Himasthla elongata: Implantation of rediae to the specific iteroparous long-living host, Littorina littorea, results in the immune rejection

All semelparous short-lived gastropods studied so far for the experimental transplantation of trematode parthenitae, from one specific host to another, showed more or less successful acceptance of implanted parasites. We implanted echinostomatid rediae, Himasthla elongata, to the specific iteroparous long-living host, coenogastropod Littorina littorea. Using simple and low-invasive implantation techniques we have tested 680 snails injected with 75 redia microhemipopulations (MHP) harvested from naturally infected snails. Neither young nor mature rediae were able to survive in the recipient periwinkles in the course of 30 days post-implantation. A strong immune response from the host was already evident within the first week after implantation: initial inactivation of motile rediae with toxic humoral immune factors, following encapsulation of the implants and increased hemocyte counts. In contrast, rediae from the same MHPs showed perfect survival rates in primary in vitro axenic cultures. The failure of the transplantation experiments is explained in terms of the compatibility matching phenotype model. In the studied host-parasite combination all periwinkles are potentially susceptible and all rediae MHPs are potentially infective, however the probability of the compatible phenotypes matching is virtually low. Low investment in L. littorea annual reproduction would result in increased investment in self maintenance and immune mechanisms, causing the general resistance to the trematode infestation. Presumably, this resistance is relatively higher in long-lived iteroparous gastropods compare to semelparous short-lived mollusks such as pulmonates.

Variation among genotypes in responses to increasing temperature in a marine parasite: evolutionary potential in the face of global warming?

Climates are changing worldwide, and populations are under selection to adapt to these changes. Changing temperature, in particular, can directly impact ectotherms and their parasites, with potential consequences for whole ecosystems. The potential of parasite populations to adapt to climate change largely depends on the amount of genetic variation they possess in their responses to environmental fluctuations. This study is, to our knowledge, the first to look at differences among parasite genotypes in response to temperature, with the goal of quantifying the extent of variation among conspecifics in their responses to increasing temperature. Snails infected with single genotypes of the trematode Maritrema novaezealandensis were sequentially acclimatised to two different temperatures, 'current' (15°C) and 'elevated' (20°C), over long periods. These temperatures are based on current average field conditions in the natural habitat and those predicted to occur during the next few decades. The output and activity of cercariae (free-swimming infective stages emerging from snails) were assessed for each genotype at each temperature. The results indicate that, on average, both cercarial output and activity are higher at the elevated acclimation temperature. More importantly, the output and activity of cercariae are strongly influenced by a genotype-by-temperature interaction, such that different genotypes show different responses to increasing temperature. Both the magnitude and direction (increase or decrease) of responses to temperature varied widely among genotypes. Therefore, there is much potential for natural selection to act on this variation, and predicting how the trematode M. novaezealandensis will respond to the climate changes predicted for the next century will prove challenging.

Identification of thyroid hormone receptor homologs in the fluke Opisthorchis felineus (Platyhelminthes)

The liver fluke, Opisthorchis felineus of the Opisthorchiidae family, is a well-known causative agent of opisthorchiasis in Russia and Europe. The aim of this work was to identify genes encoding thyroid hormone receptors in O. felineus, and to analyze the expression of possible target genes in response to treatment with exogenous thyroid hormones. We identified two genes encoding thyroid hormone receptors in the O. felineus genome, THRA and THRB. The genes were differentially expressed through the life cycle. The maximal level of mRNA expression of THRA1 and THRB was observed in adult worms. Treatment of the worms with triiodothyronine and thyroxine resulted in an increase in glucose 6-phosphatase mRNA expression and a decrease in malate dehydrogenase mRNA expression, potential gene targets of thyroid hormones. These data indicate that thyroid hormone receptors may perform essential roles in physiological processes in adult O. felineus.

Experimental evidence for parasite-induced over-winter mortality in juvenile Rhodeus amarus

In this study, the effects of the eye fluke Diplostomum pseudospathaceum (Trematoda) infection on over-winter survival of young-of-the-year (YOY) European bitterling Rhodeus amarus (Cyprinidae) were examined between September 2010 and April 2011. The fish were reared in semi-natural conditions to ensure that results were not confounded by other parasite infections. The cumulative mortality of R. amarus from November until April was significantly higher in D. pseudospathaceum-infected fish (57·3%) compared to controls (42·1%). Infection of the parental generation did not have any effect on the mortality of juveniles. The results indicate that D. pseudospathaceum infection increases over-winter mortality of YOY R. amarus. The possible mechanisms causing mortality are discussed.

A checklist of helminth parasite fauna in anuran Amphibia (frogs) of Nagaland, Northeast India

An exhaustive exploratory survey on helminth parasite fauna of anuran frogs was carried out in several localities falling under 5 districts of western region of Nagaland state. Altogether 34 parasite species were recovered from a total of 29 host species surveyed. The parasite spectrum (represented in all the localities by at least one or more parasite species) comprises 2 monogenean, 15 trematode (13 adult and 2 metacercaria stages), 4 cestode (3 adult and 1 larval stages), 12 nematode and 1 acanthocephalan taxa. A checklist of both the parasite and host species with short remarks for each parasite species is provided herein.

How might flukes and tapeworms maintain genome integrity without a canonical piRNA pathway?

Surveillance by RNA interference is central to controlling the mobilization of transposable elements (TEs). In stem cells, Piwi argonaute (Ago) proteins and associated proteins repress mobilization of TEs to maintain genome integrity. This defense mechanism targeting TEs is termed the Piwi-interacting RNA (piRNA) pathway. In this opinion article, we draw attention to the situation that the genomes of cestodes and trematodes have lost the piwi and vasa genes that are hallmark characters of the germline multipotency program. This absence of Piwi-like Agos and Vasa helicases prompts the question: how does the germline of these flatworms withstand mobilization of TEs? Here, we present an interpretation of mechanisms likely to defend the germline integrity of parasitic flatworms.

Change in rank of Megaperidae (Trematoda) to Megaperinae within the Apocreadiidae and description of Haintestinum amplum n. g., n. sp

Haintestinum amplum n. g., n. sp. is described from the scrawled cowfish, Acanthostracion quadricornis, collected in the Eastern Gulf of Mexico off Florida, USA. The new species is relatively large and shares characters of the Apocreadiidae and Megaperidae but conforms to the diagnosis of neither. It belongs in a new genus possessing a pharynx with lobed anterior margin and intestine terminating in paired ani, like in megaperids, and, when compared with apocreadiids, it shares important anatomical features, including an I-shaped excretory vesicle, canicular seminal vesicle, eye-spot remnants, and pretesticular uterus and lacks a cirrus and cirrus sac. The H-shaped intestine and large funnel-shaped oral sucker without a U-shaped sphincter encircling half the anterior aperture are the most notable diagnostic characters of the new monotypic genus. Additionally, the phylogenetic position of the Megaperidae is investigated for the first time, using analysis of partial 28S rDNA gene sequences from H. amplum, two species in the Megapera, Thysanopharynx elongatus, and previously published 28S sequences of species from members of the Apocreadiata, Haploporoidae, Lepocreadiata, and Opisthorchiata. The resulting analysis demonstrated a close relationship among the new genus and the three species of megaperids, and the megaperids were most closely allied with Schistorchis zancli of the apocreadiids. Moreover, we now consider Megaperidae as the subfamily Megaperinae within the Apocreadiidae.

Genotypic and phenotypic variation in transmission traits of a complex life cycle parasite

Characterizing genetic variation in parasite transmission traits and its contribution to parasite vigor is essential for understanding the evolution of parasite life-history traits. We measured genetic variation in output, activity, survival, and infection success of clonal transmission stages (cercaria larvae) of a complex life cycle parasite (Diplostomum pseudospathaceum). We further tested if variation in host nutritional stage had an effect on these traits by keeping hosts on limited or ad libitum diet. The traits we measured were highly variable among parasite genotypes indicating significant genetic variation in these life-history traits. Traits were also phenotypically variable, for example, there was significant variation in the measured traits over time within each genotype. However, host nutritional stage had no effect on the parasite traits suggesting that a short-term reduction in host resources was not limiting the cercarial output or performance. Overall, these results suggest significant interclonal and phenotypic variation in parasite transmission traits that are not affected by host nutritional status.