For more than a year the world has been on the lookout for any sign of avian flu spreading from birds to humans. The H5N1 virus has not yet mutated into a form easily transmissible from bird-to-man and thence from man-to-man, but because the devastation from a replay of an epidemic along the lines of 1918 would be so great, the vigilance and preparation has been high and sustained.

And this is a very, very wise course. One that should be emulated when it comes to the often equally deadly virus that transmits the most radical form of Islamist jihadism --the sort that triggers suicidal violence against everyone, including fellow Muslims, but most especially against America and Israel, their allies, and Jews everywhere.

It would be very useful if the world began to think of anti-Semitic rage as a virus that has sometimes consumed large parts of the globe and other times been suppressed to the point of invisibility. We have entered a period where the virus is replicating at an extraordinary rate, and where transmission is easy, and the appearance of the violent derangement that anti-Semitic Islamist extremism produces is both sudden and deadly.

In the years since 9/11, I count five discreet, possible instances of this virus suddenly appearing in the U.S., each of which resulted in death:

* The July 4, 2002 attack on the El Al counter at Los Angeles International airport;

* The October 1 University of Oklahoma suicide bombing outside of a crowded football game.

* The March 4, 2006 attack on the UNC campus

* The July 28, 2006 attack on Seattle's Jewish Community Center; and

* The August 29, 2006 attacks on pedestrians in San Francisco.

None of these five incidents is the sort of terrorist attack that we are most concerned about --the meticulously planned, coordinated attempt to cause spectacular devastation and casualties in the hundreds if not thousands. The London airlines bombing plot, like the London Tube attack, the Madrid rail attack, Bali resort bombing, and the Beslan school massacre are examples of this sort of terrorist atatck, and they rightly receive the bulk of Homeland Security's attention and analysis.

But isolated, single terrorist attacks are of great concern, and not just because of their real victims, but because of what they tell us about the spread of the hatred, and its potential to spread farther and faster than we ever dreamed.

It seems possible that we are close to a tipping point where so much anti-Semitic propaganda has been pumped into the world via new technologies and emboldened regimes and charismatic fanatics like Osama, Nasrallah and Ahmadinejad that the madness we would hope was confined to caves in Afghanistan and poor madrassas of Pakistan has in fact traveled far and at a furious pace, deep into France, now deep into London, and now we have to worry, deep into the United States.

It does not have to spread widely in American Muslim circles to provoke terrible violence by a few. There is no evidence of anything like the scale of Islamist hatred that consumes parts of France appearing in the U.S., but neither is it impossible that it will arrive here. What the five examples above underscore is that a segment of the Muslim population is susceptible to the deranging effects of anti-Western screeds from radical imams. That segment might be limited to the already deranged --the driver/killer in San Francisco and the shooter/killer in Seattle are both said to suffer from mental instability.

But the point is the segment exists, and individuals within it have killed. Continued...