WASHINGTON » Nearly seven in 10 people under age 50 — more than 3.7 billion teens and adults worldwide — are infected with herpes simplex virus type 1, a highly infectious and incurable disease, the World Health Organization announced Wednesday.

More than 1 billion people are infected with HSV-1 in the Western Pacific region, while Southeast Asia has nearly 1 billion cases, according to WHO’s first global estimates, published Wednesday in an article in the journal PLOS ONE.

More than 700 million people are infected in Africa, nearly 400 million in Europe and 320 million in North and South America.

Known as “oral herpes” and typically spread through kissing, oral sex and the use of shared objects like eating utensils, HSV-1 typically causes cold sores around the mouth. But it can also cause genital herpes, which leads to painful blisters and ulcers in the anal and genital areas.

Although most cases of genital herpes are caused by herpes simplex virus type 2, which is transmitted almost entirely through sexual activity, “we know that increasingly HSV-1 is showing up in genital infections, and that’s sort of a trend that public health folks are watching,” said Fred Wyand, communications director at the American Sexual Health Association in Research Triangle Park, N.C.

About 140 million people worldwide between ages 15 and 49 have an HSV-1 genital infection, WHO reported.

Worldwide, some 417 million people ages 15 to 49 have the HSV-2 infection.

“The new estimates highlight the crucial need for countries to improve data collection for both HSV types and sexually transmitted infections in general,” said Dr. Marleen Temmerman, director of WHO’s Department of Reproductive Health and Research.

Wyand said the new numbers come as no surprise to public health officials. He said the U.S. Centers for Disease Control and Prevention has estimated that 54 percent of Americans carry the virus.

After infection through oral secretions or skin sores, the oral herpes virus settles in nerve tissue at the top of the spine, while genital herpes sets up shop in the base of the spine. Once activated, both move up nerve pathways to the skin’s surface, sometimes without signs or symptoms.

The majority of genital herpes infections go unrecognized and undetected because most people have no pronounced symptoms, Wyand said.

In fact, transmission of the herpes virus usually occurs with mild or no symptoms, and most people don’t realize they have it until virus antibodies are detected in the blood. Prescription antiviral medications treat outbreaks ofherpes symptoms, but there’s no “permanent and curative treatment,” the WHO noted. And recurring episodes are common.

“WHO and partners are working to accelerate development of (herpes) vaccines and topical microbicides, which will have a crucial role in preventing these infections in the future,” the organization said in a statement.

HSV-1 infections can have more severe symptoms and more frequent recurrences in people with weak immune systems. In rare cases, HSV-1 infections can cause encephalitis or eye disease.

While fewer children are becoming infected with HSV-1 in higher-income nations because of better hygiene, they remain at risk of contracting the disease genitally through oral sex.

Wyand said the presence of HSV-1 antibodies is, in fact, decreasing among U.S. teens and young adults. But because they haven’t built up a resistance to the virus, these unexposed young people could be more susceptible to a genital infection if they contract HSV-1 through sexual activity later in life.

“Access to education and information on both types of herpes and sexually transmitted infections is critical to protect young people’s health before they become sexually active,” Temmerman said.

Correct and consistent use of latex condoms can cut the risk of genital herpes, but outbreaks can occur in areas left uncovered, according to the CDC. It urges people with herpes to abstain from sexual activity with partners when sores or other symptoms are present.