More than half the world’s population is infected with the form of the herpes virus that causes cold sores, according to new numbers from the World Health Organization.

The study, published in the journal PLoS ONE, reports that 3.7 billion people under age 50 carry herpes simplex virus Type 1 (HSV-1), which is transmitted through saliva.

In the Americas, around 39 per cent of women and 49 per cent of men are infected, while in the Eastern Mediterranean, 75 per cent of both men and women are infected. In Africa, that number rises to 87 per cent.

CTV News’ infectious diseases expert Dr. Neil Rau says the reason the global numbers are so high is that many people with herpes don’t show symptoms, but their infection stays with them for life.

“Only one in 12 people who have herpes know that they have it, so there’s a huge ocean of people who are carriers of the virus and who have no idea,” Rau told CTV’s Canada AM Thursday.

Although most people with herpes have Type 1, about 20 per cent of the population has Type 2, which causes genital herpes. Many of these people don’t realize they are infected either because they too have no symptoms. It’s also possible to have both types of herpes at the same time.

Rau says herpes is an unusual virus in that the body has no way of getting rid of it.

“It’s the type of virus that once you get it, you don’t actually clear it. It goes into a dormant state,” he said. “Most people have no symptoms, some reactivate once in a blue moon. Some people don’t reactivate but they shed the virus from time to time and that’s how they pass it to others.”

While the majority of genital herpes is due to Type 2, Rau says, it is also possible to contract it from Type 1, most commonly from oral sex. The report found that this method of transmission is increasing, and Rau says that’s due to changing sexual practices.

“Because more people are practising oral sex… we are now seeing more Type 1 herpes causing genital herpes,” Rau said.

There are medications to suppress the herpes virus and prevent outbreaks, but there is no cure nor any way to prevent infection.

Rau says the antiviral treatments haven’t changed much over the last 20 years and attempts at vaccines have not been successful.

The World Health Organization says it hopes this paper estimating the global burden of herpes will lead to the development of better treatments and tests, “and ultimately, develop HSV vaccines.”