Schistosomiasis is a neglected tropical disease that affects more than 200 million people worldwide. The main disease-causing agents, Schistosoma japonicum, S. mansoni and S. haematobium, are blood flukes that have complex life cycles involving a snail intermediate host. In Asia, S. japonicum causes hepatointestinal disease (schistosomiasis japonica) and is challenging to control due to a broad distribution of its snail hosts and range of animal reservoir hosts. In China, extensive efforts have been underway to control this parasite, but genetic variability in S. japonicum populations could represent an obstacle to eliminating schistosomiasis japonica. Although a draft genome sequence is available for S. japonicum, there has been no previous study of molecular variation in this parasite on a genome-wide scale. In this study, we conducted the first deep genomic exploration of seven S. japonicum populations from mainland China, constructed phylogenies using mitochondrial and nuclear genomic data sets, and established considerable variation between some of the populations in genes inferred to be linked to key cellular processes and/or pathogen-host interactions. Based on the findings from this study, we propose that verifying intraspecific conservation in vaccine or drug target candidates is an important first step toward developing effective vaccines and chemotherapies against schistosomiasis.
Amphiboloidea is a small but widespread group of snails found exclusively, and often abundantly, in mudflat and associated salt marsh or mangrove habitat. This study uses molecular data from three loci (COI, 16S and 28S) to infer phylogenetic relationships in Amphiboloidea and examine its position in Euthyneura. All but two of the named extant species of Amphiboloidea and additional undescribed taxa from across Southeast Asia and the Arabian Gulf were sampled. In contrast to the current morphology-based classification dividing Amphiboloidea into three families, analysis of molecular data supports revision of the classification to comprise two families. Maningrididae is a monotypic family basal to Amphibolidae, which is revised to comprise three subfamilies: Amphibolinae, Phallomedusinae and Salinatorinae. Sequence divergence between Asian populations of Naranjia is relatively large and possibly indicative of species complexes divergent across the Strait of Malacca. Salinatorrosacea and Salinator burmana do not cluster with other Salinator species, and require generic reassignment. In addition, sequences were obtained from an undescribed species of Lactiforis from the Malay Peninsula. Reconstruction of ancestral distributions indicates a plesiomorphic distribution and centre of origin in Australasia, with two genera subsequently diversifying throughout Asia. Increasing the sampling density of amphiboloid taxa in a phylogenetic analysis of Euthyneura did not resolve the identity of the sister taxon to Amphibolidae, but confirmed its inclusion in Pulmonata/Panpulmonata.
Schistosomiasis in Southeast Asia, caused by Schistosoma japonicum, Schistosoma mekongi and Schistosoma japonicum-like, have been reported from six different countries. The S. japonicum infections are highly prevalent in the Philippines with Oncomelania hupensis quadrasi as the vector snail, and in localized areas in Indonesia with O.h. lindoensis as the snail vector. The S. mekongi infections are recent discovery in the Lower Mekong Basin in Laos and Kampuchea, with Tricula aperta as the vector snail. The S. japonicum-like infections are found as isolated cases diagnosed by the finding of S. japonicum-like eggs in the faeces, rectal biopsy, tissue biopsy or at necropsy in Thailand and Malaysia. The control measures of schistosomiasis have been implemented in the Philippines and Indonesia, while further research studies are being conducted in Thailand and Malaysia.
Tropical ectotherms are predicted to be especially vulnerable to climate change because their thermal tolerance limits generally lie close to current maximum air temperatures. This prediction derives primarily from studies on insects and lizards and remains untested for other taxa with contrasting ecologies. We studied the HCT (heat coma temperatures) and ULT (upper lethal temperatures) of 40 species of tropical eulittoral snails (Littorinidae and Neritidae) inhabiting exposed rocky shores and shaded mangrove forests in Oceania, Africa, Asia and North America. We also estimated extremes in animal body temperature at each site using a simple heat budget model and historical (20 years) air temperature and solar radiation data. Phylogenetic analyses suggest that HCT and ULT exhibit limited adaptive variation across habitats (mangroves vs. rocky shores) or geographic locations despite their contrasting thermal regimes. Instead, the elevated heat tolerance of these species (HCT = 44.5 ± 1.8°C and ULT = 52.1 ± 2.2°C) seems to reflect the extreme temperature variability of intertidal systems. Sensitivity to climate warming, which was quantified as the difference between HCT or ULT and maximum body temperature, differed greatly between snails from sunny (rocky shore; Thermal Safety Margin, TSM = -14.8 ± 3.3°C and -6.2 ± 4.4°C for HCT and ULT, respectively) and shaded (mangrove) habitats (TSM = 5.1 ± 3.6°C and 12.5 ± 3.6°C). Negative TSMs in rocky shore animals suggest that mortality is likely ameliorated during extreme climatic events by behavioral thermoregulation. Given the low variability in heat tolerance across species, habitat and geographic location account for most of the variation in TSM and may adequately predict the vulnerability to climate change. These findings caution against generalizations on the impact of global warming across ectothermic taxa and highlight how the consideration of nonmodel animals, ecological transitions, and behavioral responses may alter predictions of studies that ignore these biological details.
A study of heavy metal contents in freshwater snails from rice fields have been made. The results indicate that the levels of heavy metals, Pb, Cu, Zn and Cd, are low and within the permissible limit of Malaysian Food Regulations. The results can serve as background data for further reference.
Shell morphological characters and allozyme electrophoresis were used to study the relationships among six geographical populations of land snails collected from Peninsular Malaysia. Allozyme electrophoresis was used to study the genetic variations to complement the morphological features studied that included shell lengths, numbers of whorls and shell colour. Ten loci coding for six enzymes (MDH, LAP, ALP, PGM, G6PDH and EST) could be reliably scored in samples from the six populations studied. The dendrogram showed two major clusters with one cluster comprising Subulinidae populations from Perak, Selangor, Johor, Terengganu and Pahang while the other cluster included only the Streptaxidae Huttonella bicolor (red) population. The Subulinidae populations were grouped into two subclusters: one subcluster included the Subulina sp. populations from Perak, Selangor an Johor while the other subcluster included the Opeas sp. populations from Terengganu and Pahang. Morphological features can identify the different families and therefore they can complement the allozyme genetic studies on the land snail populations. Like other reports in the literature, our results also underline the importance of a genetic approach in conjunction with a morphological approach, for discriminating land snail species. The present results suggest that small land snails, which were similar in colour but different in sizes, were not of the same family/genus.
As part of a search for novel inhibitors of HIV-1 reverse transcriptase, the acetone extract of the giant African snail, Achatina fulica, was shown to be active. Fractionation of the extract yielded inophyllums A, B, C, and E and calophyllolide (1a, 2a, 3a, 3b, and 6), previously isolated from Calophyllum inophyllum Linn., a known source of nutrition for A. fulica. From a methanol/methylene chloride extract of C. inophyllum, the same natural products in considerably greater yield were isolated in addition to a novel enantiomer of soulattrolide (4), inophyllum P (2b), and two other novel compounds, inophyllums G-1 (7) and G-2 (8). The absolute stereochemistry of inophyllum A (1a) was determined to be 10(R), 11(S), 12(S) from a single-crystal X-ray analysis of its 4-bromobenzoate derivative, and the relative stereochemistries of the other inophyllums isolated from C. inophyllum were established by a comparison of their 1H NMR NOE values and coupling constants to those of inophyllum A (1a). Inophyllums B and P (2a and 2b) inhibited HIV reverse transcriptase with IC50 values of 38 and 130 nM, respectively, and both were active against HIV-1 in cell culture (IC50 of 1.4 and 1.6 microM). Closely related inophyllums A, C, D, and E, including calophyllic acids, were significantly less active or totally inactive, indicating certain structural requirements in the chromanol ring. Altogether, 11 compounds of the inophyllum class were isolated from C. inophyllum and are described together with the SAR of these novel anti-HIV compounds.
A serosurvey of various indigenous interior tribes (Orang Ulu) in upper Rejang River Basin Sarawak Malaysia, the site of a multibillion Ringgit hydroelectric power project, found 6.8% of the individual surveyed were seropositive for schistosomiasis, as determined by ELISA method using the soluble egg antigen of Schistosoma malayensis Baling strain. In all age group, the seroprevalence rate is higher (9.5%) in males than in females (4.5%) except for the 31-40 age group. Seroprevalence of schistosomiasis was found to increase with age with the above 60 age group having the highest rate followed by the 31-40 age group. Seroprevalence rate among the tribes ranges from 4.1% among the Penan to 11.6% among the Kajang. There was no seroevidence of schistosomiasis among the Ukits. A snail survey found four snail species including Brotia species, the intermediate host of the lung fluke Paragonimus westermani, however no schistosome snail host was identified. Although schistosomiasis malayensis-like infection may be endemic in the area, its public health significance remains undetermined.
Laboratory experiments were carried out to study the susceptibility of snail vectors to Oriental anthropophilic Schistosoma. Oncomelania hupensis hupensis was readily infected with the local strain of Schistosoma japonicum (Chinese strain), and also infected with S. japonicum (Philippines strain). O.h. quadrasi was only susceptible to its S. japonicum (Philippines strain). The Oncomelania races were refractory to S. mekongi, S. japonicum-like species (Malaysian strain). Tricula aperta (beta race) was readily infected with S. mekongi, S. sinensium and S. japonicum-like species from Malaysia, but not S. japonicum. T. bollingi was susceptible to S. sinensium and S. mekongi. Robertsiella kaporensis was only susceptible to the local strain, S. japonicum-like species from Malaysia. Geographical isolation may be the cause of these differences in compatibility between the snail vectors and the schistosome parasites.
An ecologic study on Paragonimus in Malaysia was attempted from May to September 1967. Seven streams located in various directions and distances from Kuala Lumpur were surveyed for the study of intermediate hosts, snail and crab. One Malayan village and one aborigine village where infected crabs were found, and two tuberculosis hospitals in K.L. were surveyed for the study of human population. Intradermal tests along with sputum or stool examination to detect human infection by Paragonimus were employed. Wild animals, only a few, were shot in the vicinity of the aborigine village and several domestic cats from the Malayan village were bought. These animals were autopsied and examined for adult Paragonimus. Among five species of crab collected from the study areas, only two species, Potamon jahorenes and Parathelphusa maculata were found to be infected with Paragonimus. P. maculata seemed to be better crab host for the Paragonimus because this species had higher infection rate and metacercarial density than the other in the very same area. Three out of seven streams had infected crabs and the infection rate as well as the infection intensity varied from one stream to another. Only avilable snail in the streams was identified as Brotia costula. The infection rate of the snail was very low, six snails out of 11,898, which is about the same rate reported from other countries. Infected snail, however, had thousands of rediae uncountable containing about twelve microcercocercariae in each redia, sufficient enough to maintain the life cycle of the parasite even with only a few infected snail, the amplifier. This is the first confirmed report on the snail host of Paragonimus from Malaysia where the existence of Paragonimus had been reported in 1923. The first trial to study human population by means of intradermal test, sputum and/or stool examinations in Malaysia showed no evidence of human infection of Paragonimus. The number of animals, wild and domestic, examined for natural infection was too small to draw any statement. These examined animals were all negative for adult Paragonimus. Even though more extensive studies on wild animals and human population may be necessary for the definite conclusion, the facts that infected crabs from jungle stream where human contacts are extreamely rare, and also highly infected crabs from the area where none of humans or domestic animals were infected, strongly suggest the life cycle of Paragonimus in this area may be maintained by wild animal hosts rather than by human host. The morphology of all stages of the parasite, the pattern of penetrating glands, flame cells and excretroy bladder of cercaria, lancet shaped single cuticular spines and 6 branched ovary of adult worm obtained from experimentally infected cat, and the shape of egg including all measurements agree well with the characteristics of Paragonimus westermani.