Biological, biochemical and histological features of Bradybaena similaris (Gastropoda: Pulmonata) infected by Heterorabditis indica (Rhabditida: Heterorhabditidae) strain LPP1

Occurrence of Cruzia tentaculata Larvae in the Land Snail Megalobulimus abbreviatus-Influence of Natural Parasite Load on Snail Physiology

The nematode Cruzia tentaculata is reported here for the first time in the land snail Megalobulimus abbreviatus in southern Brazil. The snails were infected with a high prevalence of larvae up to the L3 stage (68.6%). Cysts were located mainly in the mantle (pulmonary cavity) and the nerve ring. No other helminths were identified in the collected snails. Some physiological aspects were compared between snails infected with L3 larvae and non-infected snails and among infected animals with different parasite loads. No differences were found in hemolymph protein, glucose, or urea content between L3-infected and non-infected snails, nor among animals with different parasite loads. Discontinuous lesions in the rectum associated with the presence of encapsulated larvae were visible in animals with high parasite loads and were more frequent in adult animals. All analyses were carried out during the breeding season; however, the albumen glands of mature snails had a smaller volume in those with higher parasite loads. Ovotestis weight was also significantly negatively correlated with parasite load. Snail reproductive capacity could, therefore, be partially impaired but only for individuals with higher parasite loads. Considering only the measured parameters, natural infection by C. tentaculata does not appear to affect intermediary metabolism of M. abbreviatus. A greater number of larvae and greater severity of tissue injuries are more frequently observed in older snails.

Alterations in the metabolism of Pseudosuccinea columella (Mollusca: Gastropoda) caused by Heterorhabditis bacteriophora HP88 (Rhabditida: Heterorhabditidae)

The gastropod Pseudosuccinea columella participates in the dissemination of Fasciola hepatica in the environment, acting as the main intermediate host of this parasite in Brazil. The present study sought to elucidate the possible pathogenic effects of the entomopathogenic nematode (EPN) Heterorhabditis bacteriophora on P. columella, by evaluating the influence of infection on alanine aminotransferase (ALT) and aspartate aminotransferase (AST), as well as the concentrations of total protein, uric acid, and urea in the snail's hemolymph. For this, the snails were exposed to EPNs for 24 and 48 h, and for each exposure time, 20 snails were dissected after 7, 14 and 21 days for hemolymph collection. The primary findings suggest a significant proteolysis alongside elevated levels of uric acid and urea in P. columella infected individuals. These findings reveal that H. bacteriophora HP88 infection induced serious changes in the snail's metabolism, triggering important deleterious effects.

Heterorhabditis bacteriophora (Rhabditida: Heterorhabditidae), isolate HP88, induces reproductive and physiological alterations in Biomphalaria glabrata (Gastropoda: Planorbidae): an alternative for biological control of schistosomiasis

Heterorhabditis bacteriophora is an entomopathogenic nematode (EPN) that is mutually associated with Photorhabdus luminescens, utilized globally for biological control of numerous organisms. Freshwater snails of the species Biomphalaria glabrata have been incriminated as the main intermediate hosts of Schistosoma mansoni in Brazil, but virtually nothing is known about the susceptibility of these gastropod to EPNs. Information in this respect is relevant for control of these intermediate hosts, and thus of the helminthiases they transmit. This paper for the first time reports the susceptibility of B. glabrata to infective juveniles of H. bacteriophora (isolate HP88) under laboratory conditions. For that purpose, six groups were formed: three Control groups (not exposed) and three Treated groups, in which the snails were exposed to 300 juveniles infecting the nematode over three weeks. The entire experiment was conducted in triplicate, using a total of 270 snails. Significant physiological alterations in B. glabrata were observed in response to the infection by H. bacteriophora HP88, characterized by decreased levels of hemolymphatic glucose as well as reduced contents of glycogen stored in the host's digestive gland. In parallel, the hemolymphatic activity of lactate dehydrogenase increased in the infected snails, indicating that the infection induces breakdown of carbohydrate homeostasis in B. glabrata. Additionally, all the reproductive parameters analyzed were reduced as a consequence of the infection. The results indicate the occurrence of the phenomenon of parasitic castration in the B. glabrata/H. bacteriophora HP88 interface, probably due to the depletion of galactogen in the parasitized organism. Although the infection did not cause lethality in the population of infected snails, H. bacteriophora HP88 compromised the reproductive performance of B. glabrata, suggesting its applicability in programs for biological control of this planorbid.

Susceptibility of embryos of Biomphalaria tenagophila (Mollusca: Gastropoda) to infection by Pochonia chlamydosporia (Ascomycota: Sordariomycetes)

Schistosoma mansoni is a heteroxenous parasite, meaning that during its life cycle needs the participation of obligatory intermediate and definitive hosts. The larval development occurs in aquatic molluscs belonging to the Biomphalaria genus, leading to the formation of cercariae, which emerge to infect the final vertebrate host. For this reason, studies for control of the diseases caused by digenetic trematodes often focus on combating the snail hosts. Thus, the objective of this study was to evaluate the susceptibility of Biomphalaria tenagophila embryos to the fungus Pochonia chlamydosporia (isolate Pc-10). The entire experiment was conducted in duplicate, with five replicates for each repetition (five egg masses/replicate), utilizing a total of 100 egg masses, with 20-30 eggs/egg mass. At the end of 15 days, the egg masses were evaluated under a stereomicroscope to analyze the hatching of B. tenagophila embryos in both experimental groups. After days of interaction, the exposure to the fungal hyphae bodies significantly impaired the viability of the B. tenagophila eggs, inhibiting the embryogenesis process by 83.7% in relation to the control group. Transmission and scanning electron microscopic images revealed relevant structural alterations in the egg masses exposed to the hyphae action of the fungus, interfering in the development and hatching of the young snails under analysis. These results indicate the susceptibility of B. tenagophila embryos to the fungus P. chlamydosporia (isolate Pc-10) and suggest the potential of Pc-10 to be used in the control of intermediate host, for its ovicidal capacity and for being an ecologically viable option, but in vivo experiments become necessary.

Entomopathogenic nematode-gastropod interactions

Entomopathogenic nematodes (EPNs) infect and kill insects and have been successfully used in the biological control of some insect pests. Slugs and snails are known to be significant pests of agriculture and serve as vectors for disease-causing microbes that can affect crops and humans. The potential of EPNs to be used in the biological control of gastropods has not been well-studied. The few studies that have been performed on the efficacy of EPNs in controlling gastropod pests and vectors were reviewed. Suggested criteria for further assessments of EPN-gastropod interactions are: Dose of EPNs used, length of infection assays, host biology, nematode biology and development, and Koch's postulates. There are provocative data suggesting that EPNs may be useful biological control agents against gastropod pests of agriculture and vectors of disease, though additional studies using the suggested criteria are needed, including the publication of negative data or studies where EPNs were not efficacious or successful in controlling gastropods.

Sequencing of Transcriptome and Small RNA Revealed the Xenobiotic Metabolism-Related Genes and Potential Regulatory miRNA in Asian Tramp Snail

The Asian tramp snail, Bradybaena similaris (Ferusssac), is an invasive land snail species and has been a rising agricultural pest in south of China. As a pest, it also plays a role in transmission of Angiostrongylus cantonensis. However, present studies on this species are rare and the molecular information is limited. For this purpose, we sequenced the transcriptome and small RNA of B. similaris collected from citrus orchards. In total, 89,747 unigenes with an N50 size of 1287 bp and an average length of 817 bp were generated from ∼8.9 Gb transcriptome and 31 Mb clean reads were generated from ∼36 Mb small RNA library. To demonstrate the usefulness of these two datasets, we analyzed a series of genes associated with xenobiotic metabolism and core RNAi machinery. Analysis of the transcripts resulted in annotation of 126 putative genes encoding cytochrome P450 monooxygenases (CYP, 45), carboxyl/cholinesterases (CCE, 13), glutathione-S-transferases (GST, 24), and ATP-binding cassette transporters (ABC, 44). Analysis of the small RNA detected 42 miRNAs. In addition, four genes involved in small RNA pathways (miRNA, piRNA, and siRNA) were identified, and a total of 430 genes that can be targeted by miRNAs were predicted. Moreover, we found that a few miRNAs could target certain genes involved in xenobiotic metabolism. Therefore, we believe that these two datasets and the characterization of the identified/predicted genes will facilitate the molecular study of this species as well as other land snails with agricultural importance.

Natural resistance to Fasciola hepatica (Trematoda) in Pseudosuccinea columella snails: A review from literature and insights from comparative "omic" analyses

The snail Pseudosuccinea columella is one of the main vectors of the medically-important trematode Fasciola hepatica. In Cuba, the existence of natural P. columella populations that are either susceptible or resistant to F. hepatica infection offers a unique snail-parasite for study of parasite-host compatibility and immune function in gastropods. Here, we review all previous literature on this system and present new "omic" data that provide a molecular baseline of both P. columella phenotypes from naïve snails. Comparison of whole snail transcriptomes (RNAseq) and the proteomes of the albumen gland (2D-electrophoresis, MS) revealed that resistant and susceptible strains differed mainly in an enrichment of particular biological processes/functions and a greater abundance of proteins/transcripts associated with immune defense/stress response in resistant snails. These results indicate a differential allocation of molecular resources to self-maintenance and survival in resistant P. columella that may cause enhanced responsiveness to stressors (i.e. F. hepatica infection or tolerance to variations in environmental pH/total water hardness), possibly as trade-off against reproduction and the ecological cost of resistance previously suggested in resistant populations of P. columella.

Ovicidal potential of Pochonia chlamydosporia isolate Pc-10 (Ascomycota: Sordariomycetes) on egg masses of the snail Pseudosuccinea columella (Mollusca: Gastropoda)

Snails of the species Pseudosuccinea columella are considered intermediate hosts of Fasciola hepatica, a digenetic trematode that infects bile ducts of ruminants and humans, causing economic damage and serious problems for public health. These gastropods inhabit ponds, have high reproductive capacity, and lay their egg masses in submerged substrates on pond edges where they are exposed to desiccation and microbes, including fungi, that may exert pathogenic effects on the snail and its embryos. This information is relevant for control of the intermediate host and therefore of fasciolosis. With the objective of evaluating ovicidal potential of Pochonia chlamydosporia (Pc-10 isolate), a nematophagous fungus used as antagonistic agent for a wide variety of helminths of medical and veterinary importance, on egg masses of P. columella, we compared a treated group, where the egg masses were exposed to Pc-10 for a period of 25 days, and a control group, in which there was no exposure to the fungus. The results indicated that the embryogenesis process was significantly inhibited (93.15%) by Pc-10, suggesting its applicability in biological control programs of lymnaeid snails. In addition, ultrastructure showed the occurrence of different types of interactions between the egg masses with the mycelia of Pc-10: type 1, biochemical effects by the adherence of hyphae; type 2, morphological alterations, but without hyphal penetration; and type 3, lytic effect, morphological damage caused by penetration of hyphae by the fungus, resulting in some important structural modifications, thus compromising the viability of the eggs. The results demonstrate the susceptibility of P. columella egg masses to an isolate of P. chlamydosporia under laboratory conditions, providing valuable information for the biological control of this intermediate host.