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326 Viral Diversity of HIV in Cameroon: Evidence for Five HIV-1 Group O Subtypes
J. Yamaguchi1, A. S. Vallari1, P. Swanson1, P. Bodelle1, L. Kaptué2, C. Ngansop2, L. Zekeng3, L. G. Gürtler4, S. G. Devare1, and C. A. Brennan*1
1Abbott Labs, Abbott Park, IL, USA; 2Univ. de Yaoundé, Cameroon; 3Lab. de Santé Hygiène Mobile, Yaoundé, Cameroon; and 4Loeffler Inst., Univ. of Greifswald, Germany
Background and Methods: We examined HIV viral diversity in 404 plasma specimens collected in Cameroon between 1996 and 1999. Based on serological testing, the panel consisted of 374 HIV-1 group M, 29 HIV-1 group O, and 1 HIV-2 infections. To facilitate phylogenetic analysis of group O, gag p24 (693 nts), pol p32 (864 nts), and env gp160 (~2,700 nts) were sequenced from the 29 group O isolates as well as 11 group O isolates from the US, Cameroon, Equatorial Guinea, and Germany. In addition to determine the extent of group M strain variation in Cameroon, phylogenetic analyses of segments of gag p24 and env gp41 were performed on 62 group M infections.
Results: Phylogenetic analysis of HIV-1 group O sequences resulted in identification of 5 subtypes that are equidistant from each other and supported by high bootstrap values. The existence of additional subtypes is suggested by isolates that branch independently and are equidistant from other isolates. Group O subtype A is further subdivided into sub-subtypes: A1 (includes ANT70), A2, and A3, which may consist of additional sub-subtypes. The average intra-, sub-, and inter-subtype distances are similar for group O and group M subtypes. The subtype classification is congruent across gag, pol, and env suggesting the absence of inter-subtype recombination. Of the 62 group M infections analyzed, the predominant strain is subtype A (41; 66%). Most of the subtype A specimens (32; 52%) group with CRF02_AG. Eleven (18%) specimens were inter-subtype recombinants of subtypes A/D, A/E, A/F2, A/G, and A/H. Subtypes D (7; 11%), F2 (2; 3%), and G (1; 1.5%) were also found.
Conclusions: The level of HIV viral diversity in Cameroon is high. In contrast to a high percentage of inter-subtype recombinants among the group M isolates, no evidence of recombination within group O was found. The star phylogeny of group O is consistent with a single introduction into humans of the ancestral virus of group O. In addition, the high genetic diversity within group O isolates collected in Cameroon suggests that Cameroon is the epicenter for group O.
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