Introduction of HIV type 1 into an isolated population: molecular epidemiologic study from Greenland

Introduction of HIV-1 into a population may not always give rise to a subsequent epidemic. Greenland is an isolated and sparsely populated island in The Danish Kingdom. We aimed to estimate the number of introductions of HIV-1 into Greenland, the number of subsequent epidemics, and the countries from which the virus was introduced. Phylogenetic analyses were performed on three regions of HIV-1 (gag, pol, and env) in samples from 70 Greenlandic patients. Furthermore, we included gene sequences from contemporary Danish HIV-1-infected patients and sequences from the Los Alamos HIV Sequence Database. All Greenlandic sequences were subtype B except one sequence found to be a recombinant (probably CRF13). Sequence clusters in the phylogenetic trees indicated that there had been at least nine introductions of HIV-1 into Greenland. One cluster, supported by bootstrap values of 81, 76, and 96% for gag, pol, and env, corresponding to one introduction, contained 53 (76%) of the Greenland patients. The patients in the cluster differed from other Greenlandic patients in epidemiological parameters. Two distinct subgroups within the main cluster were concentrated around the two largest Greenlandic towns. Although HIV-1 has been introduced into Greenland at least nine times, only one introduction gave rise to an epidemic. The phylogeny did not indicate from where the main Greenland cluster had been introduced as no database sequence from outside Greenland was genetically close to this cluster. The large diversity between the main Greenland cluster and the rest of the sequences is most likely due to a founder effect.