A distinctive clade B HIV type 1 is heterosexually transmitted in Trinidad and Tobago

Abstract

HIV-1 transmission worldwide is predominantly associated with heterosexual activity, and non-clade B viruses account for the most spread. The HIV-1 epidemic in Trinidad/Tobago and the Caribbean shares many features with such heterosexual epidemics, including a prominent role for coincident sexually transmitted diseases. This study evaluates the molecular epidemiology of HIV-1 in Trinidad/Tobago during a period when abrupt transition from homosexual to heterosexual transmission occurred in the absence of injecting drug use, concomitant with a rapid rise in HIV-1 prevalence in the heterosexual population. Of 31 viral isolates studied during 1987-1995, all cluster with subtype B reference strains. In the analysis of full env genes from 22 early seroconverters, the Trinidad isolates constitute a significant subcluster within the B subtype. The Trinidad V3 consensus sequence differs by a single amino acid from the prototype B V3 consensus and demonstrates stability over the decade of this study. In the majority of isolates, the V3 loop of env contains a signature threonine deletion that marks the lineage of the Trinidad HIV-1 clade B epidemic from pre-1984. No phenotypic features, including syncitium induction, neutralization profiles, and chemokine receptor usage, distinguish this virus population from other subtype B viruses. Thus, although the subtype B HIV-1 viruses being transmitted in Trinidad are genetically distinguishable from other subtype B viruses, this is probably the result of a strong founder effect in a geographically circumscribed population rather than genetic selection for heterosexual transmission. These results demonstrate that canonical clade B HIV-1 can generate a typical heterosexual epidemic.

Figure 1

Phylogenetic analysis of whole envelope sequences from 22 Trinidad HIV-1 isolates. Trinidad isolates are represented by a Q designation, prototypic B clade isolates and representative isolates from other clades are designated. Two subclusters with 100% bootstrap values, (QH0865 and QH0679) and (QH0550, QH0908, QH0136, QH0605, QH0065, and QH0020) represent possible epidemiologically linked transmission.

Figure 2

Phylogenetic analysis of Trinidad HIV-1 C2-V5 sequences and comparison with clade B sequences from the San Francisco Men's Health Study (SFMHS) and Thailand heterosexuals/drug users. Black triangles designate five of 31 isolates lacking the signature threonine deletion in the V3 loop. Yellow triangles represent 26 of 31 isolates with the threonine deletion. RH0011 refers to a 1987 isolate from a gay man ascertained as seropositive in 1983. QH samples represent incident infections from 1993–1997, QZ samples represent prevalent cases from 1987–1993 except for QZ4374, which came from an incident case in 1993.