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Journal of Clinical Microbiology, August 2003, p. 3748-3756, Vol. 41, No. 8
0095-1137/03/$08.00+0     DOI: 10.1128/JCM.41.8.3748-3756.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.

Geographic Diversity among Genotypes of Entamoeba histolytica Field Isolates

Department of Parasitology, National Institute of Infectious Diseases,¹ Department of Tropical Medicine and Parasitology, Keio University School of Medicine, Shinjuku-ku,³ Precursory Research for Embryonic Science and Technology, Japan Science and Technology Corporation, Tachikawa, Tokyo, Japan,⁵ Department of Parasitology and Mycology, Shaheed Beheshti University of Medical Sciences, Tehran, Iran,² Department of Microbiology and Immunology, Mahidol University, Bangkok, Thailand⁴

Received 26 December 2002/ Returned for modification 10 February 2003/ Accepted 27 May 2003

It has been known that only 5 to 10% of those infected with Entamoeba histolytica develop symptomatic disease. However, the parasite and the host factors that determine the onset of disease remain undetermined. Molecular typing by using polymorphic genetic loci has been proven to aid in the close examination of the population structure of E. histolytica field isolates in nature. In the present study, we analyzed the genetic polymorphisms of two noncoding loci (locus 1-2 and locus 5-6) and two protein-coding loci (chitinase and serine-rich E. histolytica protein [SREHP]) among 79 isolates obtained from different geographic regions, mainly Japan, Thailand, and Bangladesh. When the genotypes of the four loci were combined for all isolates that we have analyzed so far (overlapping isolates from mass infection events were excluded), a total of 53 different genotypes were observed among 63 isolates. The most remarkable and extensive variations among the four loci was found in the SREHP locus; i.e., 34 different genotypes were observed among 52 isolates. These results demonstrate that E. histolytica has an extremely complex genetic structure independent of geographic location. Our results also show that, despite the proposed transmission of other sexually transmitted diseases, including human immunodeficiency virus infection, from Thailand to Japan, the spectra of the genotypes of the E. histolytica isolates from these two countries are distinct, suggesting that the major E. histolytica strains prevalent in Japan at present were likely introduced from countries other than Thailand. Although the genetic polymorphism of the SREHP locus was previously suggested to be closely associated with the clinical presentation, e.g., colitis or dysentery and liver abscess, no association between the clinical presentation and the SREHP genotype at either the nucleotide or the predicted amino acid level was demonstrated.

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