Human T-cell lymphotropic virus type I (HTLV-I) has been identified as the causative agent of both adult T-cell leukemia (ATL) and HTLV-I-associated myelopathy/tropical spastic paraparesis (HAM/TSP). Similar to other retroviruses, HTLV-I has a positive strand RNA diploid genome consisting of four genes: gag, pol, env and pX. The pX region codes for the two regulatory proteins tax and rex. Tax protein is essential for efficient virus expression and plays an important role for activation of cellular genes, such as cytokine genes and protooncogenes. Rex protein induces the expression of unspliced and single spliced mRNAs and regulates a fine balance between the levels of expression of the viral proteins. HTLV-I is widely spread throughout the world. It is endemic in Japan, Africa, the Caribbean and South America. In Brazil, Salvador city shows the highest HTLV-I prevalence rate (1.7%) of the country. It has been established that a vast majority (nearly 95%) of HTLV-I-infected individuals will remain asymptomatic throughout their life. The mechanisms by which HTLV-I causes diseases are not fully elucidated. The HTLV-I diagnosis is based on serologic detection of specific antibodies against several antigens of the virus or through amplification of proviral sequences in the peripheral blood mononuclear cells. However, there is not an epidemiological study with populational bases and suitable methodology in order to estimate its real prevalence in Brazil.
HTLV-I; Physiopathogenesis; Epidemiology; Diagnosis