MOLECULAR EPIDEMIOLOGICAL ANALYSIS OF THE TRANSMISSION CLUSTERS OF THE HIV-1 CIRCULATING RECOMBINANT FORMS CRF01_AE AND CRF02_ AG IN BULGARIA

Background. The purpose of this study was to analyse the underlying HIV transmission clusters of individuals from different vulnerable groups infected with the recombinant forms of HIV-1 – CRF01_AE and CRF02_AG, between 1986 and 2011 using sequencing and phylogenetic analysis. Material and methods. Blood samples from randomly selected 242 individuals diagnosed with HIV-1 CRF01_AE and CRF02_AG in Bulgaria were analysed. HIV-1 pol gene fragment was sequenced using the ViroSeq HIV-1 Genotyping Test (Abbott) and/or TruGene DNA Sequencing System. The phylogenetic tree reconstruction was performed with the IQ-TREE program. Identification of the phylogenetic clusters was performed using the ClusterPicker program with two parameters to identify recent and distant infection. Results.Two main local independent epidemics confined to different geographical regions of the country were caused by HIV-1 CRF01_AE and CRF02_AG. The various viral strains circulate predominantly in two major separate regions – CRF01_AE in Sofia and CRF02_AG in Plovdiv. Most of the individuals infected with viral strains analysed in this study were people who inject drugs (PWID) or heterosexuals and only a few were men who have sex with men. The phylogenetic analysis revealed transmission clusters in both recombinant forms, few in number when confined within a short period of time and multiple clusters over an extended timeframe. Conclusions. The introduction and rapid spread of two different strains of HIV-1 into geographically distant groups of PWID triggered local epidemic outbreaks. The phylogenetic analysis indicated the accelerated transmission of HIV, which is a characteristic of the spread through injection practices. Our study demonstrated that transmission cluster monitoring is important for better understanding of the development of epidemic and could be used as a tool for the identification of risk indicator populations.