COMPARATIVE PHYLOGENETIC ANALYSIS OF COI AND NAD1 GENES IN ANIMAL AND HUMAN ISOLATES OF ECHINOCOCCUS CANADENSIS (G6 GENOTYPE) IN IRAN.

Abstract

Cystic echinococcosis (CE), caused by members of the Echinococcus granulosus sensu lato complex, remains endemic in Iran. Genotype G6, classified within Echinococcus canadensis, is epidemiologically important because of its frequent occurrence in camels and its ability to cause human infection. This study compared the genetic diversity, haplotype composition, and phylogenetic relationships of Iranian G6 isolates using 129 publicly available mitochondrial sequences derived from 120 unique GenBank records, including 79 cytochrome c oxidase subunit 1 (COI) and 50 NADH dehydrogenase subunit 1 (NAD1) sequences. COI exhibited higher haplotype diversity (Hd = 0.518) and nucleotide diversity (π = 0.00678) than NAD1 (Hd = 0.226 and π = 0.00273, respectively), indicating greater resolution for detecting intraspecific variation. Tajima's D was significantly negative for both markers, whereas Fu's Fs was strongly negative for COI, indicating an excess of low-frequency variants and departure from the standard neutral-equilibrium model. Haplotype networks and phylogenetic trees revealed shared haplotypes and intermingled lineages among isolates from different host species, with no visually evident host-associated clustering within the mitochondrial fragments examined. These findings highlight the genetic diversity and epidemiological importance of G6 in Iran and support integrated surveillance involving camels, other susceptible intermediate hosts, and canid definitive hosts. Broader population-based studies incorporating additional geographic regions, host species, and independent genetic markers are required to clarify the population structure and transmission dynamics of G6.