A strong association exists between infection with herpes simplex virus type 2 (HSV-2), the virus that causes genital herpes, and HIV infection. HSV-2 leads to inflammation and small breaks in the genital and anal skin that can make it easier for HIV to cause infection.
In 2017, a systematic review and meta-analysis of 55 prospective studies found that the risk of becoming infected with HIV was at least tripled in people with HSV-2 infection compared with people without HSV-2, after controlling for sexual behaviour and other factors. Given this large observed risk, scientists next sought to estimate how many HIV infections are likely to be attributable to HSV-2, at a global and regional level.
The study estimated that the proportion of new sexually acquired HIV infections in 2016 that were attributable to HSV-2 infection was 29·6%. However, this global figure, known as the population attributable fraction (PAF), varied greatly by region. The largest number and highest proportion of HIV infections estimated to be due to HSV-2 infection were in Africa (37·1%). This is because of the greater proportion of people in this region with HSV-2 infection and with HIV. The Americas had an estimated PAF of 21.3% and elsewhere in the world, the PAF ranged between 11 and 13%.
The estimated PAF of HIV attributable to HSV-2 was higher among women than men (34.8% compared to 26.2%), and higher among 25-49-year olds for both sexes compared with younger ages.
Using estimates to inform prevention efforts
These estimates are useful for understanding the potential magnitude of the contribution of HSV-2 infection to HIV incidence, which can help stimulate development of new interventions and guide where future prevention efforts would be best targeted for optimal effect.
Although a number of limitations and caveats surround these data, the estimates nevertheless highlight the important link between HSV-2 and HIV infections and suggest that the global contribution of HSV-2 infection to HIV acquisition could be substantial. Addressing HSV-2 infections not only has the potential to reduce the number of people suffering from genital herpes, but could also make an important contribution to HIV prevention.
In settings or populations with high HIV incidence, people with symptoms suggestive of HSV-2 infection could benefit from HIV testing and more focused HIV prevention efforts, such as pre-exposure prophylaxis. In addition, further investment is needed in development of new interventions against HSV-2 infection, such as vaccines, new antivirals, or microbicides.
The authors recognise that no single intervention will likely be sufficient to achieve global HIV prevention goals, and combination measures are needed. These estimates suggest that HSV-2 prevention measures could be an important additional tool in the fight against HIV.