Origin and Spread of HIV-1 Subtype B Among Heterosexual Individuals in Bulgaria

Abstract

Human immunodeficiency virus (HIV) was originally introduced in Bulgaria through heterosexual transmission (HET) and later transferred to other vulnerable groups along with numerous more recent introductions from outside Bulgaria. To define the diversity, origins, and dynamics of the HIV-1 subtypes prevalent in HET population in Bulgaria, we applied phylogenetic and phylodynamic analyses using polymerase (pol) sequences from HET individuals to infer the spatiotemporal evolutionary history of the HIV-1 epidemic in this population in Bulgaria. High genetic diversity was found, including 13 different HIV-1 subtypes: 45.7% subtype B, 19.9% CRF01_AE, 7.5% CRF02_AG, 7.5% sub-subtypes A1 and A6, 7.1% subtype C, 5.3% subtype F1, 4.0% URFs, 1.2% CRF05_DF, 0.6% subtype G, 0.3% CRF04_cpx, 0.3% CRF29_BF, 0.3% CRF14_BG, and 0.3% subtype H. The estimated root of the subtype B in the phylogenetic tree dated back to the year 1980 largely due to multiple introductions of subtype B from outside the country. Several significant clades have been identified highlighting six different main epidemic entrances of subtype B dating from 1989 to 2007. The Bayesian skyline plot showed two different exponential growth periods starting in the 1980s to 1990 followed by a constant phase up to about 2008, with another exponential growth period from 2008 to the year 2012. The migration analysis identified dynamic pattern of gene flow and demonstrated that many HET probably acquired the infection abroad (14.6%), while only (6.6%) of non-HET were infected outside country. The phylogenetic analysis showed an intermixing between sequences from Bulgarians with sequences from other countries, suggesting different HIV introduction in this country followed by the internal spread through local transmission networks.

Molecular Epidemiology of the HIV-1 Subtype B Sub-Epidemic in Bulgaria

“…These shared common origin characteristics and conditions for contemporary contacts may help to explain the observed evolutionary history of subtype B in these populations. Tourism in Bulgaria may also help to explain our finding of HIV-1 pol sequences from Germany, Spain, the U. K., and Russia that were ancestral to Bulgarian pol clades [13,14,41]. However, we cannot exclude that Bulgarians acquired their infections in these or other countries and introduced them into Bulgaria when they returned from abroad.…”

Analysis of the Origin and Dissemination of HIV-1 Subtype C in Bulgaria

“…It is very likely for these reasons that the clusters formed by the Bulgarian isolates are composed of only a few sequences without an epidemic outbreak. In contrast, possibly by chance, other viral strains have come into populations at risk for blood-and sexually transmitted infections, such as PWIDs or MSM, which in turn quickly disseminated the virus [24,25]. However, our studies have already shown that there may be bridges between different groups, indicating that there is a risk of transmission of viral strains from one group to another, which gives rise to serious concerns.…”

“…The detection of a significant number of HIV-infected individuals in the first years and the subsequent decline in the number of new cases later showed that the virus was spread to a limited scale in Bulgaria without allowing underhanded development of the epidemic. However, the constant arrival of new strains from abroad raises concerns that these viruses could spill into vulnerable transmission groups, including MSM and PWIDs, causing outbreaks in these at-risk populations that were already reported with other viral strains, such as CRF01_AE and CRF02_AG, in our previous studies [21,24,25,41,42].…”

“…In contrast, other clades have been characterized by limited dissemination patterns and, after being passed on to few or single partners outside the risk populations, have reached a dead-end [21]. Such multiple introductions of different viral strains from abroad have led to a wide variety of circulating HIV-1 subtypes unevenly distributed among the populations of the country, and more than half of them are not the predominant-to-Europe subtype B [24,25].…”

Molecular Epidemiological Analysis of the Transmission Clusters of the Hiv-1 Circulating Recombinant Forms Crf01_ae and Crf02_ Ag in Bulgaria

“…HIV-1 CRF01_AE and CRF02_AG have been found to be the most prevalent among the most vulnerable groups, such as PWID. In addition, according to our epidemiological data, vulnerable individuals represent a significant proportion of the current HIV+ population in Bulgaria and since 2005 there has been a sharp increase in the incidence of HIV among PWIDs, leading to an outbreak with significant involvement of the CRF01_AE and CRF02_AG viruses (4,10,11). The purpose of this national representative study was to analyse the underlying HIV-1 transmission clusters of the two most widespread recombinant forms of HIV-1 CRF01_AE and CRF02_AG in Bulgaria using the most up-to-date methods for phylogenetic analysis.…”