KIEV -- The illness that disfigured the face of opposition presidential candidate Viktor Yushchenko resulted from poisoning by the toxic substance dioxin, which might have been placed deliberately in his food, Austrian doctors who treated him told reporters in Vienna yesterday.
''The criminal investigation does not fit within our purview, but . . . there is suspicion of third-party involvement," said Michael Zimpfer, director of the private Rudolfinerhaus clinic in Vienna, where the candidate went for treatment in September after falling ill while campaigning.
The face of the once youthful-looking Yushchenko, 50, was mysteriously transformed into a blotch of lesions after he reached Austria. He also suffered severe abdominal and back pain, as well as paralysis on the left side of his face. His appearance has continued to worsen, raising public concern about his health despite his claims that he is fully recovering.
Yushchenko contends that he was poisoned in an assassination attempt by ''government officials" who feared that he would defeat Prime Minister Viktor Yanukovych in runoff elections held Nov. 21. His opponents have dismissed the charge, saying he got sick after gorging himself on bad sushi and alcohol.
Yanukovych was officially declared the winner of the Nov. 21 vote. The country's Supreme Court soon overturned that finding, citing widespread fraud, and a new election will be held Dec. 26.
The Austrian doctors, addressing reporters in Vienna yesterday, said Yushchenko's long-term prognosis was good, although it could take several years for his face to heal. For now, Yushchenko is ''fully capable of working," said Nikolai Korpan, another doctor.
''If this dose had been higher, it may have caused death," Zimpfer said, noting the dioxin could have been administered through food, such as soup.
Dioxins are a group of organic compounds that contain chlorine. They are a common byproduct in the manufacture of industrial chemicals, and are also a common contaminant from waste incineration. They are a component of the Vietnam-era defoliant Agent Orange, and many researchers have labeled them a cause of cancer and other diseases among people who were exposed to the defoliant.
Debate over dioxins' potency as a poison, as opposed to a cancer-causing agent, has swirled for decades. But the compounds are known to cause reproductive and developmental problems, in addition to extreme skin eruptions known as chloracne.
Olaf Paepke, a scientist who investigated the dioxin poisoning of two textile employees in Vienna in 1997, said dioxins are not commercially available, but can be obtained through industry contacts or made in a laboratory by people with the proper skills.
Arnold Schecter, a dioxin specialist at the University of Texas School of Public Health at Southwestern Medical Center in Dallas, said dioxins can be highly effective poison in people who are sensitive to their effects. If Yushchenko was deliberately given dioxin, it was done by ''someone was very clever and very knowledgeable," Schecter said.
''If someone put a drop of pure dioxin in his food, he wouldn't taste it, he wouldn't see it, and a few days later he'd start to get sick," Schecter said.
''If you are trying to kill someone quickly, it's not the way to go," he said. ''But if you want to disable someone and want to do it subtly and have it happen days or weeks or months after you have contact with someone, this can do it."
Paul M. Wax, with the American College of Toxicology, said two scientists he met in Volgograd, Russia, in 1992, told him that during the Soviet era they had investigated the potential of developing dioxin as a chemical weapon.
Wax expressed doubts that dioxin could be used in that way. ''It was never on anyone's list," said Wax, who now teaches courses on chemical terrorism. ''We don't think about it as an acute poison that can kill you."
A Russian government specialist challenged the Vienna doctors' findings. ''It is impossible to get a dose of dioxin today and get poisoning tomorrow," said Yury Ostapenko, head of the Toxicology Information Center at the Russian Health Ministry, speaking on the Echo Moskvy radio station. ''Dioxins do not belong to immediate-effect poisons: Poisoning develops for years and decades."
Doctors at the Austrian clinic had declined for weeks to issue a finding on the cause of the illness, but said yesterday that tests done in an Amsterdam hospital had confirmed the presence of dioxin.
Speaking to 5,000 supporters in the city of Luhansk before the announcement in Vienna, Yanukovych said of Yushchenko: ''He certainly is ill and I sympathize. Let him get well soon. As for the reasons, I know nothing. Let the specialists work on that."
Yushchenko supporters said the finding bore out what they had long believed. ''This official confirmation is another opportunity to speak the truth to the Ukrainian people and to show one more time the dirty methods that were used by the authorities," said Yuri Yekhanurov, a member of parliament, in a telephone interview.
In Vienna, Yushchenko struck an upbeat note yesterday. ''I plan to live for a long time and I plan to live happily," he said. ''I am getting better . . . every day."