Scientists unearth new instance of ‘contagious cancer’ in animals, Pg II

Key Highlights:

• Scientists have identified a fourth instance of naturally occurring contagious cancer in animals, specifically melanoma in brown bullhead catfish.
• The discovery was made by researchers from the University of Vermont, studying catfish in Lake Memphremagog, straddling the U.S.-Canada border.
• Approximately 30% of catfish collected from the lake since 2013 were found to be afflicted with this transmissible cancer.
• Genetic analysis of the cancer cells revealed they originated from a distantly related fish and have been spreading between individuals, behaving like a parasite.
• This is the first documented case of transmissible cancer in a freshwater fish species.

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Detailed Insights:

• Cancers typically arise from an individual's own cells and are not contagious, unlike infectious diseases.
• The melanoma in catfish is an aggressive cancer originating from melanocytes, skin cells responsible for pigment.
• Researchers initially suspected a virus or environmental contaminant due to the high prevalence of black lesions on the fish.
• Whole-genome sequencing showed that the tumor cells in different fish were genetically identical to each other but distinct from the host fish's normal cells.
• The cancer cells' mitochondrial DNA showed significantly more changes than normal cells, indicating an external origin.
• Reproduction, particularly during spawning when fish interact closely, is a likely mechanism for the cancer's transmission.
• This finding offers insights into how a host's immune system might not reject foreign cells, potentially aiding research into organ transplantation.
• Previous instances of transmissible cancers include Canine Transmissible Venereal Tumour (CTVT) in dogs, Devil Facial Tumour Disease (DFTD) in Tasmanian devils, and Bivalve Transmissible Neoplasia (BTN) in molluscs.
• DFTD has severely impacted Tasmanian devil populations, causing significant declines.
• BTN can spread through seawater and has even been observed to jump between different mollusc species.

Scientific/Technical Concepts Involved:

• Melanoma: A type of cancer that originates in melanocytes, the cells that produce melanin, which gives skin its color.
• Mitochondrial DNA (mtDNA): Genetic material found in mitochondria, distinct from nuclear DNA, used to trace maternal lineage and cellular origin.
• Whole-genome sequencing: A laboratory process that determines the complete DNA sequence of an organism's genome at a single time.
• Transmissible cancer: A rare type of cancer where living cancer cells themselves spread between individuals, acting like an infectious agent.