Michael Carter
Approximately 30% of new sexually transmitted HIV infections can be attributed to the herpes simplex virus-2 (HSV-2), according to research published in The Lancet Infectious Diseases . Africa was the global region with the highest proportion of HIV incidents attributable to HSV-2, followed by the Americas. The researchers, led by Dr. Katherine Looker of the University of Bristol Medical School, suggest that interventions to treat and prevent HSV-2 would not only improve the quality of life for millions of people, but would also have a tangible impact on the spread of HIV.
"These estimates are useful for understanding the potential magnitude of the contribution of HSV-2 infection to HIV, which can help stimulate the development of new interventions and guide where future prevention efforts would be best targeted for optimal effect," the authors comment. "New HSV-2 interventions, such as vaccines, new antivirals, or microbicides, have the potential to substantially reduce genital ulcer disease, which affects millions of people worldwide."
An estimated 42 million people worldwide have HSV-2, an STI that can cause recurrent and painful genital ulcers. The prevalence of infection is highest in Africa, where an estimated 31% of adults are carriers of the infection. There is also a high burden of HIV infection in this region.
In 2017, Dr. Looker and colleagues conducted a meta-analysis of 55 prospective studies that showed the risk of HIV infection tripled for people with HSV-2 infection and quadrupled for people with recently acquired HSV-2.
The risk is increased because the sores caused by HSV-2 infection provide a direct physical route of entry for HIV into an uninfected person. Another factor is the immune system's response to HSV-2 infection: activated T cells and dendritic cells, which are susceptible to HIV infection, are present in significant numbers at the site of the herpes infection.
Dr. Looker wanted to build on his previous research by calculating the proportion of new sexually transmitted HIV cases (incident infections) attributable to HSV-2 infection: the population attributable fraction (PAF). They did this by looking at global epidemiological data from 2016. The calculations also took into account established risk factors for HIV acquisition. The analysis was restricted to individuals between the ages of 15 and 49.
In 2016, there were an estimated 1.4 million new sexually transmitted HIV infections among people aged 15 to 49 years. Researchers estimated that 420,000 of these infections (30%) were due to HSV-2.
The proportion of infections attributable to HSV-2 was highest in the African region (37%), followed by the Americas (21%). In all other regions, the proportion of new HIV infections due to HSV-2 was estimated to be between 11 and 13%.
The percentage of new HIV infections due to HSV-2 was higher among women than men (36% vs. 26%) and among individuals aged 25–49 years compared with those in the 15–24 age group (32% vs. 23%). This was due to underlying trends in the epidemiology of HSV-2, with higher prevalence among women and older adults.
"Innovative treatments and technologies are needed for the prevention, treatment, and control of HSV-2."
Just over a quarter (27%) of new HIV infections among female sex workers were due to HSV-2. One-fifth of HIV cases among men who have sex with men (MSM) were attributed to HSV-2.
An editorial commentary on the article suggests that the proportion of HIV infections due to HSV-2 may be even higher when onward transmission among key risk groups such as homosexuals and other MSM is taken into account.
Only 4% of HIV infections were due to recently acquired HSV-2. "This finding may be explained by the fact that many more individuals have recently established HSV-2, especially at older ages," the authors write.
The researchers believe their findings demonstrate the importance of public health interventions to control HSV-2. However, they note that the research looking at existing antiviral treatment for HSV-2 had no effect on HIV infections. This is possibly because the drugs used in the study had insufficient impact on the levels of HIV-susceptible cells in the skin tissue around HSV-2 lesions. Therefore, innovative treatments and technologies are needed for the prevention, treatment, and control of HSV-2.
“New and more effective interventions could hold promise for impacting HSV-2 infection or clearance and reducing HIV incidence,” Dr. Looker and colleagues conclude. “A potential indirect effect of HSV-2 interventions on HIV incidence will need to be assessed in the context of existing HIV prevention interventions and for new HSV-2 interventions, particularly HSV-2 vaccines. Our estimates suggest that HSV-2 prevention measures could be an important additional tool in the fight against HIV.”
Referencias
Looker KJ et al. Global and regional estimates of the contribution of herpes simplex virus type 2 infection to HIV incidence: a population attributable fraction using published epidemiological data. The Lancet Infectious Diseases, online ahead of print, 2019 (open access).
https://doi.org/10.1016/S1473-3099(19)30470-0
Mishra S et al. Rethinking the population attributable factor of infectious diseases. The Lancet Infectious Diseases, online ahead of print, 2019 (open access).
At: http://www.aidsmap.com/news/jan-2020/third-new-sexually-transmitted-hiv-infections-directly-due-infection-herpes-simplex