HIV This Week

Abu-Raddad LJ, Magaret AS, Celum C, Wald A, Longini IM Jr, Self SG, Corey L. Genital herpes has played a more important role than any other sexually transmitted infection in driving HIV prevalence in Africa. PLoS ONE. 2008; 3(5):e2230.

Extensive evidence from observational studies suggests a role for genital herpes in the HIV epidemic. A number of herpes vaccines are under development and several trials of the efficacy of HSV-2 treatment with acyclovir in reducing HIV acquisition, transmission, and disease progression have just reported their results or will report their results in the next year. The potential impact of these interventions requires a quantitative assessment of the magnitude of the synergy between HIV and HSV-2 at the population level. A deterministic compartmental model of HIV and HSV-2 dynamics and interactions was constructed. The nature of the epidemiologic synergy was explored qualitatively and quantitatively and compared to other sexually transmitted infections. The results suggest a more substantial role for HSV-2 in fuelling HIV spread in sub-Saharan Africa than other sexually transmitted infections. Abu-Raddad and colleagues estimate that in settings of high HSV-2 prevalence, such as Kisumu, Kenya, more than a quarter of incident HIV infections may have been attributed directly to HSV-2. HSV-2 has also contributed considerably to the onward transmission of HIV by increasing the pool of HIV-positive persons in the population and may explain one-third of the differential HIV prevalence among the cities of the Four Cities study. Conversely, the authors estimate that HIV had only a small net impact on HSV-2 prevalence. In conclusion, HSV-2’s role as a biological cofactor in HIV acquisition and transmission may have contributed substantially to HIV particularly by facilitating HIV spread among the low-risk population with stable long-term sexual partnerships. This finding suggests that prevention of HSV-2 infection through a prophylactic vaccine may be an effective intervention both in nascent epidemics with high HIV incidence in the high risk groups, and in established epidemics where a large portion of HIV transmission occurs in stable partnerships.

Editors’ note: The herpes simplex-2 (HSV-2) epidemic in sub-Saharan Africa appears to have started in the first half of the twentieth century and reached its peak at about 50% prevalence prior to the HIV epidemic. Now the two viruses are happy bedfellows with HSV-2 increasing HIV acquisition and transmission more than HIV increases HSV-2 acquisition and transmission. This synergy has allowed HIV to reach a higher proportion of the general population than would have been possible without this biological interaction. An effective HSV-2 vaccine is urgently needed to protect all young people in established epidemics before sexual debut, but there is no doubt that it would be beneficial worldwide.