Differentiation of Echinococcus granulosus sensu lato species of human origin from Neuquén, Argentina, by multivariate analysis of rostellar hooks morphometry.

Cystic echinococcosis is a zoonosis caused by Echinococcus granulosus sensu lato, which leads to serious public health problems. Considerable phenotypic variation has been described between parasites depending on the intermediate host and genotype. Knowledge of species/genotypes present in an endemic region is clue for control programs. Although DNA sequencing is the most accurate tool for this purpose, its high cost makes it less affordable. A multivariate study of the morphometric parameters of rostellar hooks of E. granulosus sensu lato of human origin from Neuquén was carried out using Principal Components Analysis and classification trees. A valid classification criterion to differentiate E. granulosus species using morphometry of rostellar hooks in human hydatid cysts was determined. Seventy-six human fertile hydatid cysts (48 E. granulosus sensu stricto G1 and G3, and 28 E. canadensis G6) were included. Overall, 2,280 hooks were measured. The rostellar hooks belonging to E. granulosus sensu stricto were significantly smaller than those of E. canadensis. The Large Total Length (LTL) was sufficient to classify a new isolate into the 2 species: if LTL < 25.3 μm, then it corresponds to E. granulosus sensu stricto, and if LTL ≥ 25.3 μm to E. canadensis. This is the first multivariate study that establishes a morphometric cut-off value to discriminate between 2 species of E. granulosus sensu lato from human patients, using a significant number of cysts of both species identified by sequencing of mitochondrial genes. It constitutes a useful predictive tool in endemic areas where both human infective species overlap.