The Melanoides tuberculata is an invasive species, which is natively distributed in Africa and Southeast Asia. This study describes the first mitochondrial genome of the M. tuberculata based on the whole genome sequencing data. The complete sequence length of the mitogenome is 15,821 bp, including 37 genes (2 rRNA genes, 22 tRNA genes and 13 protein-coding genes). Phylogenetic analysis using the 13 species of Cerithioidea species showed that the M. tuberculata is closely related to P. dartevellei, forming the sister group to C. sinensis and C. obtuse.

Philophthalmosis is a zoonotic ocular disease that affects mainly domestic and wild avian species in different parts of the world. However, aspects related to its epizoology in domestic animals are not completely known. In the present study, 47 Muscovy duck (Cairina moschata), 8 mallards (Anas platyrhynchos platyrhynchos) and 6 African geese (Anser cygnoides), free-living in an urban lake in Belo Horizonte, Minas Gerais, Brazil, were evaluated for eye fluke infection. The animals were manually contained, and the conjunctival sac and nictitating membrane were evaluated by direct ophthalmic examination (DOE), in which the fluke burden was estimated by a semiquantitative scale. Moreover, the conjunctival sac lavage (CSL) technique was applied for the search of parasite eggs. When possible, the detected trematodes were carefully removed for fixed for taxonomic identification. In order to characterize the parasite-host-environmental system, malacological collections were performed at the locality, and the collected intermediate host mollusks (Melanoides tuberculata) were evaluated for infection with larval philophthalmids. In addition, wild vertebrates found dead in the locality, including one common gallinule (Gallinula galeata) and two capybaras (Hydrochoerus hydrochaeris), were necropsied for the search of eye flukes. Samples from the developmental stages obtained from the hosts were subjected to morphological and molecular studies (amplification and sequencing of a partial region of the Nad-1 gene). In the DOE, the presence of eye flukes was verified in 67% (4/6), 31% (15/47) and 25% (2/8) in geese, Muscovy ducks and mallards, respectively. In most cases, the birds showed mild parasitism (1-5 trematodes), with no apparent eye damage, characterizing a subclinical infection. In only one goose, which had a high fluke burden (20 trematodes), it was possible to obtain eggs by CSL. Regarding the malacological survey, 73/4545 (1.6%) specimens of M. tuberculata evaluated were found infected with megalurous cercariae, compatible with representatives of the family Philophthalmidae. Additionally, 147 flukes were recovered from a specimen of G. galeata found dead at the lake. The morphological and molecular study of parasites obtained from different hosts evaluated in this study enabled the identification of Philophthalmus gralli, a species native from Asia and introduced in the Americas. Factors such as the wide distribution of the intermediate host and the participation of domestic and wild reservoirs in the parasite transmission chain may favor the occurrence of parasite spillover from wild to domestic birds. Furthermore, the occurrence of the life cycle of P. gralli in an urban waterbody serves as an alert to the possibility of human cases of this zoonotic eye parasite.

Prosobranch snails and adult Paramphistomoidea flukes were collected from water bodies and cattle abattoir located in Mpumalanga province of South Africa, respectively. The snails were identified based on morphological characters as well as the ITS-2 and 16S markers as Melanoides sp. and Tarebia granifera, respectively, and the Paramphistomoidea flukes were identified as Calicophoron microbothrium using the ITS-1/5.8S/ITS-2 marker. After confirming identification, the snails were bred to first filial generation (F1) under laboratory conditions. Ninety snails were randomly selected from the laboratory-bred F1 snails and 25 Melanoides sp. and 20 T. granifera were exposed to C. microbothrium miracidia, and the same numbers were maintained as non-exposed controls. Results showed that C. microbothrium successfully established in Melanoides sp. and produced cercariae, and the prepatent period recorded was 21 days. Three snails shed cercariae at day 21 postexposure (PE), and rediae and free cercariae were detected in the soft tissues of one snail on dissection at day 44 PE. The same fluke did not establish in T. granifera. Melanoides sp. started producing offspring at day 7 PE, and T. granifera at day 14 PE. In conclusion, our results showed that Melanoides sp. used in this study is a suitable intermediate host for C. microbothrium under experimental conditions, and given the wide distribution of this snail species, it is important to determine its role in the natural transmission of other Calicophoron species that have been reported in South Africa.

Xiphidiocercariae were found in the invasive snail Melanoides tuberculata collected during a malacological survey in Ceará-Mirim, State of Rio Grande do Norte, Northeastern Brazil in November 2018 and submitted to morphological and molecular analyses. The morphology revealed similarities between the larvae here reported for the first time in M. tuberculata from Brazil and other xiphidiocercariae described in thiarid snails from Asia and Africa. Phylogenetic analyses based on 28S and ITS-2 sequences revealed that the larvae correspond to an unidentified species of the family Lecithodendriidae. Aspects related to the morphology and taxonomy of xiphidiocercariae found in M. tuberculata are briefly discussed. It is possible that the parasite here reported is a newly introduced species transmitted by M. tuberculata in the American continent.

The fishborne zoonotic trematode Haplorchis pumilio (Looss, 1896) is here reported for the first time in Brazil based on morphological, experimental and molecular studies. Pleurolophocercous cercariae emerged from the invasive snail Melanoides tuberculata collected in the municipality of Ceará-Mirim, state of Rio Grande do Norte, Northeast region of Brazil, in November 2018, were used for experimental infection of guppies, Poecilia reticulata. Metacercariae were extracted from the caudal musculature of these fishes and were used to infect mice. Adult parasites recovered in the small intestine of the mice were morphologically identified as H. pumilio. Molecular sequences were obtained for the Brazilian and Peruvian isolates of H. pumilio, and were compared with data available in GenBank. Analyses of fragments of the nuclear genes 28S (1219 bp) and ITS-2 (290 bp) revealed 98.48-100% similarity between the South American and Asian isolates of H. pumilio. Moreover, new sequences of the mitochondrial gene cox-1 obtained for the Brazilian (797 bp) and Peruvian (646 pb) isolates were 100% similar to a Mexican isolate of this species and 97.54% similar to an isolate from Thailand. This finding reveals the potential for occurrence of human haplorchiasis in Brazil, especially because of the increasing popularity of raw fish dishes in the country.

The freshwater mollusk, Melanoides tuberculata, contains bioconcentration trace metals in its tissues from the surrounding area. M. tuberculata was used as a bioindicator for pollution with seven trace metals (Mn, Fe, Ni, Cu, Zn, Cd, and Pb) accumulated in snail soft tissues near Bahr El-Baqar and El-Serw agricultural drains of industrial activities in Port Said and Damietta, respectively. The biota sediment accumulation factors (BSAF) in this study reveals that all the soft tissues of the M. tuberculata snails were macro-concentrators with the exception of Ni; it was deconcentrated, and thus provides that the selective tissues as good biomonitors. The bioconcentration factor (BCF) showed the highest concentrations of Fe and Cu in the soft tissues of the M. tuberculata snail, which has the potential to be used as a biomonitoring agent for Fe and Cu contamination of the water.

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.

To understand the effect of metal pollution on the speciation process, we conducted comparative analyses of six populations of the gastropod Melanoides tuberculata, which dominated the Manzala lagoon (Nile Delta, Egypt). Geometric morphometric analysis was implemented to quantify the phenotypic plasticity of the species. The results from both Canonical Variate Analysis and Relative Warp indicated an overall decrease in the morphological breadth of M. tuberculata in the polluted sites. The favored phenotypes in the polluted sites have moderate whorl section, moderate ovate aperture, less-prominent radial ornament, and overall moderate-spired shells. Lack of morphological variations and dominance of intermediate phenotypes in the polluted sites indicate that stabilizing selection is driving the morphological pattern of this species. Moreover, analysis by using the partial least square model confirmed that metal pollution is the major predictor of the observed shape variations, whereas other biotic/abiotic traits are a minor predictor.

We investigated the transmission of the fishborne trematodes Centrocestus formosanus and Haplorchis pumilio by Melanoides tuberculata snails in Peru. We report on results of experimental, morphological, and molecular approaches and discuss the potential risk for future human cases, given the existence of food habits in the country involving the ingestion of raw fish.

BACKGROUND: The persistence of high genetic variability in natural populations garners considerable interest among ecologists and evolutionary biologists. One proposed hypothesis for the maintenance of high levels of genetic diversity relies on frequency-dependent selection imposed by parasites on host populations (Red Queen hypothesis). A complementary hypothesis suggests that a trade-off between fitness costs associated with tolerance to stress factors and fitness costs associated with resistance to parasites is responsible for the maintenance of host genetic diversity.
RESULTS: The present study investigated whether host resistance to parasites is traded off with tolerance to environmental stress factors (high/low temperatures, high salinity), by comparing populations of the freshwater snail Melanoides tuberculata with low vs. high clonal diversity. Since polyclonal populations were found to be more parasitized than populations with low clonal diversity, we expected them to be tolerant to environmental stress factors. We found that clonal diversity explained most of the variation in snail survival under high temperature, thereby suggesting that tolerance to high temperatures of clonally diverse populations is higher than that of populations with low clonal diversity.
CONCLUSIONS: Our results suggest that resistance to parasites may come at a cost of reduced tolerance to certain environmental stress factors.