Abstract
Fasciolosis is a major parasite infestation in ruminant livestock that causes public health issues and large financial losses for livestock businesses worldwide. Although additional species have been reported within the genus Fasciola, Fasciola hepatica and Fasciola gigantica have been acknowledged taxonomically as the primary causes of fasciolosis in animals and humans. However, it is limiting to differentiate the two isolates based on morphological features only. Identification and characterization using molecular techniques are important. Polymerase chain reaction (PCR) was used to detect and amplify 500 bp mitochondrial Cytochrome c Oxidase subunit 1 (COX1), 420 bp NADH Dehydrogenase Subunit 1 (NAD1), and 1100 bp nuclear ribosomal Internal Transcribed Spacers (ITS) regions of the adult Fasciola samples from the bile ducts of the infected liver. PCR, multiple sequence alignment, and phylogenetic tree reconstruction confirmed the presence of Fasciola gigantica and further confirmed the species. All the sequences phylogenetically cluster in F. gigantica clade for COX1, NAD1, and ITS-2 genes. The level of diversity in mitochondrial COX1 and NAD1 genes was significantly higher than that in the nuclear ITS region. The multiple sequence alignment also revealed genetic sites that can be employed to distinguish F. gigantica from other species. All sequenced Fasciola isolates from Ibadan were identified as Fasciola gigantica. Sequence analysis revealed relatedness between isolates from Nigeria and sub-Saharan countries. Molecular techniques are very important and reliable in the diagnosis of parasitic diseases. This will help not only differentiate between F. gigantica and F. hepatica, but also distinguish these from other related Fasciola species, and endemic from imported species.

Key words: Cattle; Fasciola gigantica; polymerase chain reaction; multiple sequence alignment