Observations of a Protistan Disease Similar to QPX inMercenaria mercenaria(Hard Clams) from the Coast of Massachusetts

Combined effects of a parasite, QPX, and the harmful-alga, Prorocentrum minimum on northern quahogs, Mercenaria mercenaria

“…One hypothesis explaining the decrease in the size of hemocytes could be that new, smaller hemocytes were produced in response to the increasing movement of hemocytes into tissues infected with QPX, as observed by the high increase of hemocytic infiltration surrounding the parasites. QPX has been shown to induce hemocytic infiltrations in tissues (Smolowitz and Leavitt, 1997;Smolowitz et al, 1998;Dove et al, 2004;Ragone Calvo et al, 2007), which were indeed much more intense in P. minimum-exposed quahogs infected with QPX, than in the un-infected clams. Moreover, the presence of QPX is often associated with phagocytic hemocytes (Ragone Calvo et al, 1998;Smolowitz et al, 1998).…”

“…Tissue from each clam was evaluated and scored for presence and intensity of QPX parasite infections, the amount of associated hemocytic infiltration, and the amount of mucus production by the QPX organisms, visible as small, clear halos around QPX cells, indicating the presence of mucus before tissue processing (Smolowitz et al, 1998). The presence and intensity of QPX was scored according to Cheville (1983) as focal (localized area within a tissue or an organ), multifocal (several foci within a tissue or an organ), focally extensive (extension of the focus to involve a considerably-larger area within a tissue or an organ), and diffuse (distributed throughout all tissues examined).…”

“…Two clams (of 7) showed QPX infections accompanied by hemocytic infiltration within the gills and connective tissues around the digestive tubules. Such infections in the connective tissues surrounding the digestive tubules and in sinusoids of the gills, in addition to the mantle, usually indicate an overall more-extensive infection of the clam, as compared to infection in the mantle alone (Smolowitz et al, 1998).…”

“…Northern quahogs, Mercenaria mercenaria (L.), from a portion of the east coast of North America (Virginia to Prince Edward Island) have demonstrated variable infection with the protozoan parasite, Quahog Parasite Unknown, QPX, Labyrintohomorpha, Thraustrochytriales (Smolowitz and Leavitt, 1997), in some locations resulting in variable and sometimes high mortalities (Smolowitz et al, 1998;Ford, 2001;Ford et al, 2002;Dahl et al, 2008). Pathogenesis of this disease begins with appearance of parasite cells in mantle and gill tissues, which induces hemocyte migration into the area of infection to isolate and destroy the QPX cells (Smolowitz et al, 1998).…”

“…Pathogenesis of this disease begins with appearance of parasite cells in mantle and gill tissues, which induces hemocyte migration into the area of infection to isolate and destroy the QPX cells (Smolowitz et al, 1998). Progression of the disease may include large, focal lesions or multifocal, granulomatous, inflammatory responses induced by the parasites, which increase with the severity of infection (Smolowitz et al, 1998).…”