Order and timing of infection with different parasite life stages impacts host and parasite life histories

Co-exposure to multiple parasites can alter parasite success and host life history when compared to single infections. These infection outcomes can be affected by the order of parasite arrival, the host immune response, and the interspecific interactions among co-infecting parasites. In this study, we examined how the arrival order of two trematode parasites, Schistosoma mansoni and Echinostoma caproni, influenced parasite ecology and the life history of their snail host, Biomphalaria glabrata. Snail hosts were exposed to E. caproni cercariae before, with, and after their exposure to S. mansoni miracidia. We then measured the effects of this timing on infection prevalence, infection intensity of E. caproni metacercariae, and cercarial output of S. mansoni, as well as on snail reproduction and survival. Snails infected only with S. mansoni and snails exposed to E. caproni after S. mansoni both shed more cercariae than simultaneously exposed snails. Additionally, S. mansoni prevalence was lower in snails that were first exposed to E. caproni compared to snails that were exposed to E. caproni after S. mansoni. Moreover, snails exposed to E. caproni before S. mansoni did not differ in their survival compared to control snails, whereas simultaneously exposed snails and snails exposed to E. caproni after S. mansoni had lower survival than control snails. Combined, this prevalence and survival data suggest a potential protective role of early E. caproni exposure. The timing of E. caproni exposure impacts S. mansoni establishment and reproduction, but host survival patterns are likely driven by S. mansoni prevalence alone.

infection in Poecilia reticulata by cercariae released from Melanoides tuberculata in Denmark

BACKGROUND

Exotic and ornamental fish are highly popular companion animals resulting in a significant transcontinental trade of fish, invertebrates and aquatic plants. A major issue is the diseases associated with these organisms, as they have a major impact on health of the fish in both public and private household aquaria. A secondary issue is the trade with these products, which potentially may expand the distribution area and spread a range of diseases to new habitats.

RESULTS

We here describe how Poecilia reticulata (guppy), produced in a private household aquarium, were invaded by cercariae of an exotic trematode released by imported Melanoides tuberculata snails. The fish presented with severe clinical signs (tremor, flashing, scraping of body against objects). A standard parasitological examination and morphometric identification showed scale pocket infections with a digenean trematode species within the genus Transversotrema. Molecular identification by PCR, sequencing and phylogenetic analyses of a 2646 bp sequence encoding ribosomal RNA (partial 18 S, ITS1, 5.8 S, ITS2, partial 28 S) was performed. The 1107 bp sequence of mitochondrial DNA (cox1) showed that the parasite differed from previously described Transversotrema species in M. tuberculata. Morphometrics of adult and larval specimens of this isolate also differed from previously described freshwater species within the genus. The new species was described and is named after Copenhagen, for its geographic origin.

CONCLUSIONS

The genus Transversotrema comprises a range of species, adapted to a microhabitat in scalepockets of teleosts. A combination of morphological and molecular characterization techniques has been shown to provide a good differentiation between species. The fish were not purchased from a pet shop but produced in the home aquarium. This indicated that an infection pressure existed in the aquarium, where the source of infection was found to be exotic intermediate host snails M. tuberculata, which originally were imported and purchased from a pet shop. The potential spread of fish diseases associated with trade of fish and snails to new geographic regions, where climate conditions are favourable, is discussed.

Activities of pumpkin seed oil against Biomphalaria alexandrina snails and the infective stages of Schistosoma mansoni with special emphasis on genotoxic and histopathological alterations

Schistosomiasis is a serious health issue in tropical regions, and natural compounds have gained popularity in medical science. This study investigated the potential effects of pumpkin seed oil (PSO) on Biomphalaria [B.] alexandrina snails (Ehrenberg, 1831), Schistosoma [S.] mansoni (Sambon, 1907) miracidium, and cercariae. The chemical composition of PSO was determined using gas chromatography/mass spectrometry. A bioassay was performed to evaluate the effects of PSO on snails, miracidia, and cercariae. The results showed no significant mortality of B. alexandrina snails after exposure to PSO, but it caused morphological changes in their hemocytes at 1.0 mg/ml for 24 hours. PSO exhibited larvicidal activity against miracidia after 2 hours of exposure at a LC50 of 618.4 ppm. A significant increase in the mortality rate of miracidia was observed in a dose- and time-dependent manner, reaching a 100% death rate after 10 minutes at LC90 and 15 minutes at LC50 concentration. PSO also showed effective cercaricidal activity after 2 hours of exposure at a LC50 of 290.5 ppm. Histological examination revealed multiple pathological changes in the digestive and hermaphrodite glands. The PSO had genotoxic effects on snails, which exhibited a significant increase [p≤0.05] in comet parameters compared to the control. The findings suggest that PSO has potential as a molluscicide, miracidicide, and cercaricide, making it a possible alternative to traditional molluscicides in controlling schistosomiasis.

Circulating cell-free DNA as a biomarker for diagnosis of Schistosomiasis japonica

BACKGROUND

Schistosomiasis, a neglected tropical disease, remains an important public health problem. Although there are various methods for diagnosing schistosomiasis, many limitations still exist. Early diagnosis and treatment of schistosomiasis can significantly improve survival and prognosis of patients.

METHODOLOGY

Circulating cell-free (cf)DNA has been widely used in the diagnosis of various diseases. In our study, we evaluated the diagnostic value of circulating cfDNA for schistosomiasis caused by Schistosoma japonicum. We focused on the tandem sequences and mitochondrial genes of S. japonicum to identify highly sensitive and specific targets for diagnosis of Schistosomiasis japonica.

RESULTS

Through data screening and analysis, we ultimately identified four specific tandem sequences (TD-1, TD-2, TD-3. and TD-4) and six mitochondrial genes (COX1(1), COX1(2), CYTB, ATP6, COX3, and ND5). We designed specific primers to detect the amount of circulating cfDNA in S. japonicum-infected mouse and chronic schistosomiasis patients. Our results showed that the number of tandem sequences was significantly higher than that of the mitochondrial genes. A S. japonicum infection model in mice suggested that infection of S. japonicum can be diagnosed by detecting circulating cfDNA as early as the first week. We measured the expression levels of circulating cfDNA (TD-1, TD-2, and TD-3) at different time points and found that TD-3 expression was significantly higher than that of TD-1 or TD-2. We also infected mice with different quantities of cercariae (20 s and 80 s). The level of cfDNA (TD-3) in the 80 s infection group was significantly higher than in the 20 s infection group. Additionally, cfDNA (TD-3) levels increased after egg deposition. Meanwhile, we tested 42 patients with chronic Schistosomiasis japonica and circulating cfDNA (TD-3) was detected in nine patients.

CONCLUSIONS

We have screened highly sensitive targets for the diagnosis of Schistosomiasis japonica, and the detection of circulating cfDNA is a rapid and effective method for the diagnosis of Schistosomiasis japonica. The levels of cfDNA is correlated with cercariae infection severity. Early detection and diagnosis of schistosomiasis is crucial for patient treatment and improving prognosis.

Molecular phylogenetic position and the life cycle of Phyllodistomum cyprini Feng et Wang, 1995 in Japan, with a note of a larval Phyllodistomum sp. from unionid mussels in North America

A gorgoderid species, Phyllodistomum cyprini Feng et Wang, 1995 obtained from ureters of common carp, Cyprinus carpio in Japan is described both morphologically and molecularly. Its larval stage is a macrocercous cercaria found in a unionid mussel, Nodularia nipponensis first described by Urabe et al. (2015). A molecular phylogenetic study revealed that P. cyprini is not closely related to rhopalocercous cercariae from unionid mussels both in Europe and North America. This result indicates that there are several distinct clades in Phyllodistomum species that use unionid mussels as a first intermediate host, and suggests that the cercarial morphology may be a more accurate indicator of the phylogeny of Phyllodistomum than molluscan host identity.

Development of the head collar and collar spines during the larval stages of Isthmiophora hortensis (Digenea: Echinostomatidae)

It is uncertain when the head collar and collar spines of Isthmiophora hortensis (Digenea: Echinostomatidae), a zoonotic echinostome species in Far Eastern Asia, develop during its larval stages. In this study, the appearance of the head collar and collar spines was studied using light and scanning electron microscopy in cercariae and metacercariae experimentally obtained from freshwater snails (Lymnaea pervia) and tadpoles (Rana nigromaculata), respectively. The cercariae were shed from the snail on day 30 after exposure to laboratory-hatched miracidia. Metacercariae were obtained from the experimental tadpoles at 3, 6, 12, 15, 20, 24, 26, and 30 h after exposure to the cercariae. The head collar was already visible in the cercarial stage, although its degree of development was weak. However, collar spines did not appear in the cercarial stage and even in the early metacercarial stage less than 24 h postinfection in tadpoles. Collar spines became visible in the metacercariae when they grew older than 24 h. It was concluded that the head collar of I. hortensis developed early in the cercarial stage, but the development of collar spines did not occur until the worms became 24-h-old metacercariae in our experimental setting. Counting the number of collar spines was concluded as an unfeasible diagnostic method for I. hortensis cercariae when they are shed from the snail host.

No time to relax: Age-dependent infectivity of cercariae in marine coastal ecosystems

Age dynamics of the ability of cercariae of two digenean species, Himasthla elongata (Himasthlidae) and Renicola parvicaudatus (Renicolidae), to infect the second intermediate host (SIH), mussels (Mytilus edulis), was investigated experimentally. This is the first study of this kind made on cercariae transmitted in the intertidal of the northern seas. The larvae of all tested ages (from 0.5 to 6 hr) were equally successful in infecting mussels. This finding disagrees with the literature data on cercariae of several freshwater digeneans, which are practically incapable of infecting the SIH during the first 1-3 hr of life. The presence of a time delay before the attainment of the maximum infectivity (TDMI) may be associated with the need for physiological maturation of cercariae in the very beginning of their life in the environment, the need for their broad dispersion, and the prevention of superinfection of the downstream host. The absence of TDMI in the cercariae examined in our study could be associated with the instability of environmental factors in the marine intertidal (wave impact, tidal currents). These factors promote a broad dispersion of cercariae in the intertidal biotope and prevent superinfection of potential SIHs. Biological and behavioural features may also play a role. We hypothesize that the presence or absence of TDMI does not depend on the taxonomic affiliation of the cercariae but is determined by the transmission conditions.

MALDI-TOF: A new tool for the identification of Schistosoma cercariae and detection of hybrids

Schistosomiasis is a neglected water-born parasitic disease caused by Schistosoma affecting more than 200 million people. Introgressive hybridization is common among these parasites and raises issues concerning their zoonotic transmission. Morphological identification of Schistosoma cercariae is difficult and does not permit hybrids detection. Our objective was to assess the performance of MALDI-TOF (Matrix Assistated Laser Desorption-Ionization–Time Of Flight) mass spectrometry for the specific identification of cercariae in human and non-human Schistosoma and for the detection of hybridization between S. bovis and S. haematobium. Spectra were collected from laboratory reared molluscs infested with strains of S. haematobium, S. mansoni, S. bovis, S. rodhaini and S. bovis x S. haematobium natural (Corsican hybrid) and artificial hybrids. Cluster analysis showed a clear separation between S. haematobium, S. bovis, S. mansoni and S. rodhaini. Corsican hybrids are classified with those of the parental strain of S. haematobium whereas other hybrids formed a distinct cluster. In blind test analysis the developed MALDI-TOF spectral database permits identification of Schistosoma cercariae with high accuracy (94%) and good specificity (S. bovis: 99.59%, S. haematobium 99.56%, S. mansoni and S. rodhaini: 100%). Most misidentifications were between S. haematobium and the Corsican hybrids. The use of machine learning permits to improve the discrimination between these last two taxa, with accuracy, F1 score and Sensitivity/Specificity > 97%. In multivariate analysis the factors associated with obtaining a valid identification score (> 1.7) were absence of ethanol preservation (p < 0.001) and a number of 2–3 cercariae deposited per well (p < 0.001). Also, spectra acquired from S. mansoni cercariae are more likely to obtain a valid identification score than those acquired from S. haematobium (p<0.001). MALDI-TOF is a reliable technique for high-throughput identification of Schistosoma cercariae of medical and veterinary importance and could be useful for field survey in endemic areas.

Consumption of trematode parasite infectious stages: from conceptual synthesis to future research agenda

Given their sheer cumulative biomass and ubiquitous presence, parasites are increasingly recognized as essential components of most food webs. Beyond their influence as consumers of host tissue, many parasites also have free-living infectious stages that may be ingested by non-host organisms, with implications for energy and nutrient transfer, as well as for pathogen transmission and infectious disease dynamics. This has been particularly well-documented for the cercaria free-living stage of digenean trematode parasites within the Phylum Platyhelminthes. Here, we aim to synthesize the current state of knowledge regarding cercariae consumption by examining: (a) approaches for studying cercariae consumption; (b) the range of consumers and trematode prey documented thus far; (c) factors influencing the likelihood of cercariae consumption; (d) consequences of cercariae consumption for individual predators (e.g. their viability as a food source); and (e) implications of cercariae consumption for entire communities and ecosystems (e.g. transmission, nutrient cycling and influences on other prey). We detected 121 unique consumer-by-cercaria combinations that spanned 60 species of consumer and 35 trematode species. Meaningful reductions in transmission were seen for 31 of 36 combinations that considered this; however, separate studies with the same cercaria and consumer sometimes showed different results. Along with addressing knowledge gaps and suggesting future research directions, we highlight how the conceptual and empirical approaches discussed here for consumption of cercariae are relevant for the infectious stages of other parasites and pathogens, illustrating the use of cercariae as a model system to help advance our knowledge regarding the general importance of parasite consumption.

Experimental water hyacinth invasion and destructive management increase human schistosome transmission potential

Invasive species cause environmental degradation, decrease biodiversity, and alter ecosystem function. Invasions can also drive changes in vector-borne and zoonotic diseases by altering important traits of wildlife hosts or disease vectors. Managing invasive species can restore biodiversity and ecosystem function, but it may have cascading effects on hosts, parasites, and human risk of infection. Water hyacinth, Eichhornia crassipes, is an extremely detrimental invader in many sites of human schistosome transmission, especially in Lake Victoria, where hyacinth is correlated with high snail abundance and hotspots of human schistosome infection. Hyacinth is often managed via removal or in situ destruction, but the effects of these strategies on snail intermediate hosts and schistosomes are not known. We evaluated the effects of water hyacinth invasion and these management strategies on the dynamics of human schistosomes, Schistosoma mansoni, and snails, Biomphalaria glabrata, in experimental mesocosms over 17 weeks. We hypothesized that hyacinth, which is inedible to snails, would affect snail growth, reproduction, and cercariae production through the balance of its competitive effects on edible algae and its production of edible detritus. We predicted that destruction would create a pulse of edible detrital resources, thereby increasing snail growth, reproduction, and parasite production. Conversely, we predicted that removal would have small or negligible effects on snails and schistosomes, because it would alleviate competition on edible algae without generating a resource pulse. We found that hyacinth invasion suppressed algae, changed the timing of peak snail abundance, and increased total production of human-infectious cercariae ~6-fold relative to uninvaded controls. Hyacinth management had complex effects on algae, snails, and schistosomes. Removal increased algal growth and snail abundance (but not biomass), and slightly reduced schistosome production. In contrast, destruction increased snail biomass (but not abundance), indicating increases in body size. Destruction caused the greatest schistosome production (10-fold more than the control), consistent with evidence that larger snails with greater access to food are most infectious. Our results highlight the dynamic effects of invasion and management on a globally impactful human parasite and its intermediate host. Ultimately, preventing or removing hyacinth invasions would simultaneously benefit human and environmental health outcomes.

A cercarial invadolysin interferes with the host immune response and facilitates infection establishment of Schistosoma mansoni

Schistosoma mansoni employs immune evasion and immunosuppression to overcome immune responses mounted by its snail and human hosts. Myriad immunomodulating factors underlie this process, some of which are proteases. Here, we demonstrate that one protease, an invadolysin we have termed SmCI-1, is released from the acetabular glands of S. mansoni cercaria and is involved in creating an immunological milieu favorable for survival of the parasite. The presence of SmCI-1 in the cercarial stage of S. mansoni is released during transformation into the schistosomula. SmCI-1 functions as a metalloprotease with the capacity to cleave collagen type IV, gelatin and fibrinogen. Additionally, complement component C3b is cleaved by this protease, resulting in inhibition of the classical and alternative complement pathways. Using SmCI-1 knockdown cercariae, we demonstrate that SmCI-1 protects schistosomula from complement-mediated lysis in human plasma. We also assess the effect of SmCI-1 on cytokine release from human peripheral blood mononuclear cells, providing compelling evidence that SmCI-1 promotes an anti-inflammatory microenvironment by enhancing production of IL-10 and suppressing the production of inflammatory cytokines like IL-1B and IL-12p70 and those involved in eosinophil recruitment and activation, like Eotaxin-1 and IL-5. Finally, we utilize the SmCI-1 knockdown cercaria in a mouse model of infection, revealing a role for SmCI-1 in S. mansoni survival.

From field to laboratory: isolation, genetic assessment, and parasitological behavior of Schistosoma mansoni obtained from naturally infected wild rodent Holochilus sciureus (Rodentia, Cricetidae), collected in Northeastern Brazil

Wild rodent species are naturally infected by Schistosoma mansoni; however, the genetic characterization of the parasite, its parasitological features, and its role in human schistosomiasis are poorly understood. In this study, we isolated and characterized Schistosoma from naturally infected Holochilus sciureus, called HS strain, collected from a schistosomiasis endemic region in Maranhão State, Brazil. To isolate the parasite, miracidia obtained from the livers of H. sciureus were used to infect Biomphalaria glabrata of sympatric (called SB) and allopatric (called BH) strains, and the produced cercariae were subcutaneously inoculated into hamsters and/or BALB/c mice. Parasitological kinetics in experimentally infected hosts were evaluated, and the tRNA^Cys-12S (referred to as 16S herein) and cox 1 regions of mtDNA from isolated worms were amplified and sequenced. Only miracidia obtained from infected mice, but not from hamsters, were capable of infecting B. glabrata, allowing maintenance of the isolated parasite. Cox1 and 16S mtDNA sequences showed 100% similarity with S. mansoni, and phylogenetic analysis showed that the HS strain of S. mansoni forms an assemblage with isolates from America and Kenya, confirming the conspecificity. Experimental infection of B. glabrata SB with S. mansoni HS resulted in two peaks of cercariae shedding at 45 and 70 days post-infection (dpi) and caused higher mortality than in B. glabrata BH. The worm recovery rate in mice was approximately 13%, and the peak of egg elimination occurred at the 10th week post-infection. Therefore, S. mansoni obtained from H. sciureus was successfully isolated, genetically characterized, and maintained in mice, allowing further study of this schistosome strain.

Elucidating the life cycle of opossum parasites: DNA sequences reveal the involvement of planorbid snails as intermediate hosts of Rhopalias spp. (Trematoda: Echinostomatidae) in Brazil

Echinostomatid digeneans belonging to the genus Rhopalias are intestinal trematodes found mainly in opossums in the New World. The genus comprises seven species, but their life cycles and intermediate hosts have been unknown until now. During our long-term study carried out in freshwater habitats within the state of Minas Gerais, Southeast Brazil, echinostomatid cercariae lacking collar spines were found in planorbid snails Biomphalaria glabrata, Biomphalaria straminea, Drepanotrema lucidum and Gundlachia ticaga in six different batches of snail samples collected between 2010 and 2019. Morphologically, the larvae reported herein are morphologically consistent with each other and characterized by the presence of 2-3 large ovoid or spherical corpuscles in each main duct of the excretory system, resembling to Cercaria macrogranulosa previously described from the same region of Brazil. Partial sequences of the ITS (ITS1-5.8S-ITS2) region and 28S gene of the nuclear ribosomal RNA operon, and partial sequences of mitochondrial nad1 and cox1 genes were obtained and compared with the data available for members of the family Echinostomatidae. Nuclear markers indicate that all samples of cercariae evaluated in the present study can be assigned to Rhopalias, but distinct from North American isolates of Rhopalias macracanthus, Rhopalias coronatus and Rhopalias oochi (divergence 0.2-1.2% in 28S and 0.8-4.7% in ITS). The lack of differences verified in both 28S and ITS in 5 out 6 studied samples suggested that they belong to the same species. However, nad1 sequences revealed that our cercariae correspond to three distinct species of Rhopalias (interspecific divergence: 7.7-9.9%), named here as Rhopalias sp. 1, found in B. straminea and G. ticaga, Rhopalias sp. 2 found in B. glabrata and D. lucidum, and Rhopalias sp. 3 also found in D. lucidum. They also differ by 10.8-17.2% from a North American isolate of R. macracanthus sequenced in this study. The cox1 sequences obtained for Rhopalias sp. 1 and Rhopalias sp. 2 (but not Rhopalias sp. 3) reveal that they are distinct from North American isolates of R. macracanthus (genetic divergence 16.3-16.5% and 15.6-15.7%, respectively), R. coronatus (9.2-9.3% and 9.3-9.5%) and Rhopalias oochi (9.0% and 9.5-10.1%). Encysted metacercariae with general morphology similar to that of the body of cercariae were found in tadpoles of Rhinella sp. from the same stream where snails harbored Rhopalias sp. 2, suggesting that the amphibians could act as second intermediate hosts of species of Rhopalias. Data obtained provide the first insights into the life cycle of this unusual echinostomatid genus.

Thinking "outside the box": The effect of nontarget snails in the aquatic community on mollusc-borne diseases

There is a great need to understand the impact of complex communities on the free-living parasite stages that are part of them. This task becomes more complex as nonnative species emerge, changing existing relationships and shaping new interactions in the community. A relevant question would be: Can the coexistence of nontarget snails with the target hosts contribute to trematodasis control? We used field and experimental approaches to investigate nonnative competitor-induced parasite dilution. During a three-year field study, we investigated digenean infection in Lymnaea stagnalis from eight Polish lakes inhabited or uninhabited by Potamopyrgus antipodarum. Additionally, we verified the presence of digenean infections in the populations of P. antipodarum. Moreover, we conducted an experimental infection of L. stagnalis with miracidia of Trichobilharzia szidati under increasing densities of P. antipodarum and aimed to infect P. antipodarum with them separately. The prevalence of avian schistosomes in lymnaeid snails was significantly higher in uninhabited lakes than in lakes inhabited by P. antipodarum. Our study indicates that waters with a higher density of invaders have a lower prevalence of avian schistosomes in lymnaeid hosts. The results of experimental studies confirmed that the presence of high densities of P. antipodarum reduces the probability of target host infection. Both field and experimental studies rule out the role of P. antipodarum as a source of avian schistosome cercariae. Here, a nonnative species was tested as a diluter, which in practice may be harmful to the local environment. This work is not a call for the introduction of nonnative species; it is intended to be a stimulus for researchers to continue searching for natural enemies of parasites because, as our results show, they exist. Finding natural enemies to the most dangerous species of human and animal parasites that will pose no threat to the local environment could be groundbreaking.

The efficacy of soap against schistosome cercariae: A systematic review

BACKGROUND

Schistosomiasis is a parasitic disease that is endemic in 78 countries and affects almost 240 million people worldwide. It has been acknowledged that an integrated approach that goes beyond drug treatment is needed to achieve control and eventual elimination of the disease. Improving hygiene has been encouraged by World Health Organisation, and one aspect of good hygiene is using soap during water-contact activities, such as bathing and doing laundry. This hygiene practice might directly reduce the skin exposure to cercariae at transmission sites. A systematic review was carried out to investigate the efficacy of soap against schistosome cercariae and to identify the knowledge gaps surrounding this topic.

METHODOLOGY

Six online databases were searched between 5th and 8th July of 2021. Records returned from these databases were screened to remove duplicates, and the remaining records were classified by reading titles, abstracts, and full texts to identify the included studies. The results were categorised into two groups based on two different protective mechanisms of soap (namely, damage to cercariae and protection of skin).

CONCLUSIONS

Limited research has been conducted on the efficacy of soap against schistosome cercariae and only 11 studies met the criteria to be included in this review. The review demonstrates that soap has the potential of protecting people against schistosome cercariae and there are two protective aspects: (1) soap affects cercariae adversely; (2) soap on the skin prevents cercariae from penetrating the skin, developing into adult worms and producing eggs. Both aspects of protection were influenced by many factors, but the differences in the reported experimental conditions, such as the cercarial endpoint measurement used and the cercaria numbers used per water sample, lead to low comparability between the previous studies. This review indicates that more evidence is needed to inform hygiene advice for people living in schistosomiasis endemic areas.

Autochthonous transmission of the Indomalayan parasite, Transversotrema patialense, in the Caribbean: Molecular, morphological, and experimental evidence

The Asian freshwater snail Melanoides tuberculata has been established since the 1960s in the Americas, where it transmits cercariae of a small number of digenetic trematode species from its native range. In 2021-2022, 24 M. tuberculata were discovered shedding transversotrematid cercariae in Puerto Rico, where parasites of this snail have not been previously studied. Adult transversotrematids (in some cases, gravid) were found on field-caught fish and on fish exposed to shedding snails, including on fish species native to Puerto Rico. Adults and cercariae were identified as Transversotrema patialense (Soparkar, 1924), a species native to the Indomalayan region. Morphological identification was supported with 28S rDNA sequences closely matching that from unidentified transversotrematid cercariae in Thailand. The absence of T. patialense in snails collected prior to 2021, increasing prevalence of infection in snails collected thereafter, and lack of variation in parasite DNA sequences (28S, internal transcribed spacer 2, cytochrome c oxidase I) from three isolates are consistent with a recently introduced and possibly expanding parasite population. Transversotrema patialense has been recorded outside its native range before, but most studies (including a prior record in the Americas) reported the parasite from captive hosts from commercial sources such as pet shops. The present results thus provide the first demonstration of natural transmission of T. patialense in the Americas. Phylogenetic analysis of 28S but not of ITS2 show the transversotrematid genus Transversotrema Witenberg, 1944 is paraphyletic, with Crusziella Cribb, Bray and Barker1992 nested within it.

Specific Nucleic AcId Ligation for the detection of Schistosomes: SNAILS

Schistosomiasis, also known as bilharzia or snail fever, is a debilitating neglected tropical disease (NTD), caused by parasitic trematode flatworms of the genus Schistosoma, that has an annual mortality rate of 280,000 people in sub-Saharan Africa alone. Schistosomiasis is transmitted via contact with water bodies that are home to the intermediate host snail which shed the infective cercariae into the water. Schistosome lifecycles are complex, and while not all schistosome species cause human disease, endemic regions also typically feature animal-infecting schistosomes that can have broader economic and/or food security implications. Therefore, the development of species-specific Schistosoma detection technologies may help to inform evidence-based local environmental, food security and health systems policy making. Crucially, schistosomiasis disproportionally affects low- and middle-income (LMIC) countries and for that reason, environmental screening of water bodies for schistosomes may aid with the targeting of water, sanitation, and hygiene (WASH) interventions and preventive chemotherapy to regions at highest risk of schistosomiasis transmission, and to monitor the effectiveness of such interventions at reducing the risk over time. To this end, we developed a DNA-based biosensor termed Specific Nucleic AcId Ligation for the detection of Schistosomes or ‘SNAILS’. Here we show that ‘SNAILS’ enables species-specific detection from genomic DNA (gDNA) samples that were collected from the field in endemic areas.

Schistosomiasis is a neglected tropical disease, caused by the parasitic trematodes of the genus Schistosoma. Schistosomiasis is endemic to regions within Africa, Asia and South America with at least 250 million people infected and a further 779 million at risk of infection. The lifecycle of schistosomes are complex and involve specific freshwater intermediate snail hosts which shed infective cercariae into the waterbodies they inhabit. Schistosomiasis is subsequently transmitted to humans or animals that contact cercariae contaminated water. In Africa, human disease is largely caused by Schistosoma mansoni and Schistosoma haematobium. However, endemic regions also typically feature animal-infecting schistosomes that can have broader economic and/or food security implications. Therefore, the development of species-specific Schistosoma detection technologies may help to inform local environmental, food security and health programmes. To this end, we re-purposed a nucleic acid detection technology to enable the detection of different schistosome species. Our DNA-biosensor, abbreviated as ‘SNAILS’, employs carefully designed probes that recognise species-specific DNA sequences, coupled with enzymatic amplification steps, and a fluorescent signal-dye to indicate a positive detection. ‘SNAILS’ successfully differentiates between S. mansoni and S. haematobium samples and could conceivably be employed within future global health programmes.

[Activity of aromatic pyrrole-based compounds against of Schistosoma japonicum cercariae and acute toxicity to fish]

OBJECTIVE

To test the activity of aromatic pyrrole-based compounds against cercariae of Schistosoma japonicum and test their acute toxicity to fish.

METHODS

A series of aromatic pyrrole-based compounds were synthesized using 4-benzyl-5-(trifluoromethyl)-1H-pyrrole-3-nitrile as the lead compound. The synthesized compounds were prepared into solutions at concentrations of 10.00, 1.00, 0.10, 0.01 mg/L, and the activity of these solutions against S. japonicum cercariae was tested in 30 min, while 0.10 mg/L and 0.01 mg/L niclosamide solutions served as a positive control and dechlorinated water with 1% dimethyl sulfoxide (DMSO) was used as a negative control, with 10 to 30 cercariae of S. japonicum in each group. In addition, the compounds were prepared into solutions at concentrations of 0.50, 0.25, 0.12, 0.06, 0.03 mg/L, and their toxicity to zebrafish was tested in 72 h, while 0.15 mg/L and 0.30 mg/L niclosamide solutions served as a positive control and dechlorinated water with 1% DMSO was used as a negative control, with 10 zebrafishes in each group.

RESULTS

A total of 7 aromatic pyrrole-based compounds were successfully synthesized. Treatment with compounds 102, 104 and 106 at a concentration of 0.01 mg/L for 30 min killed all S. japonicum cercariae, and compounds 105 and 107 showed no activity against cercariae. No death of cercariae was found in the blank control group, while treatment with 0.10 mg/L niclosamide for 10 min caused a 100% mortality rate of S. japonicum cercariae and 0.01 mg/L niclosamide failed to kill S. japonicum cercariae. No zebrafish death was found 72 h post-treatment with compounds 101, 104 and 105 at a concentration of 0.03 mg/L, and exposure to compounds 102, 103 and 106 at a concentration of 0.03 mg/L for 12 h resulted in a 100% mortality rate of zebrafish. No zebrafish death occurred 72 h post-treatment with 0.50 mg/L Compound 104, and no zebrafish death was found in the blank control group, while treatment with 0.30 mg/L niclosamide for 24 h resulted in a 100% mortality rate of zebrafish.

CONCLUSIONS

Compound 104 achieves a 100% mortality rate against S. japonicum cercariae at a concentration of 0.01 mg/L for 30 min, and causes no death of zebrafish at a concentration of 0.50 mg/L for 72 h, which may serve as a cercaricide candidate.

Population dynamics and diversity of trematode infections in Bithynia siamensis goniomphalos in an irrigated area in northeast Thailand

Several trematodes including Opisthorchis viverrini utilize Bithynia siamensis goniomphalos as a snail intermediate host in their life cycles. In order to capture a comprehensive range of host–parasite interactions and their transmission dynamic patterns, B. s. goniomphalos were sampled monthly over 4 consecutive years in an irrigated paddy-field habitat in northeast Thailand. Using a standard cercarial shedding method, a high diversity of trematodes (17 types) was recovered. Virgulate xiphidiocercariae were the most prevalent (7.84%) followed by O. viverrini (0.71%). In addition to seasonal and environmental factors, the quantity of irrigation water for rice cultivation correlated with transmission dynamics of trematodes in B. s. goniomphalos. The peak prevalence of all trematode infections combined in the snails shifted from the cool-dry season in 2010–2012 to the hot-dry season in 2013 associated with an increasing quantity of water irrigation. A low frequency of mixed trematode infections was found, indicating that the emergence of virgulate cercariae, but not of O. viverrini, was negatively impacted by the presence of other trematodes in the same snail. Taken together, the observed results suggest that interactions between host and parasite, and hence transmission dynamics, depend on specific characteristics of the parasite and environmental factors including irrigated water for rice cultivation.

Differential proteomic analysis of laser-microdissected penetration glands of avian schistosome cercariae with a focus on proteins involved in host invasion

Schistosome invasive stages, cercariae, leave intermediate snail hosts, penetrate the skin of definitive hosts, and transform to schistosomula which migrate to the final location. During invasion, cercariae employ histolytic and other bioactive products of specialized holocrine secretory cells - postacetabular (PA) and circumacetabular (CA) penetration glands. Although several studies attempted to characterize protein composition of the in vitro-induced gland secretions in Schistosoma mansoni and Schistosoma japonicum, the results were somewhat inconsistent and dependent on the method of sample collection and processing. Products of both gland types mixed during their secretion did not allow localization of identified proteins to a particular gland. Here we compared proteomes of separately isolated cercarial gland cells of the avian schistosome Trichobilharzia szidati, employing laser-assisted microdissection and shotgun LC-MS/MS, thus obtaining the largest dataset so far of the representation and localization of cercarial penetration gland proteins. We optimized the methods of sample processing with cercarial bodies (heads) first. Alizarin-pre-stained, chemically non-fixed samples provided optimal results of MS analyses, and enabled us to distinguish PA and CA glands for microdissection. Using 7.5 x 10⁶ μm³ sample volume per gland replicate, we identified 3347 peptides assigned to 792 proteins, from which 461 occurred in at least two of three replicates in either gland type (PA = 455, 40 exclusive; CA = 421, six exclusive; 60 proteins differed significantly in their abundance between the glands). Peptidases of five catalytic types accounted for ca. 8% and 6% of reliably identified proteins in PA and CA glands, respectively. Invadolysin, nardilysin, cathepsins B2 and L3, and elastase 2b orthologs were the major gland endopeptidases. Two cystatins and a serpin were highly abundant peptidase inhibitors in the glands. While PA glands generally had rich enzymatic equipment, CA glands were conspicuously abundant in venom allergen-like proteins.

Adult schistosomes have an epithelial bacterial population distinct from the surrounding mammalian host blood

Background

Schistosomiasis is a neglected tropical parasitic and chronic disease affecting hundreds of millions of people. Adult schistosomes reside in the blood stream of the definitive mammalian host. These helminth parasites possess two epithelial surfaces, the tegument and the gastrodermis, both of which interact with the host during immune evasion and in nutrient uptake.

Methods

Female ARC Swiss mice (4–6 weeks old) were infected percutaneously with Schistosoma japonicum cercariae freshly shed from Oncomelania hupensis quadrasi snails (Philippines strain). Fluorescent in situ hybridisation (FISH) was performed by using fresh adult S. japonicum perfused from those infected mice. Adult S. japonicum worms were processed to isolate the tegument from the carcass containing the gastrodermis; blood and bile were collected individually from infected and uninfected mice. Total DNA extracted from all those samples were used for microbiome profiling.

Results

FISH and microbiome profiling showed the presence of bacterial populations on two epithelial surfaces of adult worms, suggesting they were distinct not only from the host blood but also from each other. Whereas microbial diversity was reduced overall in the parasite epithelial tissues when compared with that of host blood, specific bacterial taxa, including Anoxybacillus and Escherichia, were elevated on the tegument. Minimal differences were evident in the microbiome of host blood during an active infection, compared with that of control uninfected blood. However, sampling of bile from infected animals identified some differences compared with controls, including elevated levels of Limnohabitans, Clostridium and Curvibacter.

Conclusions

Using FISH and microbial profiling, we were able to demonstrate, for the first time, that bacteria are presented on the epithelial surfaces of adult schistosomes. These schistosome surface-associated bacteria, which are distinct from the host blood microenvironment, should be considered as a new and important component of the host-schistosome interaction. The importance of individual bacterial species in relation to schistosome parasitism needs further elucidation.

Malacological and Parasitological Surveys on Ethiopian Rift Valley Lakes: Implications for Control and Elimination of Snail-Borne Diseases

Schistosomiasis is one of the snail-borne diseases responsible for the second-highest burden of diseases among neglected tropical diseases. The use of mass drug administration to the populations most at risk is a backbone of the strategy to prevent and control schistosomiasis transmission. However, it offers no protection against re-infection, and humans are often re-exposed when they return to water bodies where snails release cercariae. Surveys on cercarial infection in snails could provide better insights on human disease risk. Hence, in this study, we investigated cercarial infection in snails and also determined the epidemiology of Schistosoma mansoni among fishermen at Ethiopian Rift Valley lakes. Freshwater snails were collected from the shorelines of Ethiopian Rift Valley lakes for examination of cercarial infection during 2020. Environmental data on water quality variables and physical characteristics of snail habitats were collected. Stool samples were collected from fishermen and the Kato-Katz technique was applied for the quantification of Schistosoma mansoni eggs. A malacological survey indicated that six morphologically distinguishable types of cercariae were found in snails. Infected snails with cercaria were more likely present in habitats with high five-day biological oxygen demand and low dissolved oxygen. The overall prevalence of Schistosoma mansoni infection among the fishermen at Ethiopian Rift Valley lakes was found to be 21.5%. This indicates that fishermen at Ethiopian Rift Valley lakes are one of the groups of people harboring schistosome cercariae which are potentially responsible for the transmission of schistosomiasis to lakeshore communities who have contact with lake water. Therefore, complementary medical treatment, public health interventions, environmental management and snail reduction are needed to control the transmission of schistosomiasis.

Genetic architecture of transmission stage production and virulence in schistosome parasites

Both 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 parents, F1 parents 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 (i.e. Quantitative Trait Loci). 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.

Eye fluke effects on Danish freshwater fish: Field and experimental investigations

Eye flukes in fish are common in freshwater lakes. Fish become infected by the penetration of cercariae released from freshwater snails, and high infection pressures may be associated with mortalities in a Danish lake. Examination of two other freshwater lakes, combined with laboratory study, supported the notion. We investigated 77 freshwater fish from two lakes and the infection level suggested the occurrence of a high cercarial infection pressure in the Danish lakes. Dominant genera were Tylodelphys and Diplostomum covering a range of species identified by PCR and sequencing of the 18S (partial)-ITS1-5.8S-ITS2-28S (partial) of the rDNA. Cercariae of the prevalent species Diplostomum pseudospathaceum were used to infect zebrafish Danio rerio for the elucidation of short-term effects on the fish host. Zebrafish did not display abnormal behaviour when exposed to 200-400 cercariae, but a dosage of 600 and 1,000 cercariae/fish proved lethal. When fish were exposed to sublethal dosages, 19 out of 27 immune genes were significantly regulated and three genes encoding cytokine (IL 4/13B, IL-6 and IL-8) were upregulated at 3 hr post-infection (hpi), whereas others were downregulated especially at a later time point. We suggest that direct massive cercarial penetration of fish surfaces may be detrimental and may represent a threat to fish populations.

Germinal development in embryonic rediae of the hemiuroid digenean Bunocotyle progenetica: an ultrastructural study

Embryonic development of reproductive organs in rediae of the digenean Bunocotyle progenetica was studied using transmission electron microscopy. The germinal primordium becomes morphologically distinct in early embryos as a weakly separated cell mass with a forming cavity. It consists of undifferentiated, differentiating, and supporting cells. As embryos develop, the supporting cells form a wall around the enlarging cavity. Other cells of the germinal primordium are incorporated into the wall as solitary cells or as small cell aggregations. Those situated posteriorly give rise to an incipient germinal mass functioning during postembryonic development. Undifferentiated and differentiating cells in the middle and the anterior part of the primordium ensure a considerable growth of the cavity wall, which incorporates solitary germinal cells. In advanced embryonic rediae, these cells mature, cleave, and give rise to germinal balls, which enter the forming brood cavity. In the most mature embryonic rediae, all these early cercarial embryos reside in a brood cavity, which is lined by that time with a syncytium continuous with the supporting tissue of the incipient germinal mass. Based on our results and the literature data, we suggest that the morphogenesis of the reproductive apparatus of the daughter parthenitae in hemiuroid digeneans may be characterized by (1) emergence of an incipient brood cavity within the germinal primordium, (2) formation of the cavity lining from the cells of the germinal primordium, (3) fragmentation and uneven distribution of the germinal material of the germinal primordium around the cavity, and (4) an anticipatory development of some of this germinal material.

Effect of light on the trematode Himasthla elongata: from cercarial behaviour to infection success

The cockle Cerastoderma edule, a socioeconomically important bivalve of the northeast Atlantic, is host to several trematodes, including Himasthla elongata. In the life cycle of this trematode, cercariae (free-living stages) emerge from the first intermediate host, a snail, to infect cockles as second intermediate hosts. During their lifespan (less than 2 d), cercariae must ensure successful host-to-host transmission via the surrounding water and therefore are exposed to and impacted by different environmental conditions, including abiotic factors. Given that the light:dark cycle is one of the major drivers of behaviour in aquatic habitats, we aimed to determine the influence of light on cercariae and host behaviour based on 3 hypotheses. First, by having a benthic second intermediate host, these cercariae will display a photonegative orientation; second, and conversely, host behaviour will not be influenced by light; and third, cercariae infection success will be light-dependent. Results showed that cercariae display a photopositive orientation (first hypothesis rejected), displaying movements towards light. Host activity (evaluated by oxygen consumption) was similar among conditions, i.e. dark vs. light (second hypothesis accepted), but hosts acquired more parasites when experimentally infected in the dark (third hypothesis accepted). This light-dependent infection of the host is explained by a change of cercarial behaviour when exposed to light, decreasing their infection success. This study highlights that trematode responses to external conditions may be linked to successful life cycle completion rather than being altered by the host habitat. Light influence on cercarial behaviour resulted in increased infection success that may affect trematode population dynamics and their distributional range.

Are Melanoides tuberculata and Tarebia granifera (Gastropoda, Thiaridae), suitable first intermediate hosts of Clonorchis sinensis in Vietnam?

Background

Two thiarid snail species, Melanoides tuberculata and Tarebia granifera have been reported as first intermediate hosts of the liver fluke Clonorchis sinensis; however, their role as true first intermediate hosts has not been verified. Thus, the present study aimed to clarify the suitability of these two snail species as first intermediate hosts of C. sinensis. This was accomplished by collecting snails from a highly endemic area for C. sinensis in Vietnam, the Thac Ba reservoir, and identifying shed cercariae using molecular techniques. We also conducted experimental infections of five snail species including M. tuberculata and T. granifera with eggs of C. sinensis.

Methodology/Principal findings

A total of 11,985 snails, representing 10 species were sampled. Five snail species, M. tuberculata, T. granifera, Lymnaea swinhoei, Parafossarulus manchouricus, and Bithynia fuchsiana were found shedding cercariae with an overall prevalence of infection ranging from 0.7% to 11.5%. Seven cercarial types were recorded. Cercariae of C. sinensis were only found in Parafossarulus manchouricus. Using a multiplex PCR approach for detecting C. sinensis infection, the prevalence in P. manchouricus was 4.2%. Additionally, all five snail species were experimentally exposed to C. sinensis eggs, however only P. manchouricus was successfully infected with an infection rate of 7.87%.

Conclusions/Significance

We confirmed that in the Thac Ba reservoir, Vietnam, the two thiarids, M. tuberculata and T. granifera are not suitable first intermediate hosts of C. sinensis. Only P. manchouricus was found infected by C. sinensis in nature, and was the only species that became infected experimentally.

Currently 13 snail species are reported as first intermediate hosts of Clonorchis sinensis, including two species of the Thiaridae, Melanoides tuberculata and Tarebia granifera. Both snail species have wide distributions in tropical and subtropical waters across the World, while the distribution of C. sinensis is much narrower and only occurs in endemic areas of East Asia. The role that these two thiarid snail species plays as successful hosts of C. sinensis, however, has been refuted in other studies. The present study was conducted to clarify this issue. Based on the results from field surveys in a newly discovered and highly endemic area for C. sinensis, as well as, data obtained under experimental conditions, we confirm that in Northern Vietnam, the two thiarid snail species are not successful first intermediate host of C. sinensis. C. sinensis was only detected in a single snail species, Parafossarulus manchouricus, through observation, molecular analyses and experimental infections.

Epidemiological and genetic characterization of larval stages of Fasciola gigantica in snail intermediate hosts in Karnataka State, India

Fasciolosis in ruminants in India is caused by the liver fluke Fasciola gigantica. Radix (Lymnaea) spp. are known to carry the infective stages of this parasite. Understanding the seasonal prevalence of F. gigantica infection in the intermediate host is of extreme importance in order to elucidate the transmission dynamics of the parasite. So the present study was designed to determine the bioclimatic distribution of larval stages of F. gigantica in Radix spp. snails as well as to explore the genetic diversity of F. gigantica in three geographical regions (Deccan plateau, Western Ghats and coastal region) of Karnataka. The lymnaeid snails were sampled (n = 2077) for a period of one year (June 2015 to May 2016) at 24 sites. The snails were morphologically identified and the infection status was established through cercarial shedding and nested polymerase chain reaction (PCR) based technique targeting second internal transcribed spacers (ITS-2) of nuclear ribosomal DNA. The sensitivity of PCR (8.2%) for detection of F. gigantica infection within snail is significantly higher than cercarial shedding (4.3%) with an overall prevalence of 5.1%. The prevalence of infection was higher in winter than in the rainy and summer seasons (6.2% instead of 4.6% and 4.3% respectively). Deccan plateau (5.8%) showed a higher prevalence of infection compared to Western Ghats (5.2%) and Coastal region (3.6%). The sequencing ITS-2 region permitted the identification of the parasite as F. gigantica which is having high implication in studying the population genetic structure of the parasite in the country. In conclusion, overall results indicated that Radix spp. snails harboured F. gigantica developmental stages throughout the year and nested PCR was found to be sensitive and specific for detection of F. gigantica infection in snails compared to routine parasitological techniques.

First molecular identification of an agent of diplostomiasis, Diplostomum pseudospathaceum (Niewiadomska 1984) in the United Kingdom and its genetic relationship with populations in Europe

Trematode genus Diplostomum comprises of parasitic species which cause diplostomiasis, the 'white eye' disease in fish and heavy infection can result in mortality. The increasing availability of DNA sequences of accurately identified Diplostomum species on public data base presently enables the rapid identification of species from novel sequences. We report the first molecular evidence of the occurrence of D. pseudospathaceum in the United Kingdom. Two gene regions, nuclear internal transcribed spacer cluster (ITS1-5.8S-ITS2) and mitochondrial cytochrome c oxidase subunit 1 (cox1) of cercariae from infected aquatic snails, Lymnaea stagnalis collected in several locations in Southern England were sequenced. Phylogenetic analysis based on both sequenced genes revealed that the novel sequences were D. pseudospathaceum. Molecular diversity analysis of published D. pseudospathaceum cox1 sequences from seven countries in Europe and the novel sequences from the present study revealed high diversity, but low nucleotide divergence and a lack of gene differentiation between the populations. Haplotype network analysis depicted a star-like pattern and revealed a lack of geographic structure in the population. Fixation indices confirmed gene flow between populations and we suspect high levels of dispersal facilitated by highly mobile second intermediate (fish) and definitive (piscivorous birds) host may be driving gene flow between populations. Neutrality tests and mismatch distribution indicated recent population growth/expansion for D. pseudospathaceum in Europe.

Geographical and behavioral risks associated with Schistosoma haematobium infection in an area of complex transmission

BACKGROUND

Schistosoma haematobium infection in endemic areas varies depending on the nature and complexity of the transmission networks present. Studies of micro-geographical transmission of S. haematobium infection indicate that discrepancy in prevalence between households is associated with diverse water contact behaviors and transmission that is restricted to particular sites harboring snail intermediate hosts. Detection of variations in the transmission sources with complex transmission networks of water bodies is required for optimization of malacological control. Longitudinal parasitological and malacological surveys were conducted to investigate geographical variations in transmission of urogenital schistosomiasis in Ikingwamanoti village, Shinyanga District, Tanzania.

METHODS

Urine samples were collected at baseline and follow-up time points from 282 school-aged children and examined microscopically for the presence of S. haematobium eggs. Malacological surveys involved collection of Bulinus nasutus every month from 30 sites. Snails were examined for patent infections. Global positioning system was used to map household distances from S. haematobium transmission sites, while water contact behavior was assessed using a questionnaire.

RESULTS

Schistosoma haematobium infection was observed to be prevalent among older children (12-14 years) compared to younger groups prior to treatment, but no significant difference in infection prevalence was observed at one-year. Boys were highly infected than girls at both time points. No spatial influence was observed between children's infection and the distance from child's residence to the nearby snail habitats nor was any significant association observed between children's reported water contact behavior with S. haematobium infection. However, malacological surveys with cercarial shedding combined with GPS data detected significant variation among different water sources in the transmission of S. haematobium with children living in households near to ponds with high B. nasutus populations having the highest prevalence of infection.

CONCLUSIONS

Interaction between malacological surveys with cercarial shedding combined with GPS mapping in endemic settings can help detection of transmission sources even in areas with complex transmission networks. Subsequent studies are needed to determine whether the combination of GPS mapping and parasitology screens can aid the detection of transmission hotspots across varied transmission settings to enhance schistosomiasis control programmes.

Putative new genera and species of avian schistosomes potentially involved in human cercarial dermatitis in the Americas, Europe and Africa

New larval avian schistosomes found in planorbid snails from Brazil and USA were used for morphological and molecular studies. Eggs with a distinctive long polar filament were found in ducks infected experimentally with Brazilian cercariae. Similar eggs were reported previously in wild or experimentally infected anatids from Brazil, South Africa, and the Czech Republic. Molecular phylogenetic analyses showed that the North American and European schistosomes are sister taxa, which are both sister to the Brazilian species. However, these clades do not group with any named genus. Molecular data plus egg morphology suggest that these are new putative genera and species of avian schistosomes that can cause human cercarial dermatitis in the Americas, Africa and Europe.

[Formation and Characteristics of Fasciola hepatica Metacercariae]

The Fasciola hepatica miracidia were used to infect 10 Galba pervia in a random manner. Beginning from day 44 after infection on which 10 metacercariae were found and a total of 495 metacercariae found in 24 days. No signs of cercaria escape or metacercaria formation in the early morning observed during 8 : 00-24 : 00, regardless of the environmental change. Metacercaria formation occurred mainly in the early morning. The metacercariae could attach to any object in water, but were easy to detach themselves. The findings suggest that F. hepatica cercaria escape and metacercaria formation mainly occur in the early morning in Dali.

[Resistance of rAAV2-MfE77.43-Transferred Mice to Schistosoma japonicum Infection]

OBJECTIVE

To investigate the resistance of E77.43 gene of Microtus fortis（MfE77.43） to Schistosoma japonicum infection.

METHODS

MfE77.43 was constructed into the recombinant Adeno-associated virus AAV2. The AAV2-MfE77.43 was transfected into HEK293 cells by the calcium phosphate DNA coprecipitation method. The recombinant rAAV2-MfE77.43 was purified and total RNA was extracted from the transfected cells. The expression of E77.43 was examined by RT-PCR and the purity of rAAV2-MfE77.43 was analyzed by SDS-PAGE. Eighteen KM mice were divided into three groups （n=6 in each group）. Mice in the experiment group were intramuscularly injected on days 0, 3 and 7 with 400 μl recombinant AAV2-MfE77.43 virus which was 5-fold diluted in normal saline. Mice in negative control and blank control groups received same volume of pAAV or normal saline. Venous blood was collected through the tail before each injection, and E77.43 expression in plasma was detected by dot-ELISA method. After the last injection, each mouse was infected with 40 S. japonicum cercariae and sacrificed on day 41 after infection. Adult worms and liver eggs per gram（LEPG） were counted. Worm and egg reduction rate was calculated respectively. Egg granulomas were observed by HE staining.

RESULTS

RT-PCR resulted in a 330 bp specific band. SDS-PAGE of virus shell protein revealed three protein bands with M(r) of 87 000, 72 000 and 62 000, respectively. Dot-ELISA showed that E77.43 protein began to be expressed on day 3 after rAAV2-MfE77.43 injection, remaining stable till day 41. The adult worm number and LEPG were 20.16±3.93 and 19 800±2 715, respectively, with a worm and egg reduction rate of 27.3% and 26.2% in the experiment group. While the worm number and LEPG in the negative control group were 29.16±2.44 and 28 000±2 192（P<0.01）, respectively. HE staining and observation revealed fewer eosinophils and inflammatory cells around the liver eggs in the therapy group.

CONCLUSION

The E77.43 gene shows protective effects against S. japonicum infection, indicating that E77.43 may participate in the natural resistance of Microtus fortis to S. japonicum infection.

[T Follicular Helper Cells and Related Molecules in Schistosoma japonicum Infected Mice after Praziquantel Treatment]

OBJECTIVE

To investigate the pathological changes of liver and spleen of mice infected with Schistosoma japonicum and the changes of T follicular helper (Tfh) cells and surface molecules after praziquantel treatment.

METHODS

Fifteen female C57BL/6 mice （6-8 weeks） were randomly assigned into the praziquantel treated infection group （treated group）, infection control group (untreated group) and uninfected group （n=5 in each group）. The mice in the treated group and untreated group were each infected with 20 S. japonicum cercariae through the abdominal skin, and mice in the treated group were further administered with intragastric praziquantel [200 mg/（kg·d）] at week 6 post-infection for 3 consecutive days. Mice were sacrificed at week 4 after treatment to observe the morphological changes of liver and spleen and calculate the worm reduction rate and the liver egg reduction rate. The Tfh cell to CD4+ T cell ratio, as well as the expression of inducible T-cell costimulator （ICOS） and programmed cell death protein 1（PD-1） on peripheral blood and spleen, were determined by flow cytometry. Schistosome soluble egg antigen (SEA) specific IgG antibodies in serum were detected by ELISA.

RESULTS

The pathological changes of liver and spleen in the treated group were less severe compared with those of the untreated group, with a worm reduction rate of 84.1% and liver egg reduction rate of 69.1%. Flow cytometry showed that the percent of Tfh cells in peripheral blood and spleen was significantly higher in the treated group（14.7%-18.0%, 15.6%-25.0%） and the untreated group（13.7%-16.7%, 12.4%-18.2%） than that in the uninfected group（2.5%-6.8%, 4.9%-8.0%）, but there was no significant difference between the treated and untreated groups. The expression of ICOS in the peripheral blood and the spleen was significantly higher in untreated group（1.3%-3.2%, 4.1%-7.0%） than in the treated group（0.7%-1.1%, 1.8%-6.8%） and the uninfected group（0.2%-0.3%, 0.5%-0.8%）（P<0.01）, The expression of ICOS in the spleen was significantly higher in the treated group than in the uninfected group (P<0.01), while this difference was not found for ICOS expression in the peripheral blood. The PD-1 expression in the peripheral blood and spleen was significantly higher in the untreated group（0.8%-1.9%, 4.1%-10.7%） than in the uninfected group（0.4%-0.8%, 1.2%-1.8%）（P<0.01）, while there was no significant difference between the treated group（0.5%-1.5%, 4.5%-8.9%） and the untreated group (P>0.05). In addition, there was no significant difference in the level of SEA specific IgG between the treated group（2.015±0.061） and the untreated group（1.969±0.038） at 4 weeks after praziquantel treatment.

CONCLUSION

Praziquantel treatment can significantly alleviate the lesions of the liver and the spleen and decrease the ICOS expression by Tfh cells in the peripheral blood and spleen.

Multi-host transmission dynamics of schistosomiasis and its optimal control

In this paper we formulate a dynamical model to study the transmission dynamics of schistosomiasis in humans and snails. We also incorporate bovines in the model to study their impact on transmission and controlling the spread of Schistosoma japonicum in humans in China. The dynamics of the model is rigorously analyzed by using the theory of dynamical systems. The theoretical results show that the disease free equilibrium is globally asymptotically stable if R0 < 1, and if R0 > 1 the system has only one positive equilibrium. The local stability of the unique positive equilibrium is investigated and sufficient conditions are also provided for the global stability of the positive equilibrium. The optimal control theory are further applied to the model to study the corresponding optimal control problem. Both analytical and numerical results suggest that: (a) the infected bovines play an important role in the spread of schistosomiasis among humans, and killing the infected bovines will be useful to prevent transmission of schistosomiasis among humans; (b) optimal control strategy performs better than the constant controls in reducing the prevalence of the infected human and the cost for implementing optimal control is much less than that for constant controls; and

[Preliminary Genetic and Functional Analyses of Schistosoma japonicum Chymotrypsin-like Protease]

OBJECTIVE

To investigate the gene expression, localization and potential functions of Schistosoma japonicum chymotrypsin-like protease (SjCTRL) in the host, and evaluate its potential immune-protection efficacy against S. japonicum infection in mice.

METHODS

The physicochemical properties of SjCTRL and its phylogenetic relationship with homologous genes from other species were analyzed with bioinformatic software. The distribution of SjCTRL transcripts in 26-day-old worms was investigated using whole-mount in situ hybridization. The transcriptional levels of SjCTRL in male and female worms at four development stages (14, 18, 22, and 26 days after infection) were measured with quantitative real-time PCR. The SjCTRL-dsRNA was prepared and used to induce RNA interference (RNAi) in 26-day-old worms via soaking in vitro, and confocal microscopy was used to observe the morphological changes of worms after RNAi. Primers were designed to amplify the encoding sequence (excluding the transmembrane region) from the S. japonicum cDNA. The truncated gene was subcloned into the pET-28a plasmid, transformed into E. coli BL21 (DE3) for expression. Mice were immunized with the purified recombinant protein and challenged with cercariae. The worms and mouse liver were collected on day 35 after the challenge, and the worm-reduction rate and egg-reduction rate were calculated.

RESULTS

The in situ hybridization results showed that SjCTRL mRNA was located in the posterior segment of intestinal tract of female worms, and having abundence only in 26-day-old female worms. After RNAi with SjCTRL-dsRNA, the mRNA expression was reduced to 25.7% (P< 0.05), without significant morphological changes. Using the recombinant plasmid pET-28a/SjCTRL, expression of insoluble SjCTRL protein was induced. Mice immunized with this protein gained a worm-reduction rate of 25.4% and an egg-reduction rate of 80.5% in liver after being challenged with cercariae.

CONCLUSION

This study proves a high transcriptional level of SjCTRL in the posterior segment of intestinal tract in 26-day-old female worms, which can be reduced by RNAi treatment in vitro. Immunization with the SjCTRL protein can reduce adult worms and liver eggs.

[Plasma Metabolism and Protective Effect of Oral Administration of Niclosamide on Schistosoma japonicum Cercarial Invasion in Mice]

OBJECTIVE

To study the metabolism of niclosamide in plasma, and the protective effect of its oral administration on Schistosoma japonicum cercarial invasion in mice.

METHODS

Twenty-four female Kunming mice were randomly divided into 8 groups, each with 3 mice. Each mouse was treated orally with 120 mg niclosamide per kilogram of body weight (120 mg/kg). The plasma samples were collected at 0.25, 0.5, 1, 2, 4, 8, 16, and 24 h after treatment by retro-orbital blood sampling. The blood drug concentration was determined by HPLC. The pharmacokinetics parameters were calculated such as peak concentration (Cmax), peak time (Tmax), mean residence time (MRT), and elimination half life (T½). Thirty Kunming mice were randomly divided into 6 groups. Among them, 5 groups were treated orally with 40, 80, 120, 160, and 200 mg/kg niclosamide, respectively. The remaining untreated group served as control. One hour post-treatment, each mouse was infected with 40 ± 2 Schistosoma japonicum cercariae. Another 35 mice treated with 200 mg/kg niclosamide were randomly divided into 7 groups. Mice in each group were infected with 40 ± 2 S. japonicum cercariae on 0.25, 1, 4, 8, 12, and 24 h after treatment, named as group A, B, C, D, E, and F. Five untreated mice served as control (group G). All mice were sacrificed 35 days post-infection. Mean worm burden and worm reduction were calculated.

RESULTS

At a dose of 120 mg/kg niclosamide, the blood drug concentration was (0.40 ± 0.28) µg/ml at 0.25 h post-treatment, reached a peak of (0.91 ± 0.34) µg/ml at 1 h, and decreased to (0.49 ± 0.38) µg/ml at 2 h, and got close to 0 at 16 h. The mean residence time (MRT) in mice was (6.78 ± 1.47) h, and the elimination half time was (6.80 ± 7.05) h. No significant difference was found in worm burden between different dose groups and control group (P > 0.05). The mean worm burden in group A was significantly lower than that of the control (P < 0.05) with a mean worm reduction of 79.1%. And there was no significant difference in worm burden between other groups and the control (P > 0.05).

CONCLUSIONS

The blood drug concentration increases rapidly by gavage administration of 120 mg/kg niclosamide, reaching to the maximum concentration at 1 h post-treatment. It shows a certain potective effect of oral administration of 200 mg/kg niclosamide on Schistosoma japonicum cercarial invasion at 0.25 h after treatment.

A loop-mediated isothermal amplification (LAMP) assay for early detection of Schistosoma mansoni in stool samples: a diagnostic approach in a murine model

BACKGROUND

Human schistosomiasis, mainly due to Schistosoma mansoni species, is one of the most prevalent parasitic diseases worldwide. To overcome the drawbacks of classical parasitological and serological methods in detecting S. mansoni infections, especially in acute stage of the disease, development of cost-effective, simple and rapid molecular methods is still needed for the diagnosis of schistosomiasis. A promising approach is the loop-mediated isothermal amplification (LAMP) technology. Compared to PCR-based assays, LAMP has the advantages of reaction simplicity, rapidity, specificity, cost-effectiveness and higher amplification efficiency. Additionally, as results can be inspected by the naked eye, the technique has great potential for use in low-income countries.

METHODOLOGY/PRINCIPAL FINDINGS

A sequence corresponding to a mitochondrial S. mansoni minisatellite DNA region was selected as a target for designing a LAMP-based method to detect S. mansoni DNA in stool samples. We used a S. mansoni murine model to obtain well defined stool and sera samples from infected mice with S. mansoni cercariae. Samples were taken weekly from week 0 to 8 post-infection and the Kato-Katz and ELISA techniques were used for monitoring the infection. Primer set designed were tested using a commercial reaction mixture for LAMP assay and an in house mixture to compare results. Specificity of LAMP was tested using 16 DNA samples from different parasites, including several Schistosoma species, and no cross-reactions were found. The detection limit of our LAMP assay (SmMIT-LAMP) was 1 fg of S. mansoni DNA. When testing stool samples from infected mice the SmMIT-LAMP detected S. mansoni DNA as soon as 1 week post-infection.

CONCLUSIONS/SIGNIFICANCE

We have developed, for the first time, a cost-effective, easy to perform, specific and sensitive LAMP assay for early detection of S. mansoni in stool samples. The method is potentially and readily adaptable for field diagnosis and disease surveillance in schistosomiasis-endemic areas.

[Experimental infection of Galba pervia, Radix swinhoei and Physa acuta with Fasciola hepatica in Dali, Yunnan]

OBJECTIVE

To determine the intermediate host of Fasciola hepatica in Dali of Yunnan Province, and investigate its development and characteristics.

METHODS

F. hepatica eggs from cattle were collected from July 2012 to July 2013, and placed in 28 degrees C water bath for incubation. Galba pervia, Radix swinhoei, and Physa acuta were collected from Dali, and used to be infected with F. hepatica in the laboratory. Trematode infections were excluded from the snails before experiment. All the snails were infected with F. hepatica miracidia, reared in mud pots. Dead snails were dissected for observing the development of F. hepatica. The metacercariae were collected and identified by PCR amplification of partial sequence of mitochondrial cytochrome oxidase subunit I (COX1) gene.

RESULTS

A total of 1 146 R. swinhoei, 996 P. acuta, and 3 307 G. pervia snails were infected with F. hepatica, respectively. Mother rediae were found in two R. swinhoei snails, but no child rediae were observed in the snails. No larval forms were found in P. acuta. G. pervia was infected by F. hepatica with an infection rate of 27.2% (900/3307). The miracidium escaped from the egg and penetrated into G. pervia at temperature 22 degrees C, developed into a sporocyst after 7-15 days, which transformed into mother redia at the 11 st-20th day post-infection. The mother redia developed into daughter redia at the 30th-37th day, and produced cercaria with longtail, and became metacercaria at the 42nd-55th day. PCR confirmed that the metacercariae were that of F. hepatica, with an obvious band (approximately 500 bp).

CONCLUSION

Among the three potential intermediate hosts in Dali, G. pervia is experimentally infected with F. hepatica.

Integrative taxonomy identifies a new species of Phyllodistomum (Digenea: Gorgoderidae) from the twospot livebearer, Heterandria bimaculata (Teleostei: Poeciliidae), in Central Veracruz, Mexico

Phyllodistomum inecoli n. sp. is described from the twospot livebearer, Heterandria bimaculata (Teleostei: Poeciliidae), collected in the Río La Antigua basin, Veracruz, Mexico. The new species is described and characterised by using a combination of morphology, scanning electron microscopy, and sequences of nuclear and mitochondrial genes. Diagnostic characters of the new species of Phyllodistomum include a genital pore opening at the level of the caecal bifurcation; oval vitellarium, situated just posterior to the ventral sucker and not extended laterally and anterior extracaecal uterine loops variable in extension (reaching the anterior, median or posterior margin of the ventral sucker). P. inecoli n. sp. most closely resembles P. brevicecum, a species described as a parasite of the central mudminnow, Umbra limi, in other parts of North America; however, the genital pore in P. brevicecum is situated between the caecal bifurcation and the ventral sucker, the ovary is larger, the vitellarium is lobed and extended laterally and the anterior portion of the uterus extends to the posterior margin of the ventral sucker. Comparison of about 1,500–2,200 nucleotides of cox1 and 28S rDNA and ITS1 strongly supports the status of P. inecoli as a new species. Bayesian inference analysis of combined datasets of 28S rDNA and cox1 sequences showed that P. inecoli n. sp. and the other species found in freshwater fishes of Mexico, including the species complex of P. lacustri, are not sister species. Phylogenetic analysis based on 28S rDNA sequences of several gorgoderid taxa revealed the close relationship of P. inecoli n. sp. with several species of Phyllodistomum, Gorgodera and Gorgoderina with cystocercous cercariae developing in sphaeriid bivalves. Dot-plot analysis of ITS1 sequences of P. inecoli n. sp. revealed the presence of eight repetitive elements with different length, which together represent almost half the length of ITS1.

[Effect of toll-like receptor (TLR) 7 deficiencies on the in vivo immune response against Schistosoma japonicum]

OBJECTIVE

To explore the toll-like receptor 7 knocked out (TLR7-/-) mice immune response against Schistosoma japonicum.

METHODS

C57BL/6 mice (WT) and TLR7-/- mice (TLR7-/-) were infected with 20 S. japonicum cercariae via shaved abdomen. There were nine mice in each group. At 6 weeks post-infection, mice were sacrificed. Adult worms were harvested by perfusion of the portal venous system, and the number of adult worms was determined. At the time of perfusion, livers were collected, weighed, and digested overnight with 5% potassium hydroxide, and eggs were counted. In addition, spleens were aseptically harvested when WT and TLR7-/- mice were sacrificed at day zero and 6 weeks after S. japonicum infection. After 72 hours of the co-culture with or without S. japonicum eggs, the culture supernatants were collected for cytokine assays by ELISA assay.

RESULTS

At 6 weeks after infection, there was no significant difference in number of worms [(10.5 +/- 3.3) vs (9.8 +/- 5.2)] and eggs per gram of liver tissue [(38 251.9 +/- 4 891.5) vs (38 160.9 +/- 3 341.0)] between WT and TLR7-/- mice. As for Th1/Th2 cytokine secretion from spleen cells, the levels of TNF-alpha [(43.7 +/- 9.8) pg/ml] and INF-gamma [(215.2 +/- 35.4) pg/ml] from TLR7-/- infected mice were lower than those of WT infected mice[(63.4 +/- 22.9) pg/ml, (383.5 +/- 253.3) pg/ml]. For Th2 cytokines detection, the production of IL-10 [(1702.6 +/- 572.3) pg/ml] and IL-4 [(59.5 +/- 10.1) pg/ml] from TLR7-/- mice were higher than those of WT mice [(595.2 +/- 386.3) pg/ml, (8.3 +/- 0.9) pg/ml] (P < 0.05, P < 0.01), while IL-4 level [(63.9 +/- 33.9) pg/ml] from TLR7-/- infected mice was higher than those of WT infected mice [(23.3 +/- 11.5) pg/ml].

CONCLUSION

TLR7-/- mice has a dominant Th2 response under the normal state. The absence of TLR7 does not influence the immune response against S. japonicum infection at 6 weeks post-infection.

[In vitro effect of photoactivated hypericin on anti-Schistosoma japonicum adult male worms]

OBJECTIVE

To investigate the in vitro effect of photoactivated hypericin on anti-Schistosoma japonicum adult male worms.

METHODS

Kunming mice were infected with 60-80 Schistosoma japonicum single-sex cercariae. At 6 weeks post-infection, the mice were sacrificed and adult male worms of S. japonicum were collected. The worms were incubated in DMEM medium containing different concentrations of hypericin (0.1, 0.2, 0.5, 1.0, 1.5, 2.0, and 2.5 micromol/L) in the presence or absence of light. In photoactivated hypericin groups, after 6 h of dark incubation the worms were exposed to LED light irradiation (590 nm) for 30, 60, 90, and 120 min, respectively, and then cultured overnight in darkness (16h). In the next morning, the parasites were washed, resuspended in drug-free medium, and incubated in the dark for 48 h. These worms were observed with stereomicroscopy and scanning electron microscopy (SEM).

RESULTS

Photoactivated hypericin showed the ability to kill Schistosoma japonicum in vitro. The death rate was 20% in 0.1 micromol/L photoactivated hypericin group under 30 min irradiation, and 100% in 2 micromol/L under 90 min irradiation and 2.5 micromol/L under 60 min irradiation, respectively. In blank control group, DMSO control group, and hypericin groups without light irradiation, worms were alive. After 60 min irradiation, the worms in 1.0, 2.5, 5.0 micromol/L photoactivated hypericin groups showed spastic paralysis characterized by reduced body length, pronounced tight curl, body stiffness, and complete cessation of movement. Surface tegumental damages of adult worms in 2.0 micromol/L photoactivated hypericin group for 60 min irradiation were observed under SEM, such as vacuole formation, erosion and peeling of the tegument, collapse of the sensory papillae, and even the normal structure disappeared completely. Both death rate and morphological damage of the worms treated by photoactivated hypericin were positively correlated with hypericin dose and light irradiation time.

CONCLUSION

Photoactivated hypericin has anti-Schistosoma japonicum adult male worms effect in vitro.

[Changes of IFN-gamma, IL-4 and T cells in Schistosoma japonicum-infected mice after praziquantel treatment]

OBJECTIVE

To investigate the serum levels of IFN-gamma and IL-4, and the dynamic changes of IFN-gamma-specific and IL-4-specific lymphocytes in mice with Schistosoma japonicum infection after treatment by praziquantel.

METHODS

Ninety BALB/c mice were randomly divided into three groups (n = 30) named as infection group, treatment group and control group. The mice in treatment group and infection group were infected with (25 +/- 2) S. japonicum cercariae through the abdominal skin. At 6 weeks post-infection, the mice in treatment group were administered orally with praziquantel [300 mg/(kg x d)] for 3 d. At 4, 6, 8 and 12 weeks post-treatment, the mice were weighed, and serum samples were collected. Serum levels of IFN-gamma and IL-4 were measured by ELISA. At the same time, the spleens were aseptically removed to prepare cell suspension, and the counts of IFN-gamma and IL-4 specific lymphocytes were examined by ELISPOT after stimulation of Schistosoma japonicum soluble egg antigen (SEA).

RESULTS

From 4 to 12 weeks after praziquantel treatment, the body weight of mice in treatment group were significantly heavier than that of infection group (P < 0.05), but no significant difference was found between treatment group and control group (P < 0.05). At 4 weeks posttreatment, there was no significant difference in serum levels of IFN-gamma and IL-4 between treatment group and infection group (P > 0.05). At 6, 8, and 12 weeks after treatment, the serum levels of IFN-gamma (0.038 +/- 0.013, 0.028 +/- 0.001, and 0.027 +/- 0.007) and IL-4(0.051 +/- 0.020, 0.045 +/- 0.019, and 0.043 +/- 0.016) in treatment group were significantly lower than that of infection group (IFN-gamma: 0.057 +/- 0.004, 0.060 +/- 0.023, and 0.052 +/- 0.017; IL-4: 0.150 +/- 0.014, 0.148 +/- 0.014, and 0.123 +/- 0.017) (P < 0.05). Serum IFN-gamma and IL-4 levels in treatment group and infection group were significantly higher than that of control group (P < 0.05). ELISPOT results showed that at 4, 6 weeks post-treatment, there was no significant difference in the number of IFN-gamma-specific lymphocytes between treatment group and infection group (P > 0.05). While at 8 and 12 weeks after treatment, the IFN-gamma-specific lymphocytes in treatment group (39.9 +/- 22.8 and 38.5 +/- 6.2) were significantly less than that of infection group (141.9 +/- 39.3 and 106.8 +/- 28.6) (P < 0.05). At 4-week post-treatment, the IL-4-specific lymphocytes in treatment group were much more than that of infection group (175.6 +/- 62.3) (P < 0.05), and then began to decline. At 8 and 12 weeks after treatment, the IL-4-specific lymphocytes (111.3 +/- 14.3 and 113.0 +/- 44.2) in treatment group were significantly less than that of infection group (220.3 +/- 107.1 and 208.1 +/- 17.2) (P < 0.05). The IFN-gamma-specific and IL-4-specific lymphocytes in treatment group and infection group were significantly more than that of control group (P < 0.05).

CONCLUSION

After praziquantel treatment, the serum levels of IFN-gamma and IL-4 in mice with S. japonicum infection decrease, and the number of IFN-gamma and IL-4 specific lymphocytes reduces.

[Prokaryotic expression and function analysis of Schistosoma japonicum calpain]

OBJECTIVE

To clone and express recombinant calpain of Schistosoma japonicum (Sjcalpain), observe the distribution of Sjcalpain in S. japonicum cercariae and analyze its role in skin invasion.

METHODS

The primers were designed according to the full-length sequence of calpain (GenBank accession No. AB016726). The genes encoding catalytic domain and Ca2+ binding domain of Sjcalpain were amplified by PCR, and the target fragments were subcloned into pET-28a. The recombinant proteins were expressed in E. coli BL21 (DE3) and purified by Ni-NTA resin. The rabbit polyclonal antibodies were prepared with the two purified recombinant proteins by immunizing New Zealand white rabbits. ELISA was used to detect the titer of rabbit antiserum. Immunolocalization was used to investigate the distribution of Sjcalpain in S. japonicum cercariae. Cercariae were incubated with specific inhibitor before infection of mice and the worm reduction rate was calculated.

RESULTS

The recombinant expression vector Sjcalpain catalytic domain/pET28a and Sjcalpain Ca2+ binding domain/pET28a were constructed and the recombinant proteins were successfully expressed in E. coli BL21 (DE3) (about M(r) 43 000 and M(r) 39 000, respectively). The two target proteins were expressed as inclusion bodies. The purified target proteins were obtained through Ni-NTA affinity purification. ELISA result showed that the titer of prepared rabbit polyclonal antibodies was higher than 1 : 80 000. Immunolocalization study demonstrated that Sjcalpain protein was mainly expressed in the head of cercariae. Inhibition assays suggested that the average number of adult worms in calpain inhibitor-incubation group and control group was 19 and 23, respectively, with a worm reduction rate of 17.4%.

CONCLUSION

Sjcalpain is mainly expressed in the head of S. japonicum cercariae. Inhibition of Sjcalpain could reduce the number of invading cercariae in infected mice, which suggest that Sjcalpain may play a role in skin invasion by cercariae.

[Expression of Toll-like receptors 2 and 6 in mice liver during Schistosoma japonicum infection]

OBJECTIVE

To investigate the expression of hepatic Toll-like receptor 1 (TLR1), TLR2 and TLR6 on mice with Schistosoma japonicum infection.

METHODS

Fifty BALB/c mice were infected with 20 +/- 3 S. japonicum cercariae through abdominal skin. At 6 weeks post-infection, the mice (n = 10) in treatment group were administered intragastrically with praziquantel [250 microg/(g x d)] for 3 d. The livers of mice (n = 10) were collected at pre-infection and 5, 6, 8 and 12 weeks post-infection, and then the mRNA expression levels of hepatic TLR1, TLR2, TLR6 gene were detected with reverse transfer PCR. Hepatic TLR2, TLR6 protein levels were detected by immunohistochemical staining.

RESULTS

The mRNA levels of TLR1, TLR2, and TLR6 on 5, 6, 8 and 12 weeks post infection were significantly higher than that of uninfected mice. After praziquantel treatment, the mRNA level of TLR2 and TLR6 in murine liver of treatment group was lower than that of infection group, but the level of TLR1 mRNA had no obvious change. Furthermore, immunohistochemistry results revealed that the expression of TLR2 and TLR6 proteins in murine liver was up-regulated at 5, 6, 8 and 12 weeks post-infection. After praziquantel treatment, the percentage of TLR2 positive area in liver of infected mice without and with praziquantel treatment were (44.2 +/- 4.3)%, (8.8 +/- 3.1)%, respectively, and TLR2 protein level was considerably down-regulated (P < 0.01). The percentage of TLR6 positive area in liver of infected mice without and with praziquantel treatment was (48.4 +/- 5.4)%, (37.4 +/- 3.5)%, respectively, and TLR6 level decreased slightly (P < 0.05).

CONCLUSION

The expression level of TRL2 and TLR6 in murine liver increases after Schistosoma japonicum infection. While compared with TLR2, the role of TLR6 in this progress is a weaker one.

Differences in susceptibility and immune responses of three-spined sticklebacks (Gasterosteus aculeatus) from lake and river ecotypes to sequential infections with the eye fluke Diplostomum pseudospathaceum

BACKGROUND

The eye fluke Diplostomum pseudospathaceum is a frequent parasite of many fresh-water fish species, among those three-spined sticklebacks, particularly in lakes with lymnaeid snails, its first intermediate hosts. Cercariae released from host-snails, penetrate the skin of their fish hosts and within 24 h migrate to the immunologically inert eye lenses. Thus, individual D. pseudospathaceum are exposed to the fish immune system only for a short time, suggesting that only innate immunity can be active against the parasite. However, in nature sticklebacks are exposed to D. pseudospathaceum repeatedly since snails are shedding cercariae from late spring to autumn. Therefore, acquired immunity after initial infection would be advantageous against subsequent parasite encounters.

METHODS

We investigated if sticklebacks originating from a lake with high and from a river with low prevalence of D. pseudospathaceum differ in susceptibility to repeated exposure to the parasite. We compared infection success and immune functions in laboratory-bred sticklebacks from both habitats in naïve fish with fish that had been pre-exposed to eye flukes. Head kidney leukocytes (HKL) from experimental sticklebacks were investigated for respiratory burst activity and the proliferation of lymphocytes and monocytes 1.5, 5 and 15 days after infection.

RESULTS

Lake sticklebacks were less susceptible than river sticklebacks, however, in both populations pre-exposure led to a similar relative reduction in infection success. The respiratory burst activity was higher with HKL from lake sticklebacks and was up-regulated in pre-exposed fish but dropped 1.5d after an additional exposure, suggesting that activation of phagocytic cells is crucial for the defense against D. pseudospathaceum. Changes in lymphocyte proliferation were only detectable 1.5d after the last exposure in lake sticklebacks, but not 5 and 15d post exposure, indicating that a lymphocyte mediated acquired immune response was not induced. Proliferation of monocytes was significantly increased 1.5d after the last exposure with HKL from both stickleback populations.

CONCLUSIONS

Increased resistance to D. pseudospathaceum in sticklebacks from both populations upon pre-exposure cannot be explained by a prominent adaptive immune response. Monocytic leukocytes were more responsive, suggesting that rather cells of the innate than the adaptive immune system are active in the defense of D. pseudospathaceum.

Schistosoma japonicum egg antigen up-regulates fibrogenesis and inhibits proliferation in primary hepatic stellate cells in a concentration-dependent manner

AIM: To investigate the effects of different concentrations of Schistosoma japonicum (S. japonicum) egg antigen on fibrogenesis and apoptosis in primary hepatic stellate cells (HSCs).

METHODS: A mouse model of schistosomiasis-associated liver fibrosis (SSLF) was established by infecting mice with schistosomal cercaria via the abdomen. HSCs were isolated from SSLF mice by discontinuous density gradient centrifugation, and their identity was confirmed by immunofluorescence double staining of α-smooth muscle actin (α-SMA) and desmin. The growth inhibitory effect and 50% inhibitory concentration (IC50) of S. japonicum egg antigen for primary HSCs (24 h) were determined using a cell counting kit-8 (CCK-8) assay. The expression levels of α-SMA, matrix metalloproteinase-9 (MMOL/LP-9) and tissue inhibitor of metalloproteinases-1 (TIMP-1) in HSCs in response to different concentrations of S. japonicum egg antigen were detected by Western blotting and real-time reverse transcription-polymerase chain reaction. The levels of phospho-P38 (P-P38), phospho-Jun N-terminal kinase (P-JNK) and phospho-Akt (P-AKT) in HSCs were detected by Western blotting.

RESULTS: An SSLF mouse model was established, and primary HSCs were successfully isolated and cultured. S. japonicum egg antigen inhibited HSC proliferation in a concentration-dependent manner. The IC50 of the S. japonicum egg antigen was 244.53 ± 35.26 μg/mL. S. japonicum egg antigen enhanced α-SMA expression at both the mRNA and protein levels and enhanced TIMP-1 expression at the mRNA level in HSCs (P < 0.05), whereas the expression of MMOL/LP-9 was attenuated at both the mRNA and protein levels in a concentration-dependent manner (P < 0.05). A high concentration of S. japonicum egg antigen enhanced P-P38, P-JNK and P-AKT activation (P < 0.05). The changes in α-SMA and MMOL/LP-9 expression induced by S. japonicum egg antigen were closely correlated with P-P38 and P-JNK activation (P < 0.05). The attenuation of MMOL/LP-9 was also correlated with P-AKT activation (P < 0.05), but the increase in α-SMA expression was not. TIMP-1 expression was not correlated with P-P38, P-JNK or P-AKT activation.

CONCLUSION: S. japonicum egg antigen promotes fibrogenesis, activates the P38/JNK mitogen-activated protein kinase and AKT/PI3K signaling pathways and inhibits proliferation in primary HSCs isolated from SSLF mice in a concentration-dependent manner.

Polymerase chain reaction (PCR) investigations of prepatent Schistosoma haematobium cercariae incidence in five water bodies, South West, Nigeria

This study investigated the levels of prepatent S. haematobium infection in water samples collected from Schistosomiasis haematobium transmission namely: International Institute of Tropical Agriculture (IITA) river and Eleyele river in Oyo state, Oyan dam and Shokori river in Ogun state, Badagry Lagoon and Lagoon (University of Lagos, Lagos state).

METHODOLOGY

Polymerase chain reaction (PCR) assay amplifying the Dra I repeated sequence of S. haematobium cercariae from the water samples was used. Samples of cercariae obtained from a laboratory population of Bulinus globosus and Bulinus rohlfsi snails were assayed following DNA extraction as control. Physico-chemical parameters of the water bodies were determined.

RESULTS

Physico-chemical parameters showed that salinity, conductivity and total dissolved solids were relatively high in the Lagoon front samples (41.91 ppt, 62400.87 micros/cm, 31000.14 mg/L and 7.79), and low in the river samples (13.27 ppt, 1325.67 micros/cm, 11470 mg/L and 8.36 respectively) while pH were similar. PCR showed that 3 out of the 6 water bodies sampled namely IITA river, Eleyele river and Oyan Dam are S. haematobium endemic sites as they gave positive signals.

CONCLUSION

Three surveyed sites with relatively low salinity namely IITA river, Eleyele river and Oyan dam are high S. haematobium endemic areas and schistosomes survive perhaps best in low salinity environment. PCR could be a more valuable tool in the study of incidence and prevalence of S. haematobium infection compared with conventional cercariae shedding method. On the known strength of focal effects of environmental conditions, implications of these results in the epidemiology and design of control activities are encouraging.