A study on a possibility of predicting early relapse in leprosy using a ND-O-BSA based ELISA

International Journal of Leprosy and Other Mycobacterial Diseases, Mar 2002 by Wu, Qinxue, Yin, Yueping, Zhang, Liangfen, Chen, Xiaohong, Et al

A Study on a Possibility of Predicting Early Relapse in Leprosy Using a ND-O-BSA Based ELISA1

Relapse of leprosy is a very important clinical manifestation (7), because relapses may occur either after monotherapy or multidrug treatment (MDT) causing it to affect the final events of prevention and treatment of leprosy. With the wide coverage of leprosy patients under MDT, more and more patients are being released from treatment after completing a relatively brief period of time on chemotherapy. In a few years, monitoring these cases for relapse will likely become an important and major task for the leprosy program. A clinical examination supported with a simple test would be very helpful in defining and diagnosing cases of relapse at a very early stage. Therefore, an immunoserological tool could be useful. In view of the fact that PGL-I based ELISA is sensitive and specific in detecting IgM antibody against PGL-I from M. leprae in sera of leprosy patients, and ND-O-BSA- (an immunodominant disaccharide epitope of PGL-I linked to bovine serum albumin (BSA) via an octyl linker arm) based ELISA (ND-ELISA) has been established in our laboratory, we conducted a study on the possibility of predicting relapse among leprosy patients who had completed chemotherapy. In this article, we will mainly report the results evaluated by the ND-ELISA according to the criteria for screening the disease, then following the IgM antibody levels (IgM-AbL) against ND in sera from those individuals cured after dapsone (DDS) monotherapy (post-DDS) for a period of three years. DDS was given in 100 mg to 200 mg daily doses for multibacillary patients and in 50 mg to 100 mg daily doses for paucibacillary cases. The patients were considered cured when there was no evidence of disease activity clinically in the skin or nerves; skin smears were negative for acid-fast bacilli; and skin or nerve biopsies showed no histologic changes of leprosy.

Criteria for relapse in leprosy. The criteria for diagnosing relapse among these treated patients was a) the appearance of new skin lesions or new activity in prevously existing skin lesions or new nerve function loss or new paralysis of muscles; b) the finding of a new skin lesion or previous lesion with a high skin smear bacterial index containing solid-staining bacilli, and c) histological evidence of relapse in a skin or nerve biopsy, where specific changes of leprosy or acid-fast bacilli were found. If two of the above criteria were met, a relapse in leprosy was diagnosed.

RESULTS

The results of the studies are shown in Tables 1 to 8. Table 1 shows the results in sera from various groups tested in ND-- ELISA: a) The positivity rates of various groups not under treatment are LL 100%, BL 100%, BB 100%, BT 92.4%, TT 91.6%, TB 0%, normal controls 0% (in Dalian) and 4.3% (in Gansu). b) From TT to LL, the positivity rate gradually increased, and from BB to LL, there was the same percent positivity (100%), but from TT to BT, the positivity rate is different (higher in BT than in TT). c) In normal controls, the positivity rate is higher in Gasu than in Dalian. The reason will be discussed further.

Table 2 shows the results of evaluation of the ND-ELISA according to the criteria of screening for the disease. The results indicated that the sensitivity, specificity, PPV, NPV and YI were all more than 90%; the FPR and FNR were all very small and LR is much bigger than LR-.

Table 3 shows the relationship between BI and mean absorbance value (M^sub OD^) in the ND-ELISA. The Spearman's Rank correlation Coefficient is 6.857, indicated that there was a highly significant correlation between BI and M^sub OD^.

Table 4 shows that in multibacillary (MB) and paucibacillary (PB) patients who had been cured with DDS monotherapy and who were followed uneventfully for various periods of time, the mean antibody level remained low for many years afterwards.

Table 5 shows the three-year follow-up in leprosy patients cured with DDS monotherapy: a) Among multibacillary patients, 95 were Ab positive (Ab ), and 12 of them were diagnosed as a relapse in leprosy, an additional 335 cases were Ab negative (Ab-), and only one of them was diagnosed as a relapse in leprosy. b) In paucibacillary patients, 44 were Ab and 192 were Ab-. There was one case of a relapse of leprosy in each group. Among all 666 cases followed after cure with DDS monotherapy, a total of 15 cases of a relapse in leprosy was found. c) The risk of relapse was 6.7 times higher in multibacillary than in paucibacillary patients followed for three years after being considered cured with DDS monotherapy.

As shown in Table 6, in the Ab group, the cumulative rate of relapse (CRR) was 13.68%, and in the Ab- group, the CRR was 0.35%, for a risk ratio (RR) = 36.7. From Table 7, we should observe that, at the time of relapse, the antibody levels were all positive except one case of TT; and the antibody levels gradually decreased in all the relapsed leprosy cases after they were put back on effective treatment. The period of time for a relapse was 14-34 years after being cured, with no clustered period found, and changes in type (TT -> BT) might develop, although it was rare. Table 8 shows that, even though some of the samples were from paucibacillary patients being followed after cure with DDS, the antibody levels were positive at the time of relapse in the majority of them. Usually the relapse did not develop until the consistent positivity of antibody levels or gradually increasing values. Interestingly, with the appearance of a relapse within one to two years (two years in the majority of cases) after antibody levels became positive, the period of time for a relapse was 22-33 years, with no clustered period and no change of leprosy type.