The catch of the day is deadly.
Cancer is not normally thought of as a disease that jumps from individual to individual. Though contagious cancers have been observed in two species of mammals — the facial tumors of Tasmanian devils and sexually transmitted venereal tumors in dogs — these were considered rare exceptions.
Last year, Stephen Goff from Columbia University Medical Center discovered a third example of transmissible cancer, similar to leukemia, in soft shell clams living off the Atlantic coast.
A new study published in the journal Nature reports that contagious cancers are invading shellfish populations. Carried by sea water, these malignant cells are being transmitted among members of the same species and, even more surprisingly, from one species to another.
Goff and his colleagues examined the DNA of tumor cells from mussels, cockles, and carpet shell clams collected from the coasts of Canada and Spain.
Normally, cancer cells have the same DNA as their host, and both the cells and the host eventually die together. However, the researchers found a mismatch between the DNA of the shellfish tumor cells that of their host. They determined that it was the same line of cancerous cells that was spreading like a virus and infecting numerous shellfish.
Further, the infectious cancer cells found in the carpet shell clam were traced back to a completely different species. The researchers concluded that this cancer was due to a highly unusual case of cross-species transmission.
It is believed that the malignant cells get expelled from shellfish when they defecate or die. The cancers can live in the water for a few hours until they are accidentally consumed by another mussel, cockle, or clam.
"Now that we have observed the spread of cancer among several marine species, our future research will investigate the mutations that are responsible for these cancer cell transmissions," Goff said in a press release.