Dear Editor,

The human T-cell lymphotropic virus type 1 (HTLV-1) was the first retrovirus identified in humans, and is the causal agent of HTLV-1-associated myelopathy (also known as tropical spastic paraparesis [HAM/TSP]) and adult T-cell leukemia/lymphoma (ATLL). HTLV-1 has been neglected mainly due to the misconception that it is a low morbidity viral infection. Recently evidence has been accumulating that a large percentage of HTLV-1-infected subjects, previously only considered as carriers, have disease due to the virus, such as sicca syndrome, chronic periodontitis, overactive bladder, erectile dysfunction, uveitis, and HTLV-1-associated arthropathy.1

It is estimated that approximately 20 million individuals are infected by HTLV-1 worldwide; Brazil is considered to be the country with the highest number of cases. Epidemiologic studies have pointed out that HTLV-1 is documented in all states of Brazil.2 In this issue of the Revista Brasileira de Hematologia e Hemoterapia a seroepidemiologic study showed a prevalence of 0.15% of HLTV-1 infection among blood donors in the State of Maranhão.3 Moreover, there was a high percentage (68.6%) of co-infected individuals with hepatitis B virus (HBV).

Epidemiologic studies performed over 20 years in Brazil have contributed to evaluate the changes in the prevalence of HLTV-1 infection, and have been highly relevant to identify changes in the transmission pattern. In Salvador, the prevalence of the infection has decreased from 1987 to 2005.4,5 Regarding the transmission pattern, breastfeeding has been considered the main route of viral transmission, followed by sexual contact and use of contaminated supplies by addicts. However, the study by Viana et al.3 in this issue confirmed previous findings from Mota et al.5 and Monteiro de Castro et al.,6 who demonstrated that seroprevalence increases with age. These data support the hypothesis that, rather than breastfeeding, other forms of transmission are currently more important in the acquisition of HTLV-1 infection. Moreover, the large percentage of co-infections with HBV is new and deserves special attention. HTLV-1 increases the susceptibility to other infectious agents such as Strongyloides stercoralis and Mycobacterium tuberculosis, and increases the severity of scabies and strongyloidiasis.1 While the high prevalence of HTLV-1 and HBV co-infection may be due to changes in the pattern of transmission, it is important to determine whether HTLV-1 may predispose or modify the natural course of HBV infection.