Several clues, including discovery in Iraq of equipment labeled "smallpox," indicate the deadly virus could be part of Saddam Hussein's biological weapons arsenal, although the Bush administration has offered no public evidence to prove it.
Some biological weapons experts say the indications have convinced them that Iraq has stocks of smallpox, which was declared eradicated from the planet more than two decades ago. All samples of the virus, except those held by special labs in Atlanta and Moscow, were supposed to have been destroyed, but experts fear that some of the Russian smallpox may have been spirited away.
"I have no doubt in my mind that Iraq does have the smallpox virus," said Dr. Ken Alibek, a top official in the former Soviet Union's biological weapons program before defecting to the United States in 1992.
The official U.S. position, shared by other experts, is that it's unclear whether Iraq has the smallpox virus or, if it does, has the delivery technology to use it as a weapon. Still, worries about a possible terror attack with the virus have prompted the Bush administration to order enough smallpox vaccine to inoculate the entire U.S. population if necessary.
"We're very worried about Iraq," said Dr. D.A. Henderson, a smallpox expert and bioterrorism adviser to the Department of Health and Human Services. "Why is Saddam Hussein pushing ahead with weapons of mass destruction if at some point he is not going to use them? It's certainly got to be a factor in all of this."
Unlike anthrax, the bacteria used in last year's unsolved mail attacks, the highly contagious smallpox virus can be passed from person to person. The virus causes ugly pustules to form both on the skin and inside the mouth and throat. About a third of unvaccinated people who get the disease would die.
"As bad as anthrax is, it's not as bad as smallpox, which could run into the thousands to tens of thousands to hundreds of thousands (of deaths) in some imaginable scenarios," said Robert Gallucci, former deputy director of the U.N. weapons inspection program, now dean of Georgetown University's School of Foreign Service.
The last U.S. case of smallpox occurred in Texas in 1949, and routine vaccinations ended in America 30 years ago. That means at least two out of five Americans have not been vaccinated, and studies suggest the vaccine's protection probably fades over time.
An exercise in 2000 that simulated smallpox attacks on Philadelphia, Atlanta and Oklahoma City projected that after two months, a million people could be dead and an additional 2 million infected.
That simulation assumed that the United States had only about 12.5 million doses of smallpox vaccine rather than enough to treat the entire population. Other simulations indicated that vaccinations and other measures could contain a smallpox attack to a few hundred or a few thousand victims.
U.N. weapons inspectors and U.S. intelligence agencies have found several clues suggesting Iraq might have the smallpox vaccine.
In 1994, U.N. inspectors at an Iraqi medical complex found a freeze-dryer labeled "smallpox" in Arabic, said former inspector Jonathan Tucker.
The Iraqis claimed the equipment was used to make smallpox vaccine, Tucker said. A freeze-dryer could be used to make a weaponized form of the smallpox virus.
"It's not conclusive proof but suggestive of Iraqi interest," said Tucker, author of a recent book on smallpox.
Iraq also admitted to U.N. inspectors that its biological weapons scientists worked with camelpox, a close relative of the smallpox virus that doesn't usually infect people. Working with camelpox would give Iraq a way to perfect techniques for making smallpox weapons without endangering the researchers.
"The only explanation is they used it to see how to grow smallpox, how to concentrate it, how to deploy it. It's a perfectly good and safe model for this," said Alibek, now director of the George Mason University Center for Biodefense in Manassas, Va.
"It's hard to believe Saddam would do this work to protect his camels."
Tests on Iraqi soldiers captured during the 1991 Persian Gulf War found that some had been vaccinated for smallpox, according to a declassified Defense Intelligence Agency report. That could be evidence that Iraq was trying to protect some of its soldiers in the event it used a smallpox weapon, although the United States was vaccinating its soldiers for smallpox at the time, as well.
Another DIA report says a source of undetermined reliability reported that Soviet scientists gave Iraq smallpox samples in the 1980s. A third DIA report says a captured Iraqi soldier described seeing smallpox victims during the Iran-Iraq war that ended in 1988.
Those reports have not been publicly corroborated, however. Tucker said the reports' credibility is doubtful.
Iraq's last reported outbreak of smallpox came in 1972, the same year Iraq started biological weapons research. A World Health Organization report estimated that about 800 people were infected in that outbreak, which had spread from Iran and later spread to Syria and Yugoslavia.
"It's highly possible Iraq retained stocks of the smallpox virus (from that outbreak) into the '80s and '90s and beyond," said Elisa Harris, a biological weapons expert on the National Security Council under President Clinton.
U.N. inspectors also found Iraq had a huge number of chicken eggs, which could be used to grow smallpox or other viruses, said Harris, now with the Center for International and Security Studies at the University of Maryland.
"There's no clear-cut evidence available publicly that I'm aware of that proves the Iraqis have the virus," Harris said. "We just simply don't know. But there is a circumstantial case to be made."