Geneva: More than 3.7 billion people under 50 have the highly-infectious and incurable herpes virus that causes sores around the mouth and sometimes on the genitals, a World Health Organization report said.
There are two forms of the herpes virus and both are most often transmitted without symptoms, but for those stuck with the lifelong infection, painful and embarrassing sores can be recurring.
Two thirds of the global population under the age of 50 are infected with the herpes simplex virus type 1 (HSV-1), which tends to cause cold sores, the WHO said in report published this week.
A full 87 percent of Africans under 50 have the virus which is transmitted by mouth-to-mouth contact or through saliva, as do three quarters of those in the eastern Mediterranean and western Pacific regions.
In comparison, "only" 39 percent of men and 49 percent of women in the Americas, and 61 percent of men and 69 percent of women in Europe have the virus, the WHO said in a statement.
HSV-1 mainly causes cold soars and blisters around the mouth, as opposed to HSV-2, which is almost entirely sexually transmitted and causes genital herpes.
But new estimates indicate HSV-1 is also an important cause of genital herpes, with some 140 million people between the ages of 15 and 49 infected with a genital variant of HSV-1, the Geneva-based organisation said.
"HSV-1 has the potential to be transmitted from the oral area to the genital area through oral sex," WHO medical officer Sami Gottlieb told reporters.
Along with the 417 million people believed to have the HSV-2 infection, there are more than half a billion people under 50 who have genital infections caused by the two herpes viruses.
The UN health agency noted that in high-income countries, fewer children are becoming infected with HSV-1 due to better hygiene and living conditions, but are thus more susceptible to becoming infected with the virus once they become sexually active.