Study published in eLife says contagious cancer in mussels originated in Canada has spread to other mussel species in South America and Europe. The cancer cells collected in Europe and America is almost identical genetically. This spread initially baffled the scientists as the ocean currents might have stopped the cancer from spreading. But now researchers believe that human intervention might be the cause. The mussels and other shellfish that cling to the side of the ship and hitch a ride to new habitats must have caused the cancer to spread.
Cancers usually occur due to cell mutation and it is not contagious. However, it has been found to be contagious in Tasmanian devils, dogs and bivalves. In these cancer has been like a pathogen or parasite. So scientists concluded that the infectious cancer in bivalves spread across oceans due to human intervention.