Genetic characterization, species differentiation and detection of Fasciola spp. by molecular approaches

Fascioliasis is an important food-and water-borne parasitic zoonosis caused by liver flukes of the genus Fasciola (Platyhelminthes: Digenea: Fasciolidae) [1,2]. Fasciola spp. have a cosmopolitan distribution, with high frequency in tropical areas [1,3,4]. Human fascioliasis has been reported in numerous countries [1,3,5]. It is estimated that millions of people are infected worldwide and the number of people at risk exceeds 180 million [6]. Also, fascioliasis is one of the most important parasitic diseases in grazing animals with over 700 million production animals being at risk of infection and economic losses were estimated at > US$ 2 billion per year worldwide [6].A few species have been described within the genus Fasciola, but only three species, Fasciola hepatica, Fasciola gigantica and Fasciola jacksoni are commonly recognized as taxonomically valid, with F. hepatica mainly occurring in temperate areas, F. gigantica in tropical zones, and both taxa overlapping in subtropical areas [6-11]. F. jacksoni is known as the fasciolid of Asian elephants and its phylogenetic position is still uncertain [12]. Given the adverse impact of Fasciola infection on human health and its economic significance, rapid and accurate identification of Fasciola species is necessary for successful clinical management of infection, and for epidemiological surveys.For a long time, the identification of Fasciola spp. has been based solely on traditional morphological approaches. However, due to the limitations of morphological methods, various molecular approaches have been developed and used for the identification and differentiation of Fasciola species. Importantly, these molecular methods have raised questions and spurred debate on the recognition of the "intermediate Fasciola" as a hybrid/introgressed form between F. hepatica and F. gigantica [8,13-20]. This hybrid Fasciola represents the emergence of a natural diversity previously undetected using conventional approaches, probably bec