Researchers Spot Surprise Case of Contagious Cancer in Shellfish

Clams on display at a fish marketBEACON TRANSCRIPT – A team of researchers detected an unconventional type of contagious cancer in golden carpet shells, edible clams living off Spain coast. Scientists found that the animals, which had contagious leukemia, might spread the disease through their feces to other species.

Cancers emerge when a cancerous cell starts dividing uncontrollably and compromises the entire immune system. But if the cancer kills its host the cancerous cells die with the host as well.

Yet, in the case of golden carpets, the cancer cells live on after killing their hosts. What’s more they can be transmitted from one species to another, and scientists cannot tell whether a human with a compromised immune system could also contract the disease.

But the strange cancer didn’t start with the tiny clams. Scientists believe that the animals got the disease from the pullet shells. It is the first documented type of cancer than displays a cross-species transmission.

Other cancers are indirectly produced by viruses and parasites such as the HPV virus in cervical cancer and Helicobacter pylori bacteria in stomach cancer. But in those cases, only the pathogens are transmissible, not the cancers.

Until 2015, however, researchers were aware of just two cases of contagious cancer in animals. One was a facial tumor in the Tasmanian devil which is transmitted through bite, and another one was a veneral cancer in dogs transmitted through mating.

In 2015, another case surfaced: some clams off the U.S. east coast were decimated by a rare contagious leukemia. Marine biologists at Columbia University found that although the cancer’s DNA was different from the DNA of clams, the tumors were genetically identical. This signals that the tumors didn’t emerge in a host but they were transmitted from one host to another.

Researchers found similar tumors in different types of shellfish off Vancover and Spain coastal areas. Elizabeth Murchison who was not involved in the study but has been studying the Tasmanian cancer for years noted that scientists have long thought that contagious cancers were just a “bizarre fluke of nature,” affecting only some unfortunate species. But the recent research shows that contagious cancers are fairly common in shellfish.

The research team explained that they learned the contagious leukemia originated from pullet shells when they found that nearly 100 percent of the cancer’s DNA matched that of the marine animals.

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