A Minchinia mercenariae-like parasite infects cockles Cerastoderma edule in Galicia (NW Spain)

The cockle Cerastoderma edule fishery has traditionally been the most important shellfish species in terms of biomass in Galicia (NW Spain). In the course of a survey of the histopathological conditions affecting this species in the Ria of Arousa, a haplosporidan parasite that had not been observed in Galicia was detected in one of the most productive cockle beds of Galicia. Uni- and binucleate cells and multinucleate plasmodia were observed in the connective tissue mainly in the digestive area, gills and gonad. The parasite showed low prevalence, and it was not associated with abnormal cockle mortality. Molecular identification showed that this parasite was closely related to the haplosporidan Minchinia mercenariae that had been reported infecting hard clams Mercenaria mercenaria from the Atlantic coast of the United States. The molecular characterization of its SSU rDNA region allowed obtaining a fragment of 1,796 bp showing 98% homology with M. mercenariae parasite. Phylogenetic analysis supported this identification as this parasite was clustered in the same clade as M. mercenariae from the United States and other M. mercenariae-like sequences from the UK, with bootstrap value of 99%. The occurrence of M. mercenariae-like parasites infecting molluscs outside the United States is confirmed.

Long-term epidemiological study of disseminated neoplasia of cockles in Galicia (NW Spain): temporal patterns at individual and population levels, influence of environmental and cockle-based factors and lethality

The dynamics of disseminated neoplasia (DN) affecting cockles Cerastoderma edule (L.) in Galicia was addressed at individual and population levels. Early stage of DN was characterized by isolated neoplastic cells occurring in branchial vessels or in the connective tissue of gills, mantle, gonad or digestive gland. As disease progressed, the neoplastic cells appeared loose in foci and became widely distributed throughout the organs. In advanced stages, the connective tissue of most organs was infiltrated by neoplastic cells, which displaced normal cells, leading to the loss of the normal tissue/organ architecture. Host defence reaction was occasionally observed. A field survey performed for 7 years, in two cockle beds located in different Galician Rías, showed that DN is a hyperendemic disease usually present all year-round at high prevalence in adult cockles but with annual prevalence minima in spring likely due to the death of heavily affected cockles, concurrently with gonad ripeness-spawning. DN was detected in the cockles ranging from 10 to 39 mm in size; the highest DN prevalence and severity corresponded to the cockles of intermediate size/age (22-29 mm/0.7-1 year old). Sex did not appear to influence DN occurrence. An inhibitory effect of DN on cockle gametogenesis was detected.

Expression of mutant protein p53 and Hsp70 and Hsp90 chaperones in cockles Cerastoderma edule affected by neoplasia

High prevalence of disseminated neoplasia has been found in cockles Cerastoderma edule of Galicia (NW Spain). Disseminated neoplasia has been associated with high mortalities of various bivalve species. In vertebrates, proteins such as p53 and heat shock proteins (HSPs) play important roles in carcinogenesis. The protein p53 has been detected in neoplastic cells of bivalve molluscs such as Mytilus edulis, Mytilus trossulus, Mya arenaria, Spisula solidissima, Crassostrea rhizophorae and Crassostrea gigas. In this study, western blotting analyses were used to test the expression of Hsp70, Hsp90 and mutant p53 proteins in the cells and plasma of the haemolymph of cockles showing various intensities of neoplasia. Disseminated neoplasia was previously diagnosed by examination of stained haemolymph monolayers with light microscopy. In the present study, mutant p53 was detected in haemolymph cells of cockles diagnosed as affected by moderate and heavy neoplasia intensity, whereas it was not detected in cockles with either no or light neoplasia. The higher the neoplasia intensity, the higher the levels of Hsp70 and Hsp90. These proteins were not found in plasma. The results reveal the possible association between p53 and HSPs in neoplastic cells of cockles, which could prevent p53 from carrying out its functions, as occurs in human cancers.

Disseminated neoplasia and large foci indicating heavy haemocytic infiltration in cockles Cerastoderma edule from Galicia (NW Spain)

A histopathological survey was performed to search for the cause of high mortality in the cockle Cerastoderma edule in northern rias of Galicia (northwestern Spain). From limited sampling, 2 severe pathological conditions with high prevalence were found: disseminated neoplasia and the occurrence of numerous, large foci of heavy haemocytic infiltration. Both conditions were detected in areas affected by high mortality and were absent (foci of haemocytic infiltration) or with lower prevalence (disseminated neoplasia) in an area with unnoticeable mortality that was chosen as a reference. Advanced cases of both pathological conditions were associated with extensive tissue destruction. Because of the severity of the lesions and their high prevalence, both pathological conditions could have contributed to the high mortality.

Parasites and pathologic conditions of the cockle Cerastoderma edule populations of the coast of Galicia (NW Spain)

A survey of pathological conditions affecting cockle populations of the most economically important natural beds of Galician estuaries in NW Spain was performed. Samples of 30 adult cockles were collected from each of 34 natural beds in the spring of 1999 and processed by histological techniques. Disseminated neoplasia were seen in samples from most of the natural beds, in some cases with a high prevalence. The gregarine Nematopsis sp., larval trematode stages, and branchial extracellular large cysts enclosing bacteria-like microorganisms were the most prevalent parasites. Paravortex cardii, intracellular colonies of rickettsiae-like organisms in digestive and gill epithelium, Pseudoklossia sp. coccidians, Trichodina sp., and other ciliates were frequently seen in the samples. Copepods in gills and intestine and unidentified gregarines in intestine epithelia and surrounding connective tissue were less prevalent and were observed in samples of some natural beds. Large foci of heavy hemocytic infiltration were detected in a few sites only. Cysts of Steinhausia sp. and plasmodia and spores of a haplosporidian were seen in cockles from two localities. Inflammation was frequently observed in the samples. Some of the parasites and pathological conditions could be associated with mortality.

Seasonal variation and effects of age, food availability, size, gonadal development, and parasitism on the hemogram of mytilus galloprovincialis

The study of hemogram characteristics in a population of cultured mussels through a period of 18 months revealed that the concentration of circulating Mytilus galloprovincialis hemocytes varied, following a seasonal pattern, being positively correlated with water temperature. Most mussels had between 1 and 5 x 10(6) hemocytes/ml of hemolymph. Differential counts showed that M. galloprovincialis hemolymph contained more granulocytes than hyalinocytes. The hemolymph cell concentration was not associated with size or weight of mussels. Circulating hemocyte concentration did not decrease in mussels with reabsorbing gonad, despite the hemocytic accumulation inside and around gonad follicles. No significant difference in hemolymph cell concentration was found between two groups of mussels of different ages. Nevertheless, older mussels had higher mean values of circulating granulocytes although these differences were only significant in the winter sample. Infestation by the protistan Marteilia refringens caused a significant increase of hemocytes in the hemolymph. In addition, the occurrence of some parasites induced significant changes in the proportion of circulating hemocyte types. Results suggested that a hemocytic response was detected in hemolymph when the foreign organisms are pathogenic and evoke a heavy inflammatory reaction. Mussels with large or numerous granulocytomas had a higher number of circulating granulocytes and hyalinocytes than those without granulocytomas. Copyright 1998 Academic Press.

Enzymes Involved in Defense Functions of Hemocytes of Mussel Mytilus galloprovincialis

Mytilus galloprovincialis hemocytes contain phosphatases, esterases, proteases, and glucosidases as revealed by a semiquantitative colorimetric method. The activity levels of some enzymes changed throughout the months of the experiment without a seasonal pattern. No differences in the enzyme levels were found between the two groups of mussels of different age (cultivated 11 and 19 months on ropes hung from the same raft). Light microscopy study of hemocyte enzymes showed that hyalinocytes and granulocytes had reaction of acid phosphatase, beta-glucuronidase, alpha-naphthyl butyrate esterase, naphthol AS-D chloroacetate esterase, and alpha-naphthyl acetate esterase. Phenoloxidase and peroxidase activities were also detected in monolayers of hemocytes. Ultrastructural study revealed that the granules of hemocytes contained acid phosphatase, beta-glucuronidase, nonspecific esterases, peroxidase, and NADH oxidase. Products of beta-glucuronidase and peroxidase reaction were also localized in the plasma membrane. Lysozyme activity level was higher in hemocytes than in serum. Comparison between the two groups of different age showed a higher activity level of lysozyme in younger mussels.

Morphological characterization of the hemocytes of the clam, Ruditapes decussatus (Mollusca: Bivalvia)

Hemocytes play an important role in internal defence in molluscs. The morphology of hemolymph cells was studied for the first time in Ruditapes decussatus. Two main types of hemocytes (hyalinocytes and granulocytes) exist in R. decussatus. Three types of granulocytes were identified by light microscopy, in accordance with the presence of basophilic or acidophilic granules or a mixture of both in the cytoplasm. The existence of hyalinocytes and granulocytes was confirmed by electron microscopy. Some monoclonal antibodies (MABs) raised against hemocytes of Crassostrea gigas showed cross-reactivity with the total population of hemocytes of R. decussatus; however, none of the MABs raised against hemocytes of Mytilus edulis showed cross-reactivity. The MABs assayed did not allow us to distinguish hemocyte subpopulations.