We report the first results of a parasitological study of Dreissena polymorpha (zebra mussels) from the brackish Curonian Lagoon, SE Baltic Sea. Zebra mussels were collected monthly from May to October 2011 from a site near the mouth of the River Nemunas. Three types of endosymbionts were found in the mantle cavity and visceral mass of the molluscs during dissections, i.e. the commensal ciliate Conchophthirus acuminatus and parasitic ciliate Ophryoglena sp., and rarely encountered, unidentified nematodes. The abundances of C. acuminatus and Ophryoglena sp. were positively associated with host shell length and water temperature, but no effect of water salinity was detected. As the endosymbionts are either highly host-specific to zebra mussels (C. acuminatus and Ophryoglena sp.) or are probably free-living organisms that inadvertently infect the molluscs (nematodes), we conclude that the presence of D. polymorpha in the Curonian Lagoon does not pose any serious parasitological risk to native biota.We emphasize, however, that this conclusion should be treated with caution as it is based on a study conducted only at a single location. Our work extends the currently scarce records of D. polymorpha parasites and commensals from brackish waters, and adds to a better understanding of the ecological impact this highly invasive mollusc causes in the areas it has invaded.
Oceanologia 54(4): 701-713

Municipal wastewater treatment plants play a vital role in reducing the microbial load of sewage before the end-products are discharged to surface waters (final effluent) or local environments (biosolids). This study was to investigate the presence of human-virulent microsporidian spores (Enterocytozoon bieneusi, Encephalitozoon intestinalis, and Encephalitozoon hellem) and enterococci during treatment processes at four Irish municipal secondary wastewater treatment plants (plants A–D). Microsporidian abundance was significantly related to seasonal increase in water temperature. Plant A had the least efficient removal of E. intestinalis spores (32%) in wastewater, with almost 100% removal at other plants both in April and July. Some negative removal efficiencies were obtained for E. bieneusi (at plants C and D, −100%) and for E. hellem (at plants A and D, −90% and −50%). In addition, a positive correlation was found between the levels of enterococci and E. bieneusi in July (r = 0.72, P < 0.05). In terms of the dewatered biosolids, a median concentration as high as 32,000 spores/Kg of E. hellem was observed at plant D in July. Plant C sewage sludge contained the lowest microsporidian loadings (E. bieneusi; 450 spores/L and 1,000 spores/L in April and July, respectively). This study highlights the seasonal variation in concentrations of microsporidian spores in the incoming sewage. Spores in final effluents and dewatered biosolids can be the source of human-virulent microsporidian contamination to the local environment. This emphasizes a considerably high public health risk when sewage-derived biosolids are spread during summer months. This study also suggested enterococci as a potential indicator of the presence of microsporidian spores in wastewater, especially for E. bieneusi.
Parasitology Research (2011) 109(3), 595-603

The paper includes data on species composition of chironomid larvae which were encountered in the mantle cavity of zebra mussels (Dreissena polymorpha) within 7 waterbodies in the Republic of Belarus. All were found to be free-living species commonly present in periphyton and/or benthos. A long-term study of the seasonal dynamics of these larvae in Dreissena did not reveal any typical pattern. Our data suppose that chironomids do not have an obligate association with zebra mussels and possibly enter their mantle cavity inadvertently.
International Review of Hydrobiology (2005) Volume 90, Issue 1: 42–50