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Background: The origin of the HIV-2 infection in humans has been recently traced to the 1940s, with an epidemic spread in Guinea Bissau (GB) between 1955-1970, coincident with the independence war in that country. It has been suggested that sexual transmission was the most important factor for this spread, in spite of its known low efficiency when compared with HIV-1. Portugal is the European country with the highest rates of imported HIV-2 infection. We wanted to investigate in more detail the war-related events possibly at the cause of this HIV-2 epidemic.

Methods: 218 HIV-2-infected patients, distributed among all stages of CDC classification (A--75%, B--10%, C--15%), were followed up between 1997 and 2002. Most of them are native from GB and Cabo Verde (42% and 15%). To further investigate the role of sexual activity versus parenteral transmission during the war, we looked into the HIV status of 1022 former Portuguese soldiers in GB, all candidate blood donors gathered at our institution.

Results: For our 218 HIV-2-infected patients, men (52%) and women (48%) were equally affected and in most cases a single route of transmission is difficult to establish. The great majority (67%) of them were born between 1940-1970 (median 1957), being significantly older (p <0.0001) than HIV-1-infected patients (median year of birth: 1967). None of the candidate blood donors was found HIV-2 reactive, although 9% of them admitted sexually transmitted disease events while in GB.

Conclusions:  The median birth year of our patients fit within the 1955-1970 period, suggested as the transition time for the HIV-2 epidemic spread. Most of them are natives from GB that were young children at the time of the war, and now come to Portugal as immigrants or for health treatments. A high percentage of these HIV-2-infected patients, were born in a narrow time window, suggesting a transient factor not compatible with predominant sexual transmission, which would result in a more even distribution through all the age groups. If sexual transmission had been the main factor for the epidemic spread, we expected more Portuguese military personnel infected than those notified and HIV-2 epidemics in Portugal, France, India, or Brazil, where HIV-2 cases had been reported – which is not the case. Our findings suggest parenteral exposure (injections, vaccination, blood and their derivates, nosocomial and some traditional practices) as the principal route for the spread of this virus during the epidemic period.

Keywords: HIV-2; transmission; parenteral