Morphological and molecular characterization of Dicrocoelium isolated from sheep in the north and center of Iran
Background: Dicroceliosis is a hepatic parasitic disease of clinical and financial significance for both human health and animal breeding. Considering the health and economic importance of the disease, this study aimed to determine the morphological and molecular characterization of 28S rDNA for Dicrocoelium isolated from sheep in the north and center of Iran during 2010-11. 

Materials and Methods: A total number of 200 trematodes were collected during an abattoir inspection from livers of naturally infected sheep in East Azerbaijan, Razavi Khorasan, Mazandaran and Tehran provinces in Iran. Adult worms were morphologically identified based on morphometric characterization and 60 specimens were characterized molecularly by sequencing. For molecular study, DNA was extracted and 28S rDNA region was amplified by PCR. Then, Tru1I fastdigest restriction enzyme and also RFLP technique were used to identify the parasite species. Finally, the PCR product was sequenced.

Results: A remarked morphological characteristic was that the orientation of testes in all isolates, were in tandem. The homological comparison of sequences showed that 28S rDNA in all isolates of Dicrocoelium had 963 bp and were similar to standard strain registrated in Genbank. RFLP pattern from D.dendriticum, which had 4 cut sites, produced 116, 145, 293 and 409 bp fragments. Although the morphological characterization in various provinces was significanly different, molecular identification showed that all specimens were identical (D.dendriticum) and there was not a significant difference between sequences of the collected parasites.

Conclusion: Morphological and molecular assays show that Dicrocoelium dendriticum is the only species of Dicrocoelium among sheep in the north and center of Iran. 
Keywords: Dicrocoelium, Morphology, Sequencing, Sheep, 28S gene, rDNA, RFLP,