tracing the dispersal pathways or/and dynamics of the rodent-associated S. japonicum or others in the hilly area of China or elsewhere.

Current Status of Snail Vectors in Port-Harcourt Metropolis, Rivers State, Nigeria.

Snails act as intermediate hosts and play active role in the transmission of trematodes. Assessments of snail vectors of public health importance in Port-Harcourt metropolis were conducted following previous report on emergence and re-emergence of schistosomiasis; in twelve locations once monthly from January to June 2019. Snails were collected in each water body using scooping net and handpicking method for 45 minutes/location and identified using shell morphology. They were screened for patent infection through exposure to sunlight individually for two hours in a petri-dish that contains clean water and checked for cercarial shedding in the laboratory using a microscope. Physico-chemical parameters (pH, temperature, dissolved oxygen (DO), conductivity, and total dissolved solid (TDS)) of the water bodies were analyzed monthly using standard methods. 1812 freshwater snails were collected and relative abundance recorded was: Lymnaea natalensis 1221(67.38%), Physa sp. 518(28.58%), Indoplanorbis exutus 44(2.42%) and Oncomelania sp. 29(1.60%). The study established the absence of Bulinus sp. in Port Harcourt metropolis and revealed that the density of fresh water snails varied monthly following wet and dry seasons. There was a significant difference in snail abundance in relation to species (F=16.24, p= 0.01 at p<0.05). The difference in snail abundance across habitat was not significant (F=0.525, p= 0.873). DO was the significant parameter influencing abundance of snail host identified. It is concluded that malacological survey is therefore vital for surveillance and effective snail control programme.
 Keywords: Distribution, Snail vectors, Port-Harcourt Metropolis

Selecting accurate post-elimination monitoring tools to prevent reemergence of urogenital schistosomiasis in Morocco: a pilot study

BackgroundAfter alleged stop of transmission of schistosomiasis and further down the line in post elimination settings, sensitive tools are required to monitor infection status to prevent potential re-emergence. In Rahala, where transmission cycle of Schistosoma haematobium is interrupted since 2004 but where 30% of snails are still infected by S. bovis, potential human S. bovis infection can’t be excluded. As methods based on egg-counts do not provide the required sensitivity, antibody or antigen assays are envisaged as the most appropriate tools for this type of monitoring.MethodsIn this pilot study, the performances of three assays were compared: two commercially available antibody tests (ELISA and haemagglutination format) indicating exposure, and an antigen test (lateral flow strip format) demonstrating active infection. All 37 recruited study participants resided in Rahala (Akka, province Tata, Morocco). Participants had been diagnosed and cured from schistosomiasis in the period between 1983 and 2003. In 2015 these asymptomatic participants provided fresh clinical samples (blood and urine) for analysis with the aforementioned diagnostics tests.ResultsNo eggs were identified in the urine of the 37 participants. The haemagglutination test indicated 6 antibody positives whereas the ELISA indicated 28 antibody positives, one indecisive and one false positive. ELISA and haemagglutination results matched for 18 individuals, amongst which 5 out of 6 haemagglutination positives. With the antigen test (performed on paired serum and urine samples), serum from two participants (cured 21 and 32 years ago) indicated the presence of low levels of the highly specific Schistosoma circulating anodic antigen (CAA), demonstrating low worm level infections (less than 5 pg/ml corresponding to probably single worm pair). One tested also CAA positive with urine. ELISA indicated the presence of human anti-Schistosoma antibodies in these two CAA positive cases, haemagglutination results were negative.ConclusionsTo prevent reemergence of schistosomiasis in Morocco current monitoring programs require specific protocols that include testing of antibody positives for active infection by the UCP-LF CAA test, the appropriate diagnostic tool to identify Schistosoma low grade infections in travelers, immigrants and assumed cured cases. The test is genus specific will also identify infections related to S. bovis.

Water buffalo as sentinel animals for schistosomiasis surveillance.

Introduction About 75% of human pathogens are zoonotic, meaning that they are communicated from animals to humans. (1) Schistosomiasis is a zoonotic disease with a complex transmission cycle involving aquatic snails and least 40 species of mammals, which serve as reservoir hosts. Worldwide, more than 700 million people are at risk of schistosomiasis and over 240 million people are infected with the parasite. (2) Schistosomiasis has been eliminated in Japan and the coastal plains of China by a combination of medical treatment, health education, improved water quality and sanitation and snail control through environmental modification, molluscicide and new farming methods. The World Health Organization (WHO) targets elimination of schistosomiasis in the Eastern Mediterranean, the Caribbean, Indonesia and the Mekong river basin by 2015, and in the Western Pacific, the Americas and selected African countries by 2020. (3) Here we argue that elimination guidelines for schistosomiasis should include surveillance of the animal reservoir. Transmission patterns Mapping of the transmission patterns in humans and animals can lead to a better understanding of transmission of schistosomiasis between different host species. Parts of China, Indonesia and the Philippines are endemic for schistosomiasis caused by Schistosoma japonicum. Cattle, water buffalo, goats, dogs, pigs and rats are potentially important reservoir hosts for this parasite because of their contact with humans. Other animals including cats and horses are not significant contributors because of their limited contact with contaminated water. (4) Grazing ruminants including goats, cattle and water buffalo are exposed to the parasite in transmission sites such as rice paddies. However, goats do not contribute much to transmission as they are uncommon in areas where schistosomiasis is endemic. Cattle and water buffalo are the major animal reservoirs contributing to human transmission of S. japonicum. (4-7) In China, bovine defecation is thought to be the main cause of environmental contamination. (6) Molecular studies have also suggested that transmission is through bovines rather than other domesticated animals. Cattle are less capable of recovering from infection than water buffalo. (8) Despite the fact that buffalo are capable of clearing the parasite, they are a major reservoir host because they are repeatedly exposed to the parasite when pulling ploughs in rice paddies. (9) In rice-growing regions, water buffalo are a good choice of sentinel animal. In Anhui and Sichuan provinces of China, re-emergence of schistosomiasis in humans was attributed to the high prevalence of schistosome infection among cows and water buffalo. (10,11) These human infections could be avoided by setting up a sensitive animal surveillance system to detect infection in animals and, by treating them promptly, preventing further contamination of the environment. Diagnostic tests Microscopic examination of stool samples is a standard test for several parasitic diseases, including schistosomiasis. However, microscopy has low sensitivity in diagnosing schistosomiasis among water buffalo due to the large volume of bovine excreta. Therefore, a more sensitive and specific diagnostic test is needed to identify schistosomiasis-free areas and prevent re-emergence of the disease. In previous studies, polymerase chain reaction (PCR) (12) and recombinant antigen-based enzyme-linked immunosorbent assay (ELISA) (13) have been found to be useful in identifying S. japonicum in stool samples. Surveillance can also be carried out in abattoirs where cattle and buffalo are slaughtered. Documentation of the original source of livestock then allows schistosome-infested sites to be located. Medical and veterinary approaches The complexity of zoonotic schistosomiasis transmission has been a major hindrance to elimination of the disease. …

Dynamics of spatial clustering of schistosomiasis in the Yangtze River Valley at the end of and following the World Bank Loan Project

The 10-year (1992–2001) World Bank Loan Project (WBLP) contributed greatly to schistosomiasis control in China. However, the re-emergence of schistosomiasis in recent years challenged the long-term progress of the WBLP strategy. In order to gain insight in the long-term progress of the WBLP, the spatial pattern of the epidemic was investigated in the Yangtze River Valley between 1999–2001 and 2007–2008. Two spatial cluster methods were jointly used to identify spatial clusters of cases. The magnitude and number of clusters varied during 1999–2001. It was found that prevalence of schistosomiasis had been greatly reduced and maintained at a low level during 2007–2008, with little change. Besides, spatial clusters most frequently occurred within 16 counties in the Dongting Lake region and within 5 counties in the Poyang Lake region. These findings precisely pointed out the prior places for future public health planning and resource allocation of schistosomiasis.

Effects of multigenerational exposures of D. magna to environmentally relevant concentrations of pentachlorophenol

The re-emergence of schistosomiasis has given rise to ubiquitous concentrations of the primary control agent pentachlorophenol (PCP) in the environment, especially in the surface waters of China. In this study, the effects of environmentally relevant concentrations of PCP, namely, 0.0002, 0.002, 0.02, 0.2, and 2 μmol/L on survival, age at first reproduction, fecundity, length of mothers, and number of molts of Daphnia magna were studied over three generations. The survival of D. magna exposed to 2 μmol/L was significantly affected in the three generations. Toxic effects were enhanced in later generations. Age at first reproduction of F1 and F2 D. magna was significantly slower than that of the controls. The total number of offspring per female exposed to concentrations of 0.002 μmol/L or greater was less (23.5 to 67.6, 9.4 to 73.7, and 3.6 to 83.7%) than that of the controls in the F0, F1, and F2 generations, respectively. The body length of mothers significantly decreased (4.7 to 6.8, 9.6 to 15.1, and 13.3 to 23.2%) after exposure to 0.002 μmol/L or greater than those of unexposed individuals in the F0, F1, and F2 generations, respectively. Dose-response relationships between concentrations of PCP and length and number of molts of D. magna were observed in the F0 to F2 generations. PCP concentrations on the surface waters of China caused adverse effects to D. magna, which increased over successive generations. Significant effects were observed in the third generation. The multigenerational studies were more sensitive than the single-generation experiments. Thus, multigenerational exposure may be more predictive of chronic exposure under field conditions.

Polymorphic microsatellites in the human bloodfluke, Schistosoma japonicum, identified using a genomic resource

Re-emergence of schistosomiasis in regions of China where control programs have ceased requires development of molecular-genetic tools to track gene flow and assess genetic diversity of Schistosoma populations. We identified many microsatellite loci in the draft genome of Schistosoma japonicum using defined search criteria and selected a subset for further analysis. From an initial panel of 50 loci, 20 new microsatellites were selected for eventual optimization and application to a panel of worms from endemic areas. All but one of the selected microsatellites contain simple tri-nucleotide repeats. Moderate to high levels of polymorphism were detected. Numbers of alleles ranged from 6 to 14 and observed heterozygosity was always >0.6. The loci reported here will facilitate high resolution population-genetic studies on schistosomes in re-emergent foci.

China’s new strategy to block Schistosoma japonicum transmission: experiences and impact beyond schistosomiasis

Despite sustained efforts for its control made over the past 50+ years, the re-emergence of schistosomiasis in China was noted around the turn of the new millennium. Consequently, a new integrated strategy was proposed to stop the contamination of schistosome eggs to the environment, which emphasizes health education, access to clean water and adequate sanitation, mechanization of agriculture and fencing of water buffaloes, along with chemotherapy. Validation of this integrated control strategy in four pilot counties in the provinces of Anhui, Hubei, Hunan and Jiangxi revealed significant reductions in the rate of Schistosoma japonicum infection in humans and intermediate host snails. Importantly, this strategy showed an impact on diseases beyond schistosomiasis, signified by concomitant reductions in the prevalence of soil-transmitted helminth infections. In view of China's new integrated strategy for transmission control of schistosomiasis showing an ancillary benefit on other helminthic diseases, we encourage others to investigate the scope and limits of integrated control of neglected tropical diseases.

Remote sensing for predicting potential habitats of Oncomelania hupensis in Hongze, Baima and Gaoyou lakes in Jiangsu province, China

Political and health sector reforms, along with demographic, environmental and socio-economic transformations in the face of global warming, could cause the re-emergence of schistosomiasis in areas where transmission has been successfully interrupted and its emergence in previously non-endemic areas in China. In the present study, we used geographic information systems and remote sensing techniques to predict potential habitats of Oncomelania hupensis, the intermediate host snail of Schistosoma japonicum. Focussing on the Hongze, Baima and Gaoyou lakes in Jiangsu province in eastern China, we developed a model using the normalized difference vegetation index, a tasseled-cap transformed wetness index, and flooding areas to predict snail habitats at a small scale. Data were extracted from two Landsat images, one taken during a typical dry year and the other obtained three years later during a flooding event. An area of approximately 163.6 km2 was predicted as potential O. hupensis habitats around the three lakes, which accounts for 4.3% of the estimated snail habitats in China. In turn, these predicted snail habitats are risk areas for transmission of schistosomiasis, and hence illustrate the scale of the possible impact of climate change and other ecological transformations. The generated risk map can be used by health policy makers to guide mitigation policies targetting the possible spread of O. hupensis, and with the aim of containing the transmission of S. japonicum.