Sooner or later, the word "leper" comes into any conversation here about AIDS.

Maybe it comes from a patient who describes how it feels to be shunned by former friends, and even nurses. Maybe it comes in a story about a man with AIDS who was hounded out of a gay bar the night they held a fund-raiser for his very disease.

Or maybe it comes in tales told by a healthy homosexual about a bus driver who wouldn't touch his transfer, or the straight friend who suddenly felt uncomfortable sharing dinner, or the couple who refused to be served by a gay waiter. But at some point, the word recurs: "I felt like a leper." "They're treating us like lepers."

To Dr. Mervyn Silverman, the public health director of San Francisco, there's a special irony in the leper analogy because, "You know, leprosy isn't very contagious. When you go back to ancient times and think of the person with all the terrible sorts of things that come with Hansen's disease (leprosy) you can understand the paranoia. But even when it was discovered that leprosy wasn't easily spread, you couldn't convince most people."

Nor is AIDS very contagious. The weight of medical evidence suggests that Acquired Immune Deficiency Syndrome is transmitted through blood and semen and not through casual contact. The high-risk groups are homosexuals and bisexuals, drug users, hemophiliacs.

Not a single one of the hundreds of health professionals who care for, clean and feed AIDS patients has come down with the disease. Yet a gay man goes to work in San Francisco with nothing more than a cold and his colleagues make uncomfortable jokes. A man with AIDS shows up for jury duty here and the others jurors refuse to serve with him.

For Dr. Silverman, dealing with the second epidemic, the epidemic of fear in the straight community, is frustrating. "With all the talking I've done in interviews with the media," he says, "it seems that the paranoia grows rather than recedes."

Where does the fear come from? Uncertainty mixed with fatality and spiced with mistrust.

Both the cause and cure of AIDS are still unknown. "When you have a disease for which we in the medical profession don't have all the answers, then people naturally say, 'Wait a minute, if you don't know what the bug is, how do you know that I can't catch it casually?,'" says Silverman, "We are saying things like, 'Well, up to now it seems like, and it looks like, and it appears like. . . .' The public isn't used to hearing that."

Public health officials can plot how a disease is transmitted even when they don't know where it comes from or how to make it go away. But that isn't easy to explain in a 30-second television newscast. The anxious public is all too used to hearing the government protest the safety of dioxin or Agent Orange or Three Mile Island.

But there is something else that makes AIDS a particularly volatile disease. As a San Francisco writer tells me, "The fact that it's gay people who have the disease tossed gasoline on the fire."

The notion of a fatal disease spreading sexually through the homosexual community is rife with meaning among those who believe that homosexuals are "sick." The idea that it is catching, that it could spread to the straight world, is explosive politically and psychologically.

There are some diseases that carry enormous symbolic weight in our culture, far beyond their medical danger. This is one of them. We forget that the influenza pandemic of 1918-19 killed more people than four years of fighting in World War I. But we remember syphilis, the Black Death, TB. We will remember AIDS.

In her book, "Illness as Metaphor," Susan Sontag noted that "Illnesses have always been used as metaphors to enliven charges that a society was corrupt or unjust." Before AIDS even existed, she wrote prophetically: "Any disease that is treated as a mystery and acutely enough feared will be felt to be morally, if not literally, contagious."

The cure for paranoia is ultimately in finding a cure for AIDS. But in the meantime, a customer sitting in a gay bar watches to see if I order a drink in a bottle or a glass. In the meantime, Dr. Mervyn Silverman goes out to do another television spot saying that you can't get AIDS from a bus ticket or a handshake. In the meantime, a man with AIDS wonders whether he is society's new leper.

Copyright (c) 1983, The Boston Globe Newspaper Company.