Hyper-variable regions in 18S rDNA of Strongyloides spp. as markers for species-specific diagnosis.

Four hyper-variable regions (HVR-I to -IV) found in 18S ribosomal DNA sequences were compared among 34 isolates of 15 species of the genus Strongyloides to evaluate their diagnostic value. HVR-I to -III were short, and plural species exhibit the same nucleotide arrangement. Meanwhile, HVR-IV had 23 to 39 nucleotides, showing species-specific arrangements, except Strongyloides ransomi and Strongyloides venezuelensis, which had the same nucleotide sequence in HVR-IV but were readily distinguished by the difference in HVR-I and -III. Isolates of Strongyloides stercoralis from humans of USA, Japan, and Philippines, chimpanzees, and dogs had an identical sequence in this region. Meanwhile, intraspecific polymorphism in HVR-IV nucleotide arrangement was observed among isolates of Strongyloides fuelleborni and Strongyloides callosciureus, presumably reflecting process of geographical dispersal and adaptation to the hosts.