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Epidemiology
INTRODUCTION
The human T lymphotropic viruses, type 1 (HTLV-I) and type 2 (HTLV-II), were the first human retrovirus to be discovered (1,2). They belong to the Retrovirus of the Oncornavirus subfamily and are capable of changing human lymphocytes, which in turn can be self-sustainable in vitro. They are distantly related to the human immunodeficiency virus (HIV-1 and HIV-2), which belongs to the Retrovirus of the Lentivirus subfamily that causes the acquired immunodeficiency syndrome (Aids).
The HTLV-I and HTLV-II infections are diagnosed serologically. Presence of antibodies for the HTLV-I or HTLV-II indicates that a person has been infected by the virus. In November 1988, the US Food and Drug Administration (FDA) recommended that all blood donations should undergo serologic screening for HTLV-I (3). Since then, in the USA, the entire blood donations and its components were totally tested in order to detect anti-HTLV-I antibodies. The authorized screening tests, as well as the additional tests to confirm seroreactivity (Immunoblot (WB) and radioimmunoprecipitation assays), do not differentiate the HTLV-I from the HTLV-II antibodies precisely.
Furthermore, the authorized screening tests apply HTLV-I antigens, which vary in sensibility for the discovery of HTLV-II antibodies (4,5). In the first year of screening in the US, it was identified approximately 2,000-volunteer blood donors infected by the HTLV-I/II. After the use of amplification by polymerize chain reaction (PCR), it was verified that half were infected by the HLTV-I and the other half by the HTLV-II (6). Those donors were counseled and permanently banned to donate blood. Since a PCR is not readily available, most donors and other people were submitted to further serological tests, when it was confirmed that they were infected with the HTLV-I/II. The uncertainty towards the identify of the infecting virus, the epidemiological discrepancy, and the differentiated clinical diagnosis of the infections by the HTLV-I and HTLV-II make the counseling difficult for people infected by the HTLV-I/II.
Thus far, the only safe method available to differentiate the HTLV-I from the HTLV-II was the polymerize chain reaction (7). However, in the last few years, recombinant proteins and peptides were developed for the use in serological tests, which in turn can easily differentiate the HTLV-I antibodies from the HTLV-II ones (8,9).
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