Tehran University of Medical Sciences Iranian Journal of Parasitology 1735-7020 11 2 2016 12 21 253 258 Seyed Sajjad HASHEMINASAB Dept. of Parasitology, Faculty of Veterinary Medicine, University of Tehran, Tehran, Iran 2016 07 02 2016 07 02 Background: Genomic DNA was isolated from Parabronema skrjabini. rRNA region was amplified and sequenced. Methods: The RNA secondary structure was predicted using mfold software (http://mfold.rit.albany.edu). The secondary structure with bulge, hairpins, helices, interior, external and multi loops was predicted for 5.8srDNA of our sequence of P. skrjabini and a sequence of P. skrjabini and two species of Habronema (H. microstoma and H. muscae) in GenBank. RNA motifs were predicted by MEME program version 4.10.2.  Results: The length of 5.8S rRNA sequence for P. skrjabini#1, P. skrjabini#2, H. microstoma and H. muscae was 158, 156, 127 and 127bp, and the DG required for the formation of the secondary structure was -70.50, -56.40, -41.50 and -41.40 kcal/Mol, respectively. Common structural elements were initially recognized with the help of mfold by screening for thermodynamically optimal and suboptimal secondary structures (default settings, with T = 37 °C). The energy levels of the presumptive secondary structures were then calculated with mfold at the DNA level. Both motifs and the sequence of P. skrjabini#1 were completely different from the other analyzed samples. This difference might be due to the differences in host and geographical area. Conclusion: This is the first molecular study of P. skrjabini in sheep, which could be further used in the structure modeling across Habronematidae. https://ijpa.tums.ac.ir/index.php/ijpa/article/view/1067 https://ijpa.tums.ac.ir/index.php/ijpa/article/download/1067/704