Researchers at Johannesburg’s Chris Hani Baragwanath hospital are homing in on the link between HIV and the genital herpes virus, which is thought to infect more than half of South Africa’s adults.
A team from the hospital’s reproductive health and HIV research unit, led by Sinead Delany-Moretlwe, is running three research trials investigating whether giving daily prophylactic anti-herpes drugs to people infected with the human herpes simplex virus, HSV-2, will reduce HIV transmission.
HSV-2 may be a factor in Southern Africa’s high HIV infection rate, as there is evidence that it triggers replication of HIV within the body and triples the chances of catching it.
Two-thirds of adult women in South Africa, Zambia and Zimbabwe are thought to carry HSV-2, most without knowing they are infected. This compares with 30% among adults in Europe and 22% in the United States.
HIV-positive people who have herpes are more likely to develop Aids more rapidly, and to transmit both viruses.
HSV-2 is a lifelong passenger, disappearing during asymptomatic latent phases but able to reactivate at any time to produce ulcers.
Herpes carriers are most infectious when the disease is active, although they can transmit it at other times.
Anti-viral drugs such as acyclovir, used for more than 20 years, can ease the symptoms but not eradicate the infection.
Over the past 10 years South Africa has seen herpes go from being a relatively uncommon factor in genital ulcers to their leading cause. This is partly owing to success in treating other sexually transmitted diseases, such as syphilis, and partly to the escalating HIV epidemic, which exacerbates the severity and frequency of herpes outbreaks.
The precise interaction between the two viruses is not fully understood. However, doctors know herpes sores breach the skin’s defences, providing an entrance into, and exit from, the body for HIV.
Once inside, the virus finds a plentiful supply of its preferred infection targets in the massed CD4 cells mobilised by the immune system to fight herpes. There is growing evidence that HSV-2 releases a chemical signal that encourages HIV to replicate.
Delany-Moretlwe says there is evidence that having HSV-2 increases the chances of becoming infected with HIV as much as threefold, especially in women, and that it also makes it easier to transmit HIV.
One trial is investigating the effect on the number and severity of HSV-2 sores if people are given continuous acyclovir treatment, and whether it reduces their chances of becoming HIV-infected. The second is looking at the impact of daily acyclovir on the amount of HIV shed vaginally by women who have both HIV and HSV-2. The third looks at “serodiscordant” couples where one person has both HIV and HSV-2, checking whether daily acyclovir reduces the chances of the HIV-negative partner catching the virus.