Risk of Human Exposure to the Intestinal Schistosome, Schistosoma mansoni, across Seasons along the Senegal River

Background: Schistosomiasis is an emerging disease associated with changes to the environment that have increased human contact rates with disease-causing parasites, flatworms that are released from freshwater snails. For example, schistosomiasis remains a major public health problem in Northern Senegal, where prevalence in schoolchildren often reaches 90%. Aim: This study focuses on the impact of seasonality on the risk of human exposure (RHE) to Schistosoma mansoni, defined as the total number of cercariae (the free-living life stage that infects humans) shed from all Biomphalaria pfeifferi snails collected at a site using standardized methods. We focus on RHE because it is rarely quantified and a recent study demonstrated that snails stop shedding cercariae when snail densities increase and thus per capita snail resources become limited [2], suggesting that densities of snails might not be directly proportional to RHE to schistosomes. Method: We sampled four water access points in three villages every other week during the early (Dry1) and later dry seasons (Dry2) and the rainy season, quantifying the abundance of infected and non-infected snail intermediate hosts, cercariae released per infected snail, and water chemistry. We used simple and multiple linear regressions to assess how seasonality and environmental parameters affect non-infected and infected snail abundance and RHE. Results: Although RHE was found across all seasons, the abundance of infected and non-infected snail intermediate hosts and cercariae, as well as prevalence (23.71%), were all highest in the rainy season. In the rainy season, RHE was positively associated with the density of snail hosts and their periphyton food resource. Conclusion: Although previous studies have examined the influence of seasonality on snail densities, few studies have explored the effects of seasonality on cercarial densities, which is the primary source of infection to humans. Our study demonstrates that cercarial densities are greater in the rainy season than in the early or late dry seasons. Given that cercarial densities directly pose risk of infection to humans, unlike non-infected or infected snails, these finding should help to inform decision making and schistosomiasis control efforts in West Africa.

Genetic architecture of transmission stage production and virulence in schistosome parasites

ABSTRACTBoth theory and experimental data from pathogens suggest that the production of transmission stages should be strongly associated with virulence, but the genetic bases of parasite transmission/virulence traits are poorly understood. The blood fluke Schistosoma mansoni shows extensive variation in numbers of cercariae larvae shed and in their virulence to infected snail hosts, consistent with expected trade-offs between parasite transmission and virulence. We crossed schistosomes from two populations that differ 8-fold in cercarial shedding and in their virulence to Biomphalaria glabrata snail hosts, and determined four-week cercarial shedding profiles in F0, F1 and 376 F2 progeny from two independent crosses in inbred snails. Sequencing and linkage analysis revealed that cercarial production is polygenic and controlled by five QTLs. These QTLs act additively, explaining 28.56% of the phenotypic variation. These results demonstrate that the genetic architecture of key traits relevant to schistosome ecology can be dissected using classical linkage mapping approaches.

Analisis Kestabilan Model Matematika Penyebaran Penyakit Schistosomiasis dengan Saturated Incidence Rate

Schistosomiasis is a disease caused by infections of the genus Schistosoma. Schistosomiasis can be transmitted through schistosoma worms that contact human skin. Schistosomiasis is a disease that continues to increase in spread. Saturated incidence rates pay attention to the ability to infect a disease that is limited by an increase in the infected population. This thesis formulates and analyzes a mathematical model of the distribution of schistosomiasis with a saturated incidence rate. Based on the analysis of the model, two equilibrium points are obtained, namely non-endemic equilibrium points (E0) and endemic equilibrium points (E1). Both equilibrium points are conditional asymptotically stable. The nonendemic equilibrium point will be asymptotically stable if rh > dh, rs > ds and R0 < 1, while the endemic equilibrium point will be asymptotically stable if R0 > 1. Sensitivity analysis shows that there are parameters that affect the spread of the disease. Based on numerical simulation results show that when R0 < 1, the number of infected human populations (Hi), the number of infected snail populations (Si), the amount of cercaria density (C) and the amount of miracidia density (M) will tend to decrease until finally extinct. Otherwise at the time R0 > 1, the number of the four populations tends to increase before finally being in a constant state.

Surveillance on schistosomiasis in five provincial-level administrative divisions of the People’s Republic of China in the post-elimination era

Background The People’s Republic of China (P. R. China) has made significant progress on schistosomiasis control. Among the 12 provincial-level administrative divisions (PLADs) with schistosomiasis endemic in P. R. China, Guangdong, Shanghai, Fujian, Guangxi and Zhejiang PLADs (following as five PLADs) had successively eliminated schistosomiasis during 1985–1995. However, consolidation of the schistosomiasis elimination in these five PLADs remains challenging. In the current study, we sought to understand the epidemic situation in these post-elimination areas and their surveillance capabilities on schistosomiasis. Methods Annual data reflecting the interventions and surveillance on human beings, cattle and snails based on county level from 2005 to 2016 were collected through the national schistosomiasis reporting system and the data were analyzed to understand the epidemic status of schistosomiasis in the five PLADs. A standardized score sheet was designed to assess the surveillance capacity for schistosomiasis of selected disease control agencies in five PLADs and ten counties. Assessment on surveillance capacity including schistosomiasis diagnostic skills, identification of snails’ living and infection status and knowledge about schistosomiasis and its control were made. Descriptive analysis was used to analyze the epidemic status and evaluation results on surveillance capacities. Results The assessments showed that no local cases in humans and cattle or infected snail were found in these five PLADs since 2005. However, from 2005 to 2016, a total of 221 imported cases were detected in Zhejiang, Shanghai and Fujian, and 11.98 hm2 of new snail habitats were found in Zhejiang, Shanghai and Guangxi. In addition, snail infestation reoccurred in 247.55 hm2 of former snail habitats since 2011. For the surveillance capacity assessment, the accuracy rate of IHA and MHT were 100 and 89.3%, respectively. All participants could judge the living status of snails accurately and 98.1% on the infection status of snails. The accuracy rate of the questionnaire survey was 98.0%. Conclusions Elimination of schistosomiasis was consolidated successfully in five PLADs of P. R. China due to effective and strong post-elimination surveillance. Comprehensive consolidation strategies should be focused on the elimination of residual snails and the prevention of imported infection sources to consolidate the achievements of schistosomiasis control.

Surveillance on schistosomiasis in five PLADs of the People’s Republic of China in the post-elimination era

Background: The People’s Republic of China (P. R. China) has made significant progress on schistosomiasis control. Among the 12 provinces (municipality, autonomous region) with schistosomiasis endemic in P. R. China, Guangdong, Shanghai, Fujian, Guangxi and Zhejiang provincial-level administrative divisions (PLADs, following as five PLADs) had successively eliminated schistosomiasis during 1985–1995. However, consolidation of the schistosomiasis elimination in these five PLADs remains challenging. In the current study, we sought to understand the epidemic situation in these post-elimination areas and their surveillance capabilities on schistosomiasis. Methods: Annual data reflecting the interventions and surveillance on human beings, cattle and snails based on county level from 2005 to 2016 were collected through the national schistosomiasis reporting system and the data were analyzed to understand the epidemic status of schistosomiasis in the five PLADs. Ten counties were selected according to the endemic situation before elimination in the five PLADs. A standardized score sheet was designed to assess the surveillance capacity for schistosomiasis of selected disease control agencies in five PLADs and ten counties. Assessment on surveillance capacity including schistosomiasis diagnostic skills, identification of snails’ living and infection status and knowledge about schistosomiasis and its control were made. And the accuracy rate of the assessment was calculated. Results: The comprehensive assessments showed that no local cases in humans and cattle or infected snail were found in these five PLADs since 2005, and the surveillance abilities on schistosomiasis of the prevention and control institutions in five PLADs were appropriate. However, from 2005 to 2016, a total of 221 imported cases were detected in Zhejiang, Shanghai and Fujian PLADs, and 11.98 hm2 of new snail habitats were found in Zhejiang, Shanghai and Guangxi PLADs. In addition, snail infestation reoccurred in 247.55 hm2 of former snail habitats since 2011. For the surveillance capacity assessment on diagnosis skills, the accuracy rate of IHA was 100%, and the accuracy rate of MHT was 89.3%. For snail identification, the accuracy rate of identifying the snails’ living status was 100%, and the average accuracy rate of identifying infection status of snails was 98.1%. The average accuracy rate of the questionnaire survey was 98.0%.Conclusions: Elimination of schistosomiasis was consolidated successfully in five PLADs of P.R. China due to effective and strong post-elimination surveillance. Comprehensive consolidation strategies should be focused on the elimination of residual snails and the prevention of imported infection sources among the five PLADs to consolidate the achievements of schistosomiasis control.

Surveillance on schistosomiasis in five provinces of the People’s Republic of China in the post-elimination era

Background: The People’s Republic of China (P. R. China) has made significant progress on schistosomiasis control. Among the 12 provinces (municipality, autonomous region) with schistosomiasis endemic in P.R. China, Guangdong, Shanghai, Fujian, Guangxi and Zhejiang provinces (following called as five provinces) had successively eliminated schistosomiasis during 1985-1995. However, given the increasing mobilization of the population and goods, wetland protection, climate changes etc., consolidation of the schistosomiasis elimination in these five provinces remains challenging. In the current study, we sought to understand the epidemic situation in these post-elimination areas and their surveillance capabilities on schistosomiasis. Methods: (Ⅰ) Through the national schistosomiasis reporting system, annual data reflecting the interventions and surveillance on human beings, cattle and snails based on county level from 2005 to 2016 were collected and analyzed to understand the epidemic status of schistosomiasis in five provinces. (Ⅱ) A standardized score sheet was designed to assess the surveillance capacity for schistosomiasis of selected disease control agencies in five provinces and ten counties. Assessment on surveillance capacity consisted of two parts: the first part focused on the capacity of testing skills including schistosomiasis diagnostic skills, identification of snails’ living and infection status; the second part was to assess the knowledge level about schistosomiasis and its control.Results: The comprehensive assessments showed that no local cases in humans and cattle or infected snail were found in these five provinces from 2005, and the surveillance abilities on schistosomiasis of the prevention and control institutions in five provinces were appropriate. However, from 2005 to 2016, a total of 221 imported cases were detected in Zhejiang, Shanghai and Fujian provinces, and 11.98 hm2 of new snail habitats were found in Zhejiang, Shanghai and Guangxi provinces. In addition, snail infestation reoccurred in 247.55 hm2 of former snail habitats since 2011.Conclusions: Elimination of schistosomiasis was consolidated successfully in five provinces of P.R. China due to effective and strong post-elimination surveillance. Comprehensive consolidation strategies should be focused on the elimination of residual snails and the prevention of imported infection sources among the five provinces to consolidate the achievements of schistosomiasis control.

Surveillance on schistosomiasis in five provinces of the People's Republic of China in post-elimination era

Background: The People’s Republic of China (P. R. China) had made significant progress on schistosomiasis control. Among the 12 provinces (municipality, autonomous region with schistosomiasis endemic) in P.R. China, Guangdong, Shanghai, Fujian, Guangxi and Zhejiang provinces (following called as five provinces) had successively eliminated schistosomiasis during 1985-1995. However, given the increasing mobilization of the population and goods, wetland protection, climate changes etc., consolidation of the schistosomiasis elimination in these five provinces remain challenges. In the current study, we sought to understand the epidemic situation in these post-elimination areas and their surveillance capabilities on schistosomiasis. Methods: (Ⅰ) Through the national schistosomiasis reporting system, annual data reflecting the interventions and surveillance on human beings, cattle and snails based on county level from 2005 to 2016 were collected and analyzed to understand the epidemic status of schistosomiasis in five provinces. (Ⅱ) A standardized score sheet was designed to assess the surveillance capacity for schistosomiasis of selected disease control agencies in five provinces and ten counties. Assessment on surveillance capacity consisted of two parts: the first part focused on the capacity of testing skills including schistosomiasis diagnostic skills, identification of snails’ living and infection status; the second part was to assess the knowledge level about schistosomiasis and its control.Results: The comprehensive assessments showed that no local cases in humans and cattle or infected snail were found in these five provinces from 2005, and the surveillance abilities on schistosomiasis of the prevention and control institutions in five provinces were appropriate. However, from 2005 to 2016, a total of 221 imported cases were detected in Zhejiang, Shanghai and Fujian provinces, and 11.98 hm2 of new snail habitats were found in Zhejiang, Shanghai and Guangxi provinces. In addition, snail infestation was reoccurred in 247.55 hm2 of former snail habitats since 2011.Conclusions: Elimination of schistosomiasis was consolidated successfully in five provinces of P.R. China due to effective and strong post-elimination surveillance. Comprehensive consolidation strategies should be focused on the elimination of residual snails and the prevention of imported infection sources among the five provinces to consolidate the achievements of schistosomiasis control.

A rapid diagnostic multiplex PCR approach for xenomonitoring of human and animal schistosomiasis in a ‘One Health’ context

Studying the epidemiology of schistosomiasis—the most prevalent gastropod-borne human disease and an economic burden for the livestock industry—relies on adequate monitoring tools. Here we describe a molecular assay for detecting human and animal African schistosome species in their planorbid gastropod host (xenomonitoring) using a two-step approach. First, schistosome infections are detected and discriminated from other trematode infections using a multiplex polymerase chain reaction (PCR) that includes a trematode-specific marker (in 18S rDNA), a Schistosoma genus-specific marker (in internal transcribed spacer 2 [ITS2]) and a general gastropod marker (in 18S rDNA) as an internal control. Upon Schistosoma sp. detection, a second multiplex PCR is performed to discriminate among Schistosoma haematobium, Schistosoma mansoni, Schistosoma mattheei and Schistosoma bovis/Schistosoma curassoni/Schistosoma guineensis using markers of differential lengths in the cytochrome c oxidase subunit 1 (COX1) gene. The specificity of these assays was validated with adult worms, naturally infected gastropods and human urine and stool samples. Sensitivity was tested on experimentally infected snail specimens that were sacrificed 10 and 40 days post-infection in order to mimic a natural prepatent and mature infection, respectively. The assay provides a diagnostic tool to support the xenomonitoring of planorbid gastropods for trematode infections in a One Health context, with a focus on the transmission monitoring of schistosomiasis.

Cercarial fauna of freshwater snails in selected agricultural areas in Laguna, Philippines

SummaryFreshwater snails serve as one of trematodes’ intermediate hosts. Previous studies on trematode larval stages in the Philippines have largely focused on species with public health importance. This study sought to investigate the prevalence of cercarial morphotypes in several freshwater snail species found in different habitat types (rice field, irrigation canals, and residential area) in selected agricultural areas in Los Baños and Bay in Laguna. Cercarial emergence was induced through exposure to artificial light. A total of 2,720 freshwater snails were collected and were represented by seven species, namely, Melanoides tuberculata Muller 1774 (n = 1229), Radix quadrasi von Moellendorf (n = 630), Tarebia granifera Lamarck, 1816 (n = 417), Pomacea canaliculata Lamarck 1819 (n = 257), Vivipara angularis philippinensis Nevill (n = 18), Stenomelania sp. (n = 104), Thiara scabra Muller 1774 (n = 65). A 2.57 % over-all prevalence was recorded; the infected snail species were M. tuberculata (2.21 %), R. quadrasi (0.21 %), T. granifera (0.11 %). Four cercarial morphotypes, namely, Parapleurolophocercous cercaria (1.80 %), Virgulate xiphidiocercaria (0.26 %), Megaluruous cercaria (0.29 %), and Echinostome cercaria (0.22 %) were recovered from the infected snail species. Prevalence of cercarial infection was significantly different (p < 0.05) among habitat types.

Field Evaluation of a Loop-Mediated Isothermal Amplification (LAMP) Platform for the Detection of Schistosoma japonicum Infection in Oncomelania hupensis Snails

Schistosoma infection in snails can be monitored by microscopy or indirectly by sentinel mice. As both these approaches can miss infections, more sensitive tests are needed, particularly in low-level transmission settings. In this study, loop-mediated isothermal amplification (LAMP) technique, designed to detect a specific 28S ribosomal Schistosoma japonicum (Sj28S) gene with high sensitivity, was compared to microscopy using snail samples from 51 areas endemic for schistosomiasis in five Chinese provinces. In addition, the results were compared with those from polymerase chain reaction (PCR) by adding DNA sequencing as a reference. The testing of pooled snail samples with the LAMP assay showed that a dilution factor of 1/50, i.e., one infected snail plus 49 non-infected ones, would still result in a positive reaction after the recommended number of amplification cycles. Testing a total of 232 pooled samples, emanating from 4006 snail specimens, showed a rate of infection of 6.5%, while traditional microscopy found only 0.4% positive samples in the same materials. Parallel PCR analysis confirmed the diagnostic accuracy of the LAMP assay, with DNA sequencing even giving LAMP a slight lead. Microscopy and the LAMP test were carried out at local schistosomiasis-control stations, demonstrating that the potential of the latter assay to serve as a point-of-care (POC) test with results available within 60–90 min, while the more complicated PCR test had to be carried out at the National Institute of Parasitic Diseases (NIPD) in Shanghai, China. In conclusion, LAMP was found to be clearly superior to microscopy and as good as, or better than, PCR. As it can be used under field conditions and requires less time than other techniques, LAMP testing would improve and accelerate schistosomiasis control.