Although it is clear that HIV is the underlying cause of AIDSand AIDS-related disease, its origin remains obscure. There isfirm serological evidence of infection on the east and westcoasts of the USA from the mid 1970s, and HIV infection incentral Africa may have antedated infection in North America.Phylogenetic analysis of the HIV-1 genome has suggested anorigin in chimpanzees while, in the case of HIV-2, similarity tothe simian immunodeficiency virus (SIV) genome may point toan origin in sooty mangabey monkeys. In both cases thebutchery and consumption of these “bush meats” has beenincriminated in transmissions to the human host. Like someother RNA viruses, HIV appears to have mutated and shifted itshost range and virulence, explaining how a new pathogenicretrovirus could arise in man. Its virulence may since have beenamplified as a result of travel, population dislocation andpromiscuous sexual contact, with rapid passage of the virus.
Retroviruses are so named because their genomes encode anunusual enzyme, reverse transcriptase, which allows DNA to betranscribed from RNA. Thus, HIV can make copies of its owngenome, as DNA, in host cells such as the human CD4 “helper”lymphocyte. The viral DNA becomes integrated in thelymphocyte genome, and this is the basis for chronic HIVinfection. Integration of the HIV genome into host cells is aformidable obstacle to any antiviral treatment that would notjust suppress but also eradicate the infection. Nevertheless,modern treatment with combinations of nucleoside analoguesand protease inhibitors has transformed the prognosis forcarriers of HIV, usually achieving a sustained fall in virusconcentration in blood and restoration of the main target cell(CD4 lymphocyte) to near normal levels.
By contrast, the inherent variability of the HIV genome andthe failure of the human host to produce neutralising antibodiesto the virus, as well as technical difficulties and concerns aboutsafety, have continued to frustrate attempts to make an effectivevaccine. This must not, however, allow efforts to develop andevaluate candidate vaccines to slacken. A particular concern isthat a useful candidate vaccine (probably a recombinantenvelope vaccine developed in North America or Europe againstthe locally prevalent HIV-1 B subtype) would be ineffective inthose parts of the world where other subtypes predominate.
WHO estimates that in the year 2000 there are 36 millioncarriers of HIV worldwide, and only a small fraction of themhave access to suppressive treatment. Both their contacts, theirdependants and possibly they themselves would have their lifeprospects transformed by an effective, or even partially effective,vaccine, and successful application of antiviral treatment indeveloped countries should in no way be allowed to deflectattention from the necessity of developing and delivering aneffective vaccine and of promoting “safe sex” behaviour.
Retroviruses are so named because their genomes encode anunusual enzyme, reverse transcriptase, which allows DNA to betranscribed from RNA. Thus, HIV can make copies of its owngenome, as DNA, in host cells such as the human CD4 “helper”lymphocyte. The viral DNA becomes integrated in thelymphocyte genome, and this is the basis for chronic HIVinfection. Integration of the HIV genome into host cells is aformidable obstacle to any antiviral treatment that would notjust suppress but also eradicate the infection. Nevertheless,modern treatment with combinations of nucleoside analoguesand protease inhibitors has transformed the prognosis forcarriers of HIV, usually achieving a sustained fall in virusconcentration in blood and restoration of the main target cell(CD4 lymphocyte) to near normal levels.
By contrast, the inherent variability of the HIV genome andthe failure of the human host to produce neutralising antibodiesto the virus, as well as technical difficulties and concerns aboutsafety, have continued to frustrate attempts to make an effectivevaccine. This must not, however, allow efforts to develop andevaluate candidate vaccines to slacken. A particular concern isthat a useful candidate vaccine (probably a recombinantenvelope vaccine developed in North America or Europe againstthe locally prevalent HIV-1 B subtype) would be ineffective inthose parts of the world where other subtypes predominate.
WHO estimates that in the year 2000 there are 36 millioncarriers of HIV worldwide, and only a small fraction of themhave access to suppressive treatment. Both their contacts, theirdependants and possibly they themselves would have their lifeprospects transformed by an effective, or even partially effective,vaccine, and successful application of antiviral treatment indeveloped countries should in no way be allowed to deflectattention from the necessity of developing and delivering aneffective vaccine and of promoting “safe sex” behaviour.
