Introduction.

HIV-1 is characterized by a high evolutionary rate that led to the establishment of different viral lineages. Group M is the most widespread group representing the main source of the HIV/AIDS pandemic. Based upon latest classification, it is further divided into nine subtypes (A, B, C, D, F, G, H, J and K), six sub-subtypes (A1, A2, A3, A4, F1 and F2), an increasing number of Circulating Recombinant Forms (CRFs) (of whom 52 are known at present) and an undetermined number of Unique Recombinant Forms (URFs) [1].

As a consequence of migratory waves from low-middle income areas, non-B variants entered and circulates in almost all previously B-restricted European countries [2]–[6].

The spread of non-B clades in Italy occurred in conjunction with relevant epidemiological changes such as the increase of sexual transmission [7]. Indeed, the prevalence of non-B subtypes grew from 2.6% in 1985–1992 to 18.9% in 1993–2008. Among these non-B isolates, subtype F1 is the most frequent variant (44.3%) among European subjects followed at 50 Italian clinical Centers [8].

HIV-1 F1 subtype was firstly isolated in the Democratic Republic of Congo, where it accounts for a small percentage (<5%) of diagnosed cases at present [9]. This subtype circulates at low frequency worldwide (<1%) and has spread to South America and Europe, both as a ‘pure’ strain and as part of several B/F recombinant forms [10]. In South America, F1 subtype and BF recombinant forms account for more than 10% of HIV-1 epidemic and are associated with intravenous drug use and heterosexual route of infection [11].

In Europe, subtype F1 has a massive prevalence in Rumania (>70%), where it spread among adults few years before its striking emergence among institutionalized children around 1989 [12].

The origin of HIV-1 non-B infections in Italy has been not thoroughly investigated by specific population studies [13]–[15]. Information on epidemiological networks has been obtained in small areas or in B-subtype restricted population [16], [17].

Since HIV-1 gene sequencing for drug-resistance monitoring has been widely adopted, new phylogenetic methods have been developed which allow to infer evolutionary dynamic from sequence data [18], [19]. Molecular epidemiology may trace the origin of viral infections, reveal outbreaks within population subgroups and provide a means for monitoring the spread within and among groups with different mode of infection. Moreover, phylogenetic analysis can investigate evolutionary patterns of pathogens within a specific population, gaining useful insights on their epidemics [20].

The burden of immigration in Italy, reported by the National Institute for Statistics (ISTAT) (www.istast.it), indicates that Rumanians with about 1 million of persons, account for the main foreign community, while no information are available for specific countries of South America that contribute to immigration with about 350,000 presences. The aim of this study was to reconstruct the epidemiological features of F1 subtype in Italy by analyzing data from a nation-wide collaboration. Furthermore, we identified the epidemiological networks and established the relationships among the main demographic variables such as citizenship, route of infection and gender.

Abstract.

About 40% of the Italian HIV-1 epidemic due to non-B variants is sustained by F1 clade, which circulates at high prevalence in South America and Eastern Europe. Aim of this study was to define clade F1 origin, population dynamics and epidemiological networks through phylogenetic approaches. We analyzed pol sequences of 343 patients carrying F1 subtype stored in the ARCA database from 1998 to 2009. Citizenship of patients was as follows: 72.6% Italians, 9.3% South Americans and 7.3% Rumanians. Heterosexuals, Homo-bisexuals, Intravenous Drug Users accounted for 58.1%, 24.0% and 8.8% of patients, respectively. Phylogenetic analysis indicated that 70% of sequences clustered in 27 transmission networks. Two distinct groups were identified; the first clade, encompassing 56 sequences, included all Rumanian patients. The second group involved the remaining clusters and included 10 South American Homo-bisexuals in 9 distinct clusters. Heterosexual modality of infection was significantly associated with the probability to be detected in transmission networks. Heterosexuals were prevalent either among Italians (67.2%) or Rumanians (50%); by contrast, Homo-bisexuals accounted for 71.4% of South Americans. Among patients with resistant strains the proportion of clustering sequences was 57.1%, involving 14 clusters (51.8%). Resistance in clusters tended to be higher in South Americans (28.6%) compared to Italian (17.7%) and Rumanian patients (14.3%). A striking proportion of epidemiological networks could be identified in heterosexuals carrying F1 subtype residing in Italy. Italian Heterosexual males predominated within epidemiological clusters while foreign patients were mainly Heterosexual Rumanians, both males and females, and South American Homo-bisexuals. Tree topology suggested that F1 variant from South America gave rise to the Italian F1 epidemic through multiple introduction events. The contact tracing also revealed an unexpected burden of resistance in epidemiological clusters underlying the need of public interventions to limit the spread of non-B subtypes and transmitted drug resistance.