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A high rate of human T-lymphotropic virus type II (HTLV-II) infection has been documented in intravenous drug abusers (IVDAs) in South Vietnam. We have investigated the molecular characteristics of the virus and have shown that one HTLV-II subtype is predominant in Ho Chi Minh City. This molecular subtype, HTLV-IIb, was identified in a number of South Vietnamese by nucleotide sequence analysis of the long terminal repeat (LTR) region. HTLV-IIa was not found. These findings suggest that HTLV-IIb is endemic in IVDAs in South Vietnam, although IVDAs in urban areas in North America are predominantly infected with HTLV-IIa.

Serum specimens (n = 1899) were assayed for infections with HTLV-I, HTLV-II, and HIV-1 in seven classified groups of normal healthy controls, children, pregnant women, prostitutes, intravenous drug abusers, patients under going hemodialysis, and hemophiliacs in South and North Vietnam. Surprisingly, 125 of 954 samples from South Vietnam exhibited seropositivity for HTLV-II and 119 of these belonged to the group of IVDAs (n = 200). The remaining six positives were a healthy control, a prostitute, two children, and two patients under going hemodialysis. Two IVDAs who were seropositive for HTLV-I and 10 of 15 seropositives for HIV-1 were also positive for HTLV-II in this population. In contrast, no seropositives to any of the viruses were detected in the North Vietnamese samples (0 of 945). The HTLV-II-seropositive IVDAs exhibited increased seropositivity with age compared with HIV-1 seropositivity in the population, and there was no statistical relation between seropositivity for HTLV-II and HIV-1. The HTLV-IIs in South Vietnam IVDAs appeared, by subtype-specific peptide ELISA, to be a mixture of both subtypes a and b, with subtype a predominant. It seems possible that HTLV-II may have been introduced into this population from IVDAs from the United States during the Vietnam conflict, but in a period prior to, or early in, the introduction of HIV-1 to IVDAs.

Approximately 1% (4/500) of blood donors exhibited seropositivity for HTLV-II in South Vietnam, but none (0/500) did in North Vietnam. Further, all individuals seropositive for HTLV-II were intravenous drug abusers who were seronegative for HIV-1 and HTLV-I. These findings suggest that HTLV-II infection may be specifically prevalent in drug abusers in South Vietnam.