Cystic echinococcosis in Turkey: genetic variability and first record of the pig strain (G7) in the country

A sample of 22 Echinococcus granulosus isolates collected from 12 sheep and ten humans from a focus of cystic echinococcosis in western Turkey was examined by DNA sequencing of four mitochondrial genes (cox1, atp6, nad1, rrnS). Results demonstrated the presence of two species of E. granulosus complex, E. granulosus sensu stricto and E. canadensis. Of E. granulosus sensu stricto, the G1 genotype (including three microvariants) was found in 17 isolates from humans and sheep, the G3 genotype and an intermediate form G1/G3 in one isolate each (both from sheep). Of E. canadensis, the pig strain G7 was found in three isolates from sheep and human. This is the first report of this strain in Turkey. Its presence has implications for local control programs due to its shorter maturation rate in dogs compared with E. granulosus sensu stricto. Goat and/or wild boar are likely reservoirs for G7 in the region. We provided further data on the pattern and frequency of nucleotide substitutions within the G1/G3 cluster. Based on our results and GenBank records, G2 (Tasmanian sheep strain) is not considered as a discrete genotypic unit, as its sequences at polymorphic sites conform to microvariants of both G1 and (more often) G3.