Leprosy has always been a difficult disease to study because the bacteria that causes it can be grown only in the spleens and livers of armadillos, not in a test tube.

Researchers think they have gotten around that problem by putting all 5,000 genes of the leprosy bacteria into common laboratory bacteria that can be easily grown in a test tube.

"We can't grow the bug, but we can now grow its genes," says Dr. Barry R. Bloom, one of several authors of a recent report in the British science journal Nature and chairman of microbiology and immunology at Albert Einstein College of Medicine in New York. "This really opens the possiblities. If there are effective antigens, there's no reason why we couldn't make an unlimited supply for very little cost."

These 5,000 genes direct the production of the proteins that make up the leprosy bacteria. Five of the 5,000 proteins appear to be potent antigens that can stimulate the body's natural defense system to destroy the infection.

These five proteins could be used as a vaccine to protect uninfected individuals and even to stimulate the immune system of infected patients to fight the leprosy.

The vaccine could be used to prevent outbreaks in Third World nations with a high incidence of the disease, such as India, Uganda, Kenya, Burkina Faso (formerly Upper Volta) and Congo, and famine countries such as Somalia and Ethiopia. Leprosy currently afflicts 12 to 15 million people worldwide.

"Since there is no evidence that outside of man there is any reservoir of this disease, we could, as we did with smallpox, wipe this from the face of the earth," Bloom says. The research, which was done by scientists from the Massachusetts Institute of Technology, Pacific Medical Center in Seattle, Washington University in St. Louis, and Stanford University School of Medicine in Stanford, Calif. The technique they used may enable experts to treat other major parasitic diseases that resemble leprosy, such as schistomiasis and leishmaniasis.

Bloom, also chairman of the World Health Organization's Committee on the Immunology of Leprosy, predicts it may take another 10 years before research is complete and a vaccine has been approved by the Food and Drug Administration. "But that's not bad considering how many years scientists have been at this," he says.

Leprosy, now often called Hansen's disease, has ravaged millions of people since biblical days and thwarted scientists' efforts since the bacteria was first identified 112 years ago.

Although most cases of leprosy occur in Third World countries, 6,000 cases are known in the United States, mostly among immigrants from the Caribbean, Mexico and Southeast Asia.

Because of improved diagnostic capablities and more effective treatments, disfigurements have declined. Most people cannot recognize those who have leprosy. But prevention and cure of the disease remain unknown. Currently, it is treated with antibiotics such as rifanpicin, dapsone, clofazimine.

When 12-year-old Emmanuel Faria was told he had leprosy, he did not know what it meant. All he knew was that he had stuck a pen into his leg during school recess, and that to his and everyone else's amazement, he felt no pain.

Since being diagnosed, Faria, now 72, has been hospitalized ever since, except for seven years in the 1930s. He has learned to cope with the loss of sensation in his fingers and toes. He knows the ulcers that develop if he wears shoes too tight, and the burns that he receives from not realizing if a cup of coffee is too hot to hold. Since Faria cannot feel, he has learned to protect his body, which won't protect itself.

"It becomes a way of life -- you're not conscious of any other way," says Faria, a member of American Leprosy's board of directors. He now is being cared for at the National Hansen's Disease Center, and he speaks about leprosy without bitterness. "I knew people were quite scared and prejudiced against the disease. I never put myself into a position where I'd be embarrassed -- I didn't visit places unless I knew I'd be welcome."

Experts estimate that only about half of those who have the disease publicly admit it. Some guard the secret from employers; others do not tell their spouses or families.

"If you ask people which disease they would rather not have, leprosy ranks at the top," says Dr. John Trautman, director of the U.S. Public Health Service's National Hansen's Disease Center in Louisiana. "The life led by a patient in the U.S. is considerably better than years ago, but there is still a stigma or fear attached to this disease.

The stigma of leprosy is one of its most difficult burdens. "For some patients, this is a pyscho-social affliction as well as a physical affliction," says Dr. Robert Hastings, chief of laboratory research at National Hansen's Disease Center. "The big problem is not the bacteria but the nerve damage and the social stigma."

Even if outsiders cannot detect the symptoms, patients may feel branded by this disease, which affects the skin and nervous system. In some forms of leprosy, hands become useless and unable to grasp; fingers curl into a claw. Although this claw-like hand easily passes for one afflicted by arthritis, some patients become anxiety-ridden about what they believe is a tell-tale sign.

In an effort to lessen the stigma the name Hansen's disease (after Armur Hansen, who first identified the bacteria in 1873), has gained popularity.

Leprosy is caused by a slow-growing kind of bacteria that lives within the body's cells. First it infects specialized cells called macrophages, specifically those located in the skin. From the macrophages, the bacteria can spread to nerve cells and to bone marrow. As the disease progresses, it causes numbness and tingling sensations. In late stages of the disease, the immune system itself is suppressed and cannot fight any kind of disease.

Left untreated, the disease can progress to cause sharp pain, sterility, skin rash and gradual destruction of extremities.

"Deformity is a function of the duration of the disease," says Bloom. The discovery of five antigenic proteins may allow scientists to make a diagnostic test to detect and begin treating leprosy early than is now possible. "We'll soon be picking up people much earlier and patients' won't get the nerve damage and deformity."

About 35 percent of all leprosy victims worldwide become deformed.

Treating the disease is a slow process. It can take 13 years to arrest the most severe form of the disease, according to Hastings. Treatment does not necessarily alleviate pain, and there are sometimes unpleasant side effects. The World Health Organization currently recommends a medication called Lamprene, which can change the color of skin to brown, blue or gray.

"You are really keeping patients in check -- you're not curing them," says Dr. William R. Levis, director of New York City's Region II Hansen's Disease Program. "It requires a lifetime of treatment. If you stop the antibiotics, the recurrence rate is so high it doesn't warrant stopping."

Nor is the disease on the decline. "Even with 30 years of experience with drug treatment, the bottom line is that no statistics indicate a decrease in the number of new cases," says Levis, whose clinic will probably see about 70 of the expected 400 new cases in the United States this year.

Much is still unknown about leprosy, including how the disease is transmitted. Scientists suspect it might be from skin-to-skin contact, or from bacteria in the upper respiratory tract released by coughing and sneezing. In either case, prolonged, close contact seems to be necessary.

In the next few years, scientists will try to turn the ability to grow the leprosy genes into a cure for the disease. Says Trautman: "We hope to put ourselves out of business."