Occurrence of Rhabditid Nematodes in the Pet Giant African Land Snails (Achatina fulica)

First report of Rhabditis (Rhabditella) axei with the invasive palm borer Paysandisia archon

Rhabditis (Rhabditella) axei is a free-living, pseudoparasitic, necromenic, and parasitic nematode, depending on the host. This species feeds mainly on bacteria present in decaying organic matter, soil, and other substrates; however, in its parasitic form, it can colonize some species of snails. Moreover, the presence of R. axei has also been detected in birds and mammals, including humans. In 2021-2023, during monitoring of the palm borer Paysandisia archon in Central Italy, R. axei emerged from dead larvae of this alien invasive moth and was extracted from palm fibres of Trachycarpus fortunei in three independent sites. The nematode was identified by morphological and morphometric analyses. Molecular analyses using SSU and LSU gene fragments were used to confirm the identification and to perform Bayesian reconstruction of the phylogeny. Each sampling site showed a unique haplotype. Concerning the pathogenicity of this nematode against insects, the test performed on Galleria mellonella larvae did not show any entomopathogenic effect. This is the first time that R. axei was found associated with P. archon, and this recurrent association was discussed.

Gut microbiota in parasite-transmitting gastropods

BACKGROUND

Gastropoda, the largest class within the phylum Mollusca, houses diverse gut microbiota, and some gastropods serve as intermediate hosts for parasites. Studies have revealed that gut bacteria in gastropods are associated with various biological aspects, such as growth, immunity and host-parasite interactions. Here, we summarize our current knowledge of gastropod gut microbiomes and highlight future research priorities and perspectives.

METHODS

A literature search was undertaken using PubMed, Web of Science and CNKI for the articles on the gut microbiota of gastropods until December 31, 2022. We retrieved a total of 166 articles and identified 73 eligible articles for inclusion in this review based on the inclusion and exclusion criteria.

RESULTS

Our analysis encompassed freshwater, seawater and land snails, with a specific focus on parasite-transmitting gastropods. We found that most studies on gastropod gut microbiota have primarily utilized 16S rRNA gene sequencing to analyze microbial composition, rather than employing metagenomic, metatranscriptomic, or metabolomic approaches. This comprehensive review provided an overview of the parasites carried by snail species in the context of gut microbiota studies. We presented the gut microbial trends, a comprehensive summary of the diversity and composition, influencing factors, and potential functions of gastropod gut microbiota. Additionally, we discussed the potential applications, research gaps and future perspectives of gut microbiomes in parasite-transmitting gastropods. Furthermore, several strategies for enhancing our comprehension of gut microbiomes in snails were also discussed.

CONCLUSIONS

This review comprehensively summarizes the current knowledge on the composition, potential function, influencing factors, potential applications, limitations, and challenges of gut microbiomes in gastropods, with a specific emphasis on parasite-transmitting gastropods. These findings provide important insights for future studies aiming to understand the potential role of gastropod gut microbiota in controlling snail populations and snail-borne diseases.

The global risk of infectious disease emergence from giant land snail invasion and pet trade

BACKGROUND

Pathogen outbreaks mostly originate from animals, but some species are more likely to trigger epidemics. The giant land snail (Lissachatina fulica) is a widespread invader, a popular exotic pet, and a notorious vector of the rat lungworm, causing eosinophilic meningitis in humans. However, a comprehensive assessment of the risks of disease outbreak associated with this species is lacking.

METHODS

We assessed and mapped the risk of disease transmission associated with the invasion and pet trade of L. fulica. First, we conducted a review of the scientific literature to list all known L. fulica parasites and pathogens and query host-pathogen databases to identify their potential mammalian hosts. Then, to assess the potential for L. fulica to spread globally, we modelled its suitable climatic conditions and tested whether, within climatically suitable areas, the species tended to occur near humans or not. Finally, we used social media data to map L. fulica possession as an exotic pet and to identify human behaviours associated with increased risk of disease transmission.

RESULTS

Lissachatina fulica can carry at least 36 pathogen species, including two-thirds that can infect humans. The global invasion of L. fulica is climatically limited to tropical areas, but the species is strongly associated with densely populated areas where snails are more likely to enter in contact with humans. In temperate countries, however, climatic conditions should prevent L. fulica's spread. However, we show that in Europe, giant snails are popular exotic pets and are often handled with direct skin contact, likely increasing the risk of pathogen transmission to their owners.

CONCLUSIONS

It is urgent to raise public awareness of the health risks associated with L. fulica in both tropical countries and Europe and to regulate its trade and ownership internationally. Our results highlight the importance of accounting for multiple types of human-wildlife interactions when assessing risks of infectious disease emergence. Furthermore, by targeting the species most likely to spread pathogens, we show that it is possible to rapidly identify emerging disease risks on a global scale, thus guiding timely and appropriate responses.

Design, Synthesis, Characterization, and Molluscicidal Activity Screening of New Nicotinonitrile Derivatives against Land Snails, M. cartusiana

A new series of nicotinonitrile derivatives 2-7 was designed and synthesized from the starting material (E)-3-(4-chlorophenyl)-1-(4-methoxyphenyl)prop-2-en-1-one (1) to assess their molluscicidal activity. The newly synthesized nicotinonitrile compounds 2-7 were characterized based on FTIR, ¹H-NMR, and ¹³C-APT NMR spectra as well as elemental microanalyses. The target compounds 2-7 were screened for their toxicity effect against M. cartusiana land snails and were compared to Acetamiprid as a reference compound. The results demonstrated that the nicotinonitrile-2-thiolate salts 4a and 4b had good mortality compared with that of Acetamiprid. The results of the in vivo effect of the prepared nicotinonitrile molecules 2, 4a, and 4b on biochemical parameters, including AChE, ALT, AST, and TSP, indicated a reduction in the level of AChE and TSP as well as an increase in the concentration of transaminases (ALT and AST). A histopathological study of the digestive gland sections of the M. cartusiana land snails was carried out. The nicotinonitrile-2-thiolate salts 4a,b showed vacuolization, causing the digestive gland to lose its function. It could be concluded that the water-soluble nicotinonitrile-2-thiolate salts 4a,b could be adequate molluscicidal molecules against M. cartusiana land snails.

The invasive giant African land snail, Achatina fulica (Gastropoda: Pulmonata): global geographical distribution of this species as host of nematodes of medical and veterinary importance

The giant African land snail, Achatina fulica, is an important invasive species in many countries, where it causes losses in biodiversity and agriculture, as well as impacting the health of both humans and animals, as the intermediate host of medically important nematodes. The present study is based on a comprehensive review of the literature on the nematodes that have been found in association with A. fulica, worldwide. We searched a number of different databases and used the findings to investigate the methods used to extract and identify the nematodes, their larval stages, and environment and collecting procedures of the infected molluscs. Between 1965 and 2021, 11 nematode species were recorded in association with A. fulica in 21 countries. Most of the studies recorded associations between A. fulica and Angiostrongylus cantonensis, which causes cerebral angiostrongyliasis in humans and Aelurostrongylus abstrusus, which provokes pneumonia in felines. The nematodes were extracted primarily by artificial digestion with hydrochloric acid or pepsin, and identified based on their morphology or through experimental infection to obtain the adult. In most cases, the nematodes were at larval stage L3, and the infected A. fulica were collected from anthropogenic environments. The results demonstrate the importance of A. fulica as a host of nematodes of medical and veterinary importance, as well the contribution of anthropogenic environments to the occurrence of the parasites, and give information about the different methods used to collect and identify the nematodes found associated with this species.

Low genetic diversity and the phylogeny of Achatina fulica, an intermediate host of Angiostrongylus cantonensis in Thailand, inferred from 16S mitochondrial sequences

The giant African land snail, Achatina fulica, is a pulmonate land snail of the Achatinidae family. The snail is native of East Africa and has spread to tropical and subtropical areas in different parts of the world. Achatina fulica is an important agricultural pests and the intermediate host for Angiostrongylus spp., especially Angiostrongylus cantonensis, which causes eosinophilic meningoencephalitis in humans. However, information on the genetic diversity and phylogenetic relationships among A. fulica populations in Thailand is limited. The goal of this study was to evaluate the genetic diversity and analyze haplotype network relationships between A. fulica populations in Thailand and other areas of the world. We collected A. fulica from 22 provinces in 6 regions of Thailand and analyzed a phylogenetic tree and haplotype network based on a fragment of 239 base pairs of the 16S rRNA sequence. The maximum likelihood, neighbor joining, and Bayesian inference trees for the 133 A. fulica 16S rRNA sequences revealed only one group, closely related only to A. fulica haplotype C, in all regions of Thailand. The haplotype network analysis showed that haplotype C is associated with F, P, E, Q, H and D. The genetic distance between the haplotype and A. fulica isolates in Thailand varies from 0 and 0.024, with a total of 21 variable sites. Haplotype C is predominant in Thailand and associated with other haplotypes from several areas. As inferred from 16S rDNA sequences, this study demonstrated low genetic diversity in A. fulica in Thailand. Low genetic diversity in the population can increase susceptibility to A. cantonensis infection, which may be associated with the current distribution of A. cantonensis.

Population characterization and parasitological assessment of the giant African snail ( Achatina fulica) in urban areas of Cartagena, Colombia

Background: The giant African snail, Achatina fulica, is an invasive species recognized for being a serious agricultural pest and an intermediary vector for diverse parasites that cause diseases in humans. The knowledge of the state of African snail populations in urban areas is of great ecological and public health importance. Therefore, our objective was to characterize the status of giant African snail populations present in the city of Cartagena, Colombia, including the assessment of nematode parasites in the specimens.

Methods. Sites were visited following information from citizens affected by the presence of the African snail. The specimens were collected and transported to the laboratory; subsequently, they were weighed, measured, and classified by size. Dissections of lung tissue and soft organs were performed to search for and identify nematode parasites. Size measurement between the sampled sites was statistically compared and density and biomass indicators were established.

Results. In total, 204 snails were collected distributed among four sites within Cartagena city. Of these, 50% were juvenile specimens (10-40 mm). The size of the specimens showed significant differences between the sampling areas. The calculated density was between 0.0019-0.68 ind/m ² and the biomass between 3.92-48.75 kg/ha. No presence of nematode parasites was observed in these specimens.

Conclusions. Densities and biomasses of A. fulica in Cartagena do not reach levels considered highly harmful. On the other hand, although no parasites were found in these snails, it is relevant to continue with studies on the human health risks that represent the presence of this invasive species in urban areas of Cartagena.

Cysts and larvae of Strongyluris: A parasite of amphibians and reptiles found in an urban population of Lissachatina fulica (Férussac, 1821) in southern Brazil

We report the finding of cysts and larvae of Strongyluris in specimens of L. fulica from an urban area of the municipality of Maringá in northern Paraná State, southern Brazil. Thirty-seven young adult snails were collected at three sites: 15 in riparian forest; 14 in a vegetable garden; and eight in a residential garden. We found a total of 16 cysts with nematode larvae in three of the 15 snails collected in riparian forest. The parasites were identified as larvae of the genus Strongyluris, which are parasites of the gastrointestinal tract of amphibians and reptiles. Lissachatina fulica is established in urban areas of 33% of the municipalities of the state of Paraná. The species has spread rapidly through the urban area of the municipality of Maringá, which may contribute to the transmission of nematode larvae of medical and veterinary interest to humans and other animals.