How a contagious cancer spreads among mussels

A contagious blood cancer jumped from one mussel species to another and spread among mussels living in the Atlantic and Mediterranean, a study published today in eLife.

The results add evidence that cancer can spread among different species of bivalve molluscs and suggest that human activities may inadvertently contribute to the spread of these cancers to new sites and species.

Infectious cancers have been identified in dogs, Tasmanian devils and mussels as clams and clams. These diseases usually spread among individuals of the same species. However, previous studies have documented at least two cases of contagious cancer that spread among bivalve species.

“We set out to confirm whether a leukemia-like blood cancer found in some mussels also infects Venus verrucosa, otherwise known as wart venus mussels, found in the oceans of southern Europe,” said Daniel García-Souto, a postdoctoral fellow in genetics at the University. of Santiago de Compostela-USC, Galicia, Spain, and a co-author of the study with Alicia Bruzos and Seila Diaz at USC.

The researchers collected 345 wart-venus mussels from the coastal areas of Spain, Portugal, France, Ireland and Croatia. They found a type of blood cancer called hemic neoplasia in wart-like venous mussels collected from two different coastal areas in Spain. One group of infected mussels was found along the country’s Atlantic coast, while the other group was found more than 1,000 nautical miles away in the Mediterranean.

The team used a technique called whole-genome sequencing to reveal that the cancer originated in a single mussel, later becoming contagious and spreading among wart-like venus mussels. The cancer contained genetic sequences from both the warty mussel and another unknown mussel species. By comparing the unknown genetic sequence with a genetic database of bivalve species, the researchers were able to identify the mysterious mussel as Chamela gallina or the striped venus mussel.

Further testing of DNA taken from the cell’s mitochondria and cell nuclei in both mussel species confirmed that the cancer had jumped from the striped venus mussel to the warty venus mussels.

“The genetic similarity between the cancer cells found in warty Venus mussels in both the Atlantic and the Mediterranean suggests that human shipping activities may have transported the cancer from one region to another,” said co-author Alicia Bruzos, who was a researcher. Ph.D. Students at USC at the time the study was conducted and are now at the Francis Crick Institute in London, UK. This idea is supported by a previous study in eLife which showed that mussels carried a contagious cancer across the Atlantic by hitting ships.

The team now hopes to conduct further studies to determine the age of the tumors in their mussel samples and to investigate how long cancer may have spread among these species.

“Our work confirms that infectious cancers can jump between marine mussel species,” concludes senior author José Tubío, a researcher in genomes and disease at USC. “As this could pose a potential threat to marine ecology, we need to continue to study and monitor pathogens, including cancers, to help protect these species.”