Journal of Helminthology, page 1 of 6 doi:10.1017/S0022149X14000133 q Cambridge University Press 2014 Sequence variation in mitochondrial cox1 and nad1 genes of ascaridoid nematodes in cats and dogs from Iran F. Mikaeili 1 , H. Mirhendi 2 , M. Mohebali 1 , M. Hosseini 3 , M. Sharbatkhori 4 , Z. Zarei 1 and E.B. Kia 1 * 1 Department of Medical Parasitology and Mycology, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran: 2 Department of Medical Parasitology and Mycology, School of Public Health, National Institute of Health Research, Tehran University of Medical Sciences, Tehran, Iran: 3 Department of Epidemiology and Biostatistics, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran: 4 Laboratory Science Research Center, Golestan University of Medical Sciences, Gorgan, Iran (Received 23 September 2013; Accepted 9 February 2014) Abstract The study was conducted to determine the sequence variation in two mitochondrial genes, namely cytochrome c oxidase 1 (pcox1) and NADH dehydrogenase 1 (pnad1) within and among isolates of Toxocara cati, Toxocara canis and Toxascaris leonina. Genomic DNA was extracted from 32 isolates of T. cati, 9 isolates of T. canis and 19 isolates of T. leonina collected from cats and dogs in different geographical areas of Iran. Mitochondrial genes were amplified by polymerase chain reaction (PCR) and sequenced. Sequence data were aligned using the BioEdit software and compared with published sequences in GenBank. Phylogenetic analysis was performed using Bayesian inference and maximum likelihood methods. Based on pairwise comparison, intra-species genetic diversity within Iranian isolates of T. cati, T. canis and T. leonina amounted to 0–2.3%, 0–1.3% and 0–1.0% for pcox1 and 0–2.0%, 0–1.7% and 0–2.6% for pnad1, respectively. Inter-species sequence variation among the three ascaridoid nematodes was significantly higher, being 9.5–16.6% for pcox1 and 11.9–26.7% for pnad1. Sequence and phylogenetic analysis of the pcox1 and pnad1 genes indicated that there is significant genetic diversity within and among isolates of T. cati, T. canis and T. leonina from different areas of Iran, and these genes can be used for studying genetic variation of ascaridoid nematodes. Introduction Toxocara cati, Toxocara canis and Toxascaris leonina are common ascaridoid nematodes of cats and dogs; adult worms live within the lumen of the small intestine. Toxocariasis is a zoonotic parasitic disease caused by the migration of second-stage larvae of T. cati and T. canis (Despommier, 2003). Toxascaris leonina may also be considered as a causative agent of toxocariasis (Cho et al., 2009). Humans become infected through the ingestion of viable, embryonated eggs from the environ ment. After hatching, emerging larvae are unable to complete their life cycle and develop into mature adult worms in the human host; they may, however, migrate in the body for several months or years. The clinical *Fax: þ 98 21 88951392 E-mail: keiaeshr@sina.tums.ac.ir