AIDS in Africa: a disaster no longer waiting to happen

Epidemiological synergy of Trichomonas vaginalis and HIV in Zimbabwean and South African women

BACKGROUND

Trichomonas vaginalis (T. vaginalis) is the most common nonviral sexually transmitted infection in the world. Despite the coexisting global epidemics of T. vaginalis and HIV, little attention has focused on the emerging evidence that T. vaginalis increases susceptibility to, and potentially transmission of, HIV.

METHODS

We evaluated T. vaginalis infection in the context of a multisite, randomized controlled trial amongst women in South Africa and Zimbabwe, to determine first, if risk of HIV acquisition was increased among women recently infected with T. vaginalis, and second, if risk of T. vaginalis acquisition was increased among women infected with HIV.

RESULTS

After controlling for potential confounders, participants infected with T. vaginalis were more likely to test positive for HIV at their following visit, compared to participants uninfected with T. vaginalis (adjusted hazard ratio = 2.05; 95% CI, 1.05-4.02). Similarly, HIV-positive participants were twice as likely to have acquired T. vaginalis infection at the following visit, compared to HIV-negative participants (adjusted hazard ratio = 2.12; 95% CI, 1.35-3.32).

CONCLUSIONS

We found an increased risk of both HIV acquisition associated with T. vaginalis infection and risk of T. vaginalis acquisition associated with HIV infection. This bidirectional relationship represents a potentially important factor in sustaining the HIV epidemic in populations where T. vaginalis is endemic.

Mucin 6 in seminal plasma binds DC-SIGN and potently blocks dendritic cell mediated transfer of HIV-1 to CD4(+) T-lymphocytes

Many viruses transmitted via the genital or oral mucosa have the potential to interact with dendritic cell-specific intercellular adhesion molecule-3 grabbing non integrin (DC-SIGN) expressed on immature dendritic cells (iDCs) that lie below the mucosal surface. These cells have been postulated to capture and disseminate human immunodeficiency virus type-1 (HIV-1) to CD4(+) lymphocytes, potentially through breaches in the mucosal lining. We have previously described that BSSL (bile salt-stimulated lipase) in human milk can bind DC-SIGN and block transfer. Here we demonstrate that seminal plasma has similar DC-SIGN blocking properties as BSSL in human milk. Using comparative SDS-PAGE and Western blotting combined with mass spectrometry we identified mucin 6 as the DC-SIGN binding component in seminal plasma. Additionally, we demonstrate that purified mucin 6 binds DC-SIGN and successfully inhibits viral transfer. Mucin 6 in seminal plasma may therefore interfere with the sexual transmission of HIV-1 and other DC-SIGN co-opting viruses.

The genital tract immune milieu: an important determinant of HIV susceptibility and secondary transmission

HIV is generally sexually acquired across the genital or rectal mucosa after exposure to the genital secretions of an HIV-infected partner. Most exposures to HIV do not result in infection, likely due to protection afforded by an intact mucosal epithelium, as well as by innate and adaptive mucosal immune factors present in the genital tract. Another important mucosal determinant of transmission may be the number and activation status of potential HIV target cells, including CCR5/CD4+ T cells and DC-SIGN+ dendritic cells. The simultaneous presence of other genital infections, including classical sexually transmitted infections (STIs), can enhance HIV susceptibility either by breaching the epithelial barrier, recruiting HIV target cells to the genital tract, or by generating a pro-inflammatory local immune milieu. In HIV-infected individuals, genital co-infections increase HIV levels in the genital secretions, thereby increasing secondary sexual transmission. Co-infections that act as important HIV cofactors include human cytomegalovirus (CMV), Herpes simplex virus type 2 (HSV2), Neisseria gonorrhoeae and many others. Strategies focused on genital co-infections, such as vaccines, microbicides and suppressive therapy, are feasible in the short term and have the potential to curb the pandemic.

Humanism and the suffering of the people

Abstract Humanism includes, among its many contexts, the ideal of the universal perfection of health. Procedures for alleviation of disease existed through all epochs of human history, but efficacy was mostly lacking. The prototypic humanism of the Renaissance (ad 1300-1600) scarcely involved the medical -sciences other than human anatomy. The Enlightenment of the seventeenth century included discovery of the circulation of the blood, and applications of microscopy. Discoveries relevant to medical practice began in the nineteenth century, ushered in by vaccination and the germ theory of disease. This 200-year period saw a transformation of human health according to the surrogate marker of increased life--expectancy. This has been variously attributed to: (i) increased prosperity following the industrial revolution, (ii) efforts of humanistic social and public health reformers and, more recently, (iii) advances in medical science. Yet the beneficiaries remain a minority of the world's population. The nexus between poverty, illness and low life-expectancy between and within nations is the major challenge for the future. Contemporary science is providing ever-expanding knowledge on means to achieve the goal of perfection of human health, but the need for humanism is as great as at any previous age. Fortunately, however, the targets are more clearly visible than during the periods of poverty, plagues and pestilence of the past.

New insights into HIV-1 specific cytotoxic T-lymphocyte responses in exposed, persistently seronegative Kenyan sex workers

A clearer understanding of HIV-1 specific immune responses in highly-exposed, persistently seronegative (HEPS) subjects is important in developing models of HIV-1 protective immunity. HIV-1 specific cytotoxic T-lymphocytes (CTL) have been described in a cohort of HEPS Kenyan sex workers, and recent work has further elucidated these responses. CTL specific for HIV-1 Env were found in the blood of over half the sex workers meeting criteria for HIV resistance, and in some women recognized unmapped epitopes. The proportion of women with Env-specific CTL increased with the duration of uninfected HIV exposure, suggesting that these responses were acquired over time. CD8+ lymphocyte responses directed against predefined HIV-1 CTL epitopes from various HIV-1 genes were found in the blood and genital tract of >50% resistant sex workers, at a ten-fold lower frequency than in infected subjects. The epitope specificity of CD8+ responses differs between HEPS and HIV infected women, and in HEPS the maintenance of responses appears to be dependent on persistent HIV exposure. Several HIV-1 'resistant' sex workers have become HIV infected over the past 6 years, possibly related to waning of pre-existing HIV-specific CTL, and infection has often been associated with a switch in the epitope specificity of CD8+ responses. These findings suggest that vaccine-induced protective HIV immunity is a realistic goal, but that vaccine strategies of boosting or persistent antigen may be necessary for long-lived protection.