THE TREMATODE PARASITE Proctoeces maculatus IN Mytilus edulis: DETECTION AND VERIFICATION OF RANGE EXPANSION THROUGH qPCR  

The digenean trematode Proctoeces maculatus is a parasite of numerous molluscs including the blue mussel, Mytilus edulis. Presence of this parasite reduces mussel quality and yield, and may negatively impact mussel aquaculture efforts. The trematodes are predominately found in the mantle tissue of bivalves where they cause partial or complete castration of the host. Historically, the trematode was detected by visual observation. To provide a better diagnostic tool able to detect P. maculatus at any life stage and at low intensities, we designed a species-specific molecular assay. Primers targeting the 18S nuclear ribosomal DNA (rDNA) were used to develop an end-point polymerase chain reaction assay and a quantitative polymerase chain reaction (qPCR) assay. Specificity of the assays was demonstrated using DNA from other digenean trematodes. The qPCR assay was linear from 6.79 x10² to 6.79x10⁷ copies of the cloned target DNA, showing a detection limit of 679 copies. The number of isolated cercariae was linearly correlated to threshold cycle (C_T). Both end-point and quantitative PCR were performed on DNA extracted from samples of mussel tissue for which presence or absence of the parasite had been visually assessed through microscopy. The qPCR assay was more sensitive than either microscopy or end-point PCR. We used our molecular assay to quantify P. maculatus infections in mussels from New York, Massachusetts, New Hampshire and Maine. P. maculatus was present in mussels from Salem, MA and Dover, NH, extending the previously described northern limit of the species