Mapped: Hotspots for rare contagious cancer in mussels that can spread between individuals and species

Scientists suspect human intervention responsible for introducing these cancers into new susceptible populations and species

Seaports are hotspots for the global spread of a rare contagious cancer type affecting mussels and transmitted like parasites between individuals of the species, a new study finds.

Most often, cancer arises from mutations in DNA leading to uncontrolled cell growth in organisms and does not usually spread from one organism to another.

However, researchers have found rare infectious cancer types in some animals, including facial tumours in Tasmanian devils, some cancer in dogs, as well as leukemia-like infections in bivalve species such as mussels, clams, and cockles.

These infectious cancers may spread to more new species and pose a potential threat to ecology, scientists say.

While these cancer types usually spread between individuals of the same species, previous studies have also documented a few cases of these infections spreading among the bivalves.

Scientists suspected that human intervention may be responsible for introducing these cancers into new susceptible populations and species.

One such contagious cancer type called MtrBTN2 is known to affect mussels, especially among those living in the same sea bed, ports, and maritime transport.

Shipping traffic was thought to be the most likely explanation for the global distribution of this cancer.

Now, after studying 76 mussel populations along the coast of southern Brittany and the Vendée, researchers have found a much greater incidence of the contagious cancer in ports.

“Our results showed that ports had a higher prevalence of MtrBTN2, with a hotspot observed at a shuttle landing dock,” scientists wrote.

They suspect biofouling, whereby mussels attach themselves to ship hulls, could be behind the greater spread of the disease in seaports.

Researchers say ports may also be providing favourable conditions for the transmission of MtrBTN2, “such as high mussel density, confined sheltered shores, or buffered temperatures”.

“Our results suggest ports may serve as epidemiological hubs, with maritime routes providing artificial gateways for MtrBTN2 propagation,” they added.

The findings highlight the need for better policies to mitigate biofouling to stem the spread of the disease and preserve coastal ecosystems.