Hugo Chavez, the polarizing leader of Venezuela, died last week after a long bout with cancer, respiratory infections, and other medical problems. He had not spoken publicly since December, and was re-elected in absentia while in Cuba receiving medical treatment. Chavez’s death sparked rumors that he might have been the victim of an assassination plot by the United States.

These were not recent speculations; Chavez himself raised the question in 2011. According to a CNN story, “Venezuelan President Hugo Chavez wondered Wednesday if the United States could be infecting the region’s leaders with the illness … Chavez prefaced his remarks at a military event in Caracas by saying, ‘I don’t want to make any reckless accusations,’ but the Venezuelan president said he was concerned by something he finds ‘very, very, very strange.’ ‘Would it be strange if (the United States) had developed a technology to induce cancer, and for no one to know it?’ he asked.”

For their part, State Department spokesman Patrick Ventrell issued a statement that “Any assertion that the United States was somehow involved in causing President Chavez’s illness is absurd, and we definitively reject it.”

NEWS: Chavez To Be Embalmed: How Does That Work?

Still, government denials of sinister, clandestine assassination plots are to be expected, and did little to discourage conspiracy theorists.

As with many conspiracy theories, there are a few grains of truth that lend such stories plausibility. In his accusation Chavez pointed out that the American government performed unethical medical experiments on Guatemalan prisoners in the 1940s. Despite President Obama’s condemnation of those experiments – and apology to the Guatemalan president — such historical injustices resonate with many Latin Americans and fuel anti-American sentiment.

It is also true that the American government has tried to assassinate and poison leaders of foreign countries — most notoriously Cuba’s Fidel Castro. Given Chavez’s close relationship with Castro  – they were longtime friends and Chavez received his cancer treatments in Havana — it’s likely that the two swapped war stories of assassination attempts, both real and imagined.

There’s also some evidence that governments have used poison to target enemies of the state. In 2006, former KGB agent Alexander Litvinenko became sick and died from being poisoned by a dose of radioactive polonium-210, and before his death accused Russian president Vladimir Putin of the assassination.

NEWS: Venezuelan President Hugo Chavez Has Died

In November 2012, the body of former Palestinian leader Yasser Arafat was exhumed eight years after his death at age 74 from an illness because his wife suspects his disease was brought about by polonium poisoning, presumably at the behest of the Israeli government. Tests are ongoing, and the results will likely be released later this year.

Questionable Carcinogens

Part of the reason that cancer lends itself to conspiracies is that its etiology, or origin, is unclear. Cancer is actually not one specific disease but the name for a broad group of related diseases, which have different causes. There are countless carcinogens in our environment, from natural fungus to asbestos to sunlight. Because of this, positively linking a specific cancer to a specific incident or toxin can be difficult or impossible.

For example, there is overwhelming evidence that smoking cigarettes causes lung cancer, yet many smokers never get lung cancer, and many non-smokers die from the disease. Even with decades of research, the causes of many diseases are not absolutely certain, and any given individual’s chance of getting a disease is influenced by dozens, or even hundreds, of different factors ranging from genetics to diet to lifestyle — and a lot of random-chance, good, old-fashioned luck.

It is true, as Chavez noted, that leaders of several South American countries have battled cancer in recent years, including Argentina, Paraguay and Brazil. The fact that several of these presidents, unlike Chavez, are friendly to the United States — and that leaders of 10 other countries on the continent are cancer-free — suggests that the accusation is more informed by paranoia than reason. Given how pervasive cancer is, a cluster among this group would not be extraordinary.

Still, we are talking about a fiery, demagogic leader who once claimed during a 2006 speech at the United Nations that he could still smell the stench of Satanic sulfur left over from when George W. Bush had been in the room a day earlier. Whether or not Chavez truly believed that his cancer had been caused by the United States, he knew it made good rhetoric.

Photo: Joaquin Hernadez/Corbis