Hight prevalent of Opisthorchis viverrini infection and coincident Haplorchis metacercariae in cyprinid fishes in upper northeastern region of Thailand

Cyprinid fishes are commonly acted as second intermediate hosts of Opisthorchis viverrini and Haplorchis spp. This research investigated the prevalence and intensity of both parasites in cyprinid species. This process is regularly used as a guideline for disease surveillance and as a preventive measure in the Upper Northeastern region of Thailand. Fish samples were collected from both lentic and lotic water sources between November 2020 and October 2021, and classified them by their species. Acid pepsin-HCL solution was used to digest the individual samples and create a build-up of precipitate in order to view metacercariae using a stereomicroscope. A total of 3583 fish were caught and classified into 23 species. Out of these fish, 5.49% of them were found O. viverrini, 26.54% Haplorchis taichui, 10.04% Haplorchis pumilio, and 9.29% Haplorchoides sp. Ten species of fish were observed to have been infected with O. viverrini. Amongst the collected fish, M. obtusirostris had the highest prevalence of infection at 52.94%, while B. gonionotus had only 1.71%. The prevalence of O. viverrini infection was highest at 27.41% in Udon Thani Province. No prevalence of O. viverrini infection was observed in Bueng Kan Province. High prevalence of O. viverrini infection in cyprinid fishes was found in both lentic and lotic water sources in almost all provinces in the region. The prevalence of infection and intensity depended on the fish species and fish habitats.

Morbidity in California giant salamander (Dicamptodon ensatus Eschscholtz, 1833) caused by Euryhelmis sp. Poche, 1926 (Trematoda: Heterophyiidae)

In the fall of 2021, California Department of Fish and Wildlife reported larval and adult California giant salamanders (Dicamptodon ensatus Eschscholtz, 1833) with skin lesions at multiple creeks in Santa Clara and Santa Cruz Counties, California, USA. Field signs in both stages included rough, lumpy textured skin, and larvae with tails that were disproportionately long, flat, wavy, and flaccid. Presence of large-bodied larvae suggested delayed metamorphosis, with some larvae having cloudy eyes and suspected blindness. To determine the cause of the disease, three first-of-the-year salamanders from one location were collected, euthanized with 20% benzocaine, and submitted for necropsy to the U.S. Geological Survey, National Wildlife Health Center. Upon gross examination, all salamanders were emaciated with no internal fat stores, and had multiple pinpoint to 1.5-mm diameter raised nodules in the skin over the body, including the head, gills, dorsum, ventrum, all four limbs, and the tail; one also had nodules in the oral cavity and tongue. Histologically all salamanders had multiple encysted metacercariae in the dermis, subcutis, and skeletal muscles of the head, body, and tail that were often associated with granulomatous and granulocytic inflammation and edema. A small number of encysted metacercariae or empty cysts were present in the gills with minimal inflammation, and rarely in the kidney with no associated inflammation. Morphology of live metacercariae (Trematoda: Heterophyiidae), and sequencing of the 28S rRNA gene identified a species of Euryhelmis (Poche, 1926). Artificial digestion of a 1.65 g, decapitated, eviscerated carcass yielded 773 metacercariae, all of similar size and morphology as the live specimens. Based on these findings, the poor body condition of these salamanders was concluded to be due to heavy parasite burden. Environmental factors such as drought, increased temperature, and overcrowded conditions may be exacerbating parasite infections in these populations of salamander.

metacercariae infection in the second intermediate host dragonfly in Heilongjiang Province, China

Prosthogonimiasis poses a threat to the reproductive system of poultry and wild birds, which are the definitive hosts of the parasite causing this disease. However, the parasite infection of the second intermediate host (dragonfly), the primary vector of this pathogen, is rarely reported. In this study, the prevalence of Prosthogonimus infection in dragonflies was investigated from June 2019 to October 2022 in Heilongjiang Province, northeast China. The species of metacercariae isolated from dragonfly were identified by morphological characteristics, molecular biology techniques, and animal infection experiments. The results showed that 11 species of dragonflies and one damselfly were identified and among six of the dragonflies infected by Prosthogonimus metacercariae, Sympetrum depressiusculum (28.53%) had the highest infection rate among all positive dragonflies, followed by Sympetrum vulgatum (27.86%) and Sympetrum frequens (20.99%), which are preferred hosts, and the total prevalence was 20.39% (2061/10,110) in Heilongjiang Province. Three species of Prosthogoniumus metacercariae were isolated, including Prosthogonimus cuneatus, Prosthogonimus pullucidus, and Prosthogonimus sp., among which P. cuneatus was the dominant species in dragonflies in Heilongjiang Province. This is the first report on the prevalence of Prosthogonimus in dragonflies in China, which provides baseline data for the control of prosthogonimiasis in Heilongjiang Province and a reference for the prevention of prosthogonimiasis in other areas of China.

[Preliminary application of recombinase -aided amplification in detection of Clonorchis sinensis metacercariae in freshwater fish]

OBJECTIVE

To evaluate the performance of recombinase-aided amplification (RAA) assay in detection of Clonorchis sinensis metacercariae in freshwater fish samples, so as to provide insights into standardization and field application of this assay.

METHODS

Wild freshwater fish samples were collected in the rivers of administrative villages where C. sinensis-infected residents lived in Jiangyan District, Xinghua County and Taixing County of Taizhou City, Jiangsu Province from June to September 2022. Genomic DNA was extracted from six freshwater fish specimens (5 g each) containing 0, 1, 2, 4, 8 and 16 C. sinensis metacercariae for fluorescent RAA assay, and the diagnostic sensitivity was evaluated. Fluorescent RAA assay was performed with genomic DNA from C. sinensis, Metorchis orientalis, Haplorchis pumilio and Centrocestus formosanus metacercariae as templates to evaluate its cross-reactions. In addition, the detection of fluorescent RAA assay and direct compression method for C. sinensis metacercariae was compared in field-collected freshwater fish samples.

RESULTS

Positive amplification was found in fresh-water fish specimens containing different numbers of C. sinensis metacercariae, and fluorescent RAA assay was effective to detect one C. sinensis metacercaria in 5 g freshwater fish specimens within 20 min. Fluorescent RAA assay tested negative for DNA from M. orientalis, H. pumilio and C. formosanus metacercariae. Fluorescent RAA assay and direct compression method showed 5.36% (93/1 735) and 2.88% (50/1 735) detection rates for C. sinensis metacercariae in 1 735 field-collected freshwater fish samples, with a statistically significant difference seen (χ2 = 478.150, P < 0.001). There was a significant difference in the detection of C. sinensis metacercariae in different species of freshwater fish by both the direct compression method (χ2 = 11.20, P < 0.05) and fluorescent RAA assay (χ2 = 20.26, P < 0.001), and the detection of C. sinensis metacercariae was higher in Pseudorasbora parva than in other fish species by both the direct compression method and fluorescent RAA assay (both P values < 0.05).

CONCLUSIONS

Fluorescent RAA assay has a high sensitivity for detection of C. sinensis metacercariae in freshwater fish samples, and has no cross-reactions with M. orientalis, H. pumilio or C. formosanus metacercariae. Fluorescent RAA assay shows a higher accuracy for detection of C. sinensis infections in field-collected freshwater fish than the direct compression method.

Genetic characterization and phylogenetic relationships of Phyllodistomum parasites in Indian subcontinent: insights from freshwater fish and shrimp hosts

Phyllodistomum is the large digenean group of fish parasites, with 25 species described so far in the Indian subcontinent. Here, we redescribed two adult species of Phyllodistomum (P. srivastava Rai 1964 and P. parorchium Jaiswal 1957) collected from freshwater fish Heteropneustes fossilis Bloch, 1974 and Glossogobius giuris Ham, 1822, respectively, and an unknown Phyllodistomum metacercaria from shrimp (Macrobrachium dayanum Henderson, 1893). These parasites were genetically characterized using 28S and first and second internal transcribed spacers (ITS1 and ITS2) regions of the nuclear ribosomal DNA and CoxI region of the mitochondrial (mt) DNA to establish the link between metacercaria and adult. Morphologically, both the unknown metacercaria in shrimp and adult Phyllodistomum srivastava in fish, resembled in terms of crenulated margin of hind body, arrangement of diagonal testes, bipartite seminal vesicle, and compact paired vitelline masses. The two adult parasite species, P. srivastava from P. parorchium, were different in terms of shape and size of the body, ratio of suckers, the absence of crenulated margin of hind body, a single chambered seminal vesicle, and deeply lobed paired vitelline masses, in the former species. Comparison of the 28S, ITS, and mtCoxI sequence data suggested P. srivastava and Phyllodistomum metacercaria belong to the same species, and supported the distinction between P. srivastava and P. parorchium. Exploring the potential impact of Phyllodistomum infection on host behaviour and health would be prospective areas for future research.

Infection of Atlantic tripletail Lobotes surinamensis (Teleostei: Lobotidae) by brain metacercariae Cardiocephaloides medioconiger (Digenea: Strigeidae)

Three juvenile Atlantic tripletail Lobotes surinamensis caught opportunistically in Charleston Harbor (South Carolina, USA) and maintained in captivity for over three months displayed an altered swimming behavior. While no direct causation can be demonstrated herein, fish were infected in their brain by strigeid trematode larvae (metacercariae) of Cardiocephaloides medioconiger, which were identified via ITS2 and 28S ribosomal RNA gene sequencing. Histology showed nonencysted metacercariae within the brain ventricle between the optic tectum and tegmentum, causing distortion of tegmental parenchyma. Aggregates of mononuclear inflammatory cells were in the ventricle adjacent to metacercariae. Metacercarial infection by Cardiocephaloides medioconiger has been reported from the brain and eyes of only two other fish species from the northern US Atlantic coast: the grey mullet Mugil cephalus and silverside Menidia menidia, but this identification is problematic and needs molecular verification. Atlantic tripletail is a new report as a second intermediate host for C. medioconiger and South Carolina is a new locality. Cardiocephaloides species in general have a low host specificity and infection by C. medioconiger could propagate to other fishes and affect neighboring natural ecosystems.

The Larval Stages of Echinostoma spp. in Freshwater Snails as the First and Second Intermediate Hosts in Gilan and Mazandaran Provinces, Northern Iran

Background

Identification of the larval stages of Echinostoma spp. in freshwater snails is an essential guide to continue monitoring the possibility of their transmission and the potential of echinostomiasis in areas where trematodes are the primary agent of parasitic diseases. The aim of this study was investigate Echinostoma using morphological and molecular techniques.

Methods

The study was conducted in Gilan and Mazandaran Provinces, northern Iran, from April 2019 to October 2021. Overall, 5300 freshwater snails were randomly collected and were identified using external shell morphology. Meanwhile, snails infected with trematodes were studied via shedding and dissecting methods. Larvae stages of Echinostoma were identified and the genomic DNA of the samples was extracted. The PCR amplification of the ITSI gene was carried out for 17 isolates and products were sequenced. Seven sequences were deposited in GenBank.

Results

Totally, 3.5% of snails containing three species (Stagnicola sp., Radix sp. and Planorbis sp.) were infected with two types of cercaria, E. revolutum with 37 and Echinostoma sp. with 45 spines in the collar. Moreover, 35% of the snails were infected with Echinostoma spp. metacercaria. Phylogenetic analysis illustrated that isolates were included in two ITSI haplogroups.

Conclusion

Results showed the potential hazard of a zoonotic parasite as Echinostoma in northern Iran. The potential of disease environmental relationship investigation and resource control optimization is necessary for effective disease prevention and health management.

Pearl formation associated with gymnophallid metacercariae in Mytilus galloprovincialis from the Northwestern Adriatic coast: Preliminary observations

Gymnophallids of the genus Parvatrema are small trematodes infecting waterbirds in their adult stage. Several species of clams and mussels have been found to act as first and second intermediate hosts, in which the trematode larval stages induce the formation of pearls. In this study, a wild population of Mytilus galloprovincialis was sampled along the Northwestern coast of the Adriatic Sea to evaluate the origin and extent of visible pearls. Parasitological investigations, including morphological and molecular analyses, and histopathology were carried out on a representative sample of mussels (n = 158) from June to September 2021. The overall prevalence of infection reached 75.3 %, and the intensity of infection ranged from a few trematodes to thousands per mussel, mostly occurring in the mantle and surrounded by variable numbers of conchiolin layers. Morphological studies allowed classification of the metacercariae as belonging to the genus Parvatrema, and the pairwise comparison of the obtained sequences, encompassing the internal transcribed spacer (ITS) region, revealed a genetic similarity (96.8 %) to Parvatrema duboisi. However, the phylogenetic analysis demonstrated the independent clustering of the obtained ITS sequences compared to other available Parvatrema species. For the relevant commercial impact that pearl formation may have on farmed mussels, ecological and epidemiological aspects of this infection would deserve further investigation in the area.

Parasites of Moroccan desert Coptodon guineensis (Pisces, Cichlidae): transition and resilience in a simplified hypersaline ecosystem

Sebkha Imlili (Atlantic Sahara) is a salt flat with over 160 permanent holes of hypersaline water generated in the Holocene and inhabited by euryhaline organisms that are considered to be relics of the past, including the cichlid fish Coptodon guineensis. We surveyed the fish parasites four times over one year, to i) identify the parasites, and ii) determine possible seasonality in infection patterns. Over 60% of the fish were infected by one to three helminths: an acanthocephalan in the intestine and two digenean metacercariae in the kidney, spleen, liver, muscle, and mesenteries. The acanthocephalan Acanthogyrus (Acanthosentis) cf. tilapiae was identified morphologically and molecularly; only one digenean (the heterophyid Pygidiopsis genata) could be identified molecularly. Both identified parasites were present throughout the sampling periods; the unidentified metacercariae were present only in summer and fall. Mean intensities, but not prevalence of infection by the acanthocephalan, reflected a biannual pattern of transmission. Infection accrued with fish size, possibly due to cannibalism. Because the water holes include only a few invertebrates, the intermediate hosts of these parasites can be inferred to be the gastropod Ecrobia ventrosa for the digeneans and either the copepod Cletocamtpus retrogressus or the ostracod Cyprideis torosa for the acanthocephalan. This ecosystem appears stable and provides a window into the past, as the acanthocephalan likely switched from freshwater tilapia to C. guineensis when the Sebkha formed. However, this is a vulnerable environment where the survival of these parasites depends on interactions maintained among only very few hosts.

(2014)

Metacercariae of Diplostomum petromyzifluviatilis (Digenea, Diplostomidae) from the brain of European river lamprey Lampetra fluviatilis from the Baltic Sea basin and Arctic lamprey Lethenteron camtschaticum from the White Sea basin were studied with the use of genetic and morphological methods. Phylogenetic analysis based on cox1 marker showed that the parasites of both lamprey species were conspecific with Diplostomum sp. Lineage 4 of Blasco-Costa et al. (2014). The name Diplostomum petromyzifluviatilis Müller (Diesing, 1850) has historical precedence as a species described from the brain of lampreys and should be used in genus nomenclature. There were no morphological qualitative differences between the metacercariae from the two lamprey species but those from L. fluviatilis were larger than those from L. camtschaticum. We expanded the data on the second intermediate hosts and the localization of D. petromyzifluviatilis, showing that its metacercariae occur not only in the brain of lampreys but also in the brain and the retina of three-spined stickleback Gasterosteus aculeatus and the vitreous humour of the perch Perca fluviatilis across the European part of the Palearctic.

Studies on trematode metacercariae infecting libellulid larvae from the Western Ghats, Wayanad region

Understanding the host specificity of trematode larvae is vital in predicting the mode of trophic level transfer of trematode parasites and their evolution. In this study, six species of trematode metacercariae, Eumegacetes sp., Orthetrotrema monostomum, Ganeo tigrinus, Mehraorchis sp., Pleurogenoides sp. and Phyllodistomum sp. infecting the larvae of the odonate family Libellulidae from the water bodies in the Wayanad region of the Western Ghats are recorded. The prevalence of infection of these metacercariae was 5.8%, 2.0%, 10.4%, 9.1%, 2.6% & 1.3%, respectively. Further, the mean intensity of infection was estimated to be 4.44, 1.67, 5.38, 6.21, 6.0 & 17.5 and the mean abundance 0.26, 0.03, 0.56, 0.56, 0.16 & 0.23 respectively.

Infection rate of Opisthorchis viverrini metacercariae in cyprinoid fish from the markets and its association to human opisthorchiasis in the local community in the Northeast Thailand

The prevalence of Opisthorchis viverrini, a fish-borne zoonotic trematode that can provoke cholangiocarcinoma, is high in the Northeast Thailand. The aim of this study was to determine the prevalence of O. viverrini metacercariae in the cyprinid fish and determine its association of O. viverrini infection among the consumers who regularly buy fish in the markets. A cross-sectional study was conducted in nine provinces covering 20 districts of Thailand, and we examined 778 cyprinoid fish specimens belonging to five species purchased from local markets. Pepsin-HCl digestion method was used to recover O. viverrini metacercariae from fish. In all districts surveyed, O. viverrini metacercariae-positive fish were found with the infection rates ranging from 3.9 to 21.1%. All five fish species studied were positive for O. viverrini metacercariae: Henicorhynchus siamensis (13.7%), Cyclocheilichtys spp. (12.7%), Hampala spp. (8.1%), Systomus spp. (6.9%) and Barbonymus goniatus (5.0%). An average prevalence of O. viverrini infection was 7.1% in the fish consumers surveyed in the markets. The source of fish was determined and our results showed that parasitized fish are sold in markets up to 100 km away from the point of capture, which contributes to the dispersion and maintenance of this helminthiasis. Our results point to the transmission of liver flukes via markets, in spite of many active programs of health education, elimination, prevention and control aimed to reduce O. viverrini infection and subsequent cholangiocarcinoma in the endemic areas of Thailand.

The effect of ambient temperature on biological properties and energy metabolism of Fasciola hepatica metacercariae

Parasitic helminths mainly use carbohydrates for energy synthesis, of which glycogen is the main reserve polysaccharide. When its content decreases to the minimum value, helminths lose their invasive capability. The material for the research was F. hepatica metacercariae. The complete biological cycle of F. hepatica development, from incubation of adult helminth eggs to production of sexually mature trematodes in definitive hosts was reproduced in laboratory conditions using common methods of parasitic helminth cultivation. F. hepatica metacercariae were kept in petri dishes with distilled water on the leaves of Elytrigia repens under different temperature conditions. In experimental conditions, we observed a high stability of F. hepatica metacercariae. Their long-term storage at a constant temperature of 6 ± 2 ° C causes a gradual decrease in the biological properties of F. hepatica metacercariae: viability, invasive capability and glycogen concentration. The glycogen concentration from 0.115 to 0.061 μg in a metacercaria ensures the preservation of basic biological properties of the helminth. An increase in ambient temperature (38 ± 2 ° C) or freezing temperatures (-2 ± 2 ° C) cause a sharp decrease in the viability, the invasive capability and glycogen content. The invasive material becomes sterile after 72 h under high (38 ± 2 ° C) temperature conditions, and 96 days under freezing (-2 ± 2 ° C) conditions.

metacercariae from brain of minnows (Phoxinus phoxinus L.) in four populations of northern Europe and East Asia

Metacercariae of trematodes from the genus Diplostomum are major helminth pathogens of freshwater fish, infecting the eye or the brain. The taxonomy of the genus Diplostomum is complicated, and has recently been based mainly on the molecular markers. In this study, we report the results of the morphological and molecular genetic analysis of diplostomid metacercaria from the brain of the minnow Phoxinus phoxinus from three populations in Fennoscandia (Northern Europe) and one population in Mongolia (East Asia). We obtained the data on the polymorphism of the partial mitochondrial cox1 gene and ribosomal ITS1-5.8S-ITS2 region of these parasites. РСА-based morphological analysis revealed that the parasites in the Asian and the European groups of Diplostomum sp. were distinctly different. Metacercariae from the brain of Mongolian minnows were much larger than those from the brain of Fennoscandian minnows but had much fewer excretory granules. Considering that the two study regions were separated by a distance of about 4500 km, we also tested the genetic homogeneity of their host, the minnow, using the mitochondrial cytb gene. It was shown that Diplostomum-infected minnows from Mongolia and Fennoscandia represented two previously unknown separate phylogenetic lineages of the genus Phoxinus. Both molecular and morphological analysis demonstrated that the parasites from Fennoscandia belonged the species Diplostomum phoxini, while the parasites from Mongolia belonged to a separate species, Diplostomum sp. MТ.Each of the two studied Diplostomum spp. was associated with a specific, and previously unknown, genealogical lineage of its second intermediate host, P. phoxinus.

eamiqtrema Blend and Racz, 2020 (Microphalloidea: Zoogonidae), with notes on the phylogenetic position of the genus Steganoderma Stafford, 1904, and resurrection of the subfamily Lecithostaphylinae Odhner, 1911

Metacercariae of the zoogonid trematode Steganoderma cf. eamiqtrema ex crab Chionoecetes bairdi caught in the Sea of Okhotsk were described using morphological and molecular-genetic (ITS2 region, 28S rRNA and nd1 genes) data. These are the first molecular-genetic data for the genus Steganoderma. The studied trematodes differed from S. eamiqtrema in having a much larger body size. The phylogenetic analysis based on the 28S rRNA gene supported neither the current taxonomic hypothesis that Steganoderma belongs to the subfamily Lepidophyllinae nor the earlier views that the Steganodermatinae and the Lecithostaphylinae are synonymous. The topology of the phylogenetic tree shows that the Steganodermatinae and the Lecithostaphylinae are independent subfamilies. However, morphological differences between them are obscure. Until morphological evidence for the Steganodermatinae is found, we propose to distinguish the subfamily Lepidophyllinae sensu stricto with the genera Lepidophyllus and Urinatrema, and the subfamily Lecithostaphylinae sensu lato uniting all the other former lepidophyllines. Thus, for now, we propose to consider the Steganodermatinae as a conditional synonym for Lecithostaphylinae sensu lato.

The New Data on the Serotonin and FMRFamide Localization in the Nervous System of Opisthorchis felineus Metacercaria

BACKGROUND

Trematoda Opisthorchis felineus Rivolta, 1884 is the causative agent of dangerous parasite disease-opisthorchiasis, widespread in the Russian Federation. The details of the neuroanatomical localization of the serotoninergic and FMRFamidergic neurotransmitter elements as well as their functional roles remain not studied enough in both adult and larval forms of O. felineus. The studies in this area are important in term of the development of a new pharmacological strategy of the struggle with the causative agent of opisthorchiasis affecting the neuronal signal substances and the function of its nervous system.

PURPOSE

The aim of this work was the immunocytochemical study of the neurotransmitters serotonin (5-HT, 5-Hydroxitryptamine) and neuropeptide FMRFamide localization in the nervous system of the opisthorchiasis causative agent-O. felineus metacercaria. To study the relationship between the detected neurotransmitters and the muscular elements of the parasite, the muscle staining was carried out simultaneously using fluorophore-conjugated phalloidin.

METHODS

The localization of 5-HTergic and FMRFamidergic nerve structures was determined by immunocytochemical method. The staining samples were analyzed using a fluorescent and confocal laser scanning microscopies.

RESULTS

The new data on the presence and distribution of the serotonin-immunopositive (IP)- and FMRFa-IP components in the central and peripheral departments of the nervous system of  O. felineus metacercaria has been obtained. Besides that a number of the new anatomical details of the nervous system organization and of the innervation of the organs and tissues in the investigated parasite have been revealed.

CONCLUSION

The data obtained on the presence and localization of the 5-HTergic and peptidergic (FMRFamide) components in central and peripheral departments of the nervous system of O. felineus metacercaria elaborated and expanded the existing information about the nervous system as well as the innervations of the tissues and organs in the causative agent of opistchorchiasis.

Fasciola hepatica: the dispersal of cercariae shed by the snail Galba truncatula

Field investigations in 14 wild watercress beds located in the French region of Limousin, a known endemic area for distomatosis, were performed for three years to determine the distance that cercariae of Fasciola hepatica can reach in water before their encystment on the host plant. Each bed was located on the course of an open drainage furrow, while snails (Galba truncatula) lived upstream around the emergence of a source. Five plant species were collected in early April and examined to find metacercariae. Most cysts were noted on Nasturtium officinale (188 on 48.7 kg of dripped plants), followed by Helosciadium nodiflorum (125 on 33.4 kg). On the other plant species, there were few larvae. Most cercariae encysted on the plants growing in the most upstream part of each bed, usually on the first 50 cm in length. When water in the beds was fast running, the distribution of metacercariae was more limited and their number was fewer than those in the beds fed by a slow flow of water. Cercariae were able to swim or were carried away by the current up to a mean of 5 m in slow-flow waters before encysting; this distance was only 4 m in faster waters. Plants growing on the most upstream section of a watercress bed located in a drainage furrow are the most used by cercariae for their encystment, when snails live around the emergence of a source. The speed of the water current affected the number and distribution of metacercariae in the bed.

Low-Grade Endemicity of Opisthorchiasis, Yangon, Myanmar

We performed an epidemiologic survey of opisthorchiasis in Yangon, Myanmar. The fecal egg-positive rate of residents was 0.7%, and we recovered an adult fluke after chemotherapy and purging of an egg-positive resident. We detected Opisthorchis viverrini metacercariae in freshwater fish. We found the Yangon area to have low-grade endemicity of opisthorchiasis.

Is species identification of Echinostoma revolutum using mitochondrial DNA barcoding feasible with high-resolution melting analysis?

The taxonomic evaluation of Echinostoma species is controversial. Echinostoma species are recognized as complex, leading to problems associated with accurate identification of these species. The aim of this study was to test the feasibility of using DNA barcoding of cytochrome c oxidase subunit I (COI) and NADH dehydrogenase subunit 1 (ND1) conjugated with high-resolution melting (HRM) analysis to identify Echinostoma revolutum. HRM using COI and ND1 was unable to differentiate between species in the "revolutum complex" but did distinguish between two isolates of 37-collar-spined echinostome species, including E. revolutum (Asian lineage) and Echinostoma sp. A from different genera, e.g., Hypoderaeum conoideum, Haplorchoides mehrai, Fasciola gigantica, and Thapariella anastomusa, based on the T_m values derived from HRM analysis. Through phylogenetic analysis, a new clade of the cryptic species known as Echinostoma sp. A was identified. In addition, we found that the E. revolutum clade of ND1 phylogeny obtained from the Thailand strain was from a different lineage than the Eurasian lineage. These findings reveal the complexity of the clade, which is composed of 37-collar-spined echinostome species found in Southeast Asia. Taken together, the systematic aspects of the complex revolutum group are in need of extensive investigation by integrating morphological, biological, and molecular features in order to clarify them, particularly in Southeast Asia.

Chronological analysis of the damages caused by the metacercariae of Centrocestus formosanus in the gills of Cyprinus carpio and lesions caused by the adult flukes in Ardeola ralloides: An experimental study

Centrocestus formosanus is a digenean that requires three host species to complete its life cycle. This study was conducted to observe the damage caused by two life stages of the C. formosanus on its host species. The snail Melanoides tuberculata was induced to shed cercariae by exposing to sunlight and specimens of koi carps were experimentally infected with cercariae. Gills of two infected fish were killed and fixed in Bouin's solution daily for 21 days. Infected fish were continuously fed to a pond heron (Ardeola ralloides) for three weeks and therafter the bird was killed. Small intestine was resected as duodenum, jejunum, and ileum and fixed in formol saline. Gills and small intestine were prepared to study the histopathological damages. Flared opercula with protruding gills and increased respiratory rate were identified as the primary clinical signs of the fish. Encysted metacercariae were observed in the basal, middle and in the apical portion of the gills' filaments and gradual distortions and extensive proliferation of the cartilage of the gills resulted in loss of the respiratory epithelium. A progression of fibroblast to chondroblast encapsulation of the parasite was observed in the gill of fish as a host response. The duodenum of the heron was severely infected with adult parasites than jejunum and ileum. Flukes were observed in the villi, mucosae, submucosae, and also in the tunica muscularis of the duodenum. In conclusion, this study revealed that the heavy infection of C. formosanus could cause severe pathological lesions in both koi carps and pond heron.

Validity of the Diplostomoidea and Diplostomida (Digenea, Platyhelminthes) upheld in phylogenomic analysis

Higher systematics within the Digenea, Carus 1863 have been relatively stable since a phylogenetic analysis of partial nuclear ribosomal markers (rDNA) led to the erection of the Diplostomida Olson, Cribb, Tkach, Bray, and Littlewood, 2003. However, recent mitochondrial (mt) genome phylogenies suggest this order might be paraphyletic. These analyses show members of two diplostomidan superfamilies are more closely related to the Plagiorchiida La Rue, 1957 than to other members of the Diplostomida. A recent phylogeny based on partial cytochrome c oxidase I also indicates one of the groups implicated, the Diplostomoidea Poirier, 1886, is non-monophyletic. To determine if these results were robust to additional taxon sampling, we analyzed mt genomes from seven diplostomoids in three families. To choose between phylogenetic alternatives based on mt genomes and the prior rDNA-based topology, we analyzed hundreds of ultra-conserved genomic elements assembled from shotgun sequencing. The Diplostomida was paraphyletic in the mt genome phylogeny but supported in the ultra-conserved genomic element phylogeny. We speculate this mitonuclear discordance is related to ancient, rapid radiation in the Digenea. Both ultra-conserved genomic elements and mt genomes support the monophyly of the Diplostomoidea and show congruent relationships within it. The Cyathocotylidae Mühling, 1898 are early diverging descendants of a paraphyletic clade of Diplostomidae Poirier, 1886, in which are nested members of the Strigeidae Railliet, 1919; the results support prior suggestions that the Crassiphialinae Sudarikov, 1960 will rise to the family level. Morphological traits of diplostomoid metacercariae appear to be more useful for differentiating clades than those of adults. We describe a new species of Cotylurus Szidat, 1928, resurrect a species of Hysteromorpha Lutz, 1931, and find support for a species of Alaria Schrank, 1788 of contested validity. Complete rDNA operons from seven diplostomoid species are provided as a resource for future studies.

[Survey of epidemic status of paragonimiasis in western mountainous areas in Hubei Province]

OBJECTIVE

To understand the current status of paragonimiasis epidemic in western mountain areas in Hubei Province.

METHODS

Four counties (cities) of Western Hubei Province (Xingshan, Enshi, Yunxi, Baokang) were selected as the investigation sites for active surveillance. Crabs were captured and the metacercariae of Paragonimus were detected. Meanwhile, the blood samples were collected from the residents in the surveillance sites and the unique IgG and IgM antibodies against Paragonimus in the sera were detected by ELISA. In addition, a questionnaire survey about knowledge and behavior of prevention and control of paragonimiasis was taken among the residents.

RESULTS

A total of 1 143 residents were investigated in the active surveillance, the total positive rate of the serology test was 1.84% (21/1 143), while the rates of the male and the female were 1.78% (10/562) and 1.89% (11/581), respectively, with no statistical significance between them ( χ² = 0.002, P > 0.05). The average weight of 161 fresh-water crabs captured was 11.72 g, with the positive rate of 9.32% (15/161) and the infective density of 7.07 metacercariae per positive crab. The positive rates of the male and female crabs were 11.54% (9/78) and 7.23% (6/83), respectively ( χ² = 0.884, P > 0.05), and the infective densities were 6.67 and 7.67 metacercariae per positive crab, respectively. Totally 1 143 residents were investigated by questionnaires, and 0.44% of them had the behavior of eating raw or half-done fresh-water crab, and 0.87% of them had the behavior of drinking un-boiled stream water.

CONCLUSIONS

The transmission chain of paragonimiasis still exists in the nature environment of mountain area in Western Hubei Province. The positive rate of the second intermediate host rebounds in some investigation sites. Therefore, the measures of continuous surveillance and health education should be taken to avoid the appearance of the prevalence or outbreak.

First report of Euryhelmis parasites (Trematoda, Heterophyidae) in Africa: conservation implications for endemic amphibians

In this study, we report, through molecular identification, the first African records of a digenean trematode parasite of the genus Euryhelmis. We recovered metacercariae encysted in an anuran, the endemic Moroccan painted frog (Discoglossus scovazzi), and a vulnerable caudate, the North African fire salamander (Salamandra algira), from four localities in North Africa (Morocco). Our records go back to the past century and have been confirmed in successive fieldwork seasons thereafter. Metacercarial stages of these parasites require amphibians as the last intermediate host, but the exact identity of the primary hosts and predators of the infected animals in Africa remain unknown. Our searches with basic local alignment search tool (BLAST) from Genbank revealed that hosts were infected by parasites of Euryhelmis costaricensis, which showed almost the same genetic identity (with only one substitution) to previous reports from Costa Rica and Japan, suggesting a recent introduction in Morocco. We proceed to discuss the likely role of introduced mustelids as the potential definitive hosts of trematode adults. Under this assumption, we conclude that the infestation of Discoglossus scovazzi and Salamandra algira might pose a risk to these threatened species.

New insights on the role of the holoplanktonic mollusk Firoloida desmarestia (Gastropoda: Pterotracheidae) as host for digenetic trematodes

Interactions of holoplanktonic mollusks with symbionts and parasites are poorly known. We investigated the ecology of infection (prevalence, intensity, and abundance) in Firoloida desmarestia, caught during two sampling campaign sessions in 2012, off the Baja California Peninsula, Mexico (IMECOCAL, 83 stations) and a coastal research center near La Sorpresa Beach, Baja California Sur, in the Gulf of California (14 stations). Only females of F. desmarestia were parasitized. Hemiuroidea parthenita rediae infected 1% of F. desmarestia population at IMECOCAL, whereas young unencysted metacercariae stages of Opechona pyriformis (Lepocreadiidae) parasitized 6.6% of the same host species at La Sorpresa. Overall, finding of rediae and metacercariae represent new geographical and host records and shows that F. desmarestia has a dual host function in the life cycle of trematodes. As first intermediate host, F. desmarestia harbors hemiuroid rediae, functioning as the source of infection to other zooplanktonic groups by dispersing successive cercariae. As second intermediate hosts, it harbors infective unencysted metacercariae stages of O. pyriformis, which parasitize nektonic predators (fish), most likely through trophic interaction. Our results suggest that some trematodes are able to spend their entire life cycle infecting only pelagic hosts. Parasite-F. desmarestia interaction is shown in a conceptual model, where we propose that transmission of trematodes may occur between individuals of F. desmarestia within the same swarm. Relevance of F. desmarestia as a potential host in which life cycle abbreviation of trematodes may take place is discussed. This is the first quantitative study of helminth interaction on F. desmarestia in the Eastern Pacific.

Bovine fascioliasis in Brazil: Economic impact and forecasting

Fasciola hepatica causes liver damage and poor growth in cattle and other animals, including humans. Although the disease occurs throughout the country, it is hyperendemic in cattle in the South of Brazil. This work aimed to determine the economical loss by carcass weight variance using data from all the states where F. hepatica is found, as well as to run a disease forecast analysis for the Rio Grande do Sul State. We found a direct loss of approximately US$ 210 million/year from infected cattle in Brazil and the ARIMA model analysis revealed that an increase of fascioliasis is most probable if no parasite control program is adopted.

High prevalence of zoonotic trematodes in roach (Rutilus rutilus) in the Gulf of Finland

The intention to increase roach (Rutilus rutilus) consumption is in focus for ecological and economic reasons in Finland. However, its safety as food has not been considered comprehensively. We collected and artificially digested 85 roach halves originating from the south-eastern coast of Finland, and found trematode metacercariae in 98.8% of the samples. Based on polymerase chain reaction (PCR) and sequencing of amplicons generated from the ITS2 gene region, zoonotic parasites of the family Opistorchiidae were identified as Pseudamphistomum truncatum and Metorchis bilis, and also non-zoonotic Holostephanus dubinini (family Cyathocotylidae) and Posthodiplostomum spp. (family Diplostomidae) were identified. The species identity of other trematodes found is currently being investigated. Mixed infections of several trematode species were common. The prevalence of morphologically identified zoonotic P. truncatum was 46%, and zoonotic M. bilis was found in one sequence sample. The high prevalence of zoonotic trematode metacercariae in roach from the Gulf of Finland is alarming. Only thoroughly cooked roach products can be recommended for human or animal consumption from the area.

Life History, Systematics and Evolution of the Diplostomoidea Poirier, 1886: Progress, Promises and Challenges Emerging From Molecular Studies

Members of the Diplostomoidea mature in amniotes and employ vertebrates, annelids and molluscs as second intermediate hosts. Diplostomoid life cycles generally follow a three-host pattern typical of digeneans, but novelties have arisen in some species, including obligate four-host life cycles, vertical transmission, and intracellular parasitism. In this review, we summarize the basic biology of diplostomoids with reference to molecular studies, and present challenges, gaps and areas where molecular data could address long-standing questions. Our analysis of published studies revealed that most molecular surveys find more diplostomoid species than expected, but this tendency is influenced by how much effort goes into examining specimens morphologically and the number of sequenced worms. To date, molecular work has concentrated disproportionately on intraspecific or species-level diversity of larval stages in the Diplostomidae in temperate northern regions. Although the higher taxonomy of the superfamily is recognized to be in need of revision, little molecular work has been conducted at this level. Our phylogenetic analysis indicates several families and subfamilies require reconsideration, and that larval morphotypes are more reflective of evolutionary relationships than definitive hosts. The host associations of adult diplostomoids result from host-switching processes, whereas molecular surveys indicate that larval diplostomoid metacercariae have narrow ranges of second intermediate hosts, consistent with coevolution. Molecular data are often used to link diplostomoid developmental stages, and we provide data from adult Neodiplostomum and Mesoophorodiplostomum that correct earlier misidentifications of their larval stages and propose alternatives to collecting definitive hosts.

Collection methods of trematode eggs using experimental animal models

Although observing the eggs of human parasitic helminth is essential for medical education in parasitology, opportunities for collection of the eggs are limited. Collection of the eggs using experimental animal models is needed for a sustainable supply. The metacercariae of three trematode species, Paragonimus westermani, Clonorchis sinensis and Metagonimus yokogawai, were collected from the second intermediate hosts: freshwater crabs and fishes, which were obtained using online shopping in Japan, and inoculated to experimental animal rat and dog. Consequently, eggs of the three trematode species were obtained abundantly from the feces of the animals. The eggs are being used for student training in several Japanese universities. In this article, we introduce the collection procedures for trematode eggs.

First report of Urosporidium sp., a haplosporidian hyperparasite infecting digenean trematode Parvatrema duboisi in Manila clam, Ruditapes philippinarum on the west coast of Korea

In this study, we first report on the occurrence of Urosporidium sp., a haplosporidian hyperparasite infecting the trematode, Parvatrema duboisi, which parasitizes Manila clams, Ruditapes philippinarum on the west and south coasts of Korea. The larval P. duboisi infected by the sporocyst stage of Urosporidium sp. demonstrated numerous small yellowish spores in their tissues. The heavily infected metacercariae exhibited degenerate bodies and the larvae were often motionless. Clams heavily infected by the metacercariae of P. duboisi also displayed abnormal golden spots on the mantle tissue. In histology, different life stages of Urosporidium sp. could be identified, including the uni-nucleate, plasmodial, sporogonic stages and the acid fast mature spores released from the cyst. In scanning electron microscopy (SEM), the mature spore exhibited a semi-circular rim around the apical end and the orifice was covered internally with a flap. Loop-like filaments ornamentation was also identified from Urosporidium sp. in SEM, suggesting that Urosporidium sp. found in this study is a new member in the genus. Prevalence of Urosporidium sp.-infected trematodes in this study ranged from 2.5% to 24.0% in April 2010 and the infection was observed from 8 sampling sites out of the 26 sites surveyed on the west and south coasts.

Utilizing ribosomal DNA gene marker regions to characterize the metacercariae (Trematoda: Digenea) parasitizing piscine intermediate hosts in Manipur, Northeast India

Freshwater fishes in Manipur, Northeast India frequently harbour several types of metacercariae, which based on morphological criteria were identified as Clinostomoides brieni, Euclinostomum heterostomum (Clinostomidae) and Polylekithum sp. (Allocreadiidae). Molecular techniques utilizing PCR amplification of rDNA regions of larger subunit (LSU or 28S), smaller subunit (SSU or 18S) and inter transcribed spacers (ITS1, 2) were used for molecular characterization of these types. Sequences generated from the metacercariae were compared with their related sequences available in public databases; an analysis of the identity matrices and phylogenetic trees constructed was also carried out, which confirmed their identification. Similarly, the sequences generated from Polylekithum sp. were found to be highly similar to the species of the same genus. The rDNA ITS2 secondary structure provided additional confirmation of the robustness of the molecular marker as a tool for taxon-specific characterization.

Prevalence of Haplorchis taichui among humans and fish in Luang Prabang Province, Lao PDR

This study confirmed the prevalence of the intestinal fluke Haplorchis taichui (Trematoda: Heterophyidae) among people and fish in Luang Prabang Province, Lao PDR. Fecal specimens were collected from 559 riparian people (229 males and 330 females), residing in 4 Districts (Luang Prabang, Xieng Ngeun, Pak Ou, and Nam Bak) and were examined by the Kato-Katz fecal smear technique. The overall helminth egg positive rate was 64.9%. The positive rate for small trematode eggs (STE), which may include H. taichui and other heterophyids, Opisthorchis viverrini, and lecithodendriids, was 15.2%. For recovery of adult helminths, 10 STE-positive people were treated with 40mg/kg praziquantel and 15mg/kg pyrantel pamoate, and then purged. Mixed infections with 3 Haplorchis species (H. taichui, H. pumilio, and H. yokogawai), a species of cestode (Taenia saginata), and several species of nematodes including Enterobius vermicularis and hookworms were found. The worm load for trematodes was exclusively high for H. taichui with an average of 7691 specimens per infected person, followed by H. yokogawai (8.3 specimens) and H. pumilio (4.1 specimens). Out of 207 freshwater fish (17 species) purchased in a market in Luang Prabang District, 138 (67%) harboured H. taichui metacercariae (metacercarial burden per fish; 520). Lower prevalence of fish and lower metacercarial density were observed for H. yokogawai (52% and 50 per fish, respectively) and H. pumilio (18% and 3 per fish, respectively). STE found in the surveyed population of Luang Prabang Province were verified to be those of intestinal fukes, particularly H. taichui.

Prevalence of Clonorchis sinensis infection in freshwater fishes in northeastern China

The prevalence of Clonorchis sinensis infection in freshwater fishes was surveyed in Heilongjiang Province, northeastern China, between August 2011 and September 2013. Thirteen species of freshwater fish (n=3221) and one species of shrimp (n=93) were collected from Songhua river, Nenjiang river and other lakes or ponds in 37 sites of 15 representative cities in Heilongjiang Province. They were individually examined by digestion technique, and the C. sinensis metacercariae were identified morphologically followed by confirmation using sequences of the second internal transcribed spacer of ribosomal DNA. Ten of the 13 examined species of freshwater fishes were infected with C. sinensis metacercariae, while all shrimps were negative. The overall prevalence of C. sinensis infection in 3221 examined freshwater fishes was 19.96%, with 42.57% (272/639) in Pseudorasbora parva, 22.55% (83/368) in Hemicculter leuciclus, 20.44% (121/592) in Carassius auratus, 17.71% (68/384) in Saurogobio dabryi, 10.85% (23/212) in Rhodeus ocellatus, 10.54% (48/455) in Phoxinus lagowskii, 8.20% (21/256) in Perccottus glehnii, 6.25% (5/80) in Misgurnus anguillicaudatus, 4.55% (1/22) in Xenocypris davidi, and 1.49% (1/67) in Cyprinus carpio. The average infection intensity in P. parva was 103.3 encysted metacercariae per gram of fish meat in Zhaoyuan city. The average prevalence of C. sinensis infection in Songhua river, Nenjiang river and lakes or ponds were 31.96% (503/1574), 11.30% (102/903) and 7.93% (59/744), respectively. The prevalence of C. sinensis infection in Zhaoyuan city (43.68%) was the highest among all sampling locations. These results revealed a high-prevalence of C. sinensis infection in freshwater fishes in Heilongjiang Province, northeastern China, posing significant public health concern.

A survey of metacercarial infections in commonly edible fish and crab hosts prevailing in Manipur, Northeast India

Food-borne trematode infections, which are mainly transmitted through consumption of inadequately cooked or raw fish and crabs, affect a large section of population, particularly in Southeast Asian countries, thus eliciting a remarkable morbidity and causing serious damage to health. In India, centering in several mountainous regions of the Northeast, the natives have the habit of consuming such fish or crabs that still sustain viable infective larval stage (metacercaria) of trematode flukes in their muscle tissue. The present study was undertaken to ascertain the spectrum of metacercarial diversity in commonly edible freshwater fishes and crab species in the northeastern state of Manipur and to adjudge their zoonotic potential, if any. Commonly edible fishes belonging to 15 species from 12 localities and crabs belonging to 2 species from 11 localities across Manipur state were surveyed for the purpose. The study revealed that 3 species of fishes (Channa punctatus, C. straitus and Wallago attu) harboured 4 different types of metacercariae belonging to 4 trematode families-Euclinostomum heterostomum (Clinostomidae); Lophosicyadiplostomum sp. and Posthodiplostomum sp. (Diplostomidae); and Polylekithum sp. (Allocreadiidae) in addition to adult flukes of Isoparorchis hypselobagri (Isoparorchiidae). Among these, metacercariae of Posthodiplostomum showed the highest prevalence (2.33 %) though a low abundance, while for other species the prevalence ranged between 0.25 and 1.19 %. The crab species (Barythelphusa lugubris masoniana and Potamiscus manipuriensis) were found infected with 4 different types of metacercariae representing the genera Paragonimus (Troglotrematidae) and Microphallus (Microphallidae). The paragonimids showed a higher rate of occurrence (~4-25 %) compared to microphallids (~15 %). The crustaceans surveyed emerged as prospective intermediate hosts for lungflukes. Identifying the potent vectors for zoonotic parasites helps in control measures towards their transmission to higher mammals.

Abandoning the ship: spontaneous mass exodus of Clinostomum complanatum (Rudolphi, 1814) progenetic metecercariae from the dying intermediate host Trichogaster fasciatus (Bloch & Schneider, 1801)

The dramatic and spontaneous exodus of live Clinostomum complanatum progenetic metacercaria from the gill slits of the dying intermediate host, Trichogaster fasciatus is reported. Basic water parameter tests for dissolved oxygen, pH and temperature revealed slightly lower level of dissolved oxygen in tank water used for water change. To the best of our knowledge, it is the first report of a digenean metacercariae, en mass leaving their intermediate host, upon its death in search of an alternative host to support their survival and help in continuing their life cycle.

Occurrence of Clinostomum complanatum in Aphanius dispar (Actinoptrygii: Cyprinodontidae) collected from Mehran River, Hormuzgan Province, South of Iran

OBJECTIVE

To investigate the possibility of Aphanius dispar (A.dispar) acting as intermediate host for Clinostomum complanatum (C. complanatum), from Mehran River, Hormuzgan Province of Iran.

METHODS

During a biological study of A. dispar in Mehran River, Hormuzgan Province, South of Iran, a total of 97 fish specimens were collected in 24 January 2006.

RESULTS

4 specimens (4.12%) including 1 male and 3 female were found infected with C. complanatum metacercaria. These metacercaria were coiled in the epiderm on the body surface of infected fishes. The infection is known as yellow spot disease. The parasite abundance, intensity and prevalence were 0.05%, 1.25% and 4.12%, respectively. The infection was higher in females than males.

CONCLUSIONS

To the best of our knowledge, this is the first report on occurrence of C. complanatum metacercaria in A. dispar in Iran.