Approximately two-thirds of all people under age 50 across the globe are infected with herpes simplex virus type 1 (HSV-1), the virus most commonly associated with cold sores, according to a World Health Organization (WHO) report released today in the journal PLOS One.
That’s 3.7 billion people worldwide.
The burden of infection varies in different parts of the world and between men and women, according to the report. In the Americas, about 39% of all women are infected and 49% of men. In the Eastern Mediterranean, 75% of both men and women are infected and 87% of both men and women are infected in Africa.
And that’s just men and women under age 50. Above this age, the burden of infection would probably “trend toward 100%” in many places, says Bryan Cullen, director of the Duke University Center for Virology, although the WHO study doesn’t include these statistics.
HSV-1 is the same virus most commonly responsible for causing skin lesions, or “cold sores,” around the mouth, a disease than can be transmitted via skin-to-skin contact, such as kissing. But while cold sores are a mostly cosmetic issue, there’s good reason to collect data on the virus, argue some experts.
The research suggests that HSV-1 may be increasingly responsible for genital herpes as well, and it’s also been known to cause infections leading to blindness and, albeit rarely, encephalitis.
HSV-1 is one of two types of herpes simplex virus. The other, HSV-2, has historically been associated with genital herpes and is almost exclusively sexually transmitted. Infection with HSV-2 can have more serious consequences, too, since it has been shown to increase a person’s risk of becoming infected with HIV.
In 2012, the WHO released a report on HSV-2 estimating that its global prevalence in people between the ages of 15 and 49 is around 11.3% — low in comparison to the HSV-1 estimates released in the new paper.
This is likely because of the differing methods of transmission between the two viruses, says Anna Wald, a professor at the University of Washington’s School of Medicine whose research specialties include the herpes simplex virus.
Since HSV-2 most commonly affects the genitals, it typically isn’t transmitted until people become sexually active. HSV-1, on the other hand, has historically been commonly transmitted in early childhood, for instance if an infected adult kisses an uninfected child.
Both types of HSV can lead to genital herpes infections
However, in recent years research has increasingly shown that both HSV types can be responsible for either oral or genital infections, and either type may be transmitted via oral sex. The new paper notes that, worldwide, about half a billion people between the ages of 15 and 49 have a genital herpes infection caused by either HSV-1 or HSV-2.
This is worth noting, as genital herpes in particular can carry a heavy social stigma.
It’s thought that genital HSV-1 infections are becoming particularly prevalent in developed nations. This is likely
because rates of oral transmission in early childhood are decreasing. Once infected with the virus in one part of the body, the immune system generally protects against infection in another area.
So if fewer people are infected with the virus as children, they’re susceptible to genital infection as they become sexually active later in life, the WHO paper says.
The authors of the paper write, “In a number of developed settings (e.g., the USA, Western Europe, Australia and New Zealand) there is evidence that the proportion of first episode genital herpes that is due to HSV-1 has increased, particularly among young people. It is thought that decreases in rates of childhood infection over time, combined with increases in the frequency of oral sex in these populations, are driving this trend.”
The authors conclude that genital HSV-1 infections are becoming a public health concern in certain parts of the developed world.
In other parts of the world, such as in Africa and Southeast Asia, the authors note that oral transmission in childhood is still high and has a tendency to protect people from genital infection later on.
“The new estimates highlight the crucial need for countries to improve data collection for both HSV types and sexually transmitted infections in general,” said Marlene Temmerman, director of the WHO’s Department of Reproductive Health and Research, in a statement.
In addition to better tracking of a sexually-transmitted infection, such data collection can help scientists gain a better understanding of the ways the virus could influence other serious health conditions, Wald says.
It’s unclear whether infection with HSV-1 has a similar effect as HSV-2 in raising the risk of HIV, according to Wald.
And HSV-1 is a leading cause of a condition known as HSV keratitis, which is an infection of the cornea that can lead to blindness. In fact, it’s the “biggest cause of infectious blindness in the United States,” says Cullen.
Both types of HSV can also cause encephalitis, which is rare but can lead to severe brain damage or death. And infection of either HSV type in newborns can sometimes cause severe reactions, including high fever, seizures or even death.
Both types of HSV are usually responsible for skin lesions only, which can be painful but are not typically seen as a serious health risk. And while the lesions may recur repeatedly in some infected people, others become asymptomatic after the first outbreak — or they may never have an outbreak at all.
This behavior is part of what makes the virus so difficult to track, as many people are unaware that they are infected. And while it’s possible to perform a blood test that will show whether the virus is present, “those kinds of studies are expensive and take up a lot of resources,” Wald says.
In the absence of symptoms, many medical providers also typically do not test for either type of the virus during routine sexually transmitted diseases (STD) screenings for a variety of reasons, some of them practical and others ethical.
Since the disease carries a social stigma and currently has no cure, the CDC also notes: “Because the tests can be expensive and the diagnosis may have adverse psychological or effects for some people, widespread testing for HSV is not currently recommended.”
The Centers for Disease Control and Prevention (CDC) does not recommend testing for people who do not present with symptoms, stating, “STD screening tests are usually done for infections that can have serious outcomes if they are left untreated. … Genital herpes infections can cause intermittent symptoms that may be uncomfortable, but infection does not usually result in serious complications in healthy adults.”
Push for greater monitoring
That said, as HSV infection can be the cause of serious complications in some cases, it’s worth tracking on both a regional and global scale, Wald says.
Cullen said it is perplexing that there's not more of an effort to cure both types of the Herpes virus.
“I frankly do find it surprising that there’s not more interest in in curing a disease that is symptomatic in 20% of the population,” he said in an interview with Mashable.
While there are medications that can help prevent outbreaks, there is currently neither a cure nor a vaccine for either HSV-1 or HSV-2. Some research on this front has been attempted, but so far without great success.
In the new paper, the WHO concludes that continued global monitoring of the virus might help make a difference on that front.
Edited by Hand2HandKing - 11/25/15 at 7:53pm