[Comparative epidemiology of HTLV and HIV retroviruses]

There are interesting contrasts between the epidemiological characteristics of the two subfamilies of human retroviruses. The oncoretrovirus HTLV-I and II are endemic in Intertropical Africa, North and South Americas and in the South of Japan. The lentiretroviruses HIV 1 and 2 are epidemic in the five continents and are progressing rapidly. The sexual transmission is much more efficient for HIV than for HTLV. The mother-to-child transmission occurs mostly by breast feeding for HTLV, while it is perinatal for HIV. Concerning the cell-virus relationship, while the oncoretroviruses stimulate and eventually immortalize the T4 or T8 target cells, the lentiretroviruses are cytocidal for the T4 cells. The contrast extends to the latent period between primary infection and disease: much longer in a case of HTLV linked to either hematological (ATL) or neurological (TSP/HAM) disorders than HIV linked to AIDS. Finally, prevention by vaccine should be achievable much earlier for HTLVs than for HIVs.