New Diagnostic Test

 

Leprosy Mailing List – March 7,  2013

Ref.:    (LML) New Diagnostic Test

From:  Dr Shen Jianping, Nanjing, PR China   

---

 

Dear  Dr. Schreuder,

 

I read  with much interest the many contributions on the new diagnostic test on leprosy. Although the value of leprosy serology test is limited for the diagnosis of leprosy, it is worth to do a study on the relation of kinetic changes of antibody titer with clinical leprosy among groups of people using continuous serological tests and to monitor clinical events of the disease.

We carried out a study in a leprosy high endemic areas in China many years ago. The initially investigated numbers of people and house hold contacts were more than 1600 and 700, respectively. The antigens (ND-0-BSA) and PGL-1  were used to detect antibody in the study population. The kinetic changes of antibody titers to M.leprae were observed by continuously serological following up. The lepromin test and  skin smear test were also conducted among people with continuous high titer of antibody to M. leprae. The period of clinical investigation, follow-up, was as long as 15 year.

 

The aims of the study were:

-        to provide information for early diagnosis of leprosy; and

-        to provide a scientific basis for taking measures to prevent the developing of clinical disease by investigating kinetic changes of antibody titer before and after invasion of M. leprae into the human body;

-        the outcome of people after being infected by M.leprae, analyzing the relation of subclinical infection with clinical disease.

 

This study showed many interested findings:

1、The subclinical infection by M. leprae is always at a conversion stage. According to the extent of the exposure to M. leprae, the antibody titer among the population is always converting (swinging) between negativity and positivity.

2、Most population with high antibody titer to M.leprae did not develop clinical disease. It was common for subclinical infection in the leprosy endemic areas.

3、The people that lived in villages with higher antibody titer are not linked with high incidence of leprosy disease. It may be related to a individual immunity to M.leprae. 

 
4、It is not of much value to monitor clinical incidence of leprosy for a population in long term by only one leprosy serology positive test. Only population with continuous antibody positivity and lepromin test negativety are at real high risk to develop clinical leprosy. 
5. It was also helpful to diagnose leprosy by continuous follow-up of serology, together with lepromin tests and skin smears.

6、During the study, 11 patients were detected who developed clinical leprosy. We found that the antibody titer among multibacillary patients increased 20-36 months before developing clinical disease, and then continuously increased. This was in accordance with 2-5 years of leprosy incubation.

7、It was found that developing clinical disease from initial positive antibody titer could occur within 1 year. So we suggest that the interval  between serological test should not exceed more than a half year. Checking up at a shorter interval can easily find  changes of antibody titer and evolvement of the clinical disease. Combined with the skin smear test, it is helpful to diagnose leprosy early.

8. We found two girls who were healthy carriers  of M. leprae with positive antibody and skin smear test 3+ at the normal looking face, but the lepromin test was positive. At the next year of following up, the antibody and skin test all became negative. They did not receive any treatment.      

With best regards,

Dr Shen Jianping
Department for Leprosy Control 
National Center for Leprosy Control 
Nanjing, PR China   

 

---

LML - S Deepak, B Naafs, S Noto and P Schreuder
LML Archives: http://www.aifo.it/english/resources/online/lml-archives/index.htm
Contact: Dr Pieter Schreuder << editorlml@gmail.com >>.