Disseminated neoplasia or Hemocytic Neoplasia (HN) is a transmissible cancer observed in marine bivalves across the temperate and tropical oceans worldwide. It has been identified in populations of hard-shelled clams (Mercenaria mercenaria) along the eastern United States, in both farmed and wild hard clams. This disease is harmless to humans but appears to spread readily through the water column resulting in substantial mortality in some populations of cultured clams. Developing a rapid, less expensive, and more sensitive diagnostic test to detect HN offers an invaluable tool for the aquaculture and research community, as the traditional method of using histology is often slower and less sensitive.
A molecular test was created using reverse transcriptase quantitative polymerase chain reaction (RT-qPCR), to evaluate the gene expression associated with the presence of neoplastic cells in the clam’s hemolymph (a clam’s blood-like fluid). The expression ratio of target genes within neoplastic cells, derived from hemolymph RNA, was observed to be logarithmically upregulated with an increase histologically derived neoplasia severity. The expression ratio of these target genes was observed to be logarithmically upregulated with an increase in neoplasia severity, which was correlated with histological findings. Moreover, the RT-qPCR assay was found to be more sensitive than histology, with some individuals marked negative by histology being deemed positive by RT-qPCR. This non-lethal method (Fig. 1) offers a faster turnaround than histology, which allows shellfish farmers to more proactively manage their populations when an outbreak occurs. The methodology used here may also be helpful to others researching molecular disease diagnosis and could become an additional tool for more comprehensive bivalve disease monitoring in the region.