Perkinsus Sp Research Articles

Preliminary results of a field study on some stress-related parameters in Tapes philippinarum naturally infected by the protozoan Perkinsus sp.

The aim of the present work was to investigate the possible use of the clam Tapes philippinarum—a filter-feeding bivalve living on soft bottoms—in the monitoring of sediment pollution in the Lagoon of Venice (North-East Italy). To this end, two clam populations, exposed to different environmental conditions (a relative clean site and an industrial polluted area), have been monitored for the prevalence of the protozoan parasite Perkinsus sp. as well as for several biological parameters commonly used as determinants of contaminants exposure. First results showed a low prevalence, higher in the clean site, but a very diffuse distribution of the parasite throughout the two populations. Nevertheless, greater digestive cells height and longer lysosomal latency time were observed in clams from the clean area. As for the physiological stress-related parameters, even if clearance rates were always higher in these clams, scope for growth values indicated a more complicated biological response.

Cellular defence mechanism of the clam Tapes semidecussatus against infection by the protozoan Perkinsus sp.

The cellular defence mechanism of the clam Tapes semidecussatus (Mollusca, Bivalvia) against infection by the parasite protozoan Perkinsus sp. (Apicomplexa, Perkinsea) was studied in the gill filaments. The parasites, localized in the connective tissue, induced a cellular reaction involving infiltrated granulocytes. These showed a secretory aspect, with the cytoplasm being filled by membrane-bound granules with internal membranes. The holocrine secretion, which was proteic and slightly glycosylated, by the granulocytes gave rise to the encapsulation of the parasites. After incubation with lectins from Canavalia ensiformis, Triticum vulgaris, Helix pomatia, Glycine max, Arachis hypogaea, Ricinus communis (agglutinin), Ulex europeus I and Limax flavus, a lack of specific and/or main sugars was observed in the plasma membrane of parasite and granulocyte, and in the wall of the former. Furthermore, GalNacα1,3GalNac and β-d-gal residues were only detected in association with the internal membranes and dense regions of both granules and capsule, respectively. Blood granulocytes were observed at the periphery of the cellular reaction, close to blood vessels, and these appeared to re-differentiate to give the granulocytes of the cellular reaction. The data reported here suggest that this parasite induces the infiltration and re-differentiation of specialized cells in the host mollusc. In addition, a polarized secretion of a specific defence product is described for the first time.

Cellular defence mechanism of the clam Tapes semidecussatus against infection by the protozoan Perkinsus sp.

Cellular defence mechanism of the clam Tapes semidecussatus against infection by the protozoan Perkinsus sp.