Transmission of leprosy in Qiubei County, Yunnan, China: Insights from an 8-year molecular epidemiology investigation

Abstract

Leprosy continues to be endemic in parts of China. To track the occurrence of leprosy and determine at risk communities, molecular strain typing based on variable number of tandem repeats (VNTRs) was applied in Qiubei County, Wenshan Prefecture, Yunnan Province of the People's Republic of China, a multiethnic region that is home to four predominant ethnic minorities. A previous study, conducted between 2002 and 2005, provided the first descriptions of Mycobacterium leprae strains in the region. M. leprae strains in Qiubei are highly conserved, so only sufficiently polymorphic loci can distinguish strains. A balance between mutation rate and loci stability is needed, so that secondary transmissions can be identified as genotypic matches. The long incubation period of leprosy necessitated an extension of the study to assess the validity of VNTR typing and observe allelic shifts in the same multiethnic population. From 2006 to early 2010 the extension was performed to yield a cumulative total of 164 enrolled patients and 130 skin samples suitable for VNTR typing. Patient demographic information revealed that the case detection rate among certain minority populations in the county is considerably higher than the national rate. Cluster analysis of allele frequencies showed similar strain types within family groups and neighboring townships. Allele frequencies were not found to significantly differ between genders or clinical presentations. The percentage of cases showing near-matching genotypes varied with geography; showing a considerably higher rate in the northern townships. The northern townships continue to show strain types falling into the groups previously defined. Southern genotypes were distinct from those in the north, but clonal genetic relationships were indiscernible in the south. Social interactions and the physical, residential and occupational environments may be more conducive to transmission of community strains in the north.