Canine transmissible venereal tumor
| Canine transmissible venereal tumor | |
|---|---|
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| CTVT cells stained and viewed under an optical microscope. | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Mammalia |
| Order: | Carnivora |
| Family: | Canidae |
| Genus: | Canis |
| Species: | C. lupus |
| Subspecies: | Incertae sedis |
| Binomial name | |
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Canis lupus |
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Canine transmissible venereal tumors (CTVTs), also called transmissible venereal tumors (TVTs), canine transmissible venereal sarcoma (CTVS), sticker tumors and infectious sarcoma is a histiocytic tumor of the external genitalia of the dog and other canines, and is transmitted from animal to animal during mating. It is one of only four known transmissible cancers; another is devil facial tumor disease, a cancer which occurs in Tasmanian devils.
The tumor cells are themselves the infectious agents, and the tumors that form are not genetically related to the host dog. Although the genome of a CTVT is derived from a canid (probably a dog, wolf or coyote), it is now essentially living as a unicellular, asexually reproducing (but sexually transmitted) pathogen. Sequence analysis of the genome suggests it diverged from canids over 6,000 years ago; possibly much earlier. The most recent estimates of its time of origin place date it to about 11,000 years ago. However, the most recent common ancestor of extant tumors is more recent: it probably originated 200 to 2,500 years ago.
Canine TVTs were initially described by Russian veterinarian M.A. Novinsky (1841–1914) in 1876, when he demonstrated that the tumor could be transplanted from one dog to another by infecting them with tumor cells.
Canine transmissible venereal tumors are histiocytic tumors that may be transmitted among dogs through coitus, licking, biting and sniffing tumor affected areas. The concept that the tumor is naturally transmissible as an allograft came from three important observations. First, CTVTs can only be experimentally induced by transplanting living tumor cells, and not by killed cells or cell filtrates. Second, the tumor karyotype is aneuploid but has characteristic marker chromosomes in all tumors collected in different geographic regions. Third, a long interspersed nuclear element (LINE-1) insertion near c-myc has been found in all tumors examined so far and can be used as a diagnostic marker to confirm that a tumor is a CTVT.
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