Jerusalem carries the highest risk because of its central significance for people from three of the world's great religions - Jews, Christians and Muslims. But visitors to the art treasures of Florence, the Acropolis in Athens or to other holy destinations in India, the Middle East and Europe have also fallen under a spell that affected their mental equilibrium.
Every year, up to 100 visitors to Jerusalem are so overcome by the experience that they don white robes - hotel bed sheets make a convenient substitute - and tour the city chanting psalms. Psychiatrists from the Kfer Shaul mental health centre in the city reported a 50 per cent surge in admissions last month of pilgrims struck by the Jerusalem syndrome after being drawn by the dawn of the new millennium. They predicted the total could double by the end of this year.
It is similar to the Stendhal syndrome, named after the French writer who described feelings of deja vu and disquiet after looking at works of art in Florence. An Italian specialist, Dr Magherini, reported in 1992 on 106 cases of tourists admitted to hospitals in Florence between 1977 and 1986. In many cases a small detail in a painting or sculpture evoked an outburst of anxiety reaching psychotic dimensions.
One of the first accounts of the syndrome was given by Sigmund Freud in his 1936 essay "A disturbance of memory on the Acropolis". He experienced a sense of unreality and detachment that left him seriously shaken as he toured the monument.
Writing in the January issue of the British Journal of Psychiatry, Dr Yair Bar-El and colleagues from the Kfer Shaul mental health centre say nearly all the ordinary tourists who developed Jerusalem syndrome came from ultra- religious Protestant families. Its cause is thought to be a combination of the disorientation caused by travel, the clash of cultures and a strong religious belief.
They write: "It may be that [the victims] were unable to reconcile the idealistic subconscious image of Jerusalem as a holy place with the war- torn city it is in reality."
One sufferer, a Swiss lawyer on a group tour of Greece, Israel and Egypt, became anxious and agitated on his first night in Jerusalem. He split away from the group, became obsessed with taking baths to purify himself, used hotel bed linen to form a toga-like garment and toured the city, giving improvised sermons. After seven days the episode passed, he rejoined the group and enjoyed the rest of his holiday in good health.