About Half The World's Population Infected With Herpes Virus, WHO Says

SAN FRANCISCO (CBS SF) -- About half the world's population is infected with the herpes virus that causes cold sores, according to new numbers from the World Health Organization released Wednesday.

The study found that over 3.7 billion people up to the age of 49 are infected with HSV-1 (herpes simplex-1), with the highest prevalence in Africa, South East-Asia, and the Western Pacific.

The study, published in the PLOS ONE journal found that the global burden of HSV-1 is "huge."

HSV-1 "is a highly infectious virus which is primarily transmitted by oral-oral contact and causes (cold sores) in those infected," the study states.

Another form of the herpes virus, HSV-2, is primarily transmitted sexually.

Many people infected with either form of the virus don't know they have contracted it until symptoms occur.