"Sexual transmission is by far the most important, accounting for over 75% of all HIV infections world wide. During the early phases of the epidemic, homosexual transmission was the predominant mode in developed countries. However, during the past 5 years, there has been evidence of increasing trends for heterosexual transmission in industrialised countries. In the Caribbean, heterosexual transmission has now replaced homosexual transmission as the major mode of HIV spread."

Molecular epidemiology: the HIV-1 subtypes:
• At least nine HIV-1 subtypes (A, B, C, D, E, F, G, H and O) occur on the African continent
• Importance of understanding HIV-1 subtypes and HIV-1 genetic diversity in order to vaccinate throughout Africa
• The wonderful HIV sequence database maintained at Los Alamos National Labs in New Mexico, USA by Gerald Myers and Bette Korber
• The JAMA article on HIV-1 diversity:
  

  Hu DJ, Dondero TJ, Rayfield MA< George JR, Schochetman G, Jaffe HW, Luo C-C, Kalish ML, Weniger BG, Paul C-P, Schable CA, Curran JW. (1996). The emerging genetic diversity of HIV: the importance global surveillance for diagnostics, research, and prevention. J. Amer. Med. Assoc. (Jan 17, 1996)).

• Subtype C, even beginning to creep into the USA. This subtype is present now on five continents and in 21 nations, most recently including Malaysia (Brown et al., AIDS Res. Human Retrov. 12(17), 1655-1657.
  
• Our group is studying subtype-specific differences in the regulation of HIV-1 gene expression:
  

  Zachar V, Thomas RA, Zacharova V, Ebbesen P, Goustin AS. (1994). Basal and Tat-transactivated expression from the human immunodeficiency virus-1 long terminal repeat in human placental trophoblast rules out promoter-enhancer activation as the partial block to viral replication.
  J. Gen. Virology. 75(6), 1461-1468.

  and

  Zacharova V, Becker MLB, Zachar V, Ebbesen P, Goustin AS. (1997). DNA sequence analysis of the long terminal repeat of the C subtype of human immunodeficiency virus type 1 from southern Africa reveals a dichotomy between B subtype and African subtypes on the basis of upstream NF-IL6 motif.
  AIDS Research & Human Retroviruses 13(8), 719-724.

  A paper focused on the function of the diverse elements in the C and E subtype viruses appeared recently in J. Virol. from Max Essex' group at the Harvard AIDS Institute:

  Montano MA, Novitsky VA, Blackard JT, Cho NL, Katzenstein DA, Essex M. (1997). Divergent transcriptional regulation among expanding human immunodeficiency type 1 subtypes.
  J. Virol. 71(11), 8657-8665.

  Other issues in maternal-fetal transmission
  

  Zachar V, Hager H, Koppelhus U, Zacharova V, Liu X, Bambra C, Goustin AS, and Ebbesen P. (1997). Elevated IFN-alpha in maternal and umbilical cord blood, and in the placental trophoblast suggests natural protection against vertical transmission of HIV-1 in a Kenyan cohort.
  AIDS [London] 11, 383-384.

  Zacharova V, Zachar V, Goustin AS. (1997). Sequence of chemokine reeptor gene CCR5 in chimpanzees, a natural HIV-1 host.
  AIDS Res. Hum. Retroviruses, accepted for publication, slated for August 20, 1997 issue.

  In this paper, we report the sequence of the chemokine receptor CCR5 in chimpanzees, a species which can be infected by HIV-1, but does not succumb to HIV pathogenesis (AIDS) for reasons which are completely opaque. Chimp CCR5 differs from human CCR5 at two positions, N13D and X130X. David Kabat's group at the Oregon Health Sciences University, however, has recently reported (J Virol 1997 Nov;71(11):8642-865) that substitution of TYR by ASN at the 14 position (as found in the African green monkey CCR5) ablates the ability of AGM CCR5 to serve as a receptor for macrophage-tropic strains of HIV-1. It is not known whether substitution of ASP (D) for ASN (N) at the 13 position has a similar effect on the ability of chimp CCR5 to serve as a receptor for m-tropic HIV-1.