Fasciola gigantica is a parasitic flatworm of the class Trematoda, which causes tropical fascioliasis. It is regarded as one of the most important single platyhelminth infections of ruminants in Asia and Africa. Estimates of infection rates are as high as 80–100% in some countries. The infection is commonly called fasciolosis. The prevalence of F. gigantica often overlaps with that of Fasciola hepatica, and the two species are so closely related in terms of genetics, behaviour, and morphological and anatomical structures that distinguishing them is notoriously difficult. Therefore, sophisticated molecular techniques are required to correctly identify and diagnose the infection. Distribution Fasciola gigantica causes outbreaks in tropical areas of South Asia, Southeast Asia, and Africa. The geographical distribution of F. gigantica overlaps with F. hepatica in many African and Asian countries and sometimes in the same country, although in such cases, the ecological requirement of the flukes and their snail hosts are distinct. Infection is most prevalent in regions with intensive sheep and cattle production. In Egypt, F. gigantica has existed in domestic animals since the times of the pharaohs. Lifecycle The lifecycle of F. gigantica is: Eggs (transported with feces) → egg hatch → miracidium → miracidium infect snail intermediate host → (parthenogenesis in 24 hours) sporocyst → redia → daughter redia → cercaria → (gets outside the snail) → metacercaria → infection of the host → adult stage produces eggs. Intermediate hosts As with other trematodes, Fasciola spp. develop in a molluscan intermediate host. Species of the freshwater snails from the family Lymnaeidae are well known for their role as intermediate hosts in the lifecycle of F. gigantica; however, throughout the years, an increasing number of other molluscan intermediate hosts of F. gigantica have been reported. The lymnaeid intermediate hosts of F. gigantica are distinguishable from those of F. hepatica, both morphologically and as to habitat requirement. The species of Fasciola can become adapted to new intermediate hosts under certain conditions at least based on laboratory trials. The most important intermediate host for F. gigantica is Radix auricularia. However, other species are also known to harbour the fluke, including Lymnaea rufescens and Lymnaea acuminata in the Indian subcontinent; Radix rubiginosa and Radix natalensis in Malaysia and Africa, respectively; and the synonymous Lymnaea cailliaudi in East Africa. Other snails also serve as natural or experimental intermediates, such as Austropeplea ollula, Austropeplea viridis, Radix peregra, Radix luteola, Pseudosuccinea columella, and Galba