Microbiology and Immunology

WORLD OF MICROBIOLOGY AND IMMUNOLOGY Leprosy

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M. leprae;therefore, people who initially react to invasion by

M. leprae by making antibodies may be at risk for developing

more severe forms of leprosy. Researchers are not sure what

determines whether a person will react with a cellular response

or an antibody response; current evidence suggests that the cel-

lular immune response may be controlled by a special gene. If

a person has this gene, he or she will probably develop the less

severe tuberculoid leprosy if exposed to M. leprae.

Treatments for leprosy have improved considerably

over the past 40 years. In fact, some experts are encouraged

that the drug regimens being tested in various trials through-

out the world (including the United States) may eradicate lep-

rosy completely by the year 2010. Beginning in the 1950s, an

antibiotic called dapsone was used to treat leprosy, offering

the first hope of a cure for persons with the disease. Dapsone’s

main disadvantage was that the patient had to take the med-

ication daily throughout his or her lifetime. In addition, the M.

lepraein some patients underwent genetic mutationsthat ren-

dered it resistant to the antibiotic. In the 1960s, the problem of

resistance was tackled with the advent of multidrug therapy.

Bacteria are less likely to become resistant to several drugs

given in combination. The new multidrug treatment time was

also considerably shorter-typically about four years.

Currently, researchers offer a new drug combination that

includes an antibiotic called oflaxicin. Oflaxicin is a powerful

inhibitor of certain bacterial enzymesthat are involved in DNA

coiling. Without these enzymes, the M. lepraecannot copy the

DNA properly and the bacteria die. The treatment time for this

current regimen is about four weeks or less, the shortest treat-

ment duration so far.

One risk of treatment, however, is that antigens—the

proteins on the surface of M. lepraethat initiate the host

immune response—are released from the dying bacteria. In

some people, when the antigens combine with antibodies to M.

lepraein the bloodstream, a reaction called erythema nodosum

leprosum may occur, resulting in new lesions and peripheral

nerve damage. In the late 1990s, the drug thalidomide was

approved to treat this reaction, with good results. Because

thalidomide may cause severe birth defects, women of child-

bearing age must be carefully monitored while taking the drug.

A promising development in the treatment and manage-

ment of leprosy is the preliminary success shown by two dif-

ferent vaccines. One vaccinetested in Venezuela combined a

vaccine originally developed against tuberculosis, called

Bacille Calmette-Guerin (BCG), and heat-killed M. leprae

cultured from infected armadillos. The other vaccine uses a

relative of M. lepraecalled M. avium.The advantage of this

vaccine, currently being tested in India, is that M. aviumis

easy to culture on media and is thus cheaper than the

Venezuelan vaccine. Both vaccines have performed well in

their clinical trials, leading many to hope that a vaccine

against leprosy might soon be available.

The World Health Organizationannounced in January,

2002, that during the previous decade, the number of active

cases of leprosy worldwide had been reduced by 90%. Control

of leprosy still eludes six countries, Brazil, India, Madagascar,

Mozambique, Myanmar and Nepal, with approximately 700,

The disfiguring effect of leprosy.

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