Identifying host species driving transmission of schistosomiasis japonica, a multihost parasite system, in China.

Understanding disease transmission dynamics in multihost parasite systems is a research priority for control and potential elimination of many infectious diseases. In China, despite decades of multifaceted control efforts against schistosomiasis, the indirectly transmitted helminth Schistosoma japonicum remains endemic, partly because of the presence of zoonotic reservoirs. We used mathematical modeling and conceptual frameworks of multihost transmission ecology to assess the relative importance of various definitive host species for S. japonicum transmission in contrasting hilly and marshland areas of China. We examine whether directing control interventions against zoonotic reservoirs could further reduce incidence of infection in humans or even eliminate transmission. Results suggest that, under current control programs, infections in humans result from spillover of transmission among zoonotic reservoirs. Estimates of the basic reproduction number within each species suggest that bovines (water buffalo and cattle) maintained transmission in the marshland area and that the recent removal of bovines from this area could achieve local elimination of transmission. However, the sole use of antifecundity S. japonicum vaccines for bovines, at least at current efficacies, may not achieve elimination in areas of comparable endemicity where removal of bovines is not a feasible option. The results also suggest that rodents drive transmission in the hilly area. Therefore, although targeting bovines could further reduce and potentially interrupt transmission in marshland regions of China, elimination of S. japonicum could prove more challenging in areas where rodents might maintain transmission. In conclusion, we show how mathematical modeling can give important insights into multihost transmission of indirectly transmitted pathogens.

Genetic diversity of Schistosoma japonicum miracidia from individual rodent hosts.

Schistosoma japonicum is an important parasite in terms of clinical, veterinary and socio-economic impacts, and rodents, a long neglected reservoir for the parasite, have recently been found to act as reservoir hosts in some endemic areas of China. Any difference in the host's biological characteristics and/or associated living habitats among rodents may result in different environments for parasites, possibly resulting in a specific population structure of parasites within hosts. Therefore knowledge of the genetic structure of parasites within individual rodents could improve our understanding of transmission dynamics and hence our ability to develop effective control strategies. In this study, we aimed to describe a host-specific structure for S. japonicum and its potential influencing factors. The results showed a significant genetic differentiation among hosts. Two factors, including sampling seasons and the number of miracidia genotyped per host, showed an effect on the genetic diversity of an infrapopulation through a univariable analysis but not a multivariable analysis. A possible scenario of clustered infection foci and the fact of multiple definitive host species, the latter of which is unique to S. japonicum compared with other schistosomes, were proposed to explain the observed results and practical implications for control strategies are recommended.

[Surveillance and forecast of schistosomiasis transmission in Chaohu Lake area in Anhui Province, 2008-2010].

OBJECTIVE: To understand the dynamic changes of the potential prevalent factors of schistosomiasis in Chaohu Lake area so as to provide forecast information on the outbreak of schistosomiasis in the area. METHODS: From 2008 to 2010, fixed and mobile surveillance sites in potential endemic areas of Juchao District in Chaohu City, which was located in the southeast side of Chaohu Lake, were selected, and the schistosomiasis infection situation of local people, mobile population and livestock were investigated by immunological assays and/or stool examinations. The distribution of Oncomelania snails was surveyed in risk areas and suspicious areas, the spreading patterns of Oncomelania snails were observed in rivers that directly connected with the Yangtze River, and the Oncomelania snails were raised in the cages on the beaches of Chaohu Lake and a control area, and their survival and reproduction capacity was observed. RESULTS: In 2008, a total of 301 local people were screened by IHA, and there were no positives. From 2008 to 2010, a total of 321, 362 and 306 mobile population were examined by IHA, respectively, and the positive rate of antibody were 3.74%, 4.97% and 2.94%, respectively. The antibody positives were tested by stool examinations, and the positive rates were 66.67%, 50% and 55.56%, respectively. A total of 91 local livestock and 92 livestock from endemic areas were examined respectively by the miracidium hatching method, and there were no positives. A total of 97.8 hm2 risk areas and 193.62 hm2 suspicious areas in the potential endemic area were surveyed respectively, but no Oncomelania snails were found. The investigation results on snail spreading patterns indicated that snails could spread into Chaohu Lake by adsorbing on floating debris. The field study revealed that Oncomelania snails could survive and reproduce in the Lake. CONCLUSIONS: The imported infectious sources of schistosomiasis have been found in Chaohu Lake area, and the higher possibility of imported Oncomelania snails spreading into the Lake and surviving and reproducing in the lake is predicted. Therefore, effective measures should be taken to decrease the risks of schistosomiasis transmission in the potential endemic area.

Transmission of Schistosoma japonicum in marshland and hilly regions of China: parasite population genetic and sibship structure.

The transmission dynamics of Schistosoma japonicum remain poorly understood, as over forty species of mammals are suspected of serving as reservoir hosts. However, knowledge of the population genetic structure and of the full-sibship structuring of parasites at two larval stages will be useful in defining and tracking the transmission pattern between intermediate and definitive hosts. S. japonicum larvae were therefore collected in three marshland and three hilly villages in Anhui Province of China across three time points: April and September-October 2006, and April 2007, and then genotyped with six microsatellite markers. Results from the population genetic and sibling relationship analyses of the parasites across two larval stages demonstrated that, within the marshland, parasites from cattle showed higher genetic diversity than from other species; whereas within the hilly region, parasites from dogs and humans displayed higher genetic diversity than those from rodents. Both the extent of gene flow and the estimated proportion of full-sib relationships of parasites between two larval stages indicated that the cercariae identified within intermediate hosts in the marshlands mostly came from cattle, whereas in the hilly areas, they were varied between villages, coming primarily from rodents, dogs or humans. Such results suggest a different transmission process within the hilly region from within the marshlands. Moreover, this is the first time that the sibling relationship analysis was applied to the transmission dynamics for S. japonicum.

Contrasting reservoirs for Schistosoma japonicum between marshland and hilly regions in Anhui, China--a two-year longitudinal parasitological survey.

Schistosoma japonicum remains highly endemic in many counties in China and has recently re-emerged, to a large extent, in previously controlled areas. To test the hypothesis that small rodents and less agriculturally important domestic animals such as dogs and cats may play an important role in the transmission and potential re-emergence of this disease, an annual investigation of S. japonicum among humans, domestic animals and rodents, combined with detailed surveys of the snail intermediate host, was performed across 3 marshland villages and 3 hilly villages in Anhui province of China over 2 consecutive years. The highest infection prevalence and intensity observed across all mammals was in rodents in the hilly region; while in the marshland, bovines were suspected as the main reservoirs. However, relatively high infection prevalence levels were also found in dogs and cats in both regions. Such results may have implications for the current human- and bovine-oriented control policy for this medically and veterinarily important disease, particularly within the hilly regions of mainland China.

Evolution in a multi-host parasite: chronobiological circadian rhythm and population genetics of Schistosoma japonicum cercariae indicates contrasting definitive host reservoirs by habitat.

Schistosomiasis japonica is a disease of profound medical and veterinary importance which has remained endemic in many regions and has re-emerged where previously controlled in China. Although over 40 mammalian species are suspected as reservoirs for Schistosoma japonicum, their relative roles, particularly wildlife, remain to be ascertained. As cercarial emergence is a heritable trait shaped by the definitive hosts' behaviour, three chronobiological trials of cercarial emergence from field-collected snails from two contrasting ecological regions within China were performed, followed by genetic analyses of the parasites. Two distinct modes were identified, with late afternoon emergence mainly found in the hill region, compatible with a nocturnal rodent reservoir, and early emergence within the marshland consistent with a diurnal cattle reservoir. Furthermore, genetic analyses pointed to a clear separation between cercariae with different biological traits. The phenotypic and genotypic differentiation of the parasites identified here between and within two regions may indicate a strain complex. Such parasite diversity could, in turn, provide an explanation for the different infection scenarios observed between the two regions, and hence have important applied implications in terms of targeted control of key reservoirs.

Parasite genetic differentiation by habitat type and host species: molecular epidemiology of Schistosoma japonicum in hilly and marshland areas of Anhui Province, China.

Schistosoma japonicum, a parasite of significant public health importance in parts of China and Southeast Asia, is a true generalist pathogen with over 40 species of mammals suspected as definitive host reservoirs. In order to characterize levels of parasite gene flow across host species and identify the most important zoonotic reservoirs, S. japonicum larvae (miracidia) were sampled from a range of definitive host species in two contrasting habitat types within Anhui Province, China: a low-lying marshland region, and a hilly region, where animal reservoir populations may be predicted to differ substantially. Miracidia samples were genotyped using seven multiplexed microsatellite markers. Hierarchical F-statistics and clustering analyses revealed substantial geographical structuring of S. japonicum populations within Anhui, with strong parasite genetic differentiation between habitat types. Within most villages, there was very little or no parasite genetic differentiation among host species, suggesting frequent S. japonicum gene flow, and thus also transmission, across species. Moreover, the data provide novel molecular evidence that rodents and dogs are potentially very important infection reservoirs in hilly regions, in contrast to bovines in the marshland regions. The parasite genetic differentiation between habitat types might therefore be associated with contrasting host reservoirs. The high levels of parasite gene flow observed across host species in sympatric areas have important implications for S. japonicum control, particularly in hilly regions where control of infection among wild rodent populations could be challenging.

[Potential impact of water transfer project from Yangtze River to Huaihe River on snail spread and schistosomiasis transmission].

OBJECTIVE: To investigate the possibility of spread of snails and transmission of schistosomiasis japonica due to the construction of water transfer project from Yangtze River to Huaihe River. METHODS: In order to understand the current endemic situation of schistosomiasis in the project area, the distribution of snails was surveyed by routine methods, level of anti-schistosome antibody in human sera was detected by indirect haemagglutination test (IHA), and the prevalence of schistosomiasis in cattle was detected by egg hatching method. The snail survival and reproduction were observed in Chaohu Lake area(experimental area) and a control area for one year. RESULTS: Snail density was high in two starting points, from where the water in Yangtze River will be directed to Huaihe River. In counties of Wuwei and Hexian, through which the project will be built, the positive rate of anti-schistosome antibody in residents was 22.11% (168/760) and 18.59% (37/199), schistosomiasis prevalence in cattle was 2.42% (9/371) and 0.2% (2/997), respectively. Schistosomiasis was also endemic in Juchao District of Chaohu City. Snails respectively from grassland and hilly area were collected and put in Chaohu Lake for breed and newborn snails were found one year later. During the egg-laying season, the survival rate of snails from grassland in 2 experiment areas and a control area was 11.3%-16.7%, 3.0%-20.8% and 4.7%-14.7% respectively (chi2 = 0.093, 0.760, P > 0.05; chi2 = 0.647, 0, P > 0.05), and that of snails from hilly area was 24.1%-44.4%, 37.8%-67.3% and 86.3%-93.1% respectively (chi2 = 9.575, 5.302, P < 0.05; chi2 = 56.863, 36.218, P < 0.05). There was no significant difference between the experimental area and the control area on the number of eggs in the ovaries of the same type female snails. CONCLUSION: The one-year observation reveals that the construction of the project might result in spread of snails and transmission of schistosomiasis japonica in the relevant areas.

Studies of impact on physical fitness and working capacity of patients with advanced Schistosomiasis japonica in Susong County, Anhui Province.

To assess the impact level on physical fitness and working capacity in patients with advanced Schistosomiasis japonica, a field study was carried out. According to the records of patients with advanced schistosomiasis in Susong County, Anhui Province, 48 advanced cases without other serious chronic diseases from endemic areas in two townships and 56 healthy individuals from non-endemic area, served as control group with matched ages between 40 and 70 years and matched sex were investigated with questionnaire, anthropometric measure and hemoglobin level. The impairment level of the liver was measured by ultrasonography and physical fitness was measured by the Step test in the case and control groups. All situations including lifestyle, working, socio-economic status and residing environment was similar in the case and control groups. Average height and weight was significantly lower in the case group than in the control group (height = 156.29 and 159.41 cm; weight = 50.72 and 53.92 kg; respectively, all P < 0.05). Thirteen individuals (28.3%) in the case group had moderate reduction of working capacity or even unable to work, but only seven (12.7%) individuals in the control group had moderate reduction of working capacity and all in the control group were able to work (P < 0.01). In the past 1 year, the average working days lost was 4.11 days in the case group and 0.86 day in the control group (P < 0.01). Both groups differed significantly in symptoms of abdominal pain, diarrhea and weakness (all P < 0.05). Twenty-one cases (43.8%) had grade II impairment of the liver and eight cases (16.7%) had grade III impairment of the liver in the case group, whereas seven individuals (12.7%) had grade II impairment of the liver in the control group (P < 0.01), as assessed by ultrasound. The hemoglobin levels and the power of gripping in the case group were significantly lower than those in the control group (Hb = 111.06 and 122.27 g/l; grip = 303.83 and 344.20 N, respectively, all P < 0.01). Physical fitness scores showed the control group (score: 71.84) was significantly fitter than the case group (score: 61.09, P < 0.01). Compared with the control group, the physical fitness of the case group reduced by 15%. The results showed that physical fitness and working capacity were reduced in advanced cases. Although most of the cases were treated and had reached a status of 'clinical cure', the impact on physical fitness and working capacity still existed.