Scientists have discovered that an aggressive form of blood cancer transferred from one species of clam to another in the Atlantic Ocean and the Mediterranean Sea.

The study adds to evidence that cancers can spread among different species of bivalve clam and imply that human activities may be unintentionally contributing to the development of these cancers to new sites and species.

Cancers that are contagious have been found in dogs, Tasmanian devils, and bivalves such as clams and mussels. These illnesses are typically transmitted among members of the same species. However, earlier research has found at least two incidences of infectious malignancies spreading among bivalve species.

“We set out to confirm whether a leukemia-like blood cancer found in some bivalves also infects Venus verrucosa, otherwise known as warty venus clams that are found in the seas of southern Europe,” says Daniel García-Souto, postdoctoral researcher in genetics, University of Santiago de Compostela – USC, Galicia, Spain.

The team examined 345 warty venus clams from the coasts of Spain, Portugal, France, Ireland, and Croatia. In warty venus clams gathered from two separate coastal districts of Spain, they discovered a kind of blood cancer called hemic neoplasia. One group of infected clams was spotted along the country’s Atlantic coast, while the other was identified in the Mediterranean Sea almost 1,000 nautical miles away.

Using a technique called whole-genome sequencing, they found that cancer started in a single clam, got contagious, and spread across warty venus clams. The malignancy was found to have genetic sequences from both the warty venus clam and an unidentified clam species. The researchers were able to identify the mystery clam as Chamelea gallina, or the striped venus clam, by matching the unknown DNA sequence to a genomic database of bivalve species.

Further examination of DNA extracted from the mitochondria and nucleus of both clam species indicated that the cancer had spread from the striped venus clam to the warty venus clam.

“The genetic similarity of the cancer cells found in warty venus clams in both the Atlantic Ocean and Mediterranean Sea suggests that human shipping activities may have transported the cancer from one region to another,” adds co-first author Alicia Bruzos.

This hypothesis is reinforced by a previous study published in eLife, which demonstrated that mussels transported infectious cancer across the Atlantic on ships.

The researchers now plan to do additional research to assess the age of the tumors in their clam specimens and discover how long cancer has been spreading among these species.

“Our work confirms that contagious cancers can jump between marine clam species,” says senior author José Tubío, Researcher in Genomes and Disease at USC. “As this may pose a potential threat to marine ecology, we need to keep studying and monitoring pathogens including cancers to help protect these species.”

Source: doi.org/10.7554/eLife.66946

Image Credit: Getty

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