THREE years ago, while visiting Tehran, I was introduced to a charmless man named Muhammad Ali Samadi, who, I was told, would parse for me the Iranian theocracy's peculiar understanding of Judaism and Zionism. Mr. Samadi said that Iran's supreme leader, Ayatollah Ali Khamenei, held no brief for anti-Semitism. Then, a moment later, he deployed an epidemiological metaphor to explain the role of Jews in history. "There are always infections and diseases in man," he said. "In the world there is an infection called international Jewry."...

...the Islamic Republic of Iran, though no Semitic utopia, has not been Poland, either. Even today, the febrile ranting about Jews one hears among the intelligentsia in Beirut and Cairo is mostly absent in Tehran, except among the clerical elite, who understand the utility of anti-Semitism in their effort to gain favor with Arab Muslims.

Which is not to say that the clerics don't believe what they say. This brings us back to Mr. Samadi's unfortunate metaphor. The terminology of disease control has now thoroughly infiltrated anti-Semitic discourse in the Middle East. Four years ago, a Hezbollah leader in Lebanon's Bekaa Valley named Hussein Haj Hassan told me that Jews function "in a way that lets them act as parasites in the nations that give them shelter." The leaders of Hamas and Islamic Jihad speak in much the same manner.

One worries about overreacting, but such language echoes the passage of "Mein Kampf" in which the Austrian Haman compares the Jew to "a sponger who like a noxious bacillus keeps spreading as soon as a favorable medium invites him."

I still assume that the Jews, and the Jewish state, will survive their encounter with the Iran of Mr. Ahmadinejad and Ayatollah Khamenei. Iran's leaders don't yet have the bomb, and eschatologically minded though they are, they might not be entirely immune to the charms of rational deterrence theory. And, of course, both parable and history teach that Jews somehow always manage to survive.

Nevertheless, a great many people, in Iran and beyond, believe that the Jewish state is a cancer, and it is foolish to believe that this is an idea without consequences. As one Islamic Jihad leader told me not long ago, "Everyone knows that the cure for cancer is radiation."