[The evaluation of snail host-trematode parasite trophic relationships using stable isotope analysis]

Stable isotope ratios of carbon (13C/12C, δ13C) and nitrogen (15N/14N, δ15N) in snail-host tissue (the foot and hepatopancreas) and trematode parasites on two stages of their life cycle were analyzed. Trophic structure in co-occurring trematode larvae was examined in the following species: five species of cercariae (Echinoparyphium recurvatum, Hypodereum conoideum, Plagiorchis mutationis, Diplostomum chromatophorum and D. volvens) and two species of metacercariae (Cotylurus cornutus and Echinoparyphium recurvatum) within two closely related snail hosts Lymnaea stagnalis and L. tumida using stable isotope analyses. Snail and parasite sampling was conducted in a riverine portion of the Kargat River of the Lake Chany basin, in the south of Western Siberia (54 degrees 37'76"N, 78 degrees 13'07" E), in August 2009. Four out of five studied cercariae species were depleted in 15N as well as in 13C relatively to snail hosts tissues (foot and hepatopancreas), supporting our previously published data for Plagiorchis mutationis and Echinoparyphium recurvatum cercariae. Such fractionation of cercariae is untypical of the commonly observed relationship between consumers and their food. D. chromatophorum cercariae had demonstrated an insufficient enrichment in δ15N volume in relation to the hepatopancreas. Both two species of metacercariae (C. cornutus and E. recurvatum) showed a significant enrichment in δ15N volume relatively to the host tissue consumed (fractionation values ranging from 1.5 to 4 per thousand depending on the species). The differences in δ15N and δ13C volume between cercariae and metacercariae observed in this study illustrate the complexity of the host--parasite trophic relationships. Such isotopic differences between cercariae and metacercariae can probably be explained by selective consumption of specific amino acids or lipids or by changes in metabolism associated with the life cycle of the parasite. The present study represents the first comparative analysis of trophic relationships between the host and the endoparasite at different life cycle stages. It demonstrates the potency of the stable isotope analyses for understanding trophic relationships in multispecies parasite communities.

Three goose-type lysozymes in the gastropod Oncomelania hupensis: cDNA sequences and lytic activity of recombinant proteins

Three goose-type (g-type) lysozymes, designated as OHLysG1, OHLysG2 and OHLysG3 were identified from expressed sequence tags (ESTs) of a gastropod Oncomelania hupensis, the intermediate host of Schistosoma japonicum. The full cDNA sequences of OHLysG1, OHLysG2 and OHLysG3 consisted of 735, 909 and 808 nucleotides, with an open reading frame of 198, 214 and 249 codons containing a 21, 7 and 8 amino acid (aa) signal peptide at the N-terminus, respectively. The three g-type lysozymes shared conserved features with other g-type lysozymes, such as the substrate binding sites, the catalytic residues critical for the fundamental structure and function of g-type lysozymes. It seems possible that g-type lysozymes in molluscs shared one conserved cysteine with those in birds and mammals, and six conserved cysteines were observed for mollusc g-type lysozymes, with two unique cysteines present in the g-type lysozymes of O. hupensis. The three lysozyme genes were expressed mainly in hepatopancreas, with relatively low expression level observed in head-foot muscle and intestine. When comparing S. japonicum-infected and uninfected snails, significant increase (P<0.05) was observed for all the three lysozymes in infected snails, with the highest increase detected in hepatopancreas, and lowest in intestine, implying their defensive role in the host-parasite, i.e. snail-trematode system. The three recombinant lysozymes expressed in Escherichia coli strain M15 showed lytic activity against Aeromonas hydrophila, Vibrio fluvialis, Aeromonas sobria and Micrococcus lysodeikticus. In conclusion, the finding of three g-type lysozymes in O. hupensis provides structural and functional evidence of multiple g-type lysozymes in gastropod, which may have evolutional implication in the snail-trematode system.

Utilization of tissue habitats by Myxobolus wulii Landsberg & Lom, 1991 in different carp hosts and disease resistance in allogynogenetic gibel carp: redescription of M. wulii from China and Japan

Myxobolus wulii (=Myxosoma magna) was first described from the gills of goldfish, Carassius auratus auratus, in China. Subsequently, a myxosporean infecting the hepatopancreas of allogynogenetic gibel carp, C. auratus gibelio, was designated as a different species, Myxobolus guanqiaoensis, although the morphological features were almost identical to those of M. wulii. In Japan, an unidentified Myxobolus sp. was found in the gills and hepatopancreas of goldfish. Morphological and molecular analyses in the present study identified these myxosporeans as M. wulii, which was thus shown to use different habitats in the host fish. Phylogenetic analyses of small subunit ribosomal RNA gene sequences showed that M. wulii is closely related to two gill-infecting Myxobolus species, M. ampullicapsulatus and M. longisporus. Fish infected with M. wulii in the hepatopancreas exhibit swollen abdomens and chronic mortality. Hepatopancreas tissues are virtually destroyed and replaced with plasmodia of M. wulii. A remarkable difference in susceptibility to M. wulii between two clones of allogynogenetic gibel carp was observed, suggesting that resistance to the myxosporean infection was established in a clone of fish bred by allogynogenesis.

Superoxide dismutase activity in juvenile Litopenaeus vannamei and Nodipecten subnodosus exposed to the toxic dinoflagellate Prorocentrum lima

The toxic effect of the dinoflagellate Prorocentrum lima on juvenile American whiteleg shrimp Litopenaeus vannamei and giant lion-paw scallop Nodipecten subnodosus was evaluated. Organisms were exposed to three densities (500, 2000, or 5000 cells mL(-1)), superoxide dismutase activity and soluble protein in the hepatopancreas and muscle were determined at 1, 6, 24 and 48 h after challenge. Shrimp exposed at 5000 cells mL(-1) significantly increased SOD activity in the hepatopancreas at 1 h post-challenge, whereas enzymatic activity in muscle significantly increased at 24 h at all densities. Scallops exposed to 500 and 2000 cells mL(-1) showed significant SOD activity increase in hepatopancreas at 24 and 12 h, respectively. Mortality at 48 h was 100% in scallops exposed to 5000 cells mL(-1). Shrimp showed higher levels of SOD activity than scallops. Soluble protein content in the shrimp hepatopancreas was significantly higher at densities of 500 and 2000 cells mL(-1) at 6 and 1 h, respectively. Soluble protein content in the scallop hepatopancreas was higher than control values at 1 h after challenge. In this study, 500 cells mL(-1) was enough to trigger SOD activity in two benthic species exposed to the toxic dinoflagellate P. lima.

Infection with Hematodinium sp. in mud crabs Scylla serrata cultured in low salinity water in southern China

Dinoflagellates in the genus Hematodinium are important parasites of wild marine crustaceans, but are rarely reported in waters with salinities < 11 or from cultured crustaceans. Since 2005, the mud crab Scylla serrata, which is cultured along the coast of southeastern China, has suffered from an acute epizootic locally known as 'milky disease'. The disease mainly occurrs from September to November. The clinical signs are largely similar to those of crabs suffering from bitter crab disease (BCD) or pink crab disease (PCD), which are caused by parasites of the genus Hematodinium. To determine whether Hematodinium sp. is a pathogen of milky disease, histopathological examinations of mud crab haemolymph, hepatopancreas, heart and gill were conducted. In addition, previously reported Hematodinium molecular probes were applied to infected material. The results indicate that Hematodinium sp. is at least one of the main pathogens of milky disease. The salinity in S. serrata culture ponds was < 9. To our knowledge, this is the first report showing the Hematodinium infection in a cultured crustacean in low salinity water.

Laser-assisted microdissection: a new tool for aquatic molecular parasitology

Laser-assisted microdissection (LMD) has been developed to isolate distinct cell populations from heterogeneous tissue sections, cytological preparations, or live cell samples. Downstream applications typically include gene expression studies using real-time PCR and array platforms, diagnostic PCR, and protein expression studies. LMD techniques are now commonplace in mainstream biological research and clearly have suitable applications in the field of aquatic pathology and parasitology. The present study used LMD to isolate 2 dinoflagellate parasites (Hematodinium spp.) from formalin-fixed paraffin-embedded tissue sections from 2 crustacean hosts, Cancer pagurus and Portunus trituberculatus. DNA was isolated from LMD parasite preparations, and partial regions (up to 300 bp) of the small subunit and the first internal transcribed spacer region of the rRNA gene complex from the Hematodinium spp. were PCR amplified using diagnostic primers. The amplification products were sequenced to confirm the identity of the targeted regions. The techniques, applications, and limitations of LMD to address questions in aquatic molecular pathology and parasitology are discussed.

Tissue changes in the shore crab Carcinus maenas as a result of infection by the parasitic barnacle Sacculina carcini

We studied the effect of parasitic invasion by the barnacle Sacculina carcini on shore crabs Carcinus maenas collected from the Menai Straits in North Wales, UK. A significant reduction in serum protein and circulating granular, semi-granular and hyaline blood cells was observed in parasitised individuals, while serum ammonium and glucose concentrations were significantly increased. No difference in hepatopancreatic glycogen concentration was found between healthy and parasitised crabs. Histological analysis showed the apparent removal of fibrillar protein from infected muscle by the parasite. Hepatopancreas tubule necrosis was also routinely observed in infected individuals. Parasitisation by S. carcini dramatically affects the haemocyte population and serum chemistry of infected crabs.

Enterospora sp., an intranuclear microsporidian infection of hermit crab Eupagurus bernhardus

Recent work at our laboratory has led to the discovery of a new genus of microsporidian parasite residing in the family Enterocytozoonidae. The type species of this new genus, Enterospora canceri, is an intranuclear parasite infecting the hepatopancreatocytes of the decapod crustacean Cancer pagurus. Here we provide the second description of a parasite within the genus Enterospora, this time infecting the hermit crab Eupagurus bernhardus from U.K. waters. The pathological manifestation and ultrastructural features of the hermit crab parasite are very similar to those described for E. canceri. Further taxonomic comparisons based upon ultrastructural and molecular affinities of Enterospora are now required to define firmer links between this new genus within the Enterocytozoonidae and all other microsporidian families. The opportunistic nature of the discovery of a second intranuclear microsporidian within the Crustacea suggests that their presence may be more common than in higher animal groups.

Enterospora canceri n. gen., n. sp., intranuclear within the hepatopancreatocytes of the European edible crab Cancer pagurus

Only 1 genus (Nucleospora) within 1 family (Enterocytozoonidae) of the Microsporidia contains species that are parasitic within the nuclei of their host cells; to date, all described intranuclear Nucleospora spp. parasitise fish. This study describes the first intranuclear microsporidian parasite of an invertebrate, the European edible crab Cancer pagurus L. (Decapoda: Cancridae). Infected crabs displayed no obvious external signs, and maximum apparent prevalence of infection within a monthly sample was 3.45%. Infected hepatopancreatic tubules were characterised by varying numbers of hypertrophic and eosinophilic nuclei within epithelial cells. Parasite stages appeared as eosinophilic granular accumulations causing margination of host chromatin. In advanced cases, the tubule epithelia degenerated, with parasites and sloughed epithelial cells appearing in tubule lumens. All life stages of the parasite were observed within host nuclei. Uninucleate meronts were not detected, although binucleate stages were observed. Multinucleate plasmodia (sporogonal plasmodia) contained up to 22 nuclei in section, and late-stage plasmodia contained multiple copies of apparatus resembling the polar filament and anchoring disk, apparently associated with individual plasmodial nuclei. As such, aggregation and early assembly of sporoblast components took place within the intact sporogonial plasmodium, a feature unique to the Enterocytozoonidae. Liberation of sporoblasts from plasmodia or the presence of liberated sporoblasts was not observed in this study. However, large numbers of maturing and mature spores (measuring 1.3 +/- 0.02 x 0.7 +/- 0.01 microm) were frequently observed in direct contact with the host nucleoplasm. Considering the shared features of this parasite with microsporidians of the family Enterocytozoonidae, and the unique presence of this parasite within the nucleoplasm of decapod crustacean hepatopancreatocytes, this parasite (Enterospora canceri) is proposed as the type species of a new genus (Enterospora) of microsporidian. Molecular taxonomic work is now required, comparing Enterospora to Enterocytozoon and Nucleospora, the 2 other genera within the Enterocytozoonidae.

Characterization of a rediscovered haplosporidian parasite from cultured Penaeus vannamei

Mortalities of Penaeus vannamei, cultured in ponds in Belize, Central America, began during the last part of the grow-out cycle during the cold weather months from September 2004 through February 2005. Tissue squashes of infected hepatopancreata and histological examination of infected shrimp revealed that the mortalities might have been caused by an endoparasite. To confirm the diagnosis, DNA was extracted from ethanol preserved hepatopancreata and the small-subunit rRNA gene was sequenced. The 1838 bp sequence was novel and phylogenetic analysis placed the P. vannamei parasite within the phylum Haplosporidia as a sister taxon to a clade that includes Bonamia and Minchinia species. In situ hybridization was performed using anti-sense DNA probes that were designed to hybridize specifically with the parasite's nucleic acid. This organism presents similar characteristics to those of a haplosporidian that infected cultured P. vannamei imported from Nicaragua into Cuba, as described by Dyková et al. (1988; Fish Dis 11:15-22).

Molecular detection of Hematodinium spp. in Norway lobster Nephrops norvegicus and other crustaceans

The Norway lobster Nephrops norvegicus (L.) from the coastal waters of Scotland is seasonally infected by a parasitic dinoflagellate of the genus Hematodinium. Methods used to detect infection include a morphological index (pleopod diagnosis) and several immunoassays. The present study describes the development and application of a set of Hematodinium-specific polymerase chain reaction (PCR) primers and DNA probes based on Hematodinium ribosomal DNA (rDNA). In the PCR assay, a diagnostic band of 380 bp was consistently amplified from total genomic DNA isolated from Hematodinium-infected N. norvegicus. The sensitivity of the assay was 1 ng DNA, which is equivalent to 0.6 parasites. The primer pair also detected Hematodinium DNA in preparations of the amphipod Orchomene nanus, indicating that the amphipod may be infected with the same Hematodinium sp. infecting N. norvegicus. DNA probes detected Hematodinium parasites in heart, hepatopancreas and gill tissues from N. norvegicus, and hepatopancreas and gill tissues from Carcinus maenas, confirming Hematodinium infection in the latter.

A review of the parasitic dinoflagellates Hematodinium species and Hematodinium-like infections in marine crustaceans

Parasitic dinoflagellates in the genus Hematodinium are important parasites of marine Crustacea. Outbreaks of these parasites have damaged commercial stocks of Norway lobster Nephrops norvegicus, snow crab Chionoecetes opilio, Tanner crab C. bairdi, American blue crab Callinectes sapidus, and velvet swimming crab Necora puber. Species of Hematodinium can reach high enough levels to regulate their host populations, but mortalities are also centred on the unfished juveniles and females, hosts not normally sampled by fisheries; hence impacts are often underreported. Seasonal prevalences of up to 85 % occur annually in many host populations; in effect, these parasites form cryptic blooms in the water column with crabs and other crustaceans at risk of disease. We review the biology and ecology of Hematodinium spp. infections in crustaceans. Included is a comparison of the different infections, a synthesis of what is known, and an attempt to highlight fruitful areas for continued research.

A histopathological survey of shore crab (Carcinus maenas) and brown shrimp (Crangon crangon) from six estuaries in the United Kingdom

Invertebrates show considerable potential as sentinel organisms for the monitoring of the health status of aquatic systems. They are generally small, abundant, relatively sessile, and may readily bioaccumulate toxins. Cascade-like stress responses can occur following acute or chronic exposures to contaminated environments and as such, the overall health status of individuals within those environments, both in terms of histopathological lesions and the presence of infecting organisms, may ultimately reflect the general health status of these sites. The current study provides baseline multi-organ histopathological data for two common crustacean species, the shore crab (Carcinus maenas) and the brown shrimp (Crangon crangon) collected from six UK estuarine sites. Changes in the metabolic condition of crustaceans from these sites (measured in terms of connective tissue storage cell status) were interpreted in relation to other health measures (including parasite load and the presence of microbial pathogens). The relative ease at which a holistic assessment of health can be made using histopathology and the suitability of these species as environmental sentinels provide support for the inclusion of crustaceans as indicators of aquatic environmental health. Studies linking disease status to burdens of industrial contamination in these environments are now required.

Haemolymph parasite of the shore crab Carcinus maenas: pathology, ultrastructure and observations on crustacean haplosporidians

A protozoan parasite with some features of haplosporidians is described from the European shore crab Carcinus maenas. The parasite establishes a systemic infection through the haemal sinuses and connective tissues. Intracellular stages of the parasite were found within reserve inclusion, connective tissue, and muscle cells, while free forms were present in all haemal spaces. A uninucleate stage appeared to develop to a multinucleate plasmodial stage following multiple mitotic divisions of the nucleus. Histopathology also indicated that nuclear division may occur to form multinucleate plasmodia, in connective tissue, reserve inclusion and muscle cells, the multinucleate plasmodium being enclosed in the host-cell plasma membrane. It appears that the multinucleate plasmodium may then undergo internal cleavages which result in plasmodial fragmentation to form many uninucleate stages. Both stages, but particularly the uninucleate stage, contained cytoplasmic, large, ovoid, dense vesicles (DVs), some of which contained an internal membrane separating the medulla from the cortex, as in haplosporosomes. Golgi-like cisternae, closely associated with the nuclear membrane, formed DVs and haplosporosome-like bodies (HLBs), superficially resembling viruses. Infrequently, HLBs may condense to form haplosporosomes. The DVs, as in spores of some Haplosporidium spp. and paramyxeans, may give rise to, and are homologous with, haplosporosomes. Other features, such as the presence of an intranuclear mitotic spindle, lipid droplets, and attachment of DVs and haplosporosomes to the nuclear membrane, indicate that the C. maenas parasite is a haplosporidian. A similar organism reported from the haemolymph of spot prawns Pandalus spp., and haplosporidians reported from prawns Penaeus vannamei and crabs Callinectes sapidus may belong to this group. It is concluded that the well-characterised haplosporidians of molluscs and some other invertebrates may not be characteristic of the whole phylum, and that morphologically and developmentally similar organisms may also be haplosporidians, whether they have haplosporosomes or not.