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Diseases of Aquatic Organisms

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DAO 70:115-122 (2006)  -  doi:10.3354/dao070115

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

R. J. Gast1,*, E. Cushman2, D. M. Moran1, K. R. Uhlinger3, D. Leavitt4, R. Smolowitz3

1MS #32, Biology Department, Woods Hole Oceanographic Institution, Woods Hole, Massachusetts 02543, USA
2Biology Department, Palm Beach Atlantic University, West Palm Beach, Florida 33409, USA
3Laboratory for Aquatic Animal Medicine and Pathology, Marine Biological Laboratory, Woods Hole, Massachusetts 02543, USA
4Center for Economic and Environmental Development, Roger Williams University, Bristol, Rhode Island 02809, USA

ABSTRACT: 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.

KEY WORDS: Quahog Parasite Unknown · Detection limit · Seed clams · SSU rDNA

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