Thursday, June 07, 2007

Because you just don't have enough to worry about...

Coturnix tirelessly performs a service I would enjoy doing but I would have to retire to gain enough free time for it: he scans a ton of science news and highlights stuff that has both readability and consequences or interest for the average reader. Yesterday he pointed to a deadly cancer outbreak among Tasmanian devils.

Why be concerned? Clearly some infectious agent is involved, though pollutants have yet to be ruled out. But germs that cause cancer are well known. Take human papiloma virus [HPV] for instance, which can cause genital warts and cervical cancer. If we aren't worried enough to protect our children from HPV, why fret about some obscure and far away creatures better known for the cartoon character they inspired? Today, Amanda Marcotte takes apart the excuses used by one of the surprise enablers of that Texas-sized defeat of a common sense solution to the HPV epidemic.

I'll tell you why you should care about this. It can be boiled down to two numbers, one that indicates the efficiency with which a disease can be communicated from one individual to another and one that indicates how many infected individuals will die. I used "transmissibilty" in googling around for the links in this post but other keywords might do as well. I looked around for comparable diseases and found none, so a HIGHLY TRANSMISSIBLE cancer is a thing for us to worry about.

If you lay a guy who is carrying HPV, your chances are 4/10 of getting the disease (an average, YMMV) . That is a higher transmissivity than HIV or herpes [read section 7.1 ].

Rous Sarcoma Virus has been an animal cancer model studied since the 60s' ...I stopped having nightmares about it getting away from the laboratories by the 70's:-{ It requires injection of filtered cultures to transmit but can jump between species more easily than many viruses.

Reticuloendotheliosis virus would be a nastier disease but it does not spread as easily and antibodies develop quickly.

Another virus that causes a kind of cancer are the leukemia viruses, forms of which affect cats and cows. And the bovine form produces antibodies in humans. About half the humans tested have been exposed...meaning we got over it [100% survival rate] before we had any symptoms.

Retroviruses are quick to set up shop in their hosts. Speculating on a class of retroviruses that do affect humans, the mouse mammary tumor virus is closely related to the human mammary tumor virus which may be inherited as a genomic hitchhiker rather than an infection, and may provide diagnostic insight into the majority of breast cancer cases.

Facing the possibilty of extinction of the island's most important predator species, as well as its mascot and tourist attraction, Australian government offices and scientist have mounted a multifaceted attack on the disease and an effort to sequester uninfected populations in safe places should re-population be the only solution after a die-off. Concern, and stories on the web have increased since 2003. Oddly, the most informative article I found was not on ABC, NPR or National Geographic but a sarcastic "doomsday" site that actually gets the science , current, readable and balanced. At ZKEA, Christopher Minson reports positively the infectious agent is a retrovirus. Here is another article on the epidemic written by a person who placed poorly in his ESL class and messed up the epidemiology but adds some interesting facts about how the disease spreads. The Minson article is the one to read if you are only reading one and don't require a bibliography because it spells out the likely consequences [80% population decline] and when the outbreak began [mid 90s]. In particular, that article shows just how grim survival rates and transmission rates for cancer, a disease we don't even think of as contagious, can be.
"This epidemic is also interesting due to the fact that cancer is a basic symptom. Retroviruses that cause cancers are not unknown; in recent years a number of cancer-causing viruses have been identified. However, a sudden epidemic of such cancer-causing viruses has never before been witnessed in any species. ... Homo sapiens is subject to the same natural ecological laws as Tasmanian Devils."

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