Researchers from the University of Vermont and collaborating scientists discovered a likely transmissible cancer in wild brown bullhead catfish this month.
The finding is significant because most cancers do not spread between individuals. Instead, these cancer cells behave like parasites, moving from one fish to another to survive and proliferate.
The study focused on fish in Lake Memphremagog, a body of water that straddles the border between Vermont and Quebec. Researchers identified distinctive black skin lesions on the catfish, which have been observed for over 10 years [1]. Some reports suggest these lesions may have been present for many decades or even centuries.
To determine the nature of the disease, the team performed genetic analysis on the tumors. The results showed that tumors found on different fish were nearly identical [2]. This high level of genetic similarity indicates that the cancer did not evolve independently in each fish but originated from a single source and spread through the population [2].
This discovery adds to a small number of known contagious cancers in the animal kingdom. While the current findings are limited to Lake Memphremagog [3], other reports on contagious flesh-eating cancers in animals have cited death tolls as high as 38,000 [4].
The research team utilized field samples and genetic sequencing to track the movement of the cells. By comparing the DNA of the tumor cells across multiple individuals, the scientists confirmed the transmissible nature of the malignancy [2].
“Cancer cells are passing between individuals like parasites.”
The identification of a transmissible cancer in bullhead catfish provides a rare opportunity to study how malignant cells can evolve to survive outside a host's original immune system. Because these cells act as parasites, they offer insights into the evolution of contagion and the mechanisms that allow certain cancers to bypass the biological barriers of new hosts.
