Distribution of HIV-1 subtypes

HIV-1 subtypes Distribution

Important adaptations have been necessary for the virus to acquire the ability to be efficiently transmitted. Since its emergence, HIV-1 group M has diverged into numerous clades or subtypes (A to K) as well as circulating recombinant forms (CRFs). CRFs have segments of the genome derived from more than one subtype. The highest diversity of HIV remains in west-central Africa, the region where HIV originated. Despite the potential for divergent viruses to spread, only a few viruses have successfully expanded with 90% of the epidemic comprising of just four subtypes (A, B, C and D) and two CRFs (CRF01_AE and CRF02_AG). Currently, subtype C, subtype A, and CRF02_AG together account for majority of thousands of new infections that occur daily worldwide. Historically, many more viruses should have been emerged from Africa but failed establish themselves within transmission networks, or were of lower fitness which limited their dispersal.

The amino acid distances among different subtypes of HIV-1 group M reach approximately 25–30% in the Env gene sequence and 15% in the Gag gene sequence. The subtypes B and D are better considered as subsubtypes within a single subtype, however they have been designated as subtypes for historical reasons. To define a new subtype, subsubtype or CRF, the representative strains must be identified in at least three epidemiologically unlinked individuals. Three near full length genomic sequences are preferred, but two complete genomes with partial sequences of a third strain are sufficient to designate a new subtype, subsubtype or CRF.

Regarding HIV in the Americas, subtype B was the first to appear in the United States and the Caribbean and still remains the most prevalent (98.0%) throughout the region. One study demonstrated that the epidemic originated in Haiti around 1966 and within 5 years a single transmission event occurred that culminated in the subtype B epidemic in the US. The spread of AIDS from Kinshasa and Congo to Haiti can be explained by hundreds of educational technicians working there for UNESCO between 1960 and 1975. All were single and returned regularly on holiday to Haiti.

Distribution of HIV-1 subtypes

Group	Subtype	Distribution
Group	Subtype	Distribution
M	A	East and Central Africa
	B	North and South Africa, Europe, Asia, Oceania
	C	South and East Africa, India, Brazil
	D	Central Africa
	F	Central Africa, Romania, Latin America
	G	Central Africa, Taiwan, Russia
	H	Central Africa, Belgium
	J	Congo, Gambia, Sweden
	K	Cameroon
O		Cameroon, Gabon, France
N		Cameroon

The most prevalent HIV-1 genotypes are subtypes C (47%), A (27.2%), B (12.3%), D (5.3%) and CRF01_AE (3.2%).

 During the AIDS pandemic, it has become clear that host genetic differences between infected individuals as well as between viral species affect the susceptibility or resistance to the disease, revealing a clinical spectrum of rapid, intermediate, or slow progression or, more rarely, nonprogression to AIDS within infected populations.