Echinostomes and Other Intestinal Trematode Infections.

Intestinal trematodes are among the most common types of parasitic worms. About 76 species belonging to 14 families have been recorded infecting humans. Infection commonly occurs when humans eat raw or undercooked foods that contain the infective metacercariae. These parasites are diverse in regard to their morphology, geographical distribution and life cycle, which make it difficult to study the parasitic diseases that they cause. Many of these intestinal trematodes have been considered as endemic parasites in the past. However, the geographical limits and the population at risk are currently expanding and changing in relation to factors such as growing international markets, improved transportation systems, new eating habits in developed countries and demographic changes. These factors make it necessary to better understand intestinal trematode infections. This chapter describes the main features of human intestinal trematodes in relation to their biology, epidemiology, host-parasite relationships, pathogenicity, clinical aspects, diagnosis, treatment and control.

Neglected food-borne trematodiases: echinostomiasis and gastrodiscoidiasis.

In the present paper, we review two of the most neglected intestinal food-borne trematodiases: echinostomiasis, caused by members of the family Echinostomatidae, and gastrodiscoidiasis produced by the amphistome Gastrodiscoides hominis. Both parasitic infections are important intestinal food-borne diseases. Humans become infected after ingestion of raw or insufficiently cooked molluscs, fish, crustaceans, amphibians or aquatic vegetables. Thus, eating habits are essential to determine the distribution of these parasitic diseases and, traditionally, they have been considered as minor diseases confined to low-income areas, mainly in Asia. However, this scenario is changing and the population at risk are currently expanding in relation to factors such as new eating habits in developed countries, growing international markets, improved transportation systems and demographic changes. These aspects determine the necessity of a better understanding of these parasitic diseases. Herein, we review the main features of human echinostomiasis and gastrodiscoidiasis in relation to their biology, epidemiology, immunology, clinical aspects, diagnosis and treatment.

Timing and order of exposure to two echinostome species affect patterns of infection in larval amphibians.

The study of priority effects with respect to coinfections is still in its infancy. Moreover, existing coinfection studies typically focus on infection outcomes associated with exposure to distinct sets of parasite species, despite that functionally and morphologically similar parasite species commonly coexist in nature. Therefore, it is important to understand how interactions between similar parasites influence infection outcomes. Surveys at seven ponds in northwest Pennsylvania found that multiple species of echinostomes commonly co-occur. Using a larval anuran host (Rana pipiens) and the two most commonly identified echinostome species from our field surveys (Echinostoma trivolvis and Echinoparyphium lineage 3), we examined how species composition and timing of exposure affect patterns of infection. When tadpoles were exposed to both parasites simultaneously, infection loads were higher than when exposed to Echinoparyphium alone but similar to being exposed to Echinostoma alone. When tadpoles were sequentially exposed to the parasite species, tadpoles first exposed to Echinoparyphium had 23% lower infection loads than tadpoles first exposed to Echinostoma. These findings demonstrate that exposure timing and order, even with similar parasites, can influence coinfection outcomes, and emphasize the importance of using molecular methods to identify parasites for ecological studies.

[Characterization of Echinostoma miyagawai in domestic ducks in Wuhu City].

OBJECTIVE: To investigate the morphological characteristics of Echinostoma miyagawai in domestic ducks in Wuhu area, and to explore the feasibility of the cytochrome oxidase subunit-1 (Cox1) gene as a molecular marker for the identification of E. miyagawai. METHODS: E. miyagawai was isolated from free-ranged domestic ducks in Wuhu area, and the parasites were stained and identified. In addition, the mitochondrial Cox1 gene of E. miyagawai was amplified using a PCR assay, and the amplification product was sequenced and aligned with the GenBank database to yield the homology for the identification of parasite species in combination with morphological findings. Intra-species comparison was done based on the Cox1 gene sequence. RESULTS: The prevalence of E. miyagawai infection was 16.67% in domestic ducks in Wuhu area, and the adult E. miyagawai was 6.6 to 13.2 mm in length. The size of the E. miyagawai Cox1 gene was approximately 660 bp, which had a 99.68% homology to the E. miyagawai accessed in GenBank. The morphological findings were in agreement with molecular identification. CONCLUSIONS: E. miyagawai infection is common in domestic ducks in Wuhu area, and the mitochondrial Cox1 gene is a feasible marker of intra- and inter-species molecular identification of Echinostoma.

Suburbanization Increases Echinostome Infection in Green Frogs and Snails.

An important contribution to infectious disease emergence in wildlife is environmental degradation driven by pollution, habitat fragmentation, and eutrophication. Amphibians are a wildlife group that is particularly sensitive to land use change, infectious diseases, and their interactions. Residential suburban land use is now a dominant, and increasing, form of land cover in the USA and globally, contributing to increased pollutant and nutrient loading in freshwater systems. We examined how suburbanization affects the infection of green frog (Rana clamitans) tadpoles and metamorphs by parasitic flatworms (Echinostoma spp.) through the alteration of landscapes surrounding ponds and concomitant changes in water quality. Using sixteen small ponds along a forest-suburban land use gradient, we assessed how the extent of suburban land use surrounding ponds influenced echinostome infection in both primary snail and secondary frog hosts. Our results show that the degree of suburbanization and concurrent chemical loading are positively associated with the presence and burden of echinostome infection in both host populations. This work contributes to a broader understanding of how land use mediates wildlife parasitism and shows how human activities at the household scale can have similar consequences for wildlife health as seemingly more intensive land uses like agriculture or urbanization.

Echinostoma revolutum: Development of a high performance DNA-specific primer to demonstrate the epidemiological situations of their intermediate hosts.

Echinostomiasis caused by the Echinostoma group, in particular E. revolutum are a significant problem for both humans and other animals. This group has a large number of morphological similarities that are difficult and time-consuming to identify. The present study aimed to develop high-performance tools for the detection of the prevalence of E. revolutum and to reveal the prevalence of E. revolutum infections in intermediate snail hosts in Lopburi province, Thailand. The snail specimens were collected by stratified sampling method and examined to collect trematodes in the larval stage. The specific primer was manually designed and based on 18 s rDNA and verified the specificity and sensitivity for use as an identification tool to compare with classical method, constructed by epidemic mapping. The overall prevalence value of E. revolutum was found to be 16.26%. Tha Luang district had the highest prevalence (70.14%), followed by Chai Badan, Phatthana Nikhom, Tha Wung, Ban Mi, Khok Samrong, Nong Muang and Sa Bot at 42%, 25.14%, 2.52%, 1.73%, 2%, 1.33% and 0.40%, respectively. With regard to the specific primer, it can amplify both cercarial and metacercarial DNA (90 pg/µl.) and discriminated E. revolutum from its hosts, other trematodes and other echinostome larvae with no cross-reactions. Therefore, the developed specific primer can be used as a species-specific identification tool with a high degree of sensitivity and specificity. Consequently, this data is important for monitoring the outbreak of E. revolutum. It can be applied for initiating surveillance programs of snail-borne diseases in both medical and veterinary studies.

Echinostoma ilocanum Infection in Two Residents of Savannakhet Province, Lao PDR.

Adult specimens of Echinostoma ilocanum (Garrison, 1908) Odhner, 1911 (Trematoda: Echinostomatidae) were recovered from 2 riparian people who resided along the Mekong River in Savannakhet Province, Lao PDR. In fecal examinations done by the Kato-Katz technique, they revealed echinostome eggs together with eggs of Opisthorchis viverrini (and minute intestinal fluke eggs) and hookworms. To recover the adult flukes, they were treated with praziquantel 30-40 mg/kg in a single dose and purged with magnesium salts. A total of 658 adult fluke specimens were recovered from the 2 people; 456 from case 1 and 202 from case 2. Specimens from case 1 consisted of 335 echinostomes (301 E. ilocanum and 34 species undetermined), 120 O. viverrini, and 1 Haplorchis taichui, and those from case 2 consisted of 36 E. ilocanum, 134 O. viverrini, and 32 H. taichui. Thus, the number of E. ilocanum specimens was 337 in total (average per person, 168.5). From this study, it is suggested that foodborne intestinal flukes and liver flukes are highly prevalent along the Mekong River in Savannakhet Province. The present report describes for the first time human infections with E. ilocanum in Lao PDR.

Infection Status of Isthmiophora hortensis Metacercariae in Dark Sleepers, Odontobutis Species, from Some Water Systems of the Republic of Korea.

Present study was performed to survey on infection status of Isthmiophora hortensis (formerly Echinostoma hortense) metacercariae (IhMc) in dark sleepers, Odontobutis spp., from some water systems of the Republic of Korea. A total of 237 Odontobutis spp. was collected in the water systems of 5 rivers, i.e., Mangyeong-gang (gang means river), Geum-gang, Tamjin-gang, Seomjin-gang, and Nakdong-gang. They were all examined with artificial digestion method for 5 years (2013-2017). A total of 137 (57.8%) Odontobutis spp. were infected with 14.8 IhMc in average. The prevalence was the highest in Nakdong-gang areas (62.9%) and followed by in Mangyeong-gang (57.1%), Geum-gang (56.3%), Tamjin-gang (54.8%), and Seomjin-gang (53.9%) areas. Metacercarial densities were 28.1 (Geum-gang), 13.9 (Mangyeong-gang), 13.3 (Nakdong-gang), 13.1 (Tamjin-gang), and 2.3 (Seomjin-gang) per infected fish. Especially, in case of Yugucheon (cheon means stream), a branch of Geum-gang, IhMc were detected in all fish (100%) examined and their density was about 48 per fish. By the present study, it was confirmed that the infection status of IhMc is more or less different by the surveyed areas and the dark sleepers, Odontobutis spp., are suitable fish hosts of I. hortensis.

An update on human echinostomiasis.

Echinostomiasis, caused by trematodes belonging to the family Echinostomatidae, is an important intestinal foodborne parasitic disease. Humans become infected after ingestion of raw or insufficiently cooked molluscs, fish, crustaceans and amphibians, thus, understanding eating habits is essential to determine the distribution of the disease. Despite the public health impact of echinostomiasis, it has been neglected for years. Traditionally, echinostomiasis has been considered as a minor disease confined to low-income areas, mainly in Asia. However, the geographical boundaries and the population at risk are currently expanding and changing in relation to factors such as growing international markets, improved transportation systems, new eating habits in developed countries and demographic changes. These factors make it necessary to improve our understanding of intestinal trematode infections. Herein, we review the main features of human echinostomiasis in relation to their biology, epidemiology, host-parasite relationships, pathogenicity, clinical aspects, diagnosis, treatment and control.

Haematological changes in the laboratory rat Rattus norvegicus infected with Echinostoma caproni (Trematoda: Echinostomatidae).

To study possible indirect effects of the infection with intestinal helminths, 12 Rattus norvegicus (Wistar) were each experimentally exposed to 100 metacercariae of Echinostoma caproni, and blood samples were taken weekly up to 4 weeks post-exposure for comparison with control rats. Values of haematocrit (HCT), red blood cells (RBC), platelets (PLT), white blood cells (WBC), haemoglobin (HGB) and haematimatrix indices, and mean corpuscular haemoglobin concentrations (MCHC) were determined. In addition, leucocyte counts, including lymphocytes, neutrophils, monocytes, eosinophils and basophils were analysed. These parameters, including the leucocyte counts, showed no significant differences, except for MCHC at 4 weeks post-exposure. The present results indicate that in rats infected with E. caproni, although eosinophilia did not significantly increase, a significant reduction in MCHC was associated with an increase in the number of RBC.

High prevalence of large trematode eggs in schoolchildren in Cambodia.

Large trematode eggs (LTE) resembling Fasciola spp. eggs were reportedly found in the stools of schoolchildren in Kandal province, Cambodia. This study aimed to assess the prevalence of LTE in the stools of children attending the affected school, identify potential risk factors for infection and ascertain the trematode species. We performed a cross-sectional study involving an in-depth questionnaire administered to schoolchildren at the affected school, and examined cattle droppings in the surrounding area and the livers of slaughtered cattle. Three stool samples were examined per child, using Kato-Katz and formalin-ether concentration techniques. In addition, blood serum enzyme-linked immunosorbent assay (ELISA) and coprological polymerase chain reaction (PCR) was conducted for species clarification. Cattle droppings were examined by cup sedimentation and coprological ELISA. LTE were observed in the stools of 106 schoolchildren (46.5%). Two blood serum samples from schoolchildren were positive for Fasciola hepatica in a first ELISA but were negative in a confirmation immunofluorescence antibody test. Out of 221 PCR samples, only one tested positive for Fasciola spp. and none for Fasciolopsis buski. The consumption of raw aquatic plants (odds ratio (OR)=3.3) and fermented fish sauce (OR=2.1) were significantly associated with LTE in the stool. Fasciola spp. flukes were observed in 18.3% of 191 cattle livers. The prevalence of fascioliasis in cattle droppings was 88.8%. The low prevalence of schoolchildren that tested positive for Fasciola spp. with specific molecular diagnostics and who had no diagnostic evidence of F. buski strongly indicates that the majority of microscopically observed LTE are from Echinostoma spp. Fasciola spp. transmission from cattle to human is possible and public health services need to be alerted accordingly.

Three echinostome species from wild birds in the Republic of Korea.

Three echinostome species, i.e., Patagifer bilobus, Petasiger neocomense, and Saakotrema metatestis, are newly recorded in the trematode fauna of the Republic of Korea. They were recovered from 3 species of migratory birds (Platalea minor, Podiceps cristatus, and Egretta garzetta), which were donated by the Wildlife Center of Chungbuk (WCC) and the Conservation Genome Resource Bank for Korean Wildlife (CGRB). Only 1 P. bilobus specimen was recovered from the intestine of a black-faced spoonbill (P. minor), and characterized by the bilobed head crown with a deep dorsal incision and 54 collar spines. Twenty P. neocomense were recovered from the intestine of a great crested grebe (P. cristatus), and they had a well-developed head crown with 19 spines and 2 testes obliquely located at the posterior middle of the body. Total 70 S. metatestis were collected from the bursa of Fabricius of 1 little egret (E. garzetta). It is characterized by stout tegumental spines covered in the entire leaf-shaped body, posterior extension of the uterus, presence of the uroproct and a well-developed head crown with 12 pairs of collar spines on each side. By the present study, these 3 echinostome species are newly added to the trematode fauna in Korea.

Epidemiology and molecular genotyping of echinostome metacercariae in Filopaludina snails in Lamphun Province, Thailand.

OBJECTIVE: To analyze the prevalence of echinostome metacercariae in Filopaludina dorliaris (F. dorliaris) and Filopaludina martensi martensi (F. martensi martensi) and genotype variation of echinostome metacercariae by using random amplified polymorphic DNA (RAPD) analysis. METHODS: Filopaludina sp. snails were collected from eight localities of Lamphun Province, Northern Thailand and examined for echinostome metacercariae. RAPD-PCR was used to analyze genotype variation of echinostome metacercariae. RESULTS: A total of 3 226 F. dorliaris and F. martensi martensi snails were collected from eight localities. The overall prevalences of echinostome metacercariae in F. dorliaris and F. martensi martensi were 40.89% and 36.27%, while the intensity of infection was 20.37 and 12.04, respectively. The dendrogram constructed base on RAPD profiles, 4 well supported domains were generated; (i) group of metacercariae from Ban Hong, Mae Ta, Meaung, Pa Sang, Toong Hua Chang, and Weang Nong that were clustered in the group of E. revolutum, (ii) Ban Thi, (iii) Lee, and (iv) 3 adults of an out group. CONCLUSIONS: This research demonstrated RAPD profiling has been a useful tool to detect DNA polymorphisms to determine genetic relationship between echinostome metacercariae in Lamphun Province, Northern Thailand.

Three Echinostome Species from Wild Birds in the Republic of Korea

Three echinostome species, i.e., Patagifer bilobus, Petasiger neocomense, and Saakotrema metatestis, are newly recorded in the trematode fauna of the Republic of Korea. They were recovered from 3 species of migratory birds (Platalea minor, Podiceps cristatus, and Egretta garzetta), which were donated by the Wildlife Center of Chungbuk (WCC) and the Conservation Genome Resource Bank for Korean Wildlife (CGRB). Only 1 P. bilobus specimen was recovered from the intestine of a black-faced spoonbill (P. minor), and characterized by the bilobed head crown with a deep dorsal incision and 54 collar spines. Twenty P. neocomense were recovered from the intestine of a great crested grebe (P. cristatus), and they had a well-developed head crown with 19 spines and 2 testes obliquely located at the posterior middle of the body. Total 70 S. metatestis were collected from the bursa of Fabricius of 1 little egret (E. garzetta). It is characterized by stout tegumental spines covered in the entire leaf-shaped body, posterior extension of the uterus, presence of the uroproct and a well-developed head crown with 12 pairs of collar spines on each side. By the present study, these 3 echinostome species are newly added to the trematode fauna in Korea.

Echinostoma revolutum infection in children, Pursat Province, Cambodia.

To determine the prevalence of helminthic infections in Pursat Province, Cambodia, we tested fecal specimens from 471 children, 10-14 years of age, in June 2007. The prevalence of infection with echinostome flukes ranged from 7.5% to 22.4% in 4 schools surveyed. Adult worms were identified as Echinostoma revolutum.

Genetic variation and relationships of four species of medically important echinostomes (Trematoda: Echinostomatidae) in South-East Asia.

Multilocus enzyme electrophoresis (MEE) and DNA sequencing of the mitochondrial cytochrome c oxidase subunit 1 (CO1) gene were used to genetically compare four species of echinostomes of human health importance. Fixed genetic differences among adults of Echinostoma revolutum, Echinostoma malayanum, Echinoparyphium recurvatum and Hypoderaeum conoideum were detected at 51-75% of the enzyme loci examined, while interspecific differences in CO1 sequence were detected at 16-32 (8-16%) of the 205 alignment positions. The results of the MEE analyses also revealed fixed genetic differences between E. revolutum from Thailand and Lao PDR at five (19%) of 27 loci, which could either represent genetic variation between geographically separated populations of a single species, or the existence of a cryptic (i.e. genetically distinct but morphologically similar) species. However, there was no support for the existence of cryptic species within E. revolutum based on the CO1 sequence between the two geographical areas sampled. Genetic variation in CO1 sequence was also detected among E. malayanum from three different species of snail intermediate host. Separate phylogenetic analyses of the MEE and DNA sequence data revealed that the two species of Echinostoma (E. revolutum and E. malayanum) did not form a monophyletic clade. These results, together with the large number of morphologically similar species with inadequate descriptions, poor specific diagnoses and extensive synonymy, suggest that the morphological characters used for species taxonomy of echinostomes in South-East Asia should be reconsidered according to the concordance of biology, morphology and molecular classification.

Intermediate host availability masks the strength of experimentally-derived colonisation patterns in echinostome trematodes.

A fundamental goal of parasite evolutionary ecology is to elucidate patterns of host use and determine the underlying mechanisms of parasite colonisation. In order to distinguish the relative contributions of host encounter rates and host compatibility to infection outcomes, we compared host use in both field and experimental laboratory settings. Two years of bi-weekly snail sampling at a freshwater pond demonstrated fluctuating availability among three potential second intermediate snail host species and suggested that two trematode species (Echinostoma revolutum and Echinoparyphium sp.) did not colonise the three potential snail host species, Lymnaea elodes, Physa gyrina and Helisoma trivolvis, differentially. However, a series of experimental infections demonstrated that both parasites colonised H. trivolvis more so than the other two host species. Thus, more echinostome parasites utilised snail hosts that cannot serve as their first intermediate host. In experimental infections, host size and vagility were not strong determinants of infection. By utilising field and laboratory approaches, we were able to compare the strength of host compatibility under controlled conditions with patterns of infection in nature. Based on the results from these studies, it appears that host encounter is the primary mechanism dictating infection outcomes in the field.

Interspecific antagonism and virulence in hosts exposed to two parasite species.

Co-infection of host organisms by multiple parasite species has evolutionary consequences for all participants in the symbiosis. In this study, we co-exposed aquatic-snails (Biomphalaria glabrata) to two of their trematode parasites, Schistosoma mansoni and Echinostoma caproni. In co-exposed snails, E. caproni prevalence was 63% compared to only 23% for S. mansoni. Co-exposed E. caproni-infected snails exhibited reduced fecundity, higher mortality, and higher parasite reproduction (higher virulence) compared to hosts exposed to echinostomes alone. Conversely, co-exposed S. mansoni-infected snails released fewer parasites and produced greater numbers of eggs compared to hosts exposed to S. mansoni alone. These results suggest that co-exposure not only influences the establishment (presence or absence) of particular parasite species, but also impacts host life history, parasite reproduction, and the virulence of the interaction.

Population dynamics of and larval trematode interactions with Lymnaea tomentosa and the potential for biological control of schistosome dermatitis in Bremner Bay, Lake Wanaka, New Zealand.

Lymnaea tomentosa, the intermediate host of a schistosome which causes schistosome dermatitis in Lake Wanaka, was found to depths of 16 m. The snail recruits in January, lives for up to 21 months, is associated with all water plant species and is found in areas devoid of macroscopic plants. It is host to several trematode species. Avian schistosome infections appear in the spring when echinostome prevalence is low, and a decrease in schistosome prevalence may be correlated with an increase in echinostome prevalence during the summer. A multiple-kind lottery model analysis of parasite species richness implies that interspecific interactions may be occurring in the host snail during the months of December and January.