final program.qxd - Parallels Plesk Panel

OP 6.2
Molecular Epidemiology of HIV-1 infection: tracing how the epidemic spreads
Dimitrios Paraskevis
National Retrovirus Reference Center, Department of Hygiene and Epidemiology, Faculty
of Medicine, National and Kapodistrian University of Athens
HIV-1 originated in Africa through cross-species transmission from the chimpanzees
infected with simian immunodeficiency virus (SIVcpz). The majority of HIV-1 infections
worldwide have been caused by group M that became pandemic in contrast to group O
localized in west-central Africa, and group N, which has been documented only among a
few individuals in Cameroon. The group M has been classified into subtypes,
sub-subtypes and circulating recombinant forms (CRFs).
The prevalence of the different subtypes and CRFs differ according to the geographic
origin. The global distribution of the different HIV-1 clades provides information about the
origin and the way of spread of the infection. The spillover of the infection occurred from
the Democratic Republic of Congo (DRC) to the neighbouring countries in Africa (e.g.
Congo-Brazaville, Uganda, Tanzania and Zambia) by establishing monophyletic
epidemics of non-B subtypes in these areas. Similarly, the epidemic was spread in
Western countries, as a founder effect of subtype B, originated from Africa.
Introduction of the HIV-1 epidemic in Europe mainly occurred through sexual exposure to
men in the USA, or through heterosexual contacts with individuals from Central Africa.
During the early stages of the AIDS epidemic (early eighties), the prevalence of the
HIV-1 infection was higher among men having sex with other men (MSM) compared to
heterosexuals. For this reason subtype B, which was exclusively identified among MSM
in the US, was the predominant clade in Europe before nineties. The prevalence of
non-B subtypes have been increasingly recognized the last years in Europe and other
than B clades are mainly associated with immigrants or heterosexuals epidemiologically
linked with sub-Saharan Africa. In contrast to other European countries, subtype A
predominates in several areas in Russia, especially after 1997 when the epidemic start
spreading at a very high rate among IDUs.
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