Human ATL or HAM/TSP will develop(8). Although genome

Human T-lymphotropic virus type 1(HTLV-1)isa complex type C retrovirus belonging to thegenus deltaretrovirus. In addition to adult T-cell leukemia (ATL) and HTLV-I-associatedmyelopathy/tropical spastic paraparesis (HAM/TSP), the virus is considered to becontribute in various inflammatory diseases, most notablyuveitis, arthritis, myositis and alveolitis (2-4). Although thedistribution of HTLV-1 is global but the higher rates of infected individualshave been observed in Southern part of Japan, Africa, the Caribbean, SouthAmerica (5,6). The first infected adults weredetected by Farid in 1993 with 2.1% prevalence inMashhad, a populouscity in Northeastern of Iran with more than 25 million pilgrims and visitors annually. In these regions, between 0.5 and 20% of the general population have specificantibodies against HTLV-1 and are considered to be healthy carriers(7).

Most of HTLV-1 infected individualsremain Asymptomatic carriers (ACs) through their lives and in a few infected subjects, ATLor HAM/TSP will develop(8). Although genome similarities amongHTLV-1 strains is very high, a few nucleotide variation seems to be specific ofthe geographical origin of patients. Moreover, disease-specific sequenceshave not been found from patients with ATL or HAM/TSP, instead the genomicvariability of HTLV-1 appears to depend on geographic origin more than thepathology. The development rate of HTLV-1 is very low (particularly comparedto HIV). Currently, based on LTR sequence variation 7 subtypes have been characterizedfor this virus; the Cosmopolitan subtype (1a) that has distributed globallyand is further divided into subgroups (A–E), 4 African subtypes (1b, 1d, 1e, 1f)and a Melanesian/Australian subtype (1c).

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In 2005 the Cosmopolitan subtype(1a) was identified in Torbat-e Heydarieh, Sabzevar and Neyshabur by Rafatpanahet al. based on obtained sequences from infected adults 7.To examine the molecular epidemiology and identify the features of the local HTLV-1 strains that circulating in Mashhad community, we performed Polymerase chain reaction (PCR) to amplify the LTR region, then the fragments were purified and cloned into TA cloning vector. Furthermore, all specimens were sequenced and phylogenetic analyses describe HTLV-1 subtype a, mostly affecting the individuals from Mashhad., which is the first time this subtype has been reported in HTLV-1-associated diseases.