biostudies-literatureDonoso AInstituto de Salud Carlos III101https://www.ebi.ac.uk/biostudies/studies/S-EPMC12846359biostudies-literatureUnknown18(1)Circulating recombinant forms (CRFs) are important components of the HIV-1 pandemic. Previous studies have reported the propagation of diverse HIV-1 CRFs of South American origin in Europe. Here, through protease-reverse transcriptase (Pr-RT) and integrase sequence analyses, we identify a Spanish cluster (BC3) branching with a Brazilian virus (10BR_RJ009) previously classified as CRF146_BC. In Pr-RT, BC3 comprised 14 viruses and was nested within a larger cluster, comprising 22 Brazilian viruses and 1 Spanish virus branching outside of BC3. Near full-length genome analyses of five BC3 viruses revealed mosaic structures identical to 10BR_RJ009, with two breakpoints delimiting a ~0.3 kb subtype B fragment within an otherwise subtype C genome. Two other Brazilian viruses previously classifiedVirusesViruses Previously Classified as CRF146_BC, a Circulating Recombinant Form of HIV-1 Recently Reported in Brazil, Represent Different Recombinant Forms, One of Which Is Circulating in Spain.PMC12846359PI19CIII/00042PICIII16/00033PI22CIII/00065Donoso ASalicio YCortizo SDiez-Fuertes FBaza-Caraciolo MBDel Romero-Guerrero JZamarron PGomez-Gonzalez CCanada-Garcia JEMoreno-Lorenzo MMiqueleiz ABenito SDelgado EIribarren JAThomson MMTellez RLorente-Sorolla CMorano LfalseViruses Previously Classified as CRF146_BC, a Circulating Recombinant Form of HIV-1 Recently Reported in Brazil, Represent Different Recombinant Forms, One of Which Is Circulating in Spain.Circulating recombinant forms (CRFs) are important components of the HIV-1 pandemic. Previous studies have reported the propagation of diverse HIV-1 CRFs of South American origin in Europe. Here, through protease-reverse transcriptase (Pr-RT) and integrase sequence analyses, we identify a Spanish cluster (BC3) branching with a Brazilian virus (10BR_RJ009) previously classified as CRF146_BC. In Pr-RT, BC3 comprised 14 viruses and was nested within a larger cluster, comprising 22 Brazilian viruses and 1 Spanish virus branching outside of BC3. Near full-length genome analyses of five BC3 viruses revealed mosaic structures identical to 10BR_RJ009, with two breakpoints delimiting a ~0.3 kb subtype B fragment within an otherwise subtype C genome. Two other Brazilian viruses previously classified2026-01-01T00:00:00Z2026 Jan2026-07-02T03:15:28.306Z2026-07-02T03:08:29.713ZS-EPMC128463594160086410.3390/v18010101