Infectivity Of Cercariae Research Articles

Trematode infection modulates cockles biochemical response to climate change

Resulting mainly from atmospheric carbon dioxide (CO2) build-up, seawater temperature rise is among the most important climate change related factors affecting costal marine ecosystems. Global warming will have implications on the water cycle, increasing the risk of heavy rainfalls and consequent freshwater input into the oceans but also increasing the frequency of extreme drought periods with consequent salinity increase. For Europe, by the end of the century, projections describe an increase of CO2 concentration up to 1120 ppm (corresponding to 0.5 pH unit decrease), an increase in the water temperature up to 4 °C and a higher frequency of heavy precipitation. These changes are likely to impact many biotic interactions, including host–parasite relationships which are particularly dependent on abiotic conditions. In the present study, we tested the hypothesis that the edible cockle, Cerastoderma edule, exposed to different salinity, temperature and pH levels as proxy for climate change, modify the infection success of the trematode parasite Himasthla elongata, with consequences to cockles biochemical performance. The results showed that the cercariae infection success increased with acidification but higher biochemical alterations were observed in infected cockles exposed to all abiotic experimental stressful conditions tested. The present study suggested that changes forecasted by many models may promote the proliferation of the parasites infective stages in many ecosystems leading to enhanced transmission, especially on temperate regions, that will influence the geographical distribution of some diseases and, probably, the survival capacity of infected bivalves.

Retracted: MicroRNA‐29b‐3p prevents Schistosoma japonicum‐induced liver fibrosis by targeting COL1A1 and COL3A1

Schistosomiasis is one of the world's major public health problems in terms of morbidity and mortality, causing granulomatous inflammation and cumulative fibrosis. This study explored in vivo and vitro effects of miR-29b-3p in granulomatous liver fibrosis by targeting COL1A1 and COL3A1 in Schistosoma japonicum infection. Thirty male Balb/c mice were assigned to normal control and model (percutaneous infection of cercariae of S. japonicum) groups. NIH-3T3 mouse embryonic fibroblasts were designated into blank, NC, miR-29b-3p mimic, TGF-β1, TGF-β1 + NC, and TGF-β1 + miR-29b-3p mimic groups. HE and Masson staining were employed to observe the pathological changes and collagenous fibrosis. The expression of α-SMA, COL1A1, COL3A1, TIMP-1 was determined by immunohistochemistry. The RT-qPCR, Western blotting and immunofluorescence staining were conducted to determine expression of miR-29b-3p, COL1A1, and COL3A1. CCK-8 assay and flow cytometry were performed to evaluate viability and apoptosis. The relative expression of miR-29b-3p decreased in the model group. The model group showed marked fibrosis in liver tissues. The expression of α-SMA, COL1A1, COL3A1, TIMP-1 was higher in the model group than that in the normal control group. Dual luciferase reporter gene assay revealed that miR-29b-3p directly targeted COL1A1 and COL3A1. Compared with the blank, NC, TGF-β1 and TGF-β1 + NC groups, the miR-29b-3p mimic group exhibited up-regulated expression of miR-29b-3p and MMP-9 but down-regulated expression of TIMP-1, HSP47, α-SMA, COL1A1, and COL3A1; while lower cell viability but higher apoptosis rate showed. It indicated that miR-29b-3p prevents S. japonicum-induced liver fibrosis by inhibiting COL1A1 and COL3A1.

Alternative to plating for calcaneal fracture treatment via sinus tarsi approach

Currently in China, the schistosomiasis control program has shifted its focus from transmission control to the elimination of the disease. Effective forecast and surveillance systems of schistiosomiasis are of great importance for issuing timely and early warnings on risk of infection, and therefore implementing preventive measures to avoid infection. There is great demand in more sensitive and specific methods to improve the surveillance system for early detection of S. japonicum infection in sentinel mice. In this study, we reported a sensitive nested-PCR assay targeting a 303-bp fragment from highly repetitive retrotransposon SjCHGCS19 to detect the S. japonicum DNA in sera of experimental mice. Meanwhile, detection efficacy of the nested-PCR was compared with two conventional methods for field monitoring schistosomiasis such as ELISA and IHA. The nested-PCR assay could detect the specific DNA at 3-day post-infection in sera of mice with 5 cercariae infection, while for ELISA and IHA, both show negative results even after 2 weeks post-infection in mice with 20 cercariae infection. Our results demonstrated the DNA-based assay was more sensitive to make early diagnosis of S. japonicum infection in sentinel mice models, which will improve the early-warning ability of schistosomiasis surveillance system.

ECHINOCHASMUS, NEW SPECIES (TREMATODA: ECHINOSTOMATIDAE) FROM EGYPT

In this study a new species of Echinochasnius (Dietz, 1909) is recorded for the first time in Egypt. Life cycle of one of gymnocephalous cercariae procured from Melanoides tuberculata snail was successfully completed in the laboratory. A total of 407 Melanoides tuberculata snails were collected from Mansouriya Canal, Giza Governorate. They were individually exposed to artificial light to determine natural infection with trematode larvae, Seven snails were found infected with gymnocephalous cercariae (infection index of 1.71). These cercariae were used to infect Gambusia affinis fish as second intermediate host. The infected gills were given to clean laboratory bred Rattus norvegicus as experimental final host. Adult worms were obtained ten days post-infection from rats' intestine identified as Echinochasmus after accurate comparson with standard keys. The diagnostic morphology of developmental stages were given.

Early detection of circulating DNA of Schistosoma japonicum in sentinel mice models

Currently in China, the schistosomiasis control program has shifted its focus from transmission control to the elimination of the disease. Effective forecast and surveillance systems of schistiosomiasis are of great importance for issuing timely and early warnings on risk of infection, and therefore implementing preventive measures to avoid infection. There is great demand in more sensitive and specific methods to improve the surveillance system for early detection of S. japonicum infection in sentinel mice. In this study, we reported a sensitive nested-PCR assay targeting a 303-bp fragment from highly repetitive retrotransposon SjCHGCS19 to detect the S. japonicum DNA in sera of experimental mice. Meanwhile, detection efficacy of the nested-PCR was compared with two conventional methods for field monitoring schistosomiasis such as ELISA and IHA. The nested-PCR assay could detect the specific DNA at 3-day post-infection in sera of mice with 5 cercariae infection, while for ELISA and IHA, both show negative results even after 2 weeks post-infection in mice with 20 cercariae infection. Our results demonstrated the DNA-based assay was more sensitive to make early diagnosis of S. japonicum infection in sentinel mice models, which will improve the early-warning ability of schistosomiasis surveillance system.

Galectin-3, histone deacetylases, and Hedgehog signaling: Possible convergent targets in schistosomiasis-induced liver fibrosis.

Schistosomiasis affects approximately 240 million people in the world. Schistosoma mansoni eggs in the liver induce periportal fibrosis and hepatic failure driven by monocyte recruitment and macrophage activation, resulting in robust Th2 response. Here, we suggested a possible involvement of Galectin-3 (Gal-3), histone deacetylases (HDACs), and Hedgehog (Hh) signaling with macrophage activation during Th1/Th2 immune responses, fibrogranuloma reaction, and tissue repair during schistosomiasis. Gal-3 is highly expressed by liver macrophages (Kupffer cells) around Schistosoma eggs. HDACs and Hh regulate macrophage polarization and hepatic stellate cell activation during schistosomiasis-associated fibrogenesis. Previously, we demonstrated an abnormal extracellular matrix distribution in the liver that correlated with atypical monocyte–macrophage differentiation in S. mansoni-infected, Gal-3-deficient (Lgals3-/-) mice. New findings explored in this review focus on the chronic phase, when wild-type (Lgals3+/+) and Lgals3-/- mice were analyzed 90 days after cercariae infection. In Lgals3-/- infected mice, there was significant inflammatory infiltration with myeloid cells associated with egg destruction (hematoxylin and eosin staining), phagocytes (specifically Kupffer cells), numerically reduced and diffuse matrix extracellular deposition in fibrotic areas (Gomori trichrome staining), and severe disorganization of collagen fibers surrounding the S. mansoni eggs (reticulin staining). Granuloma-derived stromal cells (GR cells) of Lgals3-/- infected mice expressed lower levels of alpha smooth muscle actin (α-SMA) and eotaxin and higher levels of IL-4 than Lgals3+/+ mice (real-time PCR). The relevant participation of macrophages in these events led us to suggest distinct mechanisms of activation that culminate in defective fibrosis in the liver of Lgals3-/- infected mice. These aspects were discussed in this review, as well as the possible interference between Gal-3, HDACs, and Hh signaling during progressive liver fibrosis in S. mansoni-infected mice. Further studies focused on macrophage roles could elucidate these questions and clear the potential utility of these molecules as antifibrotic targets.

The first record of Centrocestus formosanus (Nishigori, 1924) (Digenea: Heterophyidae) in Egypt

The life cycle of Centrocestus formosanus (Digenea: Heterophyidae) was to be successfully completed in the laboratory in the present study. Hundreds of the thiarid snail, Melanoides tuberculata, were collected from the main water course Mansouriya Canal, Giza Governorate, Egypt. The snails were individually exposed to artificial light to determine possible infection with trematode larvae. Fifteen snails were found infected with opthalmopleurolophocercous cercariae (infection index of 1.97). These opthalmopleurolophocercous cercariae shedded from snails were collected and placed in an aquarium with fish intermediate host, Gambusia affinis, to obtain metacercariae encysted in the gills. The gills with metacercariae were fed to albino rats, Rattus norvegicus, to obtain the adult worms. Adult worms were recovered in the small intestine of rats at 7 days after infection and they were identified as Centrocestus formosanus based on the morphological characteristics and the comparison with the previous descriptions in the literature. They were small, 518 × 324 μm in average size and had characteristic 32 circumoral spines around the oral sucker. The morphological characteristics of the developmental stages, from cercariae to adults, of this heterophyid fluke were given here. Therefore, the presence of this fluke is to be confirmed for the first time in Egypt by the present study.

Auto-infection by Echinostoma spp. cercariae in Helisoma anceps.

Auto-infection is a life history strategy used by many parasitic organisms, including digenetic trematodes. The process of autoinfection most frequently involves the transfer of a life cycle stage of the parasite from one site to another inside the same host, usually accompanied by morphological transformation. Moreover, among trematodes, the stage being transferred may also move from one host to another in completing the life cycle, i.e., an indirect cycle. Echinostoma spp. parasites offer the opportunity to study auto-infection because they utilize gastropods as both first and second intermediate hosts. Rejection of a null model predicting independent infection of first and second intermediate larval stages coupled with the presence of rediae being the best predictor of metacercariae prevalence and intensity suggests that auto-infection by Echinostoma spp. cercariae is occurring in their molluscan hosts. Shell length was also found to be a significant predictor of metacercariae intensity in the snails hosts, but this is most likely attributed to larger snails being more commonly infected with Echinostoma spp. rediae as opposed to an increased likelihood of cercariae infection. Auto-infection as a life history strategy increases transmission success of the parasite, but may also have negative consequences for the parasite that necessitate auto-infection coupled with the release of cercariae to maximize transmission success and host survival.

Analysis of trait mean and variability versus temperature in trematode cercariae: is there scope for adaptation to global warming?

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.

The sources and metabolic dynamics of Schistosoma japonicum DNA in serum of the host

The polymerase chain reaction (PCR) assay has turned out to be one of the most potential tools for diagnosis of schistosomiasis. However, the source and metabolic dynamics of Schistosoma japonicum DNA in the blood of hosts is not clear. In this study, rabbit models with monosexual and mixed sexual cercariae infection were established to interpret the source of the parasite DNA in serum of the hosts. Following administration of praziquantel at 7weeks postinfection, the metabolic mechanism of S. japonicum DNA in serum of the hosts was studied. The findings showed that, for the monosexual cercariae infection, the parasite DNA was detectable in serum of the host from day 3 to week 3 postinfection, while for the mixed sexual cercariae infection, the detection results were continually positive during the 7weeks after infection. After treatment with praziquantel, detection of S. japonicum DNA in rabbit sera became positive at the second day posttreatment, and the positive period lasted 3weeks in the monosexual cercariae infection group. However, with the mixed sexual cercariae infection group, the PCR results remained positive for 16weeks after treatment. We conclude that the S. japonicum DNA in host serum primarily comes from the residual body of dead schistosomula and/or tegument shedding of worm growing in the first 4weeks postinfection, while during the spawning stage of the female schistosome, the parasite DNA mainly comes from the disintegration of inactive eggs. The duration from treatment to total elimination of worm origin DNA in serum is not exceeding 3weeks. However, the DNA release from inactive eggs can last for more than 16weeks. Further studies are needed to address the sources and metabolic dynamics of S. japonicum DNA in human serum.

Effects of ultraviolet radiation on an intertidal trematode parasite: An assessment of damage and protection

Trematode parasites are integral components of intertidal ecosystems which experience high levels of ultraviolet radiation. Although these parasites mostly live within hosts, their life cycle involves free-living larval transmission stages such as cercariae which are directly exposed to ambient conditions. UV has previously been shown to considerably reduce the survival of cercariae. Here, we investigated potential mechanisms of protection and damage related to UV in the intertidal trematode Maritrema novaezealandensis. Firstly, the presence of sunscreen compounds (i.e. mycosporine-like amino acids) was quantified in the parasite tissue producing cercariae within a snail host, as well as in the free-swimming cercariae themselves. Secondly, levels of oxidative stress in cercariae after exposure to UV were investigated (i.e. protein carbonyls, catalase and superoxide dismutase). Thirdly, the DNA damage (i.e. cyclobutane–pyrimidine dimers) was compared between cercariae exposed and not exposed to UV. Lastly, functional aspects (survival and infectivity) of cercariae were assessed, comparing cercariae under light conditions versus dark after exposure to UV. We confirmed the presence of mycosporine-like amino acids in cercariae-producing tissue from within snail hosts, but were unable to do so in cercariae directly. Results further suggested that exposure to UV induced high levels of oxidative stress in cercariae which was accompanied by a reduction in the levels of protective antioxidant enzymes present. We also identified higher levels of DNA damage in cercariae exposed to UV, compared with those not exposed. Moreover, no clear effect of light condition was found on survival and infectivity of cercariae after exposure to UV. We concluded that cercariae are highly susceptible to UV damage and that they have very little scope for protection against or repair of UV-induced damage.

Effects of ultraviolet radiation on the transmission process of an intertidal trematode parasite

The transmission of parasites takes place under exposure to a range of fluctuating environmental factors, one being the changing levels of solar ultraviolet radiation (UVR). Here, we investigated the effects of ecologically relevant levels of UVR on the transmission of the intertidal trematode Maritrema novaezealandensis from its first intermediate snail host (Zeacumantus subcarinatus) to its second intermediate amphipod host (Paracalliope novizealandiae). We assessed the output of parasite transmission stages (cercariae) from infected snail hosts, the survival and infectivity of cercariae, the susceptibility of amphipod hosts to infection (laboratory experiments) and the survival of infected and uninfected amphipod hosts (outdoor experiment) when exposed to photo-synthetically active radiation only (PAR, 400-700 nm; no UV), PAR+UVA (320-700 nm) or PAR+UVA+UVB (280-700 nm). Survival of cercariae and susceptibility of amphipods to infection were the only two steps significantly affected by UVR. Survival of cercariae decreased strongly in a dose-dependent manner, while susceptibility of amphipods increased after exposure to UVR for a prolonged period. Exposure to UVR thus negatively affects both the parasite and its amphipod host, and should therefore be considered an influential component in parasite transmission and host-parasite interactions in intertidal ecosystems.

Application of an immunomagnetic bead ELISA based on IgY for detection of circulating antigen in urine of mice infected with Schistosoma japonicum

Schistosomiasis is an important zoonosis and some livestock especially bovine and swine play a crucial role on the disease transmission in endemic areas. The gold standard for animal Schistosoma japonicum infection is fecal examination although indirect agglutination assay (IHA) is so far mostly used in field survey and laboratory examination. Lack of sensitivity, poor practicality and high false positivity limit the use of those methods for routine veterinary detection as well as human diagnosis. A novel immunomagnetic bead ELISA based on IgY (egg yolk immunoglobulin) was developed for detection of circulating schistosomal antigen (CSA) in sera of hosts infected with S. japonicum. To assess the application of this method for diagnosis of domestic animal schistosomiasis with urine sample, the immunomagnetic bead ELISA based on IgY (IgY-IMB-ELISA) was employed in the present study to detect CSA in urine of murine schistosomiasis with either light (10 S. japonicum cercariae infection per mouse) or heavy infection (30 S. japonicum cercariae infection per mouse). The results showed that the CSA levels in urine of heavily and lightly infected mice reached a peak in 8 and 10 weeks after infection, respectively, remaining at a constant plateau in both groups by the end of the experiment (14 weeks after infection). The CSA level in urine of heavily infected mice was much higher than that of lightly infected mice from 8 to 14 weeks after infection. The effect of praziquantel treatment on the CSA level in urine of heavily infected mice was also investigated. It was found that the CSA level in urine of heavily infected mice with treatment was much lower than that of untreated mice at 4 weeks post-treatment, although still higher than that of control mice, and then gradually descended to the background level by 8 weeks after treatment. Our findings suggested that the IgY-IMB-ELISA may be an efficient and practical tool in non-invasive diagnosis of schistosome infection based on antigen detection, and evaluation of the efficacy of chemotherapy as well.

Effects of salinity on an intertidal host–parasite system: Is the parasite more sensitive than its host?

Intertidal habitats are characterised by highly fluctuating environmental conditions including varying salinity regimes. Changes in salinity may be gradual or abrupt; for example, heavy rainfall or evaporation during warm periods can either decrease or increase salinity. Trematodes are the most common parasites in intertidal ecosystems and their transmission is known to be highly influenced by environmental conditions. However, effects of salinity on the transmission of intertidal trematodes are not well studied. Here, we investigated the effects of long-term (i.e. several weeks) exposure to different salinities (25, 30, 35 and 40 psu) on the transmission of Maritrema novaezealandensis from its first intermediate snail host ( Zeacumantus subcarinatus) to a second intermediate amphipod host ( Paracalliope novizealandiae), in order to evaluate overall net effects. The following steps were assessed: output of parasite transmission stages (cercariae) from infected snail hosts, survival and infectivity of cercariae, susceptibility of amphipod hosts to infection and survival of amphipod hosts including parasite development within amphipod hosts. Output and survival of cercariae increased with increasing salinity whilst infectivity of cercariae and susceptibility of amphipods to infection were not clearly affected. Survival of amphipods was significantly longer at lower salinities and parasite development in infected amphipods was concomitantly more advanced. Overall, the results suggest that the parasite and the amphipods are differentially affected, and that under normal to increased salinities conditions are more favourable for the parasite than for the amphipod host.

Effects of the Herbicide Atrazine's Metabolites on Host Snail Mortality and Production of Trematode Cercariae

Environmental stressors have the potential to greatly impact the transmission of parasites with complex, multi-host life cycles such as those of trematodes. The commonly used herbicide atrazine has been shown to affect the susceptibility of second intermediate hosts (such as larval amphibians) to trematode infection, as well as the longevity and infectivity of the free-swimming cercariae, but not eggs or the free-swimming miracidia that infect the gastropod first intermediate hosts. However, we do not know if this pesticide influences the survival of infected snails or whether it affects cercariae production within, or emergence from, these hosts. In addition, previous studies of host-parasite dynamics have only examined the parent atrazine compound, not any of the long-lasting metabolites commonly present in water bodies. Here, we report that a concentration of 0.33 µg/L of an atrazine metabolite, desethyl atrazine, increased the mortality of freshwater gastropods ( Stagnicola elodes ) infected with a gymnocephalus type of cercaria but not that of uninfected snails or those harboring a mature or dormant infection of Echinoparyphium sp. In contrast, 2 wk of exposure to desethyl atrazine did not affect the emergence of gymnocephalus cercariae from snails, although a trend for a decrease in the emergence of Echinoparyphium sp. cercariae was observed. We suggest that simultaneous trematode infection and exposure to contaminants may represent a significant combined stress to gastropods, but this is likely parasite species-specific as well as dependent on whether cercariae are being actively produced.

Artificial preparation, indoor passage, and nature breed of Oncomelania hupensis infected with Schistosoma Japonicum.

To prepare the infected Oncomelania hupensis by artificial method for the research on the activity, vaccine, and genetic variation of Schistosoma Japonicum (S. Japonicum). The mature eggs of S. Japonicum were collected by Nylon silk method and the miracidia were incubated under appropriate conditions. Negative snails were infected with miracidia in different proportion by means of individual or collective infection to seek the best method and proportion of infection between miracidia and snails. Infected snails were divided into 12 groups in total. I-VI groups were for individual infection and VII-XII groups were for collective infection. There were 200 snails in each group. The infection ratios between snails and miracidia in Group I-VI or VII-XII were 1:0,1:5,1:10,1:15,1:20,1:25, respectively. The infected snails were screened, numbered, and reared singly. The amount of cercariae was calculated once every 10 days until the infected snails died. Then cercariae shedding quantity, infection quantity, and mortality of infected snails in every group were compared to find the best infection method and the best infection proportion between miracidia and snails. The cercariae were collected from the first generation of infected snails and were used to infect experimental animals. The mature eggs of S. Japonicum were saved from the infected experimental animals and incubated to get miracidia. The snails were artificially infected by miracidium to get the second generation of infected snails. The developmental rates of adult worms, the egg density in fecal and liver were compared between artificially and naturally infected snails. Results In individual infection Group I-VI,the average infection value of snails were 0 ± 0,22.7 ± 4.2,31.7 ± 4.5,53.0 ± 5.3,39.3 ± 5.9,32.7 ± 4.7,the average fatality of snails were 21.7 ± 3.1,25.0 ± 3.6,31.3 ± 4.9,44.7 ± 6.5,78.3 ± 9.5,89.7 ± 13.6, and the average value of cercariae shedding from infected snails were 0.0 ± 0.0,308.0 ± 96.6,428.1 ± 146.2,527.0 ± 171.1,571.4 ± 148.9,602.9 ± 356.3, respectively. In collective infection Group VII-XII,the average infection value of snails were 0 ± 0,12.3 ± 2.5,18.7 ± 4.7,28.3 ± 4.2,33.3 ± 4.7,29.3 ± 5.5,and the average fatality of snails were 22.7 ± 3.8,23.7 ± 4.5,28.3 ± 5.5,47.0 ± 9.5,75.7 ± 8.5,86.3 ± 12.2, and the average value of cercariae shedding from infected snails were 0 ± 0,244.5 ± 57.3,292.3 ± 74.8,347.1 ± 100.8,477.2 ± 142.1,447.3 ± 161.4, respectively. The second generation of artificially infected snails was obtained successfully. The average infection rate and fatality rate for the second generation of artificially infected snails were 24.65% and 24.50%, both of which were not obviously different from that of the first generation of artificially infected snails (P>0.05). In the animal experiment, the worm growth rate for the naturally infected snails, the first or second generation of artificially infected snails were 68.50%,73.50% or 71.00%. There was no obvious difference among them (P>0.05). The fecal (or liver) eggs per gram for the naturally infected snails, the first or the second generation of artificially infected snails were 1 503 ± 269,1 683 ± 233, or 1 541 ± 117 (or 6 641 ± 1 819,6 272 ± 1 419, or 7 263 ± 1 643). There was no significant difference among the 3 groups (P>0.05). Infected snails can be obtained through the artificial method by using S. Japonicum miracidia to infect snails. Individual infection has the advantage over collective infection. The optimal proportion of infection between snails and miracidia is 1:15. There was no significant difference between the first and the second generation of artificially infected snails in the average of cercariae shedding, infection, and fatality average of snails. There was no significant difference between artificially and naturally infected snails in the developmental rate of adult worms, fecal and liver eggs per gram.

Monostome cercariae induced malformations in amphibians: effect of infection at the pre-limb-bud stage tadpoles of Polypedates cruciger Blyth

Abstract: Global biodiversity loss and disease emergence are interrelated and have become a challenging environmental issue. Infection by the digenetic trematode, Riberioa ondatrae induces malformations in amphibians and is considered an emerging infection. The effect of infection on amphibians is not only parasite and host species specific, but also depends on the timing of infection. Recent evidence suggests that infection by cercariae of a monostome trematode species induces severe malformations in the common hourglass tree frog, Polypedates cruciger Blyth (1852) when exposed at the limb-bud stage of development. The aim of this study was to examine whether infection by this treamtode species at the pre-limb-bud stage also induces malformations in P. cruciger . Infection at the pre-limb-bud stage resulted in malformations (64.5%) and significantly reduced survival (77.5%). It also affected the growth and lengthened the larval period. Infections acquired at the pre-limb-bud stage caused a higher mortality and induced fewer malformations than infections at the limb-bud stage, as reported in a previous study. Hence, the effect of infection of monostome cercariae seems to depend on the developmental stage at which the tadpoles are exposed. Understanding the stage specific dynamics of malformations and associated mortality might be important to amphibian conservation. Keywords : Amphibians, Polypedates cruciger , frog malformations, trematode infection. Doi: 10.4038/jnsfsr.v38i4.2651 J.Natn.Sci.Foundation Sri Lanka 2010 38 (4):241-248

Immune Events Associated with High Level Protection against Schistosoma japonicum Infection in Pigs Immunized with UV-Attenuated Cercariae

BackgroundThe vaccination of radiation-attenuated Schistosoma japonicum cercariae can induce effective protection in artiodactyl, but the immune events related to protective immunity are not fully understood. To provide a paradigm for a human recombinant antigen vaccine, we have undertaken a vaccination and challenge experiment in pigs, which was recognized as an appropriate animal model in this type of study because of their similarity to human in immunology, and investigated the relative immune events induced by the radiation-attenuated S. japonicum cercariae.Methods and FindingsWe found that pigs immunized once with 400 µw UV-irradiated cercariae exhibited 63.84% and 71.82% reductions in worm burden and hepatic eggs respectively. Protective immunity in vaccinated pigs was associated with high level productions of IgM, total IgG, IgG1 and IgG2; IgG2 was significantly increased in the acute infection. IFN-γ levels could be elicited by immunization. At week 6 post-infection, IFN-γ, IL-4 and IL-10 levels also showed a dramatic rise synchronously in vaccinated pigs. Moreover, the granzyme b, nk-lysin, ifnγ, il4 and il10 mRNA levels in early skin-draining lymph nodes of immunized pigs were higher than those in pigs with non-irradiated cercariae infection. In addition, cytotoxicity-related genes in the mesenteric lymph nodes were significantly upregulated in vaccinated pigs in the acute infection.Conclusion/SignificanceOur results demonstrated that IFN-γ and IgG2 antibody production, as well as genes related to cytotoxicity are associated with the high level protection induced by UV-irradiated Schistosoma japonicum vaccine. These findings indicated that optimal vaccination against S. japonicum required the induction of IFN-γ, IgG2 antibody related to Th1 responses and cytotoxicity effect.

Epidermal club cells do not protect fathead minnows against trematode cercariae: a test of the anti-parasite hypothesis

Epidermal club cells of fishes in the superorder ostariophysi have puzzled evolutionary biologists because they were historically linked to chemical alarm signalling and relied on group selectionist explanations. Alternative hypoth- eses to explain the existence of these cells include the possibility of an anti-pathogenic or anti-parasitic function. If this is so, individual fish should invest in increased numbers of club cells after exposure to parasites, and club cells should contain components that reduce the infectivity of skin-penetrating larvae. Infectivity of cercariae of the trematode Ornithodiplostomum sp. was significantly reduced when exposed to the skin extract of fathead minnows (an ostariophysan), but also to skin extract of mollies (a non-ostariophysan that lacks club cells), respectively, compared to controls. Moreover, club cell density was not affected by exposure to cercariae. Taken together, these results are inconsistent with an anti-parasite function for these cells and instead suggest a generic role in response to injury. © 2009 The Linnean Society of London, Biological Journal of the Linnean Society, 2009, 98, 884-890. ADDITIONAL KEYWORDS: alarm substance - anti-predation - Ornithodiplostomum - Ostariophysi - infectivity - Pimephales.

Infectivity of Diplostomum spp. in Arctic Charr: Aspects of Exposure Duration and Cercariae Morphology

The diplostomid flukes, Diplostomum spp., infect fish and cause cataract opacities in the eye lens. The effect of exposure dose on abundance of Diplostomum spp. eye flukes in fish is known, but the effect of the duration of cercariae exposure has not been studied. However, under natural conditions, the temporal window for a successful cercaria attachment on fish is very short and, consequently, differences in infectivity of eye fluke cercariae, in the short-exposure durations of a few seconds, are probably biologically the most meaningful. We investigated infectivity of Diplostomum spp. cercariae originating from snail hosts in 3 lakes (3 Lymnaea stagnalis populations and 1 Radix balthica population) in 6 exposure times, ranging from 5 sec to 15 min, in young-of-the-year Arctic charr Salvelinus alpinus. In addition, we compared the infectivity to the cross-morphology of the cercariae. In the long-exposure duration, i.e., > or = 5 min, infectivity of Diplostomum spp. did not vary between the snail host species (L. stagnalis and R. balthica) of the same lake or across the L. stagnalis populations of 3 different lakes. However, in the short-exposure duration, i.e., < or = 60 sec, Diplostomum spp. cercariae shed from L. stagnalis had higher infectivity than did cercariae from R. balthica of the same lake. This indicates that that there is an interaction between length of cercariae exposure and origin of Diplostomum spp., and that the duration of exposure may influence the results when fish are experimentally infected. Within a lake, cercariae shed from L. stagnalis were also smaller than cercariae shed from R. balthica.