Identification of IIa and IIb molecular subtypes of human T-cell lymphotropic virus type II among Italian injecting drug users.

The molecular characterization of two human T-cell lymphotropic virus type II (HTLV-II) isolates, Gu and Va, obtained from Italian injecting drug users (IDUs) has indicated that these isolates belong to the HTLV-IIb subtype. To establish whether Italian IDUs are also infected by the HTLV-IIa variant, sequencing of the gp21 env gene of proviral DNA from further patients was carried out. Two new isolates, Bo and Md, were found, which presented a divergence of 0.4-0.7% from the IIa prototype HTLV-II-Mo, thus indicating that they belong to the HTLV-IIa subtype. The results strongly support the existence of two distinct molecular subtypes of HTLV-II infecting Italian IDUs and demonstrate that, although the IIb subtype appears to be prevalent, there is the same variability for this virus in Europe as found in the United States. The Italian IIb isolates were also seen to encode an additional 25 amino acids at the C-terminal end of tax protein, as already shown for other IIb isolates. The identification of two HTLV-II molecular subtypes among Italian drug addicts will be useful in tracing the worldwide distribution of this virus and in further understanding its molecular structure and biology.