Even when they don't have an active herpes outbreak, people who carry genital herpes viruses are at risk of infecting their sex partners. With the discovery of drugs that prevent herpes outbreaks, there was hope that the drugs would also prevent herpes transmission. But there's been troubling evidence that this may not be true.
Now University of Washington researcher Christine Johnston, MD, and colleagues show that people with no herpes symptoms often shed infectious genital herpes virus -- even while taking very high doses of anti-herpes drugs.
"Short episodes of genital [herpes virus] shedding occur frequently with antiviral therapy, even for high-dose regimens," Johnston and colleagues report. "These breakthrough episodes are typically [without symptoms], last several hours, and occur at much the same rate irrespective of antiviral dose."
One in 5 Americans and Europeans carries HSV-2, the virus that causes most cases of genital herpes; HSV-1 causes some cases. Most people have few, if any, of genital herpes' painful symptoms: blisters on or around the genitals or rectum.
There's no cure for herpes infections. That's because herpes viruses travel up nerves to take up latent form in the nerve root. Powerful anti-herpes drugs -- acyclovir (Zovirax), famciclovir (Famvir), and valacyclovir (Valtrex) -- prevent most outbreaks in most people. But they don't eliminate virus hiding in nerve cells.
Recent clinical trials failed to show that herpes drugs could prevent herpes transmission. This led Johnston's team to conduct three intensive new studies.
In each study, adult volunteers already infected with HSV-2 swabbed their genital and rectal areas four times each day for eight to 14 weeks. The swabs were tested for HSV-2.
Infectious Despite High-Dose Herpes Treatment
In the first study, the volunteers were randomly given a standard 400 mg, twice-daily dose of acyclovir or an inactive placebo pill for four weeks. After a one-week washout period, they switched to the active or placebo treatment for another four weeks.
The result: Swabs were 95% less likely to test positive for HSV-2 when a person was taking acyclovir. But even during treatment, people tested positive 3% of the time.
In the second and third studies, the researchers selected volunteers who suffered frequent genital herpes outbreaks. In study two, they took either 800 mg three-a-day, high-dose acyclovir or standard 500 mg daily doses of valacyclovir. Study three compared standard-dose valacyclovir against high-dose valacyclovir (1,000 mg three times daily). As in the first study, volunteers switched treatments after a one-week washout period.
The result: None of these very high doses of active anti-herpes drugs completely prevented genital shedding of infectious herpes virus. Even with high-dose valacyclovir, 3% of swabs carried herpes virus -- and patients tested positive 7% of the time.
The findings show that herpes hiding in nerve roots doesn't sleep between outbreaks. Instead, it's frequently seeping out.
"The finding that treatment cannot fully prevent transmission should encourage patients to use condoms and adopt safe-sex practices," Philippe Van de Perre and Nicolas Nagot of the University Hospital of Montpellier, France, suggest in an editorial accompanying the Johnston report in the Jan. 5 online issue of The Lancet.