Leprosy. An update: definition, pathogenesis, classification, diagnosis, and treatment

Leprosy is a chronic granulomatous disease caused by the bacillus Mycobacterium leprae. It primarily affects the skin and peripheral nerves and is still endemic in various regions of the world. Clinical presentation depends on the patient's immune status at the time of infection and during the course of the disease. Leprosy is associated with disability and marginalization. Diagnosis is clinical and is made when the patient has at least 1 of the following cardinal signs specified by the World Health Organization: hypopigmented or erythematous macules with sensory loss; thickened peripheral nerves; or positive acid-fast skin smear or skin biopsy with loss of adnexa at affected sites. Leprosy is treated with a multidrug combination of rifampicin, clofazimine, and dapsone. Two main regimens are used depending on whether the patient has paucibacillary or multibacillary disease.

Leprosy: A great imitator

In recent years, advances in medical diagnosis and treatment have greatly attracted our attention, whereas some rare diseases, such as leprosy, have not found a place in the medical education curriculum; their existence may even be forgotten. Although the prevalence and incidence rates for leprosy have been significantly reduced as a result of the control strategies of the World Health Organization, new cases still appear. A total of 214,783 new cases were reported from 143 countries during 2016, corresponding to the global new-case detection rate of 2.9 per 100,000 population. Leprosy proves to be a very interesting model due to its immunologic properties. It joins with syphilis, mycosis fungoides, cutaneous tuberculosis, and sarcoidosis as one of the great imitators. The diagnosis of leprosy can be simple and practical, but considering the diagnosis of leprosy in the differential diagnosis is the first requisite again.

Lymphocyte transformation test in leprosy: decreased lymphocyte reactivity to Mycobacterium leprae in lepromatous leprosy, with no evidence for a generalized impairment

Untreated leprosy patients were examined with respect to lymphocyte transformation in vitro after stimulation with mycobacterial and other microbial antigens, allogeneic lymphocytes, or nonspecific mitogens. Methods were used to circumvent technical variability. The results were compared with those obtained in controls matched for age, sex, race, and environment. No evidence was found for a generalized impairment of lymphocyte transformation in vitro, whereas a specific defect towards Mycobacterium leprae was demonstrable in lepromatous leprosy patients. The response to M. leprae, investigated in untreated and treated leprosy patients, decreased along the leprosy spectrum. Moreover, the results of the one-way mixed lymphocyte cultures showed that lymphocytes from leprosy patients had a normal stimulator and responder capacity, when they were tested against a panel of allogeneic lymphocytes. The influence of serum factors was investigated in untreated leprosy patients in the mixed lymphocyte culture. On average, tuberculoid as well as lepromatous sera showed a low-level depressive effect, but some sera showed a stimulatory effect. Therefore, a depressive effect of serum factors cannot be considered to be a general feature of leprosy. The correlation between the Mitsuda type of lepromin skin test and the lymphocyte reactivity in vitro to M. leprae was studied, and a positive correlation was found.

Possible transmission of Mycobacterium leprae in a group of UK leprosy contacts

A case of infectious leprosy in residential accommodation in the UK prompted a study of the cellular and humoral response to Mycobacterium leprae in two groups of individuals who were in contact with the index case for almost a year. In the younger staff group (mean age 44 years) 23 of 30 individuals had positive Mitsuda skin tests, 25 showed lymphocyte transformation to a soluble sonciate of M leprae and 2 had slightly raised IgM antibody concentrations to the terminal disaccharide of M leprae phenolic glycolipid-1. In the older group of residents (mean age 83 years) 7 of 36 individuals were skin-test positive, 25 of 33 were positive by lymphocyte transformation, but none had raised antibody levels. When retested on two further occasions, the same 2 individuals in the younger group still had raised antibody concentrations, 1 of whom had a persistent lepromin skin-test response for over 8 months and showed a pronounced increase in lymphocyte transformation to mycobacterial antigens. The findings suggest that transmission of M leprae may have occurred in these 2 contacts, who were therefore given 6 months' chemoprophylaxis with rifampicin.

IMMUNOLOGICAL IDENTIFICATION OF FOOT-PAD ISOLATES AS MYCOBACTERIUM LEPRAE BY LEPROMIN REACTIVITY IN LEPROSY PATIENTS

Lepromin, a product containing Mycobacterium leprae from patients' tissues, fails to elicit skin reactions in lepromatous patients; this non-reactivity was utilized as a means of identifying the mycobacterium isolated in mouse foot-pads from leprosy patients. To do this a suspension of acid-fast bacilli prepared from mouse foot-pads infected with a typical isolate was compared to human lepromin. The isolate was in fourth passage, and the multiplication since first isolation had diluted the original inoculum to insignificant levels. Three preparations were tested: A, A foot-pad preparation containing 1.6 x 10⁷ organisms/ml, B, lepromin diluted to the same bacillary content, and C, undiluted lepromin containing 4.2 x 10⁷ organisms/ml. The reactions were compared in 34 lepromatous and 30 tuberculoid patients. All 34 lepromatous patients were negative in both early (Fernandez) and late (Mitsuda) reactions to all 3 antigens. In the tuberculoid patients the late reactions were positive in 66.7, 70.0 and 90.0 per cent to antigens A, B, and C, respectively. The size of the reactions to A and B were closely correlated in the individual patients. Experience in leprosy patients with suspensions prepared from 16 other mycobacterial cultures is reported or reviewed. None of them produced reactions that correlated with those of lepromin. Thus the lack of reactivity to lepromin of lepromatous patients appears to be a specific phenomenon. The results provide evidence that the foot-pad isolates and M. leprae are immunologically identical.

Leprosy: confirmation in the armadillo

Bacteria isolated from lesions of lepromatoid leprosy in the armadillo were studied in comparison with Mycobacterium leprae isolated directly from human lepromatous leprosy lesions. Three methods were used to show that the bacteria from the lesions of the armadillo were identical to those of the human lesions: (i) extraction of the bacteria with pyridine and subsequent staining with various techniques, (ii) the competence in clearing bacilli (CCB) test, and (iii) the Mitsuda test.

Reliability of Semmes Weinstein monofilament and ballpoint sensory testing, and voluntary muscle testing in Bangladesh

The reliability of methods of testing nerve function is important, since diagnostic decision making is a direct function of the quality of the test. Three methods of nerve function testing were investigated at the Danish Bangladesh Leprosy Mission (DBLM) in north Bangladesh, and assessed for inter-observer reliability. The three methods were 1) ballpoint pen test (BPT) for sensory function; 2) graded Semmes Weinstein monofilament test (SWM) for sensory function and 3) voluntary muscle testing (VMT) for motor function. The weighted kappa (kappa w) statistic was used to express inter-observer reliability. Using this statistic, 0 represents agreement no better than random, and 1.0 complete agreement. kappa w values of > or = 0.80 are reckoned to be adequate for monitoring and research. Fifty-three patients were tested, a Senior physiotechnician acting as 'gold standard' against whom four other staff physiotechnicians were assessed. All three testing methods were found to have minimal inter-observer variation, with the kappa w for inter-observer agreement using BPT being 0.86, the SWM 0.92, and VMT 0.94. It is concluded that in trained and experienced hands, all three methods are reliable and repeatable to a level allowing confident use of results obtained in monitoring and research.

Some remarks on the genetics of leprosy resistance

The mechanism and the familial pattern of the late lepromin reaction (Mitsuda reaction) have been discussed. The interpretation of the familial correlation as mainly depending on a pair of allelic genes has been analysed thoroughly. A new technique has been described for identifying constitutional resistance or susceptibility to leprosy at anin vitrotissular level. The possibilities of this technique have been stressed.

Prevention and early detection of leprosy in children

India with its 4 million cases of leprosy, accounts for one-third of the world's population of leprosy patients. One-fourth of them are below 15 years of age. We report a 5-year follow-up study of healthy children who were close contacts of leprosy patients, in order to: 1. detect subclinical infection and observe the development of overt disease by using the Fluorescent Leprosy Antibody Absorption Technique (FLA-ABS) and the lepromin test which assess the humoral and cell-mediated immunity (CMI), respectively; 2. evaluate the efficacy of dapsone as a chemoprophylactic agent in the 'at risk' contacts. Four-hundred-and-fifty-five healthy contacts were studied. Majority of the contacts of multibacillary patients (303) were FLA-ABS positive (75 percent) and lepromin negative (55 percent) showing that although most of them had been infected, the lepromin status was negative (P < 0.01). On the other hand, the majority of the contacts of paucibacillary patients (152) were lepromin positive (57 percent) (P < 0.05). Furthermore, only 61 percent of contacts of paucibacillary patients were FLA-ABS positive as compared to 75 percent of contacts of multibacillary patients demonstrating that the former had been exposed to a lesser quantum of infection (P < 0.05). On the basis of results of FLA-ABS and lepromin tests, these 455 contacts were classified into four groups, viz. Group I comprising children who were FLA-ABS positive and lepromin positive; Group II, who were FLA-ABS positive and lepromin negative; Group III, who were FLA-ABS negative and lepromin positive; and Group IV who were FLA-ABS negative and lepromin negative.(ABSTRACT TRUNCATED AT 250 WORDS)

Skin test development in leprosy: progress with first-generation skin test antigens, and an approach to the second generation

One of the most urgent needs from leprosy research is a test for infection. The lepromin test is not suitable as a diagnostic test for leprosy, and neither the Rees nor the Convit soluble antigens has appeared sufficiently specific. Because two new antigens, MLSA-LAM and MLCwA, may not fully meet the requirements for specificity, we have embarked upon the preparation of a second generation of skin test antigens. Size-fractionated cryptozoic proteins were prepared from M. leprae by electroelution from preoperative sodium dodecylsulphate-polyacrylamide gel electrophoresis, and individual fractions were probed with polyclonal and monoclonal antibody reagents to identify both known and novel proteins. In addition, immunological responses were assessed in M. leprae-sensitized guinea pigs against both crude subcellular fractions (cytosol, membrane, and soluble cell wall proteins) and the size-fractionated cytosolic proteins. A particularly promising subcellular fraction is the membrane fraction of M. leprae, which contains many proteins unique to the organism. Clinical trials of the M. leprae membrane proteins are now being planned.