HIV-2 infection spread under particular political and social circumstances during the independence wars of former Portuguese territories. In Guinea Bissau, for example, the demographic history of HIV-2 is characterized by a period of low endemicity followed by an exponential increase in the number of infections during the war (1961–1974). Increased commercial sex, unsafe blood transfusions and other events occurring in a socially and economically disrupted country probably facilitated transmission of the virus [11]. The highest prevalence

of HIV-2 infection was reported two decades ago in Guinea Bissau: Z-VAD-FMK purchase the prevalence was 8% in adults, and reached up to 20% in individuals over 40 years of age [18]. The estimated incidence of HIV-2 infection in Guinea Bissau is now declining: between 1996 and 2006 the incidence PLX3397 datasheet rate for HIV-2 infection was 0.24 per 100 person-years (0.5 per 100 person-years for HIV-1) [19]. These historical and socioeconomic circumstances might help to explain why Portugal is the country outside the African continent with the highest

number of HIV-2-infected patients. However, studies on HIV-2 epidemiology in Portugal are limited and have provided contradictory descriptions [15-17]. By investigating a larger sample, including patients from five hospitals, we have tried to minimize selection biases. Important information can be obtained by looking at epidemiological data over time. The independence wars in Portuguese Tolmetin colonies during the period 1960–1974 probably had a role in the introduction of HIV-2 to Portugal. The fact that most HIV-2-infected patients included in our sample who were diagnosed before 1990 were male (39; 68.4%), Portuguese (45; 78.9%) supports this possibility. For more than 10 years, hundreds of thousands of soldiers were sent to Africa. Heterosexual

transmission was reported for the majority of cases in the present study, but the importance of blood transfusions and/or surgical procedures performed during the war should not be underestimated. The independence wars were also responsible for a massive influx of repatriates (more than 500 000), including women, into Portugal. From 1990 to 1994, the number of diagnosed infections increased. The similar characteristics in terms of nationality (Portuguese) and area of residence (the north of the country) of most of the persons diagnosed in this period compared to those diagnosed in the previous period may reflect the ongoing transmission of HIV-2 after its introduction into the country. Further, the fact that the proportions of male and female individuals diagnosed were similar supports the hypothesis that transmission from previously infected male patients (many of them probably former soldiers) to their female partners took place. The last 5 years of the 1990s anticipated the change clearly observed from 2000 onwards, probably as a result of increased migration from West Africa, reversing previously described trends.