Snail-borne parasitic diseases: an update on global epidemiological distribution, transmission interruption and control methods

Immunological and molecular evaluation of zoonotic metacercarial infection in freshwater fish: A cross-sectional analysis

Improperly cooked fish, carrying active metacercariae (MCs), can pose a significant risk for transmitting fish-borne zoonotic trematodes (FBZTs) to human consumers. This study aimed to enhance our understanding of FBZTs by conducting a comprehensive cross-sectional analysis involving various fish species, such as Nile tilapia (Oreochromis niloticus), African catfish (Clarias gariepinus), and red-belly tilapia (Tilapia zillii). These fish specimens were collected from distinct Egyptian governorates, specifically Giza, Kafr al-Shaykh, and Fayoum. The recovered flukes from experimentally infected domestic pigeons were identified as Prohemistomum vivax, Haplorchis pumilio, and Pygidiopsis genata based on morphological features. Furthermore, the identity of the retrieved adult flukes was confirmed using three species-specific primers for PCR amplification and sequencing analysis of the ITS rDNA region and have been deposited in GenBank with the following accession numbers: P. vivax (OR291421.1 and OR291422.1), P. genata (OP099561.1), and H. pumilio (OM439581.1-OP090510.1). Quantitative real-time PCR targeting the immunological genes Tumor Necrosis Factor-alpha (TNF-alpha) and Interleukin-1 (IL-1Β) was employed to compare the cellular immune response between infected with EMCs and uninfected O. niloticus. The results indicated a significant increase in TNF- and IL-1Β levels in FBZTs-infected vs un-infected fishes. Importantly, the presence of adult flukes and EMCs led to substantial histological alterations in both experimentally infected pigeons and naturally infected fish tissues. These changes included the necrosis of fish muscle bundles and a pronounced inflammatory reaction with muscular necrosis in the digestive tracts of experimentally infected pigeons.

Awareness of parasitic zoonotic diseases among pet owners in Cairo, Egypt

Egyptians are becoming more interested in owning and raising pets; however, most of them lack essential awareness about the risk of zoonotic parasites that could be transmitted. The objective of the present investigation was to evaluate the degree of awareness Egyptian pet owners possess concerning zoonotic parasitic diseases, the risk of transmission, and preventative measures. A cross-sectional study was conducted using an e-survey. Among 246 pet owners, 64.2% (158) were females, and 67.9% (167) belonged to the 20-30 age group. The majority, 78.9% (194), were raising cats. Only 13.8% (34) visited the veterinarian regularly, with significantly higher results among dog owners (p < 0.05). Only 31.3% (77) participants were regularly deworming their pets, and 19.9% (49) were giving their pets prophylaxis against ectoparasites, with significantly higher results among those who visited the veterinarian regularly (p < 0.0001) and among dog owners (p < 0.05). Only 54.1% (133) had heard about the term "zoonoses" before, and about 8.9% (22) of participants showed a history of zoonotic parasitic diseases, with significantly higher results among those who allowed their animals to play with other animals of neighbors and friends (p < 0.05). The obtained results concluded that the surveyed group had a relatively good degree of knowledge regarding pets as a source of zoonotic illness; raising pet owners' awareness regarding the importance of routine medical examinations and minimizing the contact of pets with other stray animals is essential.

One World, One Health: Zoonotic Diseases, Parasitic Diseases, and Infectious Diseases

When we take into account how the boundaries between human, animal, and environmental health are inextricably linked and increasingly intertwined, it comes as no surprise that the One Health approach has assumed an unprecedented level of importance over the past decade [...].

Multi- and transgenerational effects of environmental chemicals on mollusks: An underexplored experimental design in aquatic (eco)toxicological studies

(Eco)toxicological studies frequently evaluate the effects of chemicals in one life stage of organisms, but the use of these outcomes can only partially estimate populational effects. In this regard, multi- and/or transgenerational studies should be performed in order to provide information on contaminant effects in a populational functioning context. The present review aimed to summarize and critically evaluate the current knowledge regarding multi- and/or transgenerational effects of traditional and emerging environmental chemicals on mollusks. Results showed that these kinds of studies were performed in aquatic mollusks (bivalve and gastropod), being Gastropoda the mollusk Class most frequently studied. Additionally, freshwater species and multigenerational studies were more common for this class. For the Bivalvia class, only marine species were evaluated, and transgenerational exposure was more commonly assessed. The effects were reported for 15 species, highlighting the marine bivalves Crassostrea gigas and Saccostrea glomerata, and the freshwater gastropod Lymnaea stagnalis. Multi- and transgenerational effects were described for 8 environmental chemical groups, mainly metals, pesticides, and pharmaceuticals. In general, multi- and transgenerational exposure induced biometric, developmental, and reproductive impairments in mollusks, indicating that environmental chemicals might lead to generational impairments, reduced population growth and reproductive capacity, and decreased fitness. The current study indicated that bivalves and gastropods are suitable organism models to assess the multi- and transgenerational adverse effects induced by traditional and emerging environmental chemicals.

Identification of freshwater snail species and survey of their trematode infections in Ordos, China

In order to investigate and study the species and distribution of freshwater snails in Ordos area of Inner Mongolia, as well as the trematode infection in different periods, and to provide a scientific basis for the effective prevention and control of livestock trematodiasis. In this paper, freshwater snails distributed in Ordos were widely collected for morphological identification, and PCR amplification of freshwater snails COI gene and ITS2 gene was carried out with the help of molecular biology. At the same time, microscopic examination was used to observe the trematode infection of freshwater snails in two different periods from May to July and July to September, and the molecular biology of the trematodes was identified. The results showed that the 1796 freshwater snails collected belonged to two orders, three families and four genera, i.e. Bellamya, Radix, Galba, and Gyraulus. Microscopic examination of snails showed that the infection rate of trematode larvae from July to September was significantly higher than that from May to July. The collected trematodes were identified as five species, namely Cotylurus marcogliesei, Fasciola hepatica, Fasciola gigantica, Paramphistomum cervi, and Parastrigea robusta. The combination of freshwater snail species in Ordos and the infection of trematode in snails showed that a large number of freshwater snails were infected with trematodes, especially from July to September, when there is more rain and suitable climate, which causes serious harm to local livestock.

Yolk proteins of the schistosomiasis vector snail Biomphalaria glabrata revealed by multi-omics analysis

Vitellogenesis is the most important process in animal reproduction, in which yolk proteins play a vital role. Among multiple yolk protein precursors, vitellogenin (Vtg) is a well-known major yolk protein (MYP) in most oviparous animals. However, the nature of MYP in the freshwater gastropod snail Biomphalaria glabrata remains elusive. In the current study, we applied bioinformatics, tissue-specific transcriptomics, ovotestis-targeted proteomics, and phylogenetics to investigate the large lipid transfer protein (LLTP) superfamily and ferritin-like family in B. glabrata. Four members of LLTP superfamily (BgVtg1, BgVtg2, BgApo1, and BgApo2), one yolk ferritin (Bg yolk ferritin), and four soma ferritins (Bg ferritin 1, 2, 3, and 4) were identified in B. glabrata genome. The proteomic analysis demonstrated that, among the putative yolk proteins, BgVtg1 was the yolk protein appearing in the highest amount in the ovotestis, followed by Bg yolk ferritin. RNAseq profile showed that the leading synthesis sites of BgVtg1 and Bg yolk ferritin are in the ovotestis (presumably follicle cells) and digestive gland, respectively. Phylogenetic analysis indicated that BgVtg1 is well clustered with Vtgs of other vertebrates and invertebrates. We conclude that, vitellogenin (BgVtg1), not yolk ferritin (Bg yolk ferritin), is the major yolk protein precursor in the schistosomiasis vector snail B. glabrata.

Genetic variation of the freshwater snail Indoplanorbis exustus (Gastropoda: Planorbidae) in Thailand, inferred from 18S and 28S rDNA sequences

Indoplanorbis exustus, a freshwater pulmonate snail, is widely distributed in tropical and subtropical zones and plays a significant role as an intermediate host for trematode parasites. Various genetic markers have been used for species identification and phylogenetic studies of this snail. However, there are limited studies about their molecular genetics based on nuclear ribosomal DNA (rDNA) genes. A genetic analysis of I. exustus in Thailand was conducted based on the nuclear 18S rDNA (339 bp) and 28S rDNA (1036 bp) genes. Indoplanorbis snails were collected from 29 localities in 21 provinces covering six regions of Thailand. Nucleotide sequences from 44 snails together with sequences from the GenBank database were examined for phylogenetic relationships and genetic diversity. All sequences of the selected nucleotide regions exhibited a high level of similarity (99%) to the sequences of I. exustus in the GenBank database. The maximum likelihood tree based on the 18S and 28S rDNA fragment sequences of I. exustus in Thailand revealed only one group with clear separation from another genus in the family Planorbidae. The I. exustus 28S rDNA sequences showed intraspecific genetic divergence ranging from 0 to 0.78% and were classified into 8 different haplotypes. Conversely, the 18S rDNA data showed lower variation than the 28S rDNA data and revealed a single haplotype and intraspecific distances of zero among all sampled individuals. The haplotype network of 28S rDNA sequences of I. exustus in Thailand revealed six unique haplotypes and two haplotypes shared by at least two regions. Overall, both markers were successful in the identification of I. exustus. However, these markers, particularly the 18S rDNA, may not be suitable for genetic analysis within the species, particularly for population genetic studies, due to their limited variation as seen in this study. In summary, this study not only enhances understanding of genetic variation in I. exustus but is also useful for the selection of molecular markers in future genetic research.

Fasciola spp. in Southeast Asia: A systematic review

BACKGROUND

Fasciolosis is an emerging public health threat in a number of regions worldwide. To date, we lack an overview of both its occurrence and distribution in Southeast Asia across all actors involved in the life cycle, which impedes the development of disease control measures. Therefore, our objective was to collect recent information on the distribution and the prevalence of Fasciola spp. and the associated risk factors for infection in humans, animals, snails and plant carriers in Southeast Asia.

METHODOLOGY

Bibliographic and grey literature databases as well as reference lists of important review articles were searched for relevant records published between January 1st, 2000, and June 30th, 2022. The systematic review was conducted according to the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines for reporting systematic reviews. A total of 3,887 records were retrieved, of which 100 were included in the final analysis.

PRINCIPAL FINDINGS

The studies focused mainly on one host species (96.0%), with Fasciola spp. infection in animals being the most studied (72.0%), followed by humans (21.0%). Based on the used inclusion and exclusion criteria, reports were retrieved describing the presence of Fasciola spp. infection in seven out of 11 countries in Southeast Asia. Depending on the diagnostic tool applied, the prevalence of Fasciola spp. infection ranged between 0.3% and 66.7% in humans, between 0% and 97.8% in animals, and between 0% and 66.2% in snails. There were no studies reporting the presence of metacercariae on plant carriers.

CONCLUSIONS/SIGNIFICANCE

Our study reconfirms that Fasciola spp. infections are widespread and highly prevalent in Southeast Asia, but it remains difficult to accurately assess the true occurrence of Fasciola spp. in absence of well-designed surveys covering all hosts. As next steps we propose to assess the occurrence of the infection across all actors involved in the transmission, to identify associated risk factors and to estimate the burden of the disease to support national and international decision makers.

One-health approach on the future application of snails: a focus on snail-transmitted parasitic diseases

Snails are fascinating molluscs with unique morphological and physiological adaptive features to cope with various environments. They have traditionally been utilized as food and feed sources in many regions of the world. The future exploitation of alternative nutrient sources, like snails, is likely to increase further. Snails, however, also serve as an intermediate host for several zoonotic parasites. A category of parasitic infections, known as snail-transmitted parasitic diseases (STPDs), is harmful to humans and animals and is mainly driven by various trematodes, cestodes, and nematodes. The environment plays a crucial role in transmitting these parasites, as suitable habitats and conditions can facilitate their growth and proliferation in snails. In light of diverse environmental settings and biologically categorized snail species, this review evaluates the dynamics of significant STPDs of zoological importance. Additionally, possible diagnostic approaches for the prevention of STPDs are highlighted. One-health measures must be considered when employing snails as an alternative food or feed source to ensure the safety of snail-based products and prevent any adverse effects on humans, animals, and the environment.

Fish and Food-Fatale: Food-borne Trematode Opisthorchis viverrini and Cholangiocarcinoma

Neglected Tropical Diseases (NTDs) are a group of communicable diseases with a long history with human beings. NTDs are the proxy of poverty since they affect those in low-income and extreme-poverty populations, as those populations lack access to proper health care, clean water, sanitary conditions, and hygiene. NTDs create losses for a nation that come from the health and the economic sectors as well since the costs of diagnosis, prevention, and treatment strain the national purse strings. One of the 20 different forms of NTDs on the list is food-borne trematodes, comprises of Fasciola, Paragonimus, Clonorchis, and Opisthorchis. Currently, it is estimated that food-borne trematodes can cause a devastating effect on mortality and morbidity. All of them are zoonotic, as humans become infected by ingestion of a second intermediate host, such as freshwater snails, fish, or water vegetables. Opisthorchis viverrini, one of the food-borne trematodes that can be found mostly in South East Asia regions, especially in the Mekong basin, is regarded as a group 1 carcinogen leading to cholangiocarcinoma (CCA). This study aims to present the updated review of Opisthorchis viverrini and CCA.

Optimized strategy for schistosomiasis elimination: results from marginal benefit modeling

BACKGROUND

Poverty contributes to the transmission of schistosomiasis via multiple pathways, with the insufficiency of appropriate interventions being a crucial factor. The aim of this article is to provide more economical and feasible intervention measures for endemic areas with varying levels of poverty.

METHODS

We collected and analyzed the prevalence patterns along with the cost of control measures in 11 counties over the last 20 years in China. Seven machine learning models, including XGBoost, support vector machine, generalized linear model, regression tree, random forest, gradient boosting machine and neural network, were used for developing model and calculate marginal benefits.

RESULTS

The XGBoost model had the highest prediction accuracy with an R2 of 0.7308. Results showed that risk surveillance, snail control with molluscicides and treatment were the most effective interventions in controlling schistosomiasis prevalence. The best combination of interventions was interlacing seven interventions, including risk surveillance, treatment, toilet construction, health education, snail control with molluscicides, cattle slaughter and animal chemotherapy. The marginal benefit of risk surveillance is the most effective intervention among nine interventions, which was influenced by the prevalence of schistosomiasis and cost.

CONCLUSIONS

In the elimination phase of the national schistosomiasis program, emphasizing risk surveillance holds significant importance in terms of cost-saving.

Occurrence of digenean parasites in freshwater snails in the Murrumbidgee catchment area, Australia

Freshwater snails are important hosts in the life cycles of many medically important parasites, particularly for digenetic trematodes such as liver flukes and schistosomes. The current study was conducted to determine the infection of freshwater snails with parasites that can potentially be transmitted to humans within the Murrumbidgee catchment area which is an area of widespread intensive aquaculture in Australia. A total of 116 freshwater snails, belonging to three species (Isidorella hainesii, Glyptophysa novaehollandica and Bullastra lessoni), were examined for the presence of parasites in both man-made and natural environments. The analysis of sequence data, including the internal transcribed spacers (ITS) of nuclear ribosomal DNA, small subunit (18S) ribosomal DNA, and large subunit (28S) ribosomal DNA, indicated that the collected parasites belonged to two distinct genera, namely Clinostomum and Echinostoma. It is noteworthy that species of both of these digenean parasites have the potential to be zoonotic. Cercariae of both Clinostomum and Echinostoma were observed in snails collected from aquaculture settings. It is important to highlight that infectious stages of Clinostomum  has been previously detected in edible fish within Australia. This information raises concerns regarding the potential transmission of these parasites to humans through the consumption of contaminated fish. These findings emphasize the importance of monitoring and controlling the presence of Clinostomum and Echinostoma in aquaculture environments to minimise the risk of zoonotic infections and ensure food safety. Further research and surveillance are needed to better understand the prevalence, transmission dynamics, and potential public health implications associated with these parasites in the context of aquaculture in Australia.

Trematode Cercariae from Lymnaea gedrosiana in the Caspian Sea Littoral in Iran: a one health concern

Introduction

Lymnaea gedrosiana snails are hosts to a variety of trematode cercaria of public and veterinary health importance. In Guilan Province, Iran, a region with a high level of fish and bird farming and wetlands important for migratory birds, little is known about the trematode cercaria from L. gedrosiana.

Methods

From April 2020 to October 2021, six freshwater sites in Guilan Province were sampled for Lymnaeidae snails three times per season (spring, summer, autumn and winter). Snails were exposed to light and heat to induce cercaria shedding and shredded cercaria were identified morphologically and molecularly.

Results

In total, 5,712 Lymnaeidae snails were collected of which 3,288 (57.6%) were identified to be L. gedrosiana with 54.3% containing trematode cercaria. Snail and cercaria recovery were highest in the spring and summer. Trematode cercaria identified included Telorchis assula, Hypoderaeum conoideum, Apharyngostrigea pipientis, Sanguinicola cf. inermis, Opisthioglyphe ranae, Diplostomum pseudospathaceum, and Australapatemon burti.

Discussion

The four trematodes D. pseudospathaceum, S. inermis, A. burti, and A. pipientis have not been previously reported in Iran; all four of these can infect migratory birds. The most common cercaria found, H. conoideum (18.3% of the snails) is of zoonotic importance. The third most common cercaria found, S. inermis (10.0% of the snails) is detrimental to fish production. Given the importance of the wetlands in the region for wildlife and migratory birds as well as the number of fish and bird farms in the area, efforts to control L. gedrosiana snails are needed to protect wildlife and human health. In addition, monitoring programs should be implemented to identify and prevent introductions of new trematode species.

Barriers with Valve Mechanisms Are Predicted to Protect Crops from Slug Carriers of Rat Lungworm Disease

Angiostrongyliasis (Rat Lungworm disease) is an emerging parasitic disease caused by the ingestion of gastropods infected with the neurotropic nematode Angiostrongylus cantonensis. The reduction of crop infestation with infected slug carriers may vary widely by protection method. We explored the application of barriers with valve mechanisms, whereby selective directional forces caused a greater number of slugs to exit than enter the protected plot, leading to decreased slug population densities at a steady state. Using field data, we constructed predictive models to estimate slug population densities at a steady state in protected plots with (1) no valve effect, (2) a valve effect, (3) no valve effect with a single breach of the barrier, (4) a valve effect with a single breach of the barrier, (5) a valve effect with a constant breach of the barrier, and (6) a repelling effect. For all scenarios, plots protected using a barrier with a valve effect had consistently lower slug densities at a steady state. Our findings support the use of barriers with valve mechanisms under different conditions, and potentially in combination with other interventions to reduce the contamination of crops by slug carriers of A. cantonensis. Improving barriers extends beyond disease mitigation to economic and cultural impacts on the local farmer and consumer communities.

Exploring the mechanisms underlying the toxicity of boric acid against the land snail, Theba pisana

BACKGROUND

The land snail, Theba pisana, is one of the most important threats facing agriculture around the globe. Boric acid (BOA) is currently used as a safe alternative molluscicide to control land snails in sustainable agriculture, but the mechanisms of toxicity have not yet been investigated. The present study characterizes the lethal and sub-lethal (0.5 and 1 mg g^-1 ) toxic effects of BOA-contaminated food for 14 days by examining physiological, biochemical and histopathological indicators in T. pisana to understand the mechanisms underlying its toxic action.

RESULTS

BOA was found to be lethal against T. pisana with LC₅₀ values of 24.7 and 8.05 mg g^-1 after 3 and 7 days of exposure, respectively. BOA sublethal concentrations led to a significant reduction in food consumption and growth of snails after 14 days of exposure. BOA also caused a significant increase in testosterone levels, whereas an opposite effect was observed in estradiol levels. An increase in progesterone levels in snails in the 0.5 mg g^-1 BOA group and a decrease in the 1 mg g^-1 BOA group were observed after all exposure times. Moreover, the lipid peroxidation level and catalase activity were elevated, whereas acetylcholinesterase activity was inhibited in the treated snails. Alteration in glutathione-S-transferase activity was noticed after exposure to both sublethal concentrations. In addition, BOA induced histopathological alterations in the digestive gland of T. pisana.

CONCLUSION

Our findings provide novel insights into how physiological, biochemical and histopathological alterations can be used to explore the mechanisms underlying BOA toxicity against snails. © 2022 Society of Chemical Industry.

Three Gorges Dam: the changing trend of snail density in the Yangtze River basin between 1990 and 2019

BACKGROUND

The area of Oncomelania hupensis snail remains around 3.6 billion m², with newly emerging and reemergent habitats continuing to appear in recent years. This study aimed to explore the long-term dynamics of snail density before and after the operation of Three Gorges Dam (TGD).

METHODS

Data of snail survey between 1990 and 2019 were collected from electronic databases and national schistosomiasis surveillance. Meta-analysis was conducted to estimate the snail density. Joinpoint model was used to identify the changing trend and inflection point. Inverse distance weighted interpolation (IDW) was used to determine the spatial distribution of recent snail density.

RESULTS

A total of 3777 snail survey sites with a precise location of village or beach were identified. For the downstream area, snail density peaked in 1998 (1.635/0.11 m², 95% CI: 1.220, 2.189) and fluctuated at a relatively high level before 2003, then declined steadily from 2003 to 2012. Snail density maintained lower than 0.150/0.11 m² between 2012 and 2019. Joinpoint model identified the inflection of 2003, and a significant decreasing trend from 2003 to 2012 with an annual percentage change (APC) being - 20.56% (95% CI: - 24.15, - 16.80). For the upstream area, snail density peaked in 2005 (0.760/0.11 m², 95% CI: 0.479, 1.207) and was generally greater than 0.300/0.11 m² before 2005. Snail density was generally lower than 0.150/0.11 m² after 2011. Snail density showed a significant decreasing trend from 1990 to 2019 with an APC being - 6.05% (95% CI: - 7.97, - 7.09), and no inflection was identified. IDW showed the areas with a high snail density existed in Poyang Lake, Dongting Lake, Jianghan Plain, and the Anhui branch of the Yangtze River between 2015 and 2019.

CONCLUSIONS

Snail density exhibited a fluctuating downward trend in the Yangtze River basin. In the downstream area, the operation of TGD accelerated the decline of snail density during the first decade period, then snail density fluctuated at a relatively low level. There still exists local areas with a high snail density. Long-term control and monitoring of snails need to be insisted on and strengthened.

Potential of 3-octanone as a lure and kill agent for control of the Brown Garden Snail

The brown garden snail (Cornu aspersum) is a major agricultural pest, causing damage to a wide range of economically important crops. Withdrawal or restricted use of pollutant molluscicides like metaldehyde has prompted a search for more benign control products. This study investigated the response of snails to 3-octanone; a volatile organic compound (VOCs) produced by the insect pathogenic fungus Metarhizium brunneum. Concentrations of 1 - 1000 ppm of 3-octanone were first assessed in laboratory choice assays to determine behavioural response. Repellent activity was found at 1000 ppm whereas attractance was found for the lower concentrations of 1, 10 and 100 ppm. These three concentrations 3-octanone were carried forward in field evaluations to assess potential for use in "lure and kill" strategies. The highest concentration (100 ppm) was the most attractive to the snails but also the most lethal. Even at the lowest concentration this compound proved toxic making 3-octanone an excellent candidate for the development as a snail attractant and molluscicide.

Biocontrol of snail-borne parasites with the glossiphoniid leech, Helobdella austinensis

Parasites in which freshwater snails are intermediate hosts pose a serious threat to human health worldwide. We show here that freshwater snails can potentially be controlled by leech predation; in principle, this approach could significantly reduce snail-borne parasitic diseases (SBPDs). Specifically, glossiphoniid leeches, Helobdella austinensis and congener species, consume freshwater snails indiscriminately, while other common leeches do not. A single adult H. austenensis, for example, can consume up to its weight in snails, e.g. Physella acuta, per day. Our predator-prey models suggest that snail populations could be eliminated in relatively short time periods (approximately six months) using a leech biocontrol approach. This could have considerable impact on global SBPDs by breaking the intermediate host life cycle.

Fasciola gigantica Cathepsin L1H: High Sensitivity and Specificity of Immunochromatographic Strip Test for Antibody Detection

Fasciolosis is a zoonotic disease caused by Fasciola gigantica or F. hepatica infections, which are frequently occurring parasites in animals and humans. The present gold-standard diagnostic technique involves finding parasite eggs through microscopy. However, this method is also restricted due to low specificity and low sensitivity. An alternative to coprological diagnosis is the immunochromatographic strip (ICS) test, which is rapid, simple, convenient, and cost-effective, with high sensitivity and high specificity. Cathepsin L1H (CathL1H) is a cysteine protease secreted by F. gigantica, which is found in high amounts in newly excysted juvenile (NEJ) and juvenile stages. Cathepsin L1H plays an important role in both the immune response to invading pathogens and in the ability of some pathogens to evade the host immune system. The present study aims to develop an ICS test and detect antibodies against CathL1H in mice and cattle serum using the recombinant F. gigantica Cathepsin L1H (rFgCathL1H) and rabbit anti-rFgCathL1H antibody. The F. gigantica-infected serum and non-infected serum of mice and cattle were tested using the ICS test. Moreover, the strip results were confirmed with an indirect enzyme-linked immunosorbent assay (indirect ELISA). The relative sensitivity, specificity, and accuracy of the ICS strip were 97.5, 99.99, and 99.00%, respectively. Therefore, these data suggest that the ICS method could be used to detect F. gigantica antibodies to highly enhance throughput, reduce costs, and determine the best alternative on-site method.

Prevalence, coinfection, and risk factors associated with Fasciola hepatica and other gastrointestinal parasites in cattle from the Peruvian Amazon

Background and Aim

Extensive cattle rearing is a major source of economy for the inhabitants of the Amazon region of Peru. Milk and meat production is generally affected by the prevalence of various parasites, including hepatic and gastrointestinal parasites, as these products provide ideal conditions for parasitic growth. This poses a serious public health threat. This study aimed to estimate the prevalence, coinfection, and risk factors associated with the liver fluke (Fasciola hepatica) and other gastrointestinal parasites in cattle from the Amazon region of Peru.

Materials and Methods

Fecal samples obtained from 1450 bovine specimens were analyzed using flotation and sedimentation methods to identify parasites, including Eimeria spp., strongyle-type eggs (STEs), and F. hepatica. We collected information about the specimens, including age, sex, origin, breed, category, frequency of deworming, farm size, herd size, water sources, and rearing system by conducting simple inspections and interviewing owners. The data obtained were statistically evaluated using the Chi-square test (p < 0.05) to determine the association between the qualitative variables. We also calculated the odds ratio at a 95% confidence interval to identify the risk factors.

Results

We observed that F. hepatica, Eimeria spp., and STEs were 45.6%, 39.8%, and 35.3% prevalent, respectively. We found risk factors related to distomatosis in the animals from Huambo, where the drinking water sources are mainly streams, ditches, and rivers, while the specimens from Valle Chico were predisposed to coccidiosis. Further, the risk factors related to the presence of STEs in feces were age (61-90 months), origin (Valle Chico), herd size (<50 animals), and type of extensive rearing. Furthermore, significant coinfection was observed between Eimeria spp. and STEs.

Conclusion

The high percentages of parasites in cattle observed were related to epidemiological factors, such as the origin of the sample, water sources, age, herd size, and extensive breeding. Similarly, the presence of STEs was a risk factor for contracting coccidiosis. Our future goals include investigating these parasites using a larger sample size and identifying more risk factors using more sensitive and specific diagnostic tests.

Effects of Land-Use and Environmental Factors on Snail Distribution and Trematode Infection in Ethiopia

Freshwater snails are intermediate hosts for several snail-borne diseases affecting humans and animals. Understanding the distribution of snail intermediate hosts and their infection status is very important to plan and implement effective disease prevention and control interventions. In this study, we determined the abundance, distribution, and trematode infection status of freshwater snails in two agro-ecological zones of Ethiopia. We sampled snails from 13 observation sites and examined them for trematode infections using a natural cercarial shedding method. A redundancy analysis (RDA) was used to examine the relationship between snail abundance and environmental variables. Overall, a total of 615 snails belonging to three species were identified. Lymnea natalensis and Bulinus globosus were the dominant snail species, representing 41% and 40% of the total collection, respectively. About one-third of the total snail population (33%) shed cercariae. The cercariae species recorded were Xiphidiocercaria, Brevifurcate apharyngeate distome (BAD), Echinostome, and Fasciola. Snail species were found in high abundance in aquatic habitats located in the agricultural landscape. Therefore, land-use planning and protection of aquatic habitats from uncontrolled human activities and pollution can be considered as important strategies to prevent and control the spread of snail-borne diseases in the region.

Spatial parasitology and the unmapped human helminthiases

Helminthiases are a class of neglected tropical diseases that affect at least 1 billion people worldwide, with a disproportionate impact on resource-poor areas with limited disease surveillance. Geospatial methods can offer valuable insights into the burden of these infections, particularly given that many are subject to strong ecological influences on the environmental, vector-borne or zoonotic stages of their life cycle. In this study, we screened 6829 abstracts and analysed 485 studies that use maps to document, infer or predict transmission patterns for over 200 species of parasitic worms. We found that quantitative mapping methods are increasingly used in medical parasitology, drawing on One Health surveillance data from the community scale to model geographic distributions and burdens up to the regional or global scale. However, we found that the vast majority of the human helminthiases may be entirely unmapped, with research effort focused disproportionately on a half-dozen infections that are targeted by mass drug administration programmes. Entire regions were also surprisingly under-represented in the literature, particularly southern Asia and the Neotropics. We conclude by proposing a shortlist of possible priorities for future research, including several neglected helminthiases with a burden that may be underestimated.

Knowledge, attitudes and practices related to neglected tropical diseases (schistosomiasis and fascioliasis) of public health importance: A cross-sectional study

Background

Snails play an important role as an intermediate host in various parasitic diseases, which are referred to as snail-borne parasitic diseases (SBPDs). The prevalence of the SBPDs, schistosomiasis and fascioliasis is low in Pakistan compared to other countries. The present study investigated knowledge, attitudes, and practices related to these two SPBDs and risk factors associated with them among the humans living in close contact with livestock and pets from three regions of Pakistan: Punjab, Islamabad and Azad Jammu and Kashmir (AJK).

Methods

A cross-sectional survey was conducted using a structured questionnaire to assess participants' knowledge, attitude and practices related to schistosomiasis and fascioliasis during 2021-2022.

Results

The majority of the 507 participants who were interviewed had good knowledge of schistosomiasis and fascioliasis: 43% were aware of schistosomiasis and 57% were aware of fascioliasis, but only 25% knew about snails as an intermediate host. Most respondents had a positive attitude toward treatment, prevention and control of the diseases but they did not have any healthcare facilities.

Conclusion

This study highlights the importance of the public's awareness for the need to control SBPDs. It also draws attention to the need for health education for risk reduction and the prevention of SBPDs in endemic areas.

Environmental Factors Affecting Freshwater Snail Intermediate Hosts in Shenzhen and Adjacent Region, South China

Sound knowledge of the local distribution and diversity of freshwater snail intermediate hosts and the factors driving the occurrence and abundance of them is crucial to understanding snail-borne parasitic disease transmission and to setting up effective interventions in endemic areas. In this study, we investigated the freshwater snails, water quality parameters, physical characteristics of habitats, predators and competitors, and human activity variables at 102 sites during December 2018 and August 2019 in Shenzhen and adjacent areas in China. We used decision tree models and canonical correspondence analysis to identify the main environmental and biotic factors affecting the occurrence and abundance of snail species. A total of nine species of snail were collected throughout the study area, with Biomphalaria straminea, Sinotaia quadrata, and Physella acuta being the most predominant species. Our study showed that the most important variables affecting the abundance and occurrence of snail species were the presence of predators and competitors, macrophyte cover, chlorophyll-a, substrate type, river depth, and water velocity. In terms of human activities, snail species occurred more frequently and in larger numbers in water bodies affected by human disturbances, especially for sewage discharge, which may reduce the occurrence and abundance of snail predators and competitors. These findings suggest that proper management of water bodies to reduce water pollution may increase the abundance of snail predators and competitors, and should be considered in integrated snail control strategies in the study area.

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.

Distribution and seasonal abundance of Biomphalaria snails and their infection status with Schistosoma mansoni in and around Lake Tana, northwest Ethiopia

Biomphalaria snails, namely B. pfeifferi and B. sudanica, are the principal intermediate hosts for Schistosoma mansoni infection in Ethiopia. Epidemiological studies of Biomphalaria snails and their infection status with S. mansoni is vital for public health planning. This study aimed to assess the spatial and seasonal abundance of Biomphalaria snails as well as their infection status with S. mansoni around Lake Tana, northwest Ethiopia. Malacological survey was conducted from January 2021 to December 2021 in ten different collection sites in and around Lake Tana. Snail collection was performed for 20 min from each collection site seasonally (four times in a year) using a standard scoop and handpicking from aquatic vegetation. All collected snails were carefully examined based on their morphological features and all live Biomphalaria snails were subjected to cercariae shedding experiment. Descriptive statistics were used to determine the prevalence of S. mansoni infection and its relationship with snail collection sites and seasons. A total of 3886 freshwater snails were collected from ten collection sites around Lake Tana. Out of the total snails collected, 1606 (41.3%; 95% CI 39.77-42.89%) were Biomphalaria spp. The highest (374) and the lowest numbers (98) of Biomphalaria snails were collected from Shinne River and Qunzela Lakeshore, respectively. Out of the 1375 live Biomphalaria snails, 14.4% (95% CI 12.59-16.37%) snails shed cercariae, but only 4.87% (95% CI 3.79-6.15%) were cercariae of S. mansoni. The infection prevalence of S. mansoni ranged from 10.59% at the Cherechera site to 1.49% at Gumara River. Biomphalaria snail infections with S. mansoni cercariae were observed throughout the season, the highest and the lowest infection rates being in the spring and summer seasons. Significant differences in the prevalence of S. mansoni infection in Biomphalaria snails were observed across study sites and seasons (p < 0.05). Biomphalaria snails were the most abundant freshwater snails found in nearly all of snail collection sites throughout the year. It was revealed that nearly five percent of Biomphalaria snails were infected with S. mansoni cercariae. This study highlights the importance of appropriate snail control strategies to support the ongoing prevention and control of schistosomiasis around Lake Tana.

The Biosafety Evaluation for Crustaceans: A Novel Molluscicide PBQ Using against Oncomelania hupensis, the Intermediate Host of Schistosoma japonica

A new formulation (suspension concentrate, SC) of PBQ [1-(4-chlorophenyl)-3-(pyridin-3-yl) urea] was used in water network schistosomiasis-endemic areas to test its molluscicidal efficacy and the acute toxicity to crustaceans. PBQ (20% SC), 26% metaldehyde, and niclosamide suspension concentrate [MNSC (26% SC)] were used both in ditch and field experiments for the molluscicidal efficacy comparison. Acute toxicity tests of two molluscicides were conducted using Neocaridina denticulate and Eriocheir sinensis. Both in the field and ditch experiments, PBQ exhibited comparable molluscicidal efficacy with MNSC. At doses of 0.50 g/m3 and 0.50 g/m2, the snail mortalities were more than 90% three days after PBQ (20% SC) application. Compared with previous tests, PBQ (20% SC) exhibited higher molluscicidal activity than PBQ (25% wettable powder, 25% WP) used in Jiangling and showed similar mollucicidal activity to PBQ (25% WP) used in Dali and Poyang Lake. The 96 h LC50 value of MNSC against Eriocheir sinensis was 283.84 mg a.i./L. At the concentration of PBQ (20% SC) 1000 mg a.i./L, all Eriocheir sinensis were alive. The 96 h LC50 values of PBQ and MNSC against Neocaridina denticulate were 17.67 and 14.05 mg a.i./L, respectively. In conclusion, PBQ (20% SC) had a comparable molluscicidal efficacy with MNSC (26% SC) and PBQ (25% WP). Furthermore, it showed lower toxicity to the crustacean species, better solubility, no floating dust, and convenience for carriage. PBQ (20% SC) was suitable for controlling snails in the water network schistosomiasis-endemic areas.

Exploring the role of macrophages in determining the pathogenesis of liver fluke infection

The food-borne trematodes, Opisthorchis viverrini and Clonorchis sinensis, are classified as group 1 biological carcinogens: definitive causes of cancer. By contrast, infections with Fasciola hepatica, also a food-borne trematode of the phylum Platyhelminthes, are not carcinogenic. This review explores the premise that the differential activation of macrophages during infection with these food-borne trematodes is a major determinant of the pathological outcome of infection. Like most helminths, the latter stages of infection with all 3 flukes induce M2 macrophages, a phenotype that mediates the functional repair of tissue damaged by the feeding and migratory activities of the parasites. However, there is a critical difference in how the development of pro-inflammatory M1 macrophages is regulated during infection with these parasites. While the activation of the M1 macrophage phenotype is largely suppressed during the early stages of infection with F. hepatica, M1 macrophages predominate in the bile ducts following infection with O. viverrini and C. sinensis. The anti-microbial factors released by M1 macrophages create an environment conducive to mutagenesis, and hence the initiation of tumour formation. Subsequently, the tissue remodelling processes induced by the M2 macrophages promote the proliferation of mutated cells, and the expansion of cancerous tissue. This review will also explore the interactions between macrophages and parasite-derived signals, and their contributions to the stark differences in the innate immune responses to infection with these parasites.

A relatively high zoonotic trematode prevalence in Orientogalba ollula and the developmental characteristics of isolated trematodes by experimental infection in the animal model

Background

Food-borne parasitic diseases decrease food safety and threaten public health. The snail species is an intermediate host for numerous human parasitic trematodes. Orientogalba ollula has been reported as intermediate hosts of many zoonotic trematodes. Here, we investigated the prevalence of zoonotic trematodes within O. ollula in Guangxi, China, and assessed their zoonotic potential.

Methods

Snails were collected from 54 sites in 9 cities throughout Guangxi. The snail and trematode larvae species were determined by combining morphological characteristics and molecular markers. The trematodes prevalence and constituent ratio were calculated and compared among different habitat environments. Phylogenetic trees of the trematode species were constructed using the neighbor-joining method with nuclear internal transcribed spacer 2 (ITS2) sequences. The developmental cycles of the isolated trematodes were examined by experimental infection in ducks. The developmental characteristics of Echinostoma revolutum was recorded by dissecting infected ducklings from 1-day post infection (dpi) to 10 dpi.

Results

The overall prevalence of trematode larvae was 22.1% (1818/8238) in O. ollula from 11 sample sites. Morphological together with molecular identification, showed that E. revolutum, Australapatemon sp., Hypoderaeum conoideum, Pharyngostomum cordatum, and Echinostoma sp. parasitized O. ollula, with the highest infection rate of E. revolutum (13.0%). However, no Fasciola larvae were detected. The trematodes prevalence and constituent ratio varied in two sub-biotypes (P < 0.01). A neighbor-joining tree analysis of ITS2 sequences resulted in distinct monophyletic clades supported by sequences from isolated larvae with high bootstrap values. Ducklings exposed to O. ollula infected with Echinostoma sp., E. revolutum, and H. conoideum larvae were successfully infected. The animal model for Echinostoma revolutum was successfully established. E. revolutum matured from larvae to adult at 10 dpi in the intestine of the duck, and the developmental characteristics of E. revolutum were characterized by the maturation of the reproductive and digestive organs at 6–8 dpi.

Conclusions

This study revealed a high prevalence of zoonotic trematodes in O. ollula from Guangxi, China. Existing trematodes infection in animals and human clinical cases, coupled with the wide geographical distribution of O. ollula, necessitate further evaluations of the potential risk of spillover of zoonotic infection from animal to human and vice versa.

Graphical Abstract

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-022-01014-7.

Toxicity of plant-based silver nanoparticles to vectors and intermediate hosts: Historical review and trends

Green nanoparticles (GNPs), mainly green silver nanoparticles (Ag NPs), have been recommended as sustainable and eco-friendly technologies to control vectors and intermediate hosts. The aim of the current study is to carry out a historical and systematic literature review about the use of green plant-based Ag NPs (GP-Ag NPs) to control medically important mosquito, tick and gastropods. Data about the number of studies published per year, geographical distribution of studies (mailing address of the corresponding author), synthesis type (plant species, plant structure and extract types), physicochemical properties of GP-Ag NPs, experimental designs, developmental stages and the toxic effects on mosquitoes, ticks and gastropods were summarized and discussed. Revised data showed that GP-Ag NPs synthesis and toxicity in mosquitoes, ticks and snails depend on plant species, plant part, extract types, exposure condition and on the analyzed species. GP-Ag NPs induced mortality, tissue damage, biochemical and behavioral changes in mosquitoes and reduced their fecundity, oviposition, egg hatching and longevity. Ticks exposed to GP-Ag NPs presented increased mortality and reduced oviposition, while on snails, studies demonstrated mortality, oxidative stress, and DNA damage. Immune responses were also observed in snails after their exposure to GP-Ag NPs. GP-Ag NPs reduced the reproduction and population of several vectors and intermediate hosts. This finding confirms their potential to be used in gastropod control programs. Future studies about current gaps in knowledge are recommended.

Rumen Fluke in Cattle and Buffaloes in Asia: A Review

Rumen fluke is a parasitosis that infects ruminant animals across a wide geographical range of countries. It is a severe infection in temperate and tropical climate regions of Asia, Australia, Africa, and Europe, which cause significant economic losses. In this review, the available information to date on rumen fluke species infecting cattle and buffaloes in Asian countries is evaluated. The citation search was performed through specific keywords, literature published from 1964 to 2021, retrieved from electronic databases: Scopus, Web of Science, Pub Med, Education Resources Information Center (ERIC), Science Direct, Elsevier, and Google Scholar. Twenty-six (26) rumen fluke species belonging to two families: Paramphistomidae 61.5% (16/26) and Gastrothylacidae 38.4% (10/26), were reported in cattle and buffaloes in fourteen Asian countries. Paramphistomum cervi and Cotylophoron cotylophorum are the most prevalent species with broader distribution in countries than the other genera. The coprological prevalence varies from 0.8% to 98.17% and 0.86% to 78.4% in cattle and buffaloes, respectively. The prevalence of rumen fluke by fluke counts method range between 6.45% to 90.6% and 4.29% to 75.07% in cattle and buffaloes, respectively. The sedimentation method and fluke count are reliable tests for detecting rumen fluke in live and slaughtered animals. In conclusion, the rumen fluke should be considered a critical production disease that affects cattle and buffaloes in Asia. Further studies are necessary to determine the rumen fluke-snail associations, develop diagnostic tests to detect prepatent infections in the definitive host, determine the economic importance of rumen fluke, and determine the efficacy of different anthelmintic in the treatment of patent infections in the definitive host.

Prevalence and factors associated with transmission of schistosomiasis in school-aged children in South Sudan: a cross-sectional study

Introduction

South Sudan is affected by a high burden of Neglected Tropical Diseases (NTDs). The country is very vulnerable to NTDs due to its favourable tropical climate and multiple risk factors. However, the distribution of the diseases and the populations at risk for the various NTDs is unknown. This paper described the distribution of schistosomiasis in 58 counties and 261 schools in South Sudan.

Methods

a descriptive quantitative cross-sectional study of schistosomiasis in 58 counties in 8 states of South Sudan recruited school-aged children. Using different laboratory techniques, the children were tested for Schistosoma mansoni (S. mansoni) and Schistosoma haematobium (S. haematobium). A quantitative descriptive statistical was performed to determine the prevalence rates and the endemicity of schistosomiasis among 13,286 school-aged children.

Results

the overall prevalence of S. mansoni and S. haematobium were 6.1% and 3.7% using Kato Katz and urine filtration concentration testing techniques. The highest state prevalence was reported in Western Equatoria for both S. mansoni (14.7%) and S. haematobium (7.3%). The age of the participants varied from 4 to 18 years; of these, children 10 to 12 years old had the highest prevalence of S. mansoni (6.8%) and S. haematobium (3.7%). The prevalence of S. mansoni (7% male vs 5% female) and S. haematobium (3.6% male vs 3.1% female) were higher in males than females. The likelihood of the prevalence of S. mansoni in males was 1.42 (95% CI:1.23, 1.64) higher than in females, while for S. haematobium, 1.36 (95% CI:1.12, 1.65) higher than in females. The prevalence of S. mansoni and S. haematobium showed a statistically significant gender difference (P< 0.05).

Conclusion

the study had provided evidence of the distribution of schistosomiasis in South Sudan for policy direction and recommended annual preventive chemotherapy with praziquantel in all endemic areas.

The Life Histories of Intermediate Hosts and Parasites of Schistosoma haematobium and Schistosoma mansoni in the White Nile River, Sudan

Background: The epidemiology of schistosomiasis transmission varies depending on the circumstances of the surrounding water bodies and human behaviors. We aimed to explore cercarial emergence patterns from snails that are naturally affected by human schistosomiasis and non-human trematodes. In addition, this study aimed to explore how schistosomiasis infection affects snail survival, reproduction, and growth. Methods: We measured the survival rate, fecundity, and size of Biomphalaria pfeifferi snails and the cercarial rhythmicity of S. haematobium and S. mansoni. The number of egg masses, eggs per egg mass, and snail deaths were counted for 7 weeks. The survival rate and cumulative hazard were assessed for infected and non-infected snails. Results: S. haematobium and S. mansoni cercariae peaked at 9:00–11:00 a.m. Infection significantly reduced the survival rate of B. pfeifferi, which was 35% and 51% for infected and non-infected snails, respectively (p = 0.02), at 7 weeks after infection. The hazard ratio of death for infected snails compared to non-infected snails was 1.65 (95% confidence interval: 1.35–1.99; p = 0.01). Conclusions: An understanding of the dynamics of schistosomiasis transmission will be helpful for formulating schistosomiasis control and elimination strategies. Cercarial rhythmicity can be reflected in health education, and the reproduction and survival rate of infected snails can be used as parameters for developing disease modeling.

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.

A review of Fasciolopsis buski distribution and control in Indonesia

Fasciolopsiasis is a parasitic infection caused by the flatworm Fasciolopsis buski. Since 1982, fasciolopsiasis has been reported in Indonesia's Hulu Sungai Utara (HSU) Regency, South Kalimantan Province. Fasciolopsiasis occurs when contaminated raw or undercooked aquatic plants are consumed. Cercariae of the parasite encyst in a variety of aquatic plants and grow into metacercariae that infect and reproduce in the human intestine. Until now, treatment for F. buski infection in the HSU Regency has been comparatively short, with patients receiving only a single dose of praziquantel, 30 mg/kg body weight, without further observation. A long-term effort through health promotion activities and intensive health education, particularly for elementary school children enrolled in the School Health Program, is ongoing to help prevent fasciolopsiasis from spreading and to improve environmental sanitation. Through 2018, intervention efforts successfully reduced the incidence of F. buski infection. Sustaining surveillance and investigation of fasciolopsiasis, including identification of new cases and community education, is critical for the elimination of the parasite from Indonesia. This review describes the spread of F. buski and its possible impact on public health to understand the critical nature of continuing F. buski surveillance and control efforts.

Iberian Distribution of the Freshwater Snail Genus Bithynia Leach, 1818 (Mollusca: Truncatelloidea), Vector of Opisthorchiasis and Metorchiasis

BACKGROUND

Opisthorchis felineus and Metorchis bilis are trematodes that cause opisthorchiasis and metorchiasis, respectively. The freshwater snails Bithynia hispanica and B. tentaculata are the respective intermediate hosts for these parasites in the Iberian Peninsula, where both parasites are present.

METHODS

To study the distribution of these snail species, an exhaustive literature review and revision of museum collections was performed.

RESULTS

A total of 370 localities were compiled and mapped. B. tentaculata were found throughout the Iberian Peninsula, both in Spain and Portugal, while B. hispanica was found only in the Mediterranean coast of Spain.

CONCLUSION

Knowing the distribution of the Bithynia species found in the Iberian Peninsula is highlighted in terms of public health, as the presence of the snail is related to the presence of the disease and can be used as a tool to face future outbreaks.

Transmission Dynamics of Schistosoma haematobium among School-Aged Children: A Cohort Study on Prevalence, Reinfection and Incidence after Mass Drug Administration in the White Nile State of Sudan

The reinfection rate of schistosomiasis after mass drug administration (MDA) has not been documented in Sudan. We aimed to explore the transmission dynamics of urogenital schistosomiasis after MDA, targeting school-aged children in the White Nile State of Sudan, assessing the prevalence, reinfection rate, and incidence. A single dose of praziquantel (40 mg/kg) was administered to 1951 students in five primary schools from January to February 2018 immediately after a baseline survey, and follow-up surveys were performed at 2 weeks and 6 months after treatment. We examined Schistosoma haematobium eggs by centrifugation methods. The overall reinfection rate at 6 months after treatment was 9.8% (95% confidence interval: 0.5-17.4%). By school, the reinfection rate was highest in the Al Hidaib school, whose prevalence was highest at baseline. The reinfection rate was significantly higher in high-infection areas than low-infection areas (p = 0.02). Of the prevalence at 6 months in high-infection areas, 41% of cases were due to reinfection. MDA interventions are decided upon and undertaken at the district level. A more targeted treatment strategy should be developed with a particular focus on tracking high-risk groups, even within a school or a community.

Molecular Characterization of Rotifers and Their Potential Use in the Biological Control of Biomphalaria

Background

Schistosomiasis is one of the most important tropical parasitic diseases worldwide. Biomphalaria straminea, the intermediate host of Schistosoma mansoni, has invaded and spread to Southern China since 1974 and may pose enormous threats to public health. Controlling intermediate host snails is an effective strategy in schistosomiasis intervention. However, the only effective chemical molluscicide, niclosamide, currently recommended by WHO may cause environmental pollution, loss of biodiversity, and high costs. Thus, to counter intermediate hosts, a sustainable and environmentally friendly tool is urgently needed. Here, we conducted field investigations to collect and identify a potential snail competitor rotifer and evaluated its molluscicide effect.

Results

In this study, we collected two samples of rotifers from Shenzhen. We found both red and black phenotypic B. straminea snails at the sampling sites. We identified the rotifer population as a species of the genus Philodina according to the amplification and phylogenetic analysis results of coxI gene. We found that rotifer exposure did not significantly affect the hatching rate of B. straminea eggs but promoted the killing of juvenile snails. Meanwhile, rotifer exposure did not significantly alter the fecundity of B. straminea quantified by the number of eggs per egg mass, the number of egg masses per snail, and the number of eggs per snail; but the snails exposed to rotifers showed lower fecundity performance than the control snails. Importantly, rotifer exposure could significantly affect the development of juvenile B. straminea, showing a smaller shell diameter of the exposed snails than that of the control snails. In addition, rotifer exposure affected the life span of B. straminea snails, showing a 16.61% decline in the average life span. After rotifer exposure, the S. mansoni-infected B. straminea snails died significantly faster than those without rotifer exposure. Similar findings were observed in S. mansoni-infected Biomphalaria glabrata snails. These results implied that rotifer exposure significantly promoted the mortality of S. mansoni-infected B. straminea and B. glabrata.

Conclusions

Our study demonstrated the potential molluscicide effect of rotifers on intermediate hosts under laboratory conditions. Our findings may provide new insights into the development of biocontrol strategies for snail-borne disease transmission.

Eosinophilic meningitis in New Caledonia: The role of Angiostrongylus cantonensis?

INTRODUCTION

Eosinophilic meningitis is a rare form of meningitis with sequelae or death occurring in approximately 2-3% of cases. The most frequent etiological agent is the parasite Angiostrongylus cantonensis. The aim of this study was to characterize New Caledonian cases and to assess the extent to which of A. cantonensis was involved.

MATERIAL AND METHODS

We performed a retrospective study of all cases of eosinophilic meningitis (EM) admitted to the Territorial Hospital of New Caledonia, from 2004 to 2019. We performed a descriptive and a multivariate analysis to identify association of variables with severe and fatal cases (or cases with sequelae).

CONCLUSION

Angiostrongyliasis was confirmed as being responsible for 17 of the 92 reported EM cases in New Caledonia from 2004 to 2019 with most being young adults and non-walking infants, and with two peaks of incidence one during the dry season and one during the rainy season. Considering the high incidence and regularity of cases, the potential reservoirs should be identified to target prevention campaigns.

Mobilizing molluscan models and genomes in biology

Molluscs are among the most ancient, diverse, and important of all animal taxa. Even so, no individual mollusc species has emerged as a broadly applied model system in biology. We here make the case that both perceptual and methodological barriers have played a role in the relative neglect of molluscs as research organisms. We then summarize the current application and potential of molluscs and their genomes to address important questions in animal biology, and the state of the field when it comes to the availability of resources such as genome assemblies, cell lines, and other key elements necessary to mobilising the development of molluscan model systems. We conclude by contending that a cohesive research community that works together to elevate multiple molluscan systems to 'model' status will create new opportunities in addressing basic and applied biological problems, including general features of animal evolution. This article is part of the Theo Murphy meeting issue 'Molluscan genomics: broad insights and future directions for a neglected phylum'.

Impact of micro-environmental factors on survival, reproduction and distribution of Oncomelania hupensis snails

Background

Schistosomiasis japonica is a chronic parasitic disease that seriously harms people's health. Oncomelania hupensis is the only intermediate host of Schistosoma japonicum. The micro-environmental factors surrounding the snail have a great impact on the survival, growth and reproduction of O. hupensis, but there are few relevant systematic analyses until the present. This scoping review aims to identify and summarize the micro-environmental factors that greatly affect O. hupensis, and to find gaps in research thus to provide directions for future in-depth studies.

Main body

This scoping review searched databases with search terms of the combinations of “Micro(-)environment”, “Oncomelania” and their expanded aspects. A total of 133 original articles were recruited. Predefined data fields were extracted including research methods, influencing factors, and their effects on O. hupensis. Most studies focused on vegetation factors (54.1%), and other factors noted were soil composition (27.8%), water environmental factors (24.1%), and predator (3.0%), respectively. The factors with positive impacts included water level, pH value, soil temperature, soil humidity, the coverage and height of vegetation at suitable levels. This could provide more detailed information for O. hupensis habitat identification and prediction. The factors with negative impacts included plant extracts, snail control and disease prevention forests, and microorganisms with molluscicidal activities. It revealed a potential application as ecological molluscicides in the future. Factors such as physico-chemical properties of water, soil chemistry showed a gap in scientific studies, thus required further extensive research.

Conclusions

Micro-environmental factors including water quality, soil composition as well as the technology and application of biomolluscicides (plant extracts and microorganisms) deserve more attention. Relative study findings on micro-environment have good potentials in snail control applications. Further studies should be implemented to investigate the impact of micro-environmental factors on snails and close the research gaps.

Supplementary Information

The online version contains supplementary material available at 10.1186/s40249-021-00826-3.

Modelling the present and future distribution of Biomphalaria species along the watershed of the Middle Paranapanema region, São Paulo, Brazil

The Middle Paranapanema region in the state of São Paulo, Brazil, is an area with high diversity for Biomphalaria species, with municipalities historically marked by cases of schistosomiasis transmission. The objectives of the study were to evaluate the current distribuition and predict the future distribution of habitats of Biomphalaria species at a high spatial resolution along 114 freshwater sites in the Middle Paranapanema watershed. The modelling encompassed 55 municipalities of the Middle Paranapanema region, which were analyzed through the maximum entropy algorithm. All geographic coordinates of the Biomphalaria species collected from 2015-2018 and environmental data were obtained through WorldClim, HydroSHEDS, TOPODATA and Secretaria do Meio Ambiente for the 1970-2017 period. For the 2041-2060 period we used the HadGEM2-ES climate model. Due to climate change, MaxEnt showed that there was a high probability for the maintenance of B. glabrata habitats near Ourinhos and Assis, an expansion of scattered spots, and a 50% probability that the species will spread throughout new suitable areas. The results showed that the geographical range of B. straminea will most likely expand in the future along the Middle Paranapanema hydrographic basin, especially in the municipalities near Ourinhos. For B. glabrata and B. straminea, the geographic expansion was related to the predicted increase in the annual temperature range. The habitats suitable for B. tenagophila and B. peregrina seemed to slightly expand around the west border of the Middle Paranapanema region. Biomphalaria occidentalis may have a small reduction in its distribution due to climate change. The variables that contributed the most to the future modelling for these three species were precipitation and temperature. Identifying the sites with intermediate hosts for schistosomiasis may guide public health measures to avoid or reduce future transmissions in this region.

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.

RNA-seq: The early response of the snail Physella acuta to the digenetic trematode Echinostoma paraensei

To analyze the response of the snail Physella acuta to Echinostoma paraensei, a compatible digenetic trematode, Illumina RNA-seq data were collected from snails with early infection (5 snails at 2 days post-exposure [DPE]) and established infection (4 snails, 8 DPE), and 7 control (unexposed) snails. A reference transcriptome (325,563 transcripts, including 98% of eukaryotic universal single-copy orthologs; BUSCO) and a draft P. acuta genome (employing available genomic Illumina reads; 799,945 scaffolds, includes 88% BUSCO genes) were assembled to guide RNA-seq analyses. Parasite exposure of P. acuta led to 10,195 differentially expressed (DE) genes at 2 DPE and 8,876 DE genes at 8 DPE with only 18% of up-regulated and 22% of down-regulated sequences shared between these time points. Gene ontology (GO) analysis yielded functional annotation of only 1.2% of DE genes but did not indicate major changes in biological activities of P. acuta between 2 and 8 DPE. Increased insights were achieved by analysis of expression profiles of 460 immune-relevant DE transcripts, identified by BLAST and InterProScan. Physella acuta has expanded gene families that encode immune-relevant domains, including CD109/TEP, GTPase IMAP, Limulus agglutination factor (dermatopontin), FReD (≥82 sequences with fibrinogen-related domains), and transcripts that combine C-type lectin (C-LECT) and C1q domains, novel among metazoa. Notably, P. acuta expressed sequences from these immune gene families at all time points, but the assemblages of unique transcripts from particular immune gene families differed between 2 and 8 DPE. The shift in profiles of DE immune genes, from early exposure to parasite establishment, suggests that compatible P. acuta initially respond to infection but switch to express immune genes that likely are less effective against E. paraensei but counter other types of (opportunistic) pathogens and parasites. We propose that the latter expression profile is part of an extended phenotype of E. paraensei, imposed upon P. acuta through parasite manipulation of the host, following successful parasite establishment in the snail after 2 DPE.

Toxicity of engineered nanomaterials to aquatic and land snails: A scientometric and systematic review

The emerging growth of nanotechnology has attracted great attention due to its application in the parasite and intermediate host control. However, the knowledge concerning the mechanism of action (MoA) and toxicity of nanomaterials (NMs) to snails remain unclear. In this context, the present study revised the historical use of snails as experimental models in nanotoxicological studies and summarized the MoA and toxicity of NMs in aquatic and land snails. The data concerning the bioaccumulation, reproductive and transgenerational toxicity, embryotoxicity, genotoxicity and potential molluscicidal activity of NMs were revised. Furthermore, the data about the experimental conditions, such as exposure time, concentrations, cell and tissue-specific responses, snail species and nanoparticle types are discussed. Revised data showed that the toxic effects of NMs were reported for 21 snail species with medical, veterinary and ecological importance. The NM toxicity to snails is dependent on the physical and chemical properties of NMs, as well as their environmental transformation and experimental design. The NM bioaccumulation on snails was related to several toxic effects, such as reactive oxygen species (ROS) production, oxidative stress, following by oxidative damage to DNA, lipids and proteins. The NM metabolism in snails remains unknown. Results showed the potential use of NMs in the snail control program. Also, significant research gaps and recommendations for future researches are indicated. The present study confirms that snails are suitable invertebrate model system to assess the nanotoxicity.

A polyvalent and universal tool for genomic studies in gastropod molluscs (Heterobranchia)

Molluscs are the second most diverse animal phylum and heterobranch gastropods present ~ 44,000 species. These comprise fascinating creatures with huge morphological and ecological disparity. Such great diversity comes with even larger phylogenetic uncertainty and many taxa have been largely neglected in molecular assessments. Genomic tools have provided resolution to deep cladogenic events but generating large numbers of transcriptomes/genomes is expensive and usually requires fresh material. Here we leverage a target enrichment approach to design and synthesize a probe set based on available genomes and transcriptomes across Heterobranchia. Our probe set contains 57,606 70mer baits and targets a total of 2,259 ultra-conserved elements (UCEs). Post-sequencing capture efficiency was tested against 31 marine heterobranchs from major groups, including Acochlidia, Acteonoidea, Aplysiida, Cephalaspidea, Pleurobranchida, Pteropoda, Runcinida, Sacoglossa, and Umbraculida. The combined Trinity and Velvet assemblies recovered up to 2,211 UCEs in Tectipleura, up to 1,978 in Nudipleura, and up to 1,927 in Acteonoidea, the latter two being the most distantly related taxa to our core study group. Total alignment length was 525,599 bp and contained 52% informative sites and 21% missing data. Maximum-likelihood and Bayesian inference approaches recovered the monophyly of all orders tested as well as the larger clades Nudipleura, Panpulmonata, and Euopisthobranchia. The successful enrichment of diversely preserved material and DNA concentrations demonstrate the polyvalent nature of UCEs, and the universality of the probe set designed. We believe this probe set will enable multiple, interesting lines of research, that will benefit from an inexpensive and largely informative tool that will, additionally, benefit from the access to museum collections to gather genomic data.

Fascioliasis and fasciolopsiasis: Current knowledge and future trends

Food-borne zoonotic trematodiases are classified as neglected diseases by the World Health Organization. Among them, fascioliasis is caused worldwide by Fasciola hepatica and F. gigantica, and represent a huge problem in livestock production and human health in endemic areas. Fasciolopsis buski, restricted to specific regions of Asia, causes fasciolopsiasis. The incidence of these trematodiases is underestimated due to under-reporting and to the lack of sensitive and widely accepted tool for their diagnosis. This, together with a rising trend in reporting of drug resistance and the need for an effective vaccine against these parasites, pose a challenge in the effective control of these diseases. Here, the latest reports on fascioliasis outbreaks between 2000 and 2020 and the most recent advances in their epidemiology, diagnosis, treatment and control are revised. Finally, future needs in the field of fascioliasis and fasciolopsiasis are presented, which could be addressed based on current knowledge and by means of new emerging technologies.