PubMed Health⌕ Search

Biomedical subjects

D Leavitt

Publications and source records attributed to D Leavitt.

4 recordsLinked to original sources
PubMed2006

DGGE-based detection method for Quahog Parasite Unknown (QPX).

Quahog Parasite Unknown (QPX) is a significant cause of hard clam Mercenaria mercenaria mortality along the northeast coast of the United States. It infects both wild and cultured clams, often annually in plots that are heavily farmed. Subclinically infected clams can be identified by histological examination of the mantle tissue, but there is currently no method available to monitor the presence of QPX in the environment. Here, we report on a polymerase chain reaction (PCR)-based method that will facilitate the detection of QPX in natural samples and seed clams. With our method, between 10 and 100 QPX cells can be detected in 1 l of water, 1 g of sediment and 100 mg of clam tissue. Denaturing gradient gel electrophoresis (DGGE) is used to establish whether the PCR products are the same as those in the control QPX culture. We used the method to screen 100 seed clams of 15 mm, and found that 10 to 12% of the clams were positive for the presence of the QPX organism. This method represents a reliable and sensitive procedure for screening both environmental samples and potentially contaminated small clams.

Animals↗
PubMed2000

Optimization of primary jaw settings for stereotactic radiosurgery/radiotherapy.

The primary goal of stereotactic radiosurgery/radiotherapy is to provide a technique by which the dose to a target volume can be maximized while minimizing the dose to uninvolved structures. Initially, circular apertures were applied through the use of multiple arcs and one or more isocenters in an effort to achieve these goals. Advances in field-shaping techniques, such as more elaborate cerrobend shaping and micromultileaf collimators, have allowed for improved target conformality with further reductions in dose to normal tissues. The shape of these secondary collimation devices is usually set at the precise size and shape necessary to encompass only the volume of interest with a small margin. Often, however, the primary collimators are set at a default setting that may be much larger than required to encompass the treatment area. This results in unnecessary transmission through the secondary collimators and added dose to the uninvolved tissues. This paper compares the dose delivered to normal tissues surrounding the target volume when a "standard" collimator setting is used to dose delivered when the primary collimator setting is optimized to only that necessary to encompass the treatment volume.

Humans↗
PubMed1998

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

During the summer and fall of 1995, in clam aquaculture leases at two locations on the coast of Massachusetts, significant mortalities were observed to occur primarily in 1½- to 2-year old hard clams (Mercenaria mercenaria, quahog) planted in the leases. Examination of hard clams from those leases suggested a parasite similar to QPX (Quahog Parasite Unknown), as described by Whyte, S. K., Cawthorn, R. J., and McGladdery, S. E. (1994, Can. Dis. Ag. Org. 19, 129-136), was responsible for the poor condition of affected clams and the resulting high mortality. In clam tissues, the QPX-like parasite formed thalli surrounded by a mucofilamentous net. Larger thalli underwent endosporulation producing sporangia that contained approximately 40 endospores. Rupture of the sporangium released the endospores into the surrounding tissue. Inflammatory response by the clam to infection was chronic, active, and granulomatous. The occurrence both of phagocytic multinucleated giant inflammatory cells and inflammatory encapsulation of parasites were commonly identified as part of the response. Moderately to severely infected clams showed significantly reduced growth and a poorer condition index as compared to uninfected or mildly infected clams. Copyright 1998 Academic Press. Copyright 1998 Academic Press

Journal Article↗