People with genital herpes can still be contagious even if they don’t have symptoms, according to a study that raises the question of whether all adults should be screened for the disease.

Researchers found that people who unknowingly harbored the virus were expelling it - or “shedding” it - as much as 10 percent of the time, meaning they might infect sexual partners.

“Most people, when they shed, do not have any symptoms,” said Dr. Christine Johnston, who worked on the study. “We would like to push for a discussion of the risks and benefits of screening.”

Genital herpes can be very painful, but that’s not the only problem. It also increases the chances of getting HIV (the virus that causes AIDS) and in rare cases may jump from mothers to their babies during birth, which can be fatal.

Worldwide, more than 530 million people are infected with herpes simplex virus type 2 - the cause of genital herpes - and one in six U.S. adults has the disease.

That makes it one of the most common sexually transmitted diseases, according to the new report, which is published in the Journal of the American Medical Association.

“The people who are symptomatic are really the tip of the iceberg,” Johnston, of the University of Washington in Seattle, told Reuters Health. “We are not having any impact on the epidemic by ignoring it.”

She said condoms, antiviral drugs and letting your partner know if you’re infected have all been shown to cut the rate of transmission in half.

Johnston and her colleagues have received funding from or consulted for drug companies that make antiviral drugs, but the new study was supported by a government grant.

Other experts recommend against screening symptom-free people.

For instance, the U.S. Preventive Services Task Force, a federal expert panel, says there is no evidence that screening will actually help control genital herpes. On the other hand, knowing you carry the virus may cause a lot of worrying.

“The debate hinges on what you can do for these people and can you actually limit transmission?” said Dr. Raj Patel, an expert on genital herpes, who was not involved in the study.

“They reignite the argument, but the big question about cost-effectiveness at the population level remains,” added Patel, of Royal South Hants Hospital in Southampton, UK.

According to the U.S. Preventive Services Task Force, tests for genital herpes are available for between $10 and $40.

Researchers have known for a while that genital herpes is largely spread by people who aren’t even aware they have it. But the new study gives a better sense of how often symptom-free people with the disease are contagious.

The researchers followed 498 people who had antibodies in their blood against genital herpes - showing they’d all been infected, even though about one in six had never had any symptoms.

All of the participants swabbed their genital area every day for at least a month, regardless of whether or not they had herpes blisters, and gave the swabs to the researchers to analyze.

The swabs from people with symptoms contained virus 20 percent of the time, while those from symptom-free people did so 10 percent of the time.

Although it’s unclear how much virus is needed to infect someone else, Johnston said, the amount of virus shed in the absence of sores was the same for people with and without symptoms.

“In the absence of symptoms people can still transmit the virus, and therefore preventive measures should be used,” Johnston told Reuters Health.

Patel added that if people find out they have genital herpes, they should educate themselves about how to cope with it - for instance with condoms or by telling their partner - even if they don’t have symptoms.

“They should learn about their disease and understand the dynamics of transmission,” he said.

SOURCE: JAMA, April 12, 2011.