Soviet-era test may have caused smallpox cases

The smallpox virus as seen through a microsope.

WASHINGTON (CNN) -- A Soviet biological weapons test in 1971 may have infected 10 people with the smallpox virus and killed three of them, according to a report presented Saturday at the Institute of Medicine where experts are collaborating on whether and when to vaccinate against smallpox.

The report, summarized by Dr. Alan Zelicoff of Sandia National Laboratories, said a woman aboard a research ship carrying 11 other people in the Aral Sea in July 1971 apparently was infected by aerosolized smallpox carried by winds from the test site, located on an island miles away from the ship.

The official, Soviet-era report said the woman was infected with smallpox when she disembarked at ports of call stopped along the way. But Zelicoff said the woman told him recently that she never left the ship because women were forbidden to do so. If so, Zelicoff said, she must have been infected while aboard the ship.

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"On or about July 30, right when you predict that patient was exposed, they were south of Vozrozhdeniye Island, the mysterious island in the center of the Aral Sea that we now know was the center of biological weapons activity in the old Soviet Union," Zelicoff said.

But Dr. D.A. Henderson, who led the World Health Organization's smallpox eradication program during the 1960s and 1970s, said the woman may have contracted the disease from a natural outbreak. A smallpox epidemic was sweeping through nearby Afghanistan at the time, he said.

"What's puzzling to me is that they attribute this to an aerosol going downwind something like 15 kilometers [9 miles]," he said. During the summer, "when the virus does not hold up very well, in a hot climate, I doubt if it would last more than two to three hours in an aerosol.

"For it to have made 15 kilometers and hit that boat, and only hit the one person out of the 12, I find it taxes my imagination to put all this together and assume this was an aerosol accident."

But Zelicoff responded that the wind blows from the north in that region toward the ports of call, all of which were south of the island.

In addition, he said, the winds could easily have carried the virus the nine miles at night, when temperatures are cooler, in just an hour.

Zelicoff said he has not tracked down a second woman on the boat who also was infected. He said the women may have been at disproportionate risk for the disease, since they were expected to spend more time on deck working than were the men.

When the ship returned to the port city of Aralsk, the woman likely transmitted the virus to her brother, who survived, Zelicoff said.

In all, 10 people were infected and three died, all of the hemorrhagic form of smallpox, Zelicoff said. This form typically accounted for just 1 percent to 3 percent of smallpox cases. Whether the infectious agent had been engineered to be more virulent is a subject of disagreement.

Henderson said autopsies indicated only one of the three fatal cases was the hemorrhagic form of smallpox.

"This would be quite understandable and quite within the range of expectation of an outbreak of 10 cases," he said.

Smallpox was declared eradicated from the wild in 1980. The only two stores of virus known to exist are at the Centers for Disease Control in Atlanta and in a government laboratory in Russia.

None of the three fatalities had been inoculated against smallpox. The seven survivors had been.

Experts contend that, in the disease's natural state, the greatest transmission risk to an individual would be by face-to-face contact with someone who is infected. But if it were determined that releasing aerosolized smallpox into the wind could infect people miles away who had been vaccinated, that would raise new public health challenges.