system. Animals that have undergone population bottlenecks may be at greater risks of contracting transmissible cancers. Because of their transmission, it was initially thought that these diseases were caused by the transfer of oncoviruses, in the manner of cervical cancer caused by human papillomavirus. However, canine transmissible venereal tumor (CTVT) mutes the expression of the immune response, whereas the Syrian hamster disease spreads due to lack of genetic diversity. Canine transmissible venereal tumor Canine transmissible venereal tumor (CTVT) is sexually transmitted cancer in dogs. It was first described medically by a veterinary practitioner in London in 1810. It was experimentally transplanted between dogs in 1876 by M. A. Novinsky (1841–1914). A single malignant clone of CTVT cells has colonized dogs worldwide, representing the oldest known malignant cell line in continuous propagation, a fact that was uncovered in 2006. Researchers deduced that the CTVT went through 2 million mutations to reach its actual state, and inferred it started to develop in ancient dog species 11 000 years ago. Contagious reticulum cell sarcoma Contagious reticulum cell sarcoma of the Syrian hamster can be transmitted from one Syrian hamster to another through various mechanisms. It has been seen to spread within a laboratory population, presumably through gnawing at tumours and cannibalism. It can also be spread by means of the bite of the mosquito Aedes aegypti. Devil facial tumour disease Devil facial tumour disease (DFTD) is a transmissible parasitic cancer in the Tasmanian devil. Since its discovery in 1996, DFTD has spread and infected 4/5 of all Tasmanian devils and threatens them with extinction. A new DFTD tumor-type cancer was recently uncovered on 5 Tasmanian devils (DFT2), histologically different from DFT1, leading researchers to believe that the Tasmanian devil "is particularly prone to the emergence of transmissible cancers". Bivalves Soft-shell clams, Mya arenaria, have been found to be vulnerable to a transmissible neoplasm of the hemolymphatic system — effectively, leukemia. The cells have infected clam beds hundreds of miles from each other, making this clonally transmissible cancer the only one that does not require contact for transmission. Horizontally transmitted cancers have also been discovered in three other species of marine bivalves: bay mussels (Mytilus trossulus), common cockles (Cerastoderma edule) and golden carpet shell clams (Polititapes aureus). The golden carpet shell clam cancer was found to have been transmitted from another species, the pullet carpet shell (Venerupis corrugata). See also Allotransplantation Anne-Maree Pearse Myxosporea