Ultrastructure of Gametocyst of Parasitic Protozoan, Nematopsis sp. in Black Tiger Shrimp Penaeus monodon from the Gulf of Thailand

Ultrastructure of gametocyst of Nematopsis sp., a protozoa parasite of black tiger shrimp Penaeus monodon from the Gulf of Thailand is described. Ball-shaped gametocysts of about 110–160 µm diameter were found in close contact with the intestinal wall of shrimps. Surface of the gametocyst cyst wall or capsule is wrinkled with a circular bare area at one pole that contains a central pore 4–5 µm in diameter. The interior of the gametocyst is composed of numerous gymnospores and membranous sacs. Gymnospores varied in size with an average diameter of 6–8 µm. Ball-shaped gymnospores were composed of numerous, radially arranged, cone shaped sporozoites. Average width and length of sporozoites were 0.8–1.2 µm and 3–5 µm, respectively, with their rostral part pointing outward and caudal part, inward connecting to the residual cytoplasm in the centre of a gymospore. The rostral part of the sporozoite contains an oval nucleus, rough endoplasmic reticulum, mitochondria and a group of secretory granules. Membranous sacs were composed of two types of globular granules; large electron lucid granules and small dense granules

The phylogeography of Indoplanorbis exustus (Gastropoda: Planorbidae) in Asia

<p>Abstract</p> <p>Background</p> <p>The freshwater snail <it>Indoplanorbis exustus </it>is found across India, Southeast Asia, central Asia (Afghanistan), Arabia and Africa. <it>Indoplanorbis </it>is of economic importance in that it is responsible for the transmission of several species of the genus <it>Schistosoma </it>which infect cattle and cause reduced livestock productivity. The snail is also of medical importance as a source of cercarial dermatitis among rural workers, particularly in India. In spite of its long history and wide geographical range, it is thought that <it>Indoplanorbis </it>includes only a single species. The aims of the present study were to date the radiation of <it>Indoplanorbis </it>across Asia so that the factors involved in its dispersal in the region could be tested, to reveal potential historical biogeographical events shaping the phylogeny of the snail, and to look for signs that <it>I. exustus </it>might be polyphyletic.</p> <p>Results</p> <p>The results indicated a radiation beginning in the late Miocene with a divergence of an ancestral bulinine lineage into Assam and peninsular India clades. A Southeast Asian clade diverged from the peninsular India clade late-Pliocene; this clade then radiated at a much more rapid pace to colonize all of the sampled range of <it>Indoplanorbis </it>in the mid-Pleistocene.</p> <p>Conclusions</p> <p>The phylogenetic depth of divergences between the Indian clades and Southeast Asian clades, together with habitat and parasitological differences suggest that <it>I. exustus </it>may comprise more than one species. The timescale estimated for the radiation suggests that the dispersal to Arabia and to Southeast Asia was facilitated by palaeogeographical events and climate change, and did not require human involvement. Further samples from Afghanistan, Africa and western India are required to refine the phylogeographical hypothesis and to include the African Recent dispersal.</p

DNA-Sequence Variation Among Schistosoma mekongi Populations and Related Taxa; Phylogeography and the Current Distribution of Asian Schistosomiasis

Schistosomiasis is a disease caused by parasitic worms of the genus Schistosoma. In the lower Mekong river, schistosomiasis in humans is called Mekong schistosomiasis and is caused by Schistosoma mekongi. In the past, Mekong schistosomiasis was known only from the lower Mekong river. Here DNA-sequence variation is used to study the relationships and history of populations of S. mekongi. Populations from other rivers are compared and shown to be S. mekongi, thus confirming that this species is not restricted to only a small section of one river. The dates of divergence among populations are also estimated. Prior to this study it was assumed that S. mekongi originated in Yunnan, China, migrated southwards across Laos and into Cambodia, later becoming extinct in Laos (due to conditions unsuitable for transmission). In contrast, the dates estimated here indicate that S. mekongi entered Cambodia from Vietnam, 2.5–1 Ma. The pattern of genetic variation fits better with a more recent, and ongoing, northwards migration from Cambodia into Laos. The implications are that Mekong schistosomiasis is more widespread than once thought and that the human population at risk is up to 10 times greater than originally estimated. There is also an increased possibility of the spread of Mekong schistosomiasis across Laos

Summary statistics for the time series observations of <i>Neotricula aperta</i> population density in the Mun river at Ban Hin Laht.

<p>The sampling period was 1990–2011.</p

A Population Growth Trend Analysis for <i>Neotricula aperta</i>, the Snail Intermediate Host of <i>Schistosoma mekongi</i>, after Construction of the Pak-Mun Dam

<div><p>Background</p><p>The Pak-Mun dam is a controversial hydro-power project on the Mun River in Northeast Thailand. The dam is sited in a habitat of the freshwater snail <i>Neotricula aperta</i>, which is the intermediate host for the parasitic blood-fluke <i>Schistosoma mekongi</i> causing Mekong schistosomiasis in humans in Cambodia and Laos. Few data are available which can be used to assess the effects of water resource development on <i>N. aperta</i>. The aim of this study was to obtain data and to analyze the possible impact of the dam on <i>N. aperta</i> population growth.</p><p>Methodology/Principal Findings</p><p>Estimated population densities were recorded for an <i>N. aperta</i> population in the Mun River 27 km upstream of Pak-Mun, from 1990 to 2011. The Pak-Mul dam began to operate in 1994. Population growth was modeled using a linear mixed model expression of a modified Gompertz stochastic state-space exponential growth model. The <i>N. aperta</i> population was found to be quite stable, with the estimated growth parameter not significantly different from zero. Nevertheless, some marked changes in snail population density were observed which were coincident with changes in dam operation policy.</p><p>Conclusions/Significance</p><p>The study found that there has been no marked increase in <i>N. aperta</i> population growth following operation of the Pak-Mun dam. The analysis did indicate a large and statistically significant increase in population density immediately after the dam came into operation; however, this increase was not persistent. The study has provided the first vital baseline data on <i>N. aperta</i> population behavior near to the Pak-Mun dam and suggests that the operation policy of the dam may have an impact on snail population density. Nevertheless, additional studies are required for other <i>N. aperta</i> populations in the Mun River and for an extended time series, to confirm or refine the findings of this work.</p></div

Confidence intervals (95%) for estimates of mu, with the “best-fit” GSS model, based on the original (empirical) data set, from bootstrapped data sets and from simulations (where mu = 0).

<p>Confidence intervals (95%) for estimates of mu, with the “best-fit” GSS model, based on the original (empirical) data set, from bootstrapped data sets and from simulations (where mu = 0).</p

Model-based predictions of the 1991, 1995 and 2002 population densities.

<p>Values are given ± a 95% confidence interval (two-tailed); those for SLR and GLM are based on the standard error of the regression and those of the GSS on bootstrap resampling. The observed densities were 300 m⁻², 2108 m⁻², and 979 m⁻² for 1991, 1995 and 2002 respectively. Predictions were made using the data set excluding the 1991 observation. The time series was also extrapolated to give the expected density in 2020 under each model.</p

Fit of conventional linear models to the population density estimates for <i>Neotricula aperta</i>.

<p>For the Simple Linear Regression, t represents time in weeks from the first sample (t = 0). <i>P</i> values:. >0.2,</p>*<p><0.0001.</p><p>The equation for the negative binomial is exp(−0.0001189t+7.1245608), full data, and exp(−0.0004606t+7.382287) excluding outlier.</p

Results of a Bayesian estimation of divergence times (in millions of years) for nodes representing the most recent common ancestor (MRCA) of relevant clades.

<p>ESS, effective sample size; HPD, the 95% highest posterior density interval (equivalent to a confidence interval); Likelihood, posterior log likelihood (of the model, given the observed data); TMRCA, time to MRCA (/Ma). Explanation of clades: ingroup, MRCA of all taxa excluding the outgroup (<i>S. incognitum</i>); <i>japonicum</i>, MRCA of <i>S. japonicum</i> and all ingroup taxa excluding <i>S. sinensium</i>; <i>malayensis</i>, MRCA of <i>S. malayensis</i> and all <i>S. mekongi</i> taxa; <i>mekongi</i>, MRCA of all <i>S. mekongi</i> taxa.</p