Laboratory Transmission Studies of QPX Disease in the Northern Quahog (=hard Clam): Development of an Infection Procedure

Environmental distribution and persistence of Quahog Parasite Unknown (QPX)

“…QPX epizootics have decimated clam-growing areas, resulting in cessation of local aquaculture development in some regions. In other locales, following detection of QPX disease in selected clam beds, shellfish growers voluntarily destroyed potentially infected seed clams, worth hundreds of thousands of dollars in marketable clams, in an attempt to minimize the impact of the disease.Recent studies of the parasite have reported on the development of molecular methods to detect its presence (Ragone Calvo et al 2001, Stokes et al 2002, Lyons et al 2005a, Gast et al 2006, the mechanisms of transmission (Smolowitz et al 2001, Ford et al 2002, Dahl & Allam 2007, the general lack of genetic variation between isolates (Qian et al 2007) and the potential for macroalgae to support growth of the parasite (Lyons et al 2005b, Bugge & Allam 2007. Currently, there are also studies in progress to elucidate aspects of the parasite physiology, pathogenicity and disease development in clams.…”

Differential immune response in the hard clam (mercenaria mercenaria) against bacteria and the protistan pathogen QPX (quahog parasite unknown)

“…QPX challenged FL clams (FL-q) and their respective controls (FL-c) were not sampled at 16 h since QPX infection in the hard clam is chronic and response to QPX between clam broodstocks were likely similar after 16 h [25]. Similarly, NY-b clams were not sampled at the last sampling time (4 weeks) as clam response to bacterial challenge is usually more acute [33].…”

“…We have been successfully using these aquacultured clam lines for comparative studies because of their confirmed differential susceptibility to QPX infections in laboratory settings [23,26] and in the field [30]. A sub-sample (30 clams/stock) was checked for pre-established QPX infections before the initiation of the experiment using standard histopathology techniques [25] and all tested clams were negative. Experimental clams were acclimated for one week in the laboratory, held in 150-L tanks with recirculating water (28e30 ppt) at 21 AE 1 C and fed daily with commercial algae (DT's Live Phytoplankton, Sycamore, IL).…”

“…Water quality, temperature (21 C) and salinity (30 ppt) were controlled weekly and clams were fed daily with commercial algae (DT's Live Phytoplankton, Sycamore, IL). FL and NY clams were challenged with either bacteria (1 Â 10 7 cfu in 100 ml) or QPX (1 Â 10 5 cells in 100 ml) injected into the pericardial cavity according to Dahl and Allam [25]. Control clams were injected with 100 ml of FASW.…”

“…This geographic distribution is likely responsible for variations in clam susceptibility toward QPX among different clam stocks with lower resistance of southern (Florida and South Carolina) clam broodstocks, which are not exposed to selective mortality due to parasite pressure, as compared to northern (New Jersey, New York, Massachusetts) broodstocks growing and reproducing in enzootic areas [19,23,24]. The biological bases for the resistance process to QPX in Northern hard clams are not known although the outcome has been described as a granulomatous inflammatory response and encapsulation of parasite cells ultimately leading to the healing of infected individuals [18,20,25]. Our previous studies demonstrated the presence of factors inhibiting QPX growth in clam plasma [26].…”