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After the recent death of Venezuelan strongman Hugo Chavez, predictable accusations of CIA involvement, suggesting that somehow secret agents "infected" Chavez with colon cancer, made the headlines in Latin America. While it is in fact possible to "give" someone cancer, it's not easy.
Cancer Is a Highly Individual Disease, At Least in Humans
Many health conditions, such as heart disease or cirrhosis of the liver, come about when internal organs become delapidated. They run down, they aren't able to repair themselves, and they cease to function. These conditions never spread from person to person.
Some diseases are the result of infection, or more precisely, the body's inflammatory reaction to infection. These conditions spread from person to person in a population in predictable ways. Take away the infectious microorganism, and no one gets the disease.
Cancers are in a class all of their own. Cancers result from the overactivity of cells and tissues, rather than their atrophy. Cancers are traceable to triggering events, such as an infection or a toxin, but the process that leads to cancer is regulated by genes that have to be switched on, or switched off, as the cell becomes cancerous and eventually multiplies, and cancerous tissues eventually replace healthy tissues and spread to other parts of the body.
An Artificially Contagious Cancer
In human beings, as far as medical science knows, cancer is never contagious. There are at least three kinds of contagious cancer, however, in the animal kingdom.
In the late 1950's, researchers at the National Cancer Institute in Bethesda, Maryland, created a kind of contagious cancer in Syrian hamsters. They harvested cells from a naturally occurring kind of cancer known as a sarcoma from one hamster and injected the cells into other hamsters. When the innoculated hamster developed its own sarcoma, the researchers then harvested more cancer cells into a third hamster, and repeated the process.
After a dozen transfers of cancer cells by injection from hamster to hamster, the researchers found that hamsters could transfer the cancer to each other without injection. Biting, scratching, smearing, and dribbling the cells also "infected" previously non-cancerous hamsters with sarcoma. The researchers put 10 hamsters in the same cage to see how many would come down with cancer from a single individual, and 9 hamsters did, the tenth hamster eaten by its cage mates.