The sea turtle to the left has fibropapillomatosis, a tumor-forming disease linked to a herpes virus. While these tumors can appear grotesque, not all are malignant. Fibropapillomatosis has been around since the 1980s, but the cause has been unknown. A new paper in PLoS ONE by Van Houtan, Hargrove, and Balazs analyzed clusters of the virus in locations with high nutrient runoff. And here's where the story gets interesting... The authors discovered a relationship between eutrophication (excess nitrogen), an invasive species of algae, sea turtles, and the disease. It goes like this:
The invasive algae stores excess nutrients in a particular amino acid
Turtles eat that algae
The metabolized amino acid promotes the herpes virus infection and, in turn, tumor formation
So it turns out that the root cause of the whole chain of events--leading to the large tumors we're observing in sea turtles--is not the result of one of the usual suspects (i.e. carcinogens such as PCBs or 3-Nitrobenzanthrone). When I spoke to lead author Kyle Van Houtan, he explained, "To me what is really fascinating about the whole argument is how it all begins with simple nitrogen [inputs from runoff] and how that travels through the physical watershed, the ecosystem, and ends up promoting tumors." The paper identifies the amino acid arginine as being involved in this process and, coincidentally, clinical trials for cancer drugs for human liver cancers are specifically targeting and destroying arginine. So as Van Houten points out, "There is perhaps more to this than simply sea turtle tumors. After all, 15-20% of human cancers are viral in origin." In other words, understanding the cause of tumors in sea turtles may help researchers understand why they form in our species too.