An estimated two-thirds of world’s population under age of 50 are infected with herpes simplex virus type 1

Press release issued: 28 October 2015

More than 3.7 billion people under the age of 50 are infected with herpes simplex virus type 1 (HSV-1), which commonly causes ‘cold sores’ and can also cause genital herpes, according to new research by the University of Bristol and the World Health Organisation [WHO]. The findings, published in the journal PLOS ONE, reveal the first global estimates of HSV-1 infection.

Herpes simplex virus is categorised into two types: herpes simplex virus type 1 (HSV-1) and herpes simplex virus type 2 (HSV-2). Both HSV-1 and HSV-2 are highly infectious and incurable. HSV-1 is primarily transmitted by oral-oral contact and in many cases causes orolabial herpes or “cold sores” around the mouth. HSV-2 is almost entirely sexually transmitted through skin-to-skin contact, causing genital herpes.

The new estimates highlight, however, that HSV-1 is also an important cause of genital herpes. Some 140 million people aged 15-49 years are estimated to be infected with genital HSV-1 infection, primarily in the Americas, Europe and Western Pacific. Earlier this year, WHO published estimates of herpes simplex virus type 2 (HSV-2) infection showing that an estimated 417 million people between 15-49 years of age have infection caused by HSV-2. Taken together, these estimates suggest that over half a billion people between 15-49 years of age have a genital infection due either to HSV-1 or HSV-2. This highlights the large global burden of genital herpes caused by both HSV types.

Dr Sami Gottlieb of WHO, an author on the study says: “These findings highlight the crucial need for the health community to take into account infection by both HSV types when addressing the global burden of genital herpes.”

Dr Katharine Looker, the study’s lead author from Bristol’s School of Social and Community Medicine, commented: “It is likely that in higher-income settings, fewer people are becoming infected with HSV-1 as children. At the same time, oral sex is now common. This means that more people are able to be infected with HSV-1 genitally after becoming sexually active.”

Given the lack of a permanent and curative treatment for both HSV-1 and HSV-2, WHO and partners are working to accelerate development of HSV vaccines and topical microbicides, which will have a crucial role in preventing these infections in the future. Several candidate vaccines and microbicides are currently being studied.

Regional infection estimates

Estimates for HSV-1 prevalence by region among people aged 0-49 in 2012

Americas: 178 million women (49%), 142 million men (39%)
Africa: 350 million women (87%), 355 million men (87%)
Eastern Mediterranean: 188 million women (75%), 202 million men (75%)
Europe: 207 million women (69%), 187 million men (61%)
South-East Asia: 432 million women (59%), 458 million men (58%)
Western Pacific: 488 million women (74%), 521 million men (73%)

Estimates of new HSV-1 infections among people aged 0-49 in 2012

Americas: 6 million women, 5 million men
Africa: 17 million women, 18 million men
Eastern Mediterranean: 6 million women, 7 million men
Europe: 5 million women, 5 million men
South-East Asia: 13 million women, 14 million men
Western Pacific: 11 million women, 12 million men

Paper

‘Global and regional estimates of prevalent and incident herpes simplex virus type 1 infections in 2012’ by K. J. Looker et al in the journal PLOS ONE.

Further information

Herpes is a lifelong infection, which often has mild or no symptoms but can be detected by the presence of antibodies for HSV-1 or HSV-2 in the blood. It is difficult to determine the proportion of HSV-infected people worldwide who have symptomatic disease, as symptoms may be mild or simply not recognized as herpes. In the United States of America, about 15 per cent of people with HSV-2 infection report a prior diagnosis of genital herpes.

When genital herpes symptoms do occur, they take the form of one or more painful genital or anal blisters or ulcers. Herpes symptoms can be treated with antivirals, but after an initial episode, symptoms can recur. Recurrences of genital herpes due to HSV-1 are generally much less frequent than for HSV-2.

Transmission of HSV most often occurs without symptoms. The virus can have a significant negative impact upon an infected person’s mental wellness and personal relationships.

People with orolabial herpes symptoms may face social stigma, and can experience psychological distress as a result. In people with weak immune systems, such as those with advanced HIV infection, HSV-1 can have more severe symptoms and more frequent recurrences. Rarely, HSV-1 infection can also lead to more serious complications such as encephalitis or ocular disease.

WHO is currently working on the development of a global health sector strategy for sexually transmitted infections (STIs), including for HSV-1 and HSV-2, to be finalized for consideration at the 69^th World Health Assembly in 2016.