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Digenean larvae of hermaphroditic generation - cercariae - are known to be polymorphic at genetic and behavioural levels. Cercariae arise as a result of parthenogenetic reproduction of intramolluscan stages, and represent a clone if a snail was infected with a single miracidium. Here we investigated cercarial clones of Himasthla elongata - namely, the infectivity of cercariae with normal (negative) and deviant (positive) photoreaction. In our study, most H. elongata clones showed intraclonal variance in their response to light. The proportion of photopositive cercariae ranged between 0.2% and 60% in different H. elongata clones. Photopositive larvae demonstrated significantly reduced rates of encystment in Mytilus edulis haemolymph in vitro and in young mussels. We discuss the possible mechanisms behind intraclonal variations, such as non-specific genomic rearrangements.

Ocean warming and acidification are general consequences of rising atmospheric CO 2 concentrations. In addition to future predictions, highly productive systems such as the Humboldt Current System are characterized by important variations in both temperature and pCO 2 level, but how these physical-chemical ocean changes might influence the transmission and survival of parasites has not been assessed. This study experimentally evaluated the effects of temperature (14, 18 and 25 °C) and the combined effects of temperature (∼15 and 20 °C) and pCO 2 level (∼500 and 1400 microatmospheres (µatm) on the emergence and survival of two species of marine trematodes-Echinostomatidae gen. sp. and Philophthalmidae gen. sp.-both of which infect the intertidal snail Echinolittorina peruviana. Snails were collected from intertidal rocky pools in a year-round upwelling area of the northern Humboldt Current System (23°S). Two experiments assessed parasite emergence and survival by simulating emersion-immersion tidal cycles. To assess parasite survival, 2 h old cercariae (on average) were taken from a pool of infected snails incubated at 20-25 °C, and their mortality was recorded every 6 h until all the cercariae were dead. For both species, a trade-off between high emergence and low survival of cercariae was observed in the high temperature treatment. Species-specific responses to the combination of temperature and pCO 2 levels were also observed: the emergence of Echinostomatidae cercariae was highest at 20 °C regardless of the pCO 2 levels. By contrast, the emergence of Philophthalmidae cercariae was highest at elevated pCO 2 (15 and 20 °C), suggesting that CO 2 may react synergistically with temperature, increasing transmission success of this parasite in coastal ecosystems of the Humboldt Current System where water temperature and pH are expected to decrease. In conclusion, our results suggest that integrating temperature-pCO 2 interactions in parasite studies is essential for understanding the consequence of climate change in future marine ecosystem health., (Copyright © 2018 Australian Society for Parasitology. Published by Elsevier Ltd. All rights reserved.)

Schistosoma japonicum is a widespread human and animal parasite that causes intestinal and hepatosplenic schistosomiasis linked to colon, liver and bladder cancers, and anemia. Estimated 230 million people are currently infected with Schistosoma spp, with 779 million people at risk of contracting the parasite. Infection occurs when a host comes into contact with cercariae, a planktonic larval stage of the parasite, and can be prevented by inactivating the larvae, commonly by chemical treatment. We investigated the use of physical non-equilibrium plasma generated at atmospheric pressure using custom-made dielectric barrier discharge reactor to kill S. japonicum cercariae. Survival rate decreased with treatment time and applied power. Plasmas generated in O 2 and air gas discharges were more effective in killing S. japonicum cercariae than that generated in He, which is directly related to the mechanism by which cercariae are inactivated. Reactive oxygen species, such as O atoms, abundant in O 2 plasma and NO in air plasma play a major role in killing of S. japonicum cercariae via oxidation mechanisms. Similar level of efficacy is also shown for a gliding arc discharge plasma jet generated in ambient air, a system that may be more appropriate for scale-up and integration into existing water treatment processes.

Schistosoma mansoni cercariae display specific behavioral responses to abiotic/biotic stimuli enabling them to locate and infect the definitive human host. Here we report the effect of such stimulants on signaling pathways of cercariae in relation to host finding and invasion. Cercariae exposed to various light/temperature regimens displayed modulated protein kinase C (PKC), extracellular signal-regulated kinase (ERK) and p38 mitogen-activated protein kinase (p38 MAPK) activities, with distinct responses at 37 °C and intense light/dark, when compared to 24 °C under normal light. Kinase activities were localized to regions including the oral sensory papillae, acetabular ducts, tegument, acetabular glands, and nervous system. Furthermore, linoleic acid modulated PKC and ERK activities concurrent with the temporal release of acetabular gland components. Attenuation of PKC, ERK, and p38 MAPK activities significantly reduced gland component release, particularly in response to linoleic acid, demonstrating the importance of these signaling pathways to host penetration mechanisms., (© The Author 2015. Published by Oxford University Press on behalf of the Infectious Diseases Society of America.)

The potential of species for evolutionary adaptation in the context of global climate change has recently come under scrutiny. Estimates of phenotypic variation in biological traits may prove valuable for identifying species, or groups of species, with greater or lower potential for evolutionary adaptation, as this variation, when heritable, represents the basis for natural selection. Assuming that measures of trait variability reflect the evolutionary potential of these traits, we conducted an analysis across trematode species to determine the potential of these parasites as a group to adapt to increasing temperatures. Firstly, we assessed how the mean number of infective stages (cercariae) emerging from infected snail hosts as well as the survival and infectivity of cercariae are related to temperature. Secondly and importantly in the context of evolutionary potential, we assessed how coefficients of variation for these traits are related to temperature, in both cases controlling for other factors such as habitat, acclimatisation, latitude and type of target host. With increasing temperature, an optimum curve was found for mean output and mean infectivity, and a linear decrease for survival of cercariae. For coefficients of variation, temperature was only an important predictor in the case of cercarial output, where results indicated that there is, however, no evidence for limited trait variation at the higher temperature range. No directional trend was found for either variation of survival or infectivity. These results, characterising general patterns among trematodes, suggest that all three traits considered may have potential to change through adaptive evolution., (Copyright © 2014 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved.)

Parasite transmission takes place in the context of a multitude of simultaneously fluctuating environmental factors. As a particularly vulnerable step in the transmission, trematode cercariae are directly exposed to ambient conditions during their search for a host. Here, we investigated the survival of cercariae of the intertidal trematode Maritrema novaezealandensis in a multifactorial experiment (2 × 2 × 2 design) with temperature (20 and 30 °C), salinity (35 and 40 practical salinity units (psu)) and ultraviolet radiation (UVR; exposed and not exposed) as main factors. All factors had significant effects, with cercariae dying faster at the higher temperature, increased salinity and when exposed to UVR. Full activity ceased within ~6 h in all treatments at 30 °C, except at 35 psu under no exposure to UV; in all other treatments full activity was maintained for >6 h. Several factor interactions were identified, of which the interactive negative effect of temperature and UVR was the most important. These results imply that conditions during the main transmission window of M. novaezealandensis are highly challenging for cercariae. Our findings highlight the importance of considering multiple environmental factors in the study of parasite transmission to gain a more ecologically relevant understanding of transmission dynamics.

This study reports further observations on encystment and excystment of the paramphistomid trematode Zygocotyle lunata. Of numerous substrates tested in the laboratory for cercarial encystment, i.e. plastic and glass dishes, Styrofoam™, aluminium foil, snail shells, and cheesecloth, all but cheesecloth allowed for 100% encystment within 4 h of cercarial release at 28°C. Numerous physical and chemical factors were tested to kill cysts, and their capacity to do so was determined by the subsequent inability of cysts to excyst within a chemical excystment medium. Vinegar, Italian salad dressing, soy sauce and 10% solutions of sucrose, acetic acid and sodium chloride were the most detrimental. Freezing, boiling and storage of cysts for more than 2 years also killed them. Several marinades such as lemon juice, Worcestershire sauce, and various concentrations of potassium permanganate, did not kill the majority of cysts tested. Since Z. lunata is a potential foodborne trematode for humans and animals, it is important to determine suitable ways to control or kill these cysts.