Phylogenetic Positioning of a Strongyloides stercoralis Isolate Recovered from a Korean Patient and Comparison with Other Asian Isolates

Strongyloidiasis is caused by <i>Strongyloides stercoralis</i> and is one of the most neglected tropical diseases in tropical and subtropical regions. Although several strongyloidiasis cases have been reported in Korea, genetic analysis of Korean isolates is still incomplete. In this study, a parasite was isolated from a 61-year-old man diagnosed with strongyloidiasis during the treatment of lymphoma on his retroperitoneal lymph node. Diffuse symmetric wall thickening from the ascending to descending colon and a nematode-infected intestine was observed following microscopic examination. Genomic DNA was isolated from a patient tissue block, and <i>S. stercoralis</i> was identified by PCR and sequencing (18S rDNA). In order to determine phylogenetic location of a Korean isolate (named KS1), we analyzed <i>cox</i>1 gene (500-bp) and compared it with that from 47 previous <i>S. stercoralis</i> isolates (28 human isolates and 19 canid isolates) from Asian countries. Our results showed that phylogenetic tree could clearly be divided into 5 different groups according to hosts and regions. KS1 was most closely related with the Chinese isolates in terms of genetic distance.