MOLECULAR VIROLOGICAL ANALYSIS OF THE TRANSMISSION CLUSTERS AND RESISTANCE MUTATIONS OF HIV-1 SUBTYPE B IN BULGARIA (2012-2020)

HIV-1 infection in Bulgaria is known for its high level of genetic diversity. Previous studies have indicated that subtype B is the most common strain in Bulgaria, particularly among men who have sex with men, who are at a high risk of transmission. The primary objective of this study was to identify any transmission clusters and transmission resistance in individuals newly diagnosed with HIV-1 who have not yet received antiretroviral therapy (ART). To this end, we sequenced the HIV-1 pol gene in the samples from the study participants using either the Viroseq HIV-1 Genotyping Test (Abbott) and the Applied Biosystems 3130xl genetic analyzer or the TruGene DNA Sequencing System (Siemens Healthcare) and an OpenGene DNA sequencing system. We then subtyped the HIV-1 pol sequences, and further analyzed those that met the criteria for subtype B. The study included a total of 595 HIV-1 subtype B sequences. Our analysis revealed that the majority of those diagnosed with HIV-1 subtype B were male and lived in Sofia region. The most common transmission mode was through sexual intercourse among men who have sex with men, followed by heterosexual transmission. We also observed the presence of multiple transmission clusters , and a low percentage of transmitted drug resistance mutations (TDRMs). Overall, our study confirms that HIV-1 subtype B remains the most dominant strain in Bulgaria.