Rétrovirus humains HTLV-1 et HTLV-2

HTLV-1 (Human T cell leukemia /Lymphoma virus type 1), the first oncogenic retrovirus discovered in Human in 1980, possesses the classical gag, pol, and env genes coding the structural and enzymatic proteins as well as a unique region (named pX) coding the regulatory proteins Tax and Rex. Tax stimulates the viral transcription and also plays a fundamental role in leukemogenesis by modifying the expression of several genes crucial for the survival as well as the proliferation of the cell. HTLV-1 is principally an etiological agent of two diseases associated to a very bad prognosis: malignant T cell lymphoproliferation; the adult T cell leukemia/lymphoma (ATLL) and a chronic neuromyelopathy, the tropical spastic parapareris/HTLV-1 associated myelopathy. HTLV-1 is not ubiquitous. Fifteen to 20 millions of individuals are infected worldwide, mainly in high endemic areas such as Southern Japan, intertropical Africa, the Caribbean region and the surrounding areas including parts of South America. In these areas, 0.5 % to 50 % of the people, depending on age and sex, are infected by the virus and are therefore HTLV-1 seropositive. HTLV-1 is transmitted from mother to child through prolonged breast-feeding, by sexual contacts mainly from male to female and by blood transfusion through passage of infected lymphocytes. The distribution of the different molecular subtypes (genotypes) is linked to the geographical origin of the infected populations rather than to the pathology (leukemia vs. neuromyelopathy). The great genetic stability of HTLV-1 can be used as a molecular mean to gain new insights into the origin, evolution and dissemination of this virus and of its host. HTLV-2, which is genetically related to HTLV-1, differs however from the latter by some specific epidemiological features. Indeed, HTLV-2 is mainly endemic in several Amerindians tribes and in some groups of intravenous drug users living mainly in the United States and in some European countries. Few cases of chronic neuromyelopathy have been associated with HTLV-2 and there is still no strong evidence that this retrovirus is linked to any malignant lymphoproliferation.