The really sexy dog STD, though, is something called canine transmissible venereal tumor, a very rare example of what's known as a parasitic cancer. Unlike most other contagious cancers such as cervical cancer in humans, CTVT isn't spread by a virus but (as recently proved) by cancerous cells themselves. Genetic analysis suggests the tumor originated in an individual wolf or domesticated dog, probably in east Asia, between 200 and 2,500 years ago. This long-dead canid's much-mutated cells are still alive and being passed along during coitus (or sometimes through casual contact) centuries later, making it the longest-lived mammalian cell line known. The disease is now found throughout the world, especially where there are large populations of strays. It can be treated with surgery, radiation, and chemo, but most otherwise healthy dogs recover spontaneously after several months.
Luckily for us, there are no known parasitic cancers in humans, and only two additional ones affect animals. One arose spontaneously in a laboratory hamster around 1960: it's a reticulum-cell sarcoma that can be spread by casual contact, cannibalism (hamsters' souls are a lot darker than you might think), and mosquito bites; the tumor grows in the larynx and eventually leads to suffocation. The other is a condition threatening Tasmanian devils with extinction in the wild, called devil facial-tumor disease. First noted in the 90s, it's spread by bites; the tumors grow around the mouth and eventually cause death by starvation.
zombie wolf's cells still killing dogs, hundreds or thousands of years later
Cecil says:
Tags: doomed, mutants, perversions, zombies
4 Responses:
Devil cancer is spread by bites, but it is effectively an STD also. Tasmanian devils bite each other on the face repeatedly when they mate. The cancer kills them faster than their gestation period, so there's some concern that devil cancer will kill every last one of them.
There was a neat Harper's article about it a few months ago, but it's behind a pay wall.
Are there any sci-fi stories featuring a cancer vector like this as an interesting plot point? TSOR just got me more hits on versions of this article.
I did a journal club presentation on it. It had been shown that the Devil transmissible tumor was clonal--all originally came from one devil, and it was being passed from one animal to another as a graft. Effectively it was a tissue transplant. But no one knew why devils weren't rejecting it, the way you'd reject a mis-matched liver. Some thought that their marsupial immune system was just crappy that way. Some thought that the tumor was down-regulating the immune response (that's what the canine version does).
Turns out, it was neither of those things. Due to people hunting Devils nearly to extinction in the early twentieth century (they were believed to harm sheep, and, yum, taste like veal), all remaining devils are closely related immunologically. Their MHC loci have very little variation from one individual to another, meaning they can't recognize the tumor as "other".
You can see what the tumor does to the poor devils.
Man, humans suck
Damn, I took as many courses in oncology as I could, but I'd never heard about either of these or even the concept of a parasitic cancer. Even as a scientist I find this freaky.
Not really my area, but this is absolutely fascinating and, in an odd sort of way, seems to make sense as a niche that hasn't been exploited very heavily.