Contagious blood cancer spreads through multiple species of clam: study

Warty venus clams (Venus verrucosa) (Alicia Bruzos and Seila Díaz Costas (CC BY-SA 4.0))

A new study tracked the spread of a contagious blood cancer that raged through various species of clams across the Atlantic Ocean and the Mediterranean Sea.

And the research, published Wednesday in the journal eLife, suggests that human activity may be contributing to the spread of cancer among bivalve shellfish such as clams and mussels.

Cancers that are contagious are rare, but have been identified before in Tasmanian devils, dogs and bivalve species. The tumour cells in a contagious cancer act as parasites that can be transmitted between individuals. In the case of clams getting cancer, the cancer cells can leave the original host and drift in the sea until they infect another susceptible candidate in the bivalve population.

In this study, researchers were attempting to track a type of blood cancer called hemic neoplasia in warty venus clams, a saltwater clam that lives off the Atlantic coast of Europe and also in the Mediterranean Sea.

“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,” Daniel García-Souto, a postdoctoral researcher in genetics at the University of Santiago de Compostela (USC) and a co-first author of the study, said in a press release.

They collected 345 warty venus clams from eight sampling points along the coast of Spain, Portugal, France, Ireland and Croatia, and found clams with cancer in two regions of Spain — one group on the Atlantic coast, and the other more than 1,000 nautical miles away in the Mediterranean Sea.

But when researchers sequenced the cancer, they found DNA from another distinct clam species, showing that the cancer had jumped from one species to the warty venus.

“Our work confirms that contagious cancers can jump between marine clam species,” senior author José Tubío, a researcher in Genomes and Disease at USC, said in the release. “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.”

Through genome-sequencing, they tracked the origin of the cancer to a single clam, which later became infectious and spread the cancer to other clams around it.

The second species of clam, where the blood cancer had originated, was identified as the striped venus clam, which can be found in the same regions as the warty venus. Researchers screened an additional 200 striped venus clams from the regions and found no evidence of continuing cancer, suggesting that after the cancer made the jump to warty venus, it is only active in that species now.

And the research suggests that this isn’t just a marine problem to keep an eye on. It’s something we play a role in as well.

“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,” Alicia Bruzos, co-first author, said in the release. She was a PhD Student at USC at the time the study was carried out, and is now at the Francis Crick Institute in London, UK.

The research was funded largely through Scuba Cancers, an ERC starting grant project.