Molecular epidemiology of Entamoeba spp.: Evidence of a bottleneck (Demographic sweep) and transcontinental spread of diploid parasites

Entamoeba histolytica causes amebic colitis and liver abscess in developing countries such as Mexico and India. Entamoeba dispar is morphologically id entical but is not associated with disease. Here we determined the ploidy o f E. histolytica and developed PCR-based methods for distinguishing field i solates off. histolytica or E. dispar. Fluorescence in situ hybridization s howed that E. histolytica trophozoites are diploid for five "single- copy" probes tested. Intergenic sequences between superoxide dismutase and actin 3 genes of clinical isolates of E. histolytica from the New and Old Worlds were identical, as were those off. dispar. These results suggest a bottlene ck or demographic sweep in entamoebae which infect humans. In contrast, E. histolytica and E. dispar genes encoding repeat antigens on the surface of trophozoites (Ser-rich protein) or encysting parasites (chitinase) were hig hly polymorphic. chitinase alleles suggested that the early axenized strain s of E. histolytica, HM-1 from Mexico City, Mexico, and NIH-200 from Calcut ta, India, are still present and that similar E. dispar parasites can be id entified in both the New and Old Worlds. Ser-rich protein alleles, which su ggested the presence of the HM-1 strain in Mexico City, included some E. hi stolytica genes that predicted Ser-rich proteins with very few repeats. The se results, which suggest diversifying selection at chitinase and Ser-r ich protein loci, demonstrate the usefulness of these alleles for distinguishi ng clinical isolates of E. histolytica and E. dispar.