A severe outbreak of a rare contagious cancer has been identified in soft-shell clams in Washington state's Puget Sound. Researchers found evidence that the disease was recently introduced to the Pacific Northwest from Atlantic Coast populations, crossing the continent or an ocean.
The finding marks a significant spread of the transmissible cancer, which is unusual because cancers are typically not contagious. In clams, however, a type of leukemia-like disease can spread through seawater, with cancer cells moving between individuals.
The team traced the outbreak's genetic signature to Atlantic Coast strains, suggesting a long-distance jump. The mechanism of transport remains unclear, but ballast water from ships or the movement of infected shellfish are possible vectors.
This outbreak could have serious implications for clam populations and the shellfish industry in the region. Soft-shell clams are both ecologically important and commercially harvested along the Pacific coast.
Scientists stress the need for further surveillance to prevent additional introductions and to understand how these cancers evolve and spread across marine environments.