Highly Contagious Blood Cancer Detected in Clams Threaten Marine Ecology

For humans, cancers are mostly hereditary and not contagious. However, the case may be different for clam species.

A very rare finding confirms that contagious blood cancer has spread among clam species in the Atlantic Ocean and the Mediterranean Sea, and human activity may have unintentionally contributed to the spread.

(Photo : Photo by Buddhika Weerasinghe/Getty Images)
HIMEJI, JAPAN - MAY 03: A basket of clams seen at Shinmaiko Beach on May 3, 2014 in Himeji, Japan. Clam digging is one of the popular leisure activities during the Golden Week, the holiday season from April 29 to May 6.

New research published in eLife reveals the "rare instance" of cancer contagion between clam species in the seas of Southern Europe. According to the study, such cases of leukaemia-like transmissible cancers have been observed in individuals from different species such as dogs and clams.

Researchers even suspect that a certain type of contagious cancer is also among the "greatest current threats" to Tasmanian devils.

"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," study co-first author Daniel García-Souto, of the University of Santiago de Compostela (USC), Spain, said in the news release.

The type of transmissible cancers known as hemic neoplasias (HN) has been observed among clams in two regions in Spain.

A threat to the marine environment

Researchers tracked down the origin of the cancer and came up with an interesting finding. Among the 345 warty venus clams from coastal areas in Spain, Portugal, France, Croatia and Ireland, they were able to narrow down the search to two regions in Spain.

To their surprise, these two populations were actually 1,000 nautical miles away from each other, which suggests that human activity may have been involved, such as the shipping "from one region to another".

The genomes of the tumors from both populations showed that the cancer cells originally developed in a species known as striped venus clams, and then jumped to warty venus clam.

"These findings confirm that contagious cancers can jump between clam species, which could be threat to the marine environment," the researchers wrote. "The fact that the cancer was so similar in clams from the Atlantic coast and from the Mediterranean Sea, however, suggests that it may have emerged very recently, or that human activity helped it to spread from one place to another."

Further analysis revealed that the cancer only affects warty venus clams.

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Preventing spread through human intervention

Study co-first author Alicia Bruzos, of the Francis Crick Institute in London said that it was possible that shipping activities have helped the cancer move from one place to another. According to the team, "if human activity is indeed a factor in the spread of the cancers, then it would also be possible to prevent its further spread through human intervention."

"Our work confirms that contagious cancers can jump between marine clam species," study senior author José Tubío, of USC, said in the news 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."

Although there are still many unanswered questions about contagious cancers in bivalves, experts show broad interest in the clear findings and well-supported conclusion of the study.

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