By Gary Marx | Chicago Tribune foreign correspondent

Rebutting reports he is suffering from Parkinson’s disease, Cuban President Fidel Castro told the nation in a televised speech ending early Friday that he is feeling “better than ever.”

Dressed in his trademark combat fatigues, a seemingly fit Castro stood at a wooden lectern for close to six hours and joked about an American intelligence assessment that he may be suffering from Parkinson’s and could deteriorate in coming years.

“They have tried to kill me off so many times,” Castro said.

But diplomats and experts say that only Castro’s inner circle—including a team of top-flight physicians—know whether the 79-year-old Cuban leader has Parkinson’s or any other chronic ailment or is merely showing signs of aging.

“We were always trying to figure that out,” Vicki Huddleston, the top U.S. diplomat in Cuba from 1999 to 2002, said in a recent interview. “It’s all speculation. We really don’t know.”

Like most aspects of his personal life, Castro’s health is a closely guarded secret.

Reports of Castro’s failing health have surfaced over the years and ranged from strokes to heart and kidney failure to cancer.

A former U.S. official said American intelligence experts have been unable to penetrate Castro’s inner circle and thus are left to study his public movements to gain insight into his health and longevity.

Are Castro’s speeches coherent or does he lose his train of thought? Does Castro disappear from public view for long periods of time and how does he look when he re-emerges? Are his speeches shorter and less frequent?

But intelligence experts also look at factors such as how long Castro’s parents lived—his father died at about age 80—and whether the Cuban leader has maintained a healthy lifestyle.

One key event occurred in 2001, when Castro fainted while giving a speech on a blazing hot day. U.S. intelligence tried to determine whether it was heat and dehydration or some underlying illness that produced the fainting spell. The former U.S. official believes the oppressive heat and sun were the most likely causes.

In recent years Castro has slurred his words and he moves more slowly. He no longer walks long distances during government-organized rallies.

Last year Castro fell on a step and fractured his knee and right arm while leaving a speech.

“Based on his public behavior I think there is a good chance that he has Parkinson’s and that he has had it for five or six years,” said Brian Latell, a former CIA analyst and author of the book “After Fidel.”

But other experts say Castro shows tremendous endurance for a man his age and thrives on being in the spotlight. The Cuban leader gave up cigar smoking more than a decade ago.

During his latest speech, Castro held his arm outstretched and joked about not trembling—one of the symptoms most associated with Parkinson’s.

“He has a strong constitution and a strong will and he is very determined to outlive all his old enemies,” Huddleston said. “He’s doing pretty well.”

I tend to agree. This whole Parkinson claim seems to be a very clever marketing ploy to hawk a book. I wonder if the CIA is getting royalties or commisions from the sales of this book.