People who have genital herpes can transmit the disease even when they don't show any visible signs of infection, suggesting routine tests are needed to help curb the infection, researchers said Tuesday.
The herpes virus was detected about 10 percent of the time in people who tested positive without any symptoms of the infection, according to research published in the Journal of the American Medical Association. In those with symptoms, the virus was present about 20 percent of the time.
The findings quantify the risk of spreading genital herpes, or herpes simplex virus type 2, even when those infected don't have a visible outbreak, the researchers said. The condition affects an estimated 536 million people worldwide and is most often acquired through sexual contact with people who don't show symptoms, researchers said. Vaccines and tests are needed to reduce the spread, said study author Anna Wald.
"HSV-2 infection is very common in the population, but most people don't know that they have genital herpes," Wald, a professor at the University of Washington in Seattle, said. "The most important message is if you're sexually active in this country, it's best to get tested."
About 23.6 million people ages 15-49 get the disease each year, the authors said. In the U.S., only 10 percent to 25 percent of those with the virus are aware they have it, the authors wrote.
Herpes has two forms, and there is no cure. Type 1 usually causes blisters near the mouth known as cold sores or fever blisters. Type 2 creates painful sores near the genitals.
From March 1992 to April 2008, the researchers tested 410 people who were positive for genital herpes and had a history of infection and 88 people who were positive and hadn't had symptoms. Swabs of genital secretions were collected from participants for an average of 57 days. DNA testing was used to measure whether the virus was present and could be transmitted.
Bruce Hirsch, an attending physician in infectious disease at North Shore University Hospital in Manhasset, N.Y., said more studies are needed to show how much virus has to be on the surface of the genitals to infect another person and if there are ways to boost the immune system to help stop the disease from spreading.
London-based GlaxoSmithKline makes the antiviral pill Valtrex, which is approved to treat symptoms and reduce the frequency of outbreaks. Actavis Group makes a generic version of the medicine. Novartis AG's Famvir is cleared to treat or suppress outbreaks of herpes and Watson Pharmaceuticals Inc. makes a generic version of the medicine. The amino acid lysine, available as a dietary supplement, has been found in studies to reduce symptoms and outbreaks.
Genital herpes is generally not included in standard sexually transmitted disease screenings, Wald said. It is a separate blood test that people should ask for if they are concerned that they may have a sexual disease, she said.
Last year, Glaxo said its Simplirix vaccine to prevent genital herpes in women failed in a late-stage clinical trial, and the company is dropping development.