Genital herpes can return despite antiviral therapy

5th January 2012 - The virus that causes genital herpes can reactivate even when high doses of antiviral therapy are being given, a study has found.

Researchers in the US say these 'breakthrough episodes' underline the need to find new treatments to stop it being spread from person to person.

A common condition

Genital herpes is caused by the herpes simplex virus (HSV) type 1 or type 2. It is highly contagious and is passed on by direct contact. Genital herpes is usually transmitted by having sex with another person. Once an individual is infected it can cause painful blisters on the genitals and surrounding areas.

Genital herpes is a common condition. The NHS says that in 2008, nearly 29,000 people attended a sexual health clinic in the UK with a first clinical attack of genital herpes.

Three linked trials

In the latest study, researchers from the University of Washington Virology Research Clinic enrolled 113 patients with herpes simplex virus type 2 (HSV-2) for three separate but complementary trials.

Participants were divided into three trial groups to randomly receive different treatment programmes.

• In the first trial patients either received no medication or a standard dose (400mg) of acyclovir
• In the second trial participants either received a high dose of acyclovir (800mg) or a standard dose of valaciclovir (500mg)
• In the third trial patients were given either standard dose of valaciclovir or high dose valaciclovir (1g three times daily)

'Breakthroughs' continued

The researchers, led by Dr Christine Johnston, found that the virus was able to leave its dormant state - when this happens, the virus can navigate the nerve pathways to the skin surface, replicate, and may be passed to others in a process known as 'shedding' - even when patients were taking standard-dose or high-dose aciclovir and valaciclovir.

They also found that, although HSV shedding was reduced by 50% with the highest doses of valaciclovir, compared with standard dose valaciclovir, the rate of breakthrough episodes remained unchanged at about 16 to 20 occurrences each year.

New treatments needed

The authors write: "That we could not eliminate or even alter the frequency of shedding episodes with high-dose valaciclovir suggests that the maximum benefit of shedding reduction has probably been reached for currently available antiviral drugs."

They conclude that "suppressive therapies with greater potency" are needed to successfully prevent the virus being passed on.

The study is published Online First by The Lancet .

In a linked article in the same edition, two French specialists, Dr Philippe Van de Perre and Dr Nicolas Nagot, write that the latest research offers clues to the unsolved question about why HSV transmission is not stopped by existing suppressive treatments.

They note that the development of new classes of antiviral medication are unlikely to prove a panacea, partly because of the already high rates of infection in Europe and the US, where around one in five of the population is infected with HSV-2.

They add: "The finding that treatment cannot fully prevent transmission should encourage patients to use condoms and adopt safe sex practices, especially since increase of the treatment dose would not further reduce the risk of transmission to patients? partners."