As part of my degree I chose to write an essay on devil facial tumour disease (a transmissible cancer in the Tasmanian devil). While writing this it occurred to me that transmissible cancers do not really fit into the 5 major classes of pathogens (viruses, bacteria, fungi, protozoa and Helminths).
It does appear somebody had the same thought and wrote a paper about it (see below). I was wondering is there is any reason that this isn’t widely considered (or at least not widely taught) to be the case?
Article A Sixth Modality of Infectious Disease: Contagious Cancer fr...
Well... if you go specifically by the defination of a pathogen, it is a microorganism of some sort. A cancer cell isn't.
The main reason is that these transmissible cancers were rather recently discovered, so people were not writing about them years ago, before they were discovered and studied. There is a transmissible canine cancer in domestic dogs that has been studied recently too.
Article Clonal Origin and Evolution of a Transmissible Cancer
Shen-An Hwang Thank you for your response! Surely though not all parasites (e.g. tapeworms) are microorganisms and they would still fall under the classification Helminths? Also, couldn't you argue that it is ambiguous whether or not cancer cells are microorganisms?
Brian Thomas Foley Thanks for your thoughts! I actually cited that paper in my essay. I believe there are also similar transmissible cancers in soft shelled clams and hamsters.
Perhaps this is a naive question but since CTCV was first characterised in the 1800s wouldn’t this be long enough to adjust the categories accordingly? Equally I think DFTD was characterised sometime in the 90s?
You are correct, I tend to forget about the parasites...
To me, cancer cells themselves are mutated cells of the host, whereas pathogens are a different species from the host. Can they actually "infect" hosts that is not of its own species? Also... won't metastasis be a case of transmissible cancers but in the same host?
Anyway... my two cents... It's an interesting topic. Which reminds me of the whole debate about prions... pathogenic proteins...
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