Rare Cancer Spreading In Fish Raises Concern Among Scientists

Cancer is usually regarded as a disease that develops within the body of a human or animal after its own cells begin to grow uncontrollably. However, scientists have now identified a rare form of cancer that behaves very differently. Instead of remaining confined to one organism, the cancer cells appear to spread from one fish to another. The discovery, published in the journal Nature, was made in brown bullhead catfish living in Lake Memphremagog, a freshwater lake that spans the US state of Vermont and the Canadian province of Quebec. Researchers say this is the first known case of a naturally transmissible cancer in fish and the first to be documented in a freshwater ecosystem.

How Is This Cancer Different From Ordinary Cancer?

In most cases, cancer develops when genetic mutations cause a person's or animal's own cells to multiply uncontrollably. These cancer cells may spread to different organs within the same body, but they do not normally pass to another individual. The newly discovered disease is different. Scientists found that living cancer cells can move from one fish to another, where they continue growing in the new host. This makes the disease behave more like a contagious parasite than a conventional cancer. To confirm their findings, researchers compared the DNA of tumours with healthy tissue from affected catfish. The tumour samples from different fish were found to be genetically almost identical, while clearly differing from the healthy cells of the fish carrying them. This strongly suggests that the tumours originated from the same cancer cell line rather than developing independently in each fish. Previously, naturally transmissible cancers have only been identified in a handful of species, including dogs, Tasmanian devils and certain marine shellfish.

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How Might The Cancer Spread Between Fish?

Scientists have not yet determined the exact route by which the disease spreads, but they have proposed several possibilities. One theory is linked to the breeding season, when brown bullhead catfish gather in large numbers and come into close physical contact. Such interactions could allow cancer cells to pass directly from one fish to another. Another possibility involves the surrounding water. Because fish are constantly exposed through their skin, gills and mouths, researchers believe free-floating cancer cells could potentially enter another fish's body. Brown bullheads also live close to the lake bed and lack protective scales, raising the possibility that cancer cells may survive temporarily in the sediment before infecting other fish. At present, these remain scientific hypotheses, and further research is needed to identify the exact mode of transmission.

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Can This Cancer Spread To Humans?

The discovery has naturally raised questions about whether this unusual cancer poses any threat to people. Based on current evidence, scientists say there is no indication that it can spread to humans. The research focused solely on brown bullhead catfish, and there is no evidence of human transmission. Experts point out that the human immune system is highly effective at recognising and destroying foreign cells, which is one of the reasons organ transplant recipients require immune-suppressing medication to prevent rejection. Researchers believe the discovery offers valuable insights into how cancers evolve and survive in nature. They hope further studies will help explain why transmissible cancers are so rare and what they can reveal about disease evolution, wildlife health and ecosystem dynamics.

[Disclaimer: The information provided in the article is intended for general informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always seek the advice of your physician or other qualified healthcare provider with any questions you may have regarding a medical condition.]