The detection of PGL-IgM and M. leprae in nasal secretion in the application of leprosy epidemiology

Objective: To evaluate the significance of experimental epidemiology in the transmission of leprosy through detecting the infection with M. Leprae among leprosy patients, household contacts and normal population in leprosy endemic area. Methods: An epidemiological survey was conducted with the detection of PGL-IgM and M. leprae in nasal swab among leprosy patients, household contacts and normal population in leprosy endemic areas-Tonghong and Nanqiu villages, Yunnan Province. Results: (1) In leprosy household contacts, positive PGL-IgM and M. leprae nasal carriage with PCR were 30.4 % and 23.1 % respectively, but there was no significant difference in PGL-IgM positivity rates between household contacts and general villagers in the two villages. (2) No significant difference in PGL-IgM positivity rates can be found in general villagers between the two villages. The peak of PGL-IgM positivity was in the age group of 20 years and the positivity rate decreased as the age increased. However, in the group of 20 years, the positivity rates of PGL-IgM in Tonghong was much higher than those in Nanqiu village. ~Conclusion : Most new cases detected during the leprosy elimination campaigns (LEC) and after LEC were younger and it parallels to the peak of PGL-IgM positivity within the age group of 20 years. The prevalence and detection rates in Tonghong village are higher than those in Nanqiu and they are also associated with higher PGL positivity rate within the age group of 20 years in Tonghong. The phenomenon seems to support that there is correlation between leprosy prevalence and PGL positivity. Laboratory test based on PGL-ELISA is still a useful tool in the evaluation of leprosy transmission.