Differences in the compatibility of infection between the liver flukes Fascioloides magna and Fasciola hepatica in a Colombian population of the snail Galba sp

VECTOR COMPATIBILITY OF NEW MEXICO GALBA SPECIES WITH THE CANINE SCHISTOSOME HETEROBILHARZIA AMERICANA, INCLUDING THE FIRST REPORT OF GALBA SCHIRAZENSIS AS A COMPATIBLE HOST

The indigenous North American mammalian schistosome Heterobilharzia americana has recently attracted attention for causing outbreaks in dogs in states outside of its southeastern U.S. distribution. Although H. americana has yet to be reported in New Mexico, we examined 2 New Mexico isolates of Galba snails to determine their susceptibility to experimental infection with an isolate of H. americana from Utah. One of the Galba isolates from the Rio Grande bosque in the Albuquerque suburb of Corrales was identified as Galba humilis, and like specimens of the same taxon from Utah, proved susceptible to H. americana (27.6% of exposed surviving snails positive). The second Galba isolate sourced from the northern mountains of New Mexico, which surprisingly was revealed to be Galba schirazensis based on cytochrome c oxidase 1, 16S rRNA, and the internal transcribed spacer 2 markers, was also susceptible to H. americana (56.3% of exposed surviving field-derived snails and 46.4% first generation [F1] snails positive). This is the first report of the latter snail being a compatible snail host for H. americana. As G. schirazensis has a wide, albeit spotty, distribution and is considered an invasive species, it provides yet another opportunity for H. americana to expand its known range, potentially including the state of New Mexico as well.

Genetic characterization and regional distribution of lymnaeid snails in northern Patagonia, Argentina

Lymnaeid snails serve as intermediate hosts for Fasciola hepatica (Linnaeus, 1758), the etiological agent of fasciolosis, which is a widespread livestock disease in Argentina. Determining their geographic distribution and identifying the snail species involved in the transmission of fasciolosis can provide crucial information for designing strategic control programs. In this context, this work aimed at genetically characterizing the species of lymnaeid snails collected in different water bodies of northern Patagonia, Argentina. To this end, 689 snails were collected in 12 sites in the provinces of Neuquén, Río Negro and Chubut, in areas where fasciolosis is endemic. According to the morphological characteristics of their valves, they were identified as Galba spp. Twenty-three of these specimens were further identified using the nuclear sequences of the internal transcribed spacers ITS-1 and ITS-2 and 18S rRNA. The results confirmed the identity of all the analyzed snails as Galba viatrix and provided evidence that studying the variable region V2 of the 18S rRNA gene is not enough to differentiate closely related species, as observed in lymnaeid snails. Both the fact that G. viatrix was the only species identified in the endemic area surveyed and previous evidence of the high prevalence of F. hepatica infestation in grazing animals in the region suggest that this species is the main intermediate host of F. hepatica. The correct identification of lymnaeid snail species has great importance to determine risk zones and develop appropriate control measures to reduce transmission, according to the different ecological characteristics of each species.

On the arrival of fasciolosis in the Americas

Fasciola hepatica is a worldwide emerging and re-emerging parasite heavily affecting several regions in South America. Some lymnaeid snail species of American origin are among the major hosts of F. hepatica worldwide. Recent paleoparasitological findings detected its DNA in a 2300-year-old sample in Patagonia, countering the common hypothesis of the recent arrival of F. hepatica in the Americas during European colonization. Thus, the theory of an initial introduction in the 1500s can no longer be sustained. This article discusses how it was possible for F. hepatica to reach and spread in the Americas in relation to the availability and compatibility of hosts through natural and incidental introductions. Our study will serve to better understand the ongoing Neotropical scenario of fasciolosis.

DNA Multi-Marker Genotyping and CIAS Morphometric Phenotyping of Fasciola gigantica-Sized Flukes from Ecuador, with an Analysis of the Radix Absence in the New World and the Evolutionary Lymnaeid Snail Vector Filter

Simple Summary

Fasciolid flukes collected from sheep and cattle in Ecuador showed a high diversity in DNA sequences whose analyses indicated introductions from South America, European and North American countries. These results agree with the numerous livestock importations performed by Ecuador. Abnormally big-sized liver flukes were found in Ecuadorian sheep. The morphometric phenotypic CIAS study showed that its size maximum and mean very pronouncedly and significantly surpassed those of the Fasciola hepatica populations from South America and Spain and proved to be intermediate between standard F. hepatica and F. gigantica populations. Such a feature is only known in intermediate fasciolid forms in Old World areas where the two species and their specific lymnaeid snail vectors overlap. This argues about a past hybridization after F. gigantica importation from Pakistan and/or introduction of intermediate hybrids previously generated in USA. The lack of heterozygotic rDNA ITS positions differentiating the two species, and of introgressed fragments and heteroplasmic positions in mtDNA genes, indicate a post-hybridization period sufficiently long as for rDNA concerted evolution to complete homogenization and mtDNA to return to homoplasmy. The vector specificity filter due to Radix absence should act as a driving force in accelerating such lineage evolution. Public health implications are finally emphasized.

Abstract

Fascioliasis is a disease caused by Fasciola hepatica worldwide transmitted by lymnaeid snails mainly of the Galba/Fossaria group and F. gigantica restricted to parts of Africa and Asia and transmitted by Radix lymnaeids. Concern has recently risen regarding the high pathogenicity and human infection capacity of F. gigantica. Abnormally big-sized fasciolids were found infecting sheep in Ecuador, the only South American country where F. gigantica has been reported. Their phenotypic comparison with F. hepatica infecting sheep from Peru, Bolivia and Spain, and F. gigantica from Egypt and Vietnam demonstrated the Ecuadorian fasciolids to have size-linked parameters of F. gigantica. Genotyping of these big-sized fasciolids by rDNA ITS-2 and ITS-1 and mtDNA cox1 and nad1 and their comparison with other countries proved the big-sized fasciolids to belong to F. hepatica. Neither heterozygotic ITS position differentiated the two species, and no introgressed fragments and heteroplasmic positions in mtDNA were found. The haplotype diversity indicates introductions mainly from other South American countries, Europe and North America. Big-sized fasciolids from Ecuador and USA are considered to be consequences of F.gigantica introductions by past livestock importations. The vector specificity filter due to Radix absence should act as driving force in the evolution in such lineages.

Systematics and geographical distribution of Galba species, a group of cryptic and worldwide freshwater snails

Cryptic species can present a significant challenge to the application of systematic and biogeographic principles, especially if they are invasive or transmit parasites or pathogens. Detecting cryptic species requires a pluralistic approach in which molecular markers facilitate the detection of coherent taxonomic units that can then be analyzed using various traits (e.g., internal morphology) and crosses. In asexual or self-fertilizing species, the latter criteria are of limited use. We studied a group of cryptic freshwater snails (genus Galba) from the family Lymnaeidae that have invaded almost all continents, reproducing mainly by self-fertilization and transmitting liver flukes to humans and livestock. We aim to clarify the systematics, distribution, and phylogeny of these species with an integrative approach that includes morphology, molecular markers, wide-scale sampling across America, and data retrieved from GenBank (to include Old World samples). Our phylogenetic analysis suggests that the genus Galba originated ca. 22 Myr ago and today comprises six species or species complexes. Four of them show an elongated-shell cryptic phenotype and exhibit wide variation in their genetic diversity, geographic distribution, and invasiveness. The remaining two species have more geographically restricted distributions and exhibit a globose-shell cryptic phenotype, most likely phylogenetically derived from the elongated one. We emphasize that no Galba species should be identified without molecular markers. We also discuss several hypotheses that can explain the origin of cryptic species in Galba, such as convergence and morphological stasis.

Lymnaeidae from Santander and bordering departments of Colombia: Morphological characterization, molecular identification and natural infection with Fasciola hepatica

The Lymnaeidae constitute a family of freshwater gastropod molluscs whose diversity and ecology have been infrequently studied throughout Colombia. Some lymnaeid species act as intermediate hosts of trematode parasites, which are of great importance in both the veterinary and medical fields. Among trematode parasites, Fasciola hepatica is best known for being an important parasite of sheep and cattle for decades and causes significant economic losses in these livestock species. The main objective of this work is to identify the various species of lymnaeids that occupy different geographical regions of Santander and its bordering departments within Colombia. This will expand the knowledge of lymnaeid diversity in Colombia and provide further insight into their role in the transmission of F. hepatica. A total of 118 georeferenced sites between 126 m.a.s.l. and 3870 m.a.s.l. were sampled in Santander, Boyacá, Norte de Santander and Cundinamarca, respectively. Lymnaeid snails were identified according to the morphology of their shells and by several characteristics of their reproductive systems. Species identification was confirmed using DNA barcoding. Four lymnaeid species are reported in the study area: the native Galba cousini and three exotic species, Pseudosuccinea columella, G. truncatula and G. schirazensis. The four species were examined for natural infection with F. hepatica. Infected variants of the main snail host, G. cousini, were found in the Onzaga, Encino and Vetas municipalities of Santander, as well as in the Belén municipality of Boyacá. A second species, G. truncatula was also found naturally infected in Mutiscua municipality of Norte de Santander. The two other species, P. columella and G. schirazensis were found free of infection.

Prevalence of Fasciola hepatica infection in Galba cousini and Galba schirazensis from an Andean region of Ecuador

Some Lymnaeid snails are intermediate hosts of the liver fluke Fasciola hepatica, the causal agent of fasciolosis, a zoonotic parasitic disease. Human and livestock fasciolosis has been reported in a highland community located in the Chimborazo Province of the Ecuadorian Andes. However, no previous study has been carried out to identify which snail species act as intermediate host/s of F. hepatica. This study first aimed to identify the intermediate snail species and secondly to determine the prevalence of natural infection with F. hepatica in 230 lymnaeid snails sampled from irrigation and drainage canals in this area. The first objective entailed observations of shell morphology and internal organs as well as sequencing of the cytochrome oxidase subunit 1 (COI) gene. For the second objective, we used classic parasitological methods (observation of rediae and cercarial emission) and PCR amplification specie-specific to F. hepatica. COI haplotype networks were built to elucidate phylogeographic relationships between the snail populations from this highland community with other American and worldwide populations. We identified two lymnaeid Galba cousini and Galba schirazensis and found high infection rates of F. hepatica in G. cousini, but these differed according to the method used, with PCR showing a higher rate (61 ± 20%) compared to rediae observation (29 ± 17%). F. hepatica in G. schirazensis was identified only by DNA amplification. G. cousini populations were genetically structured by geographic distance whereas G. schirazensis populations showed very low genetic diversity. The higher abundance and infection rate of G. cousini compared to G. schirazensis suggests that the former is likely the specie responsible for F. hepatica transmission in this region.

Lymnaeid Snail Vectors of Fascioliasis, Including the First Finding of Lymnaea neotropica in Ecuador, Assessed by Ribosomal DNA Sequencing in the Southern Zone Close to the Peru Border

PURPOSE

Fascioliasis is a freshwater snail-borne zoonotic trematodiasis of high pathogenicity and wide veterinary repercussions. In South America, moreover, it causes serious public health problems, with high human infection rates in Andean countries. Ecuador offers a worrying risky scenario due to its physiography, including many human infection reports and animal endemicity throughout its Andean highlands.

METHODS

Endemic areas with increasing animal fascioliasis were surveyed for lymnaeid snails in the province of Loja, southern Ecuador, close to the border of Peru, the country known to present the widest human fascioliasis endemic zone. The altitude of the sampling sites ranged between 150 and 1770 m a.s.l., and their location was close to human villages. Biotopes surveyed were characterized according to fascioliasis transmission needs.

RESULTS

The species Lymnaea schirazensis and L. neotropica were identified by rDNA ITS-2 and ITS-1 sequencing. The non-transmitting L. schirazensis combined haplotype agreed with populations of this species previously reported from northern Ecuador. The finding of the efficient vector L. neotropica is reported for the first time in Ecuador and suggests a passive introduction from neighbouring Peru by uncontrolled livestock transport.

CONCLUSIONS

Rice irrigation system implementation, lymnaeid finding on Taraxacum (dandelion) plants which are consumed fresh in salads by people, and Saccharum (sugarcane), whose bark is peeled off with the teeth, represent potential infection sources for humans. The closeness to the Cajamarca human hyperendemic area in northern Peru, where the same two lymnaeids have been also found and triclabendazole resistance reported, is an additional risk to be considered regarding the livestock transborder exchange.

Population structure and genetic diversity in the invasive freshwater snail Galba schirazensis (Lymnaeidae)

We studied the population genetic structure of the freshwater snail Galba schirazensis (Küster, 1862), a potential vector of infectious diseases such as fascioliasis. Galba schirazensis has now a worldwide distribution but a poorly known origin because this species has been distinguished only recently from the morphologically similar and cosmopolitan Galba truncatula (O.F. Müller, 1774). We developed specific microsatellite markers and sequenced a mitochondrial gene (cytochrome oxidase subunit I (CO1)) to study individuals of G. schirazensis from the Old World and the New World. We found very low genetic diversity within populations, no heterozygotes, and marked population structure — a pattern observed in other highly selfing lymnaeid species with recently enlarged distributions as a result of biological invasions. The total lack of observed heterozygosity in the few populations of G. schirazensis that displayed some allelic diversity suggests high selfing rates. We also found that the center of diversity, and by extension the origin area of this species, should be found in the New World, whereas Old World populations should rather result from a recent introduction of a genetically uniform population. The microsatellite markers developed here will help to clarify the history of expansion of G. schirazensis and might help to understand its role as a potential vector of infectious diseases.

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

Background

Snail-borne parasitic diseases, such as angiostrongyliasis, clonorchiasis, fascioliasis, fasciolopsiasis, opisthorchiasis, paragonimiasis and schistosomiasis, pose risks to human health and cause major socioeconomic problems in many tropical and sub-tropical countries. In this review we summarize the core roles of snails in the life cycles of the parasites they host, their clinical manifestations and disease distributions, as well as snail control methods.

Main body

Snails have four roles in the life cycles of the parasites they host: as an intermediate host infected by the first-stage larvae, as the only intermediate host infected by miracidia, as the first intermediate host that ingests the parasite eggs are ingested, and as the first intermediate host penetrated by miracidia with or without the second intermediate host being an aquatic animal. Snail-borne parasitic diseases target many organs, such as the lungs, liver, biliary tract, intestines, brain and kidneys, leading to overactive immune responses, cancers, organ failure, infertility and even death. Developing countries in Africa, Asia and Latin America have the highest incidences of these diseases, while some endemic parasites have developed into worldwide epidemics through the global spread of snails. Physical, chemical and biological methods have been introduced to control the host snail populations to prevent disease.

Conclusions

In this review, we summarize the roles of snails in the life cycles of the parasites they host, the worldwide distribution of parasite-transmitting snails, the epidemiology and pathogenesis of snail-transmitted parasitic diseases, and the existing snail control measures, which will contribute to further understanding the snail-parasite relationship and new strategies for controlling snail-borne parasitic diseases.

Electronic supplementary material

The online version of this article (10.1186/s40249-018-0414-7) contains supplementary material, which is available to authorized users.

A new multiplex PCR assay to distinguish among three cryptic Galba species, intermediate hosts of Fasciola hepatica

A molecular tool described here allows in one step for specific discrimination among three cryptic freshwater snail species (genus Galba) involved in fasciolosis transmission, a worldwide infectious disease of humans and livestock. The multiplex PCR approach taken targets for each species a distinctive, known microsatellite locus which is amplified using specific primers designed to generate an amplicon of a distinctive size that can be readily separated from the amplicons of the other two species on an agarose gel. In this way, the three Galba species (G. cubensis, G. schirazensis, and G. truncatula) can be differentiated from one another, including even if DNA from all three were present in the same reaction. The accuracy of this new molecular tool was tested and validated by comparing multiplex PCR results with species identification based on sequences at mitochondrial and nuclear markers. This new method is accurate, inexpensive, simple, rapid, and can be adapted to handle large sample sizes. It will be helpful for monitoring invasion of Galba species and for developing strategies to limit the snail species involved in the emergence or re-emergence of fasciolosis.