Fewer people are being exposed to herpes simplex type 1 (HSV-1) in childhood, although they still risk catching it in adulthood, according to a new study published in BMJ Global Health.

Two-thirds of children and youth have their first sexual activity without exposure to herpes, which often manifests as cold sores, according to the study. The investigators said the rates of the virus appear to be declining in younger people, but it could be increasingly likely to be transmitted sexually.

HSV-1 is mainly transmitted by oral-to-oral contact during childhood, causing oral herpes, but it can also cause genital herpes. Herpes simplex type 2 (HSV-2) is sexually transmitted and causes genital herpes. According to the study authors, the prevalence of HSV-1 in Europe is falling by 1% per year.

“HSV-1 epidemiology in Europe is in transition and shifting away from its historical pattern of oral acquisition in childhood,” the authors wrote in a press release.

Both forms of the virus are lifelong, with an estimated 3.7 billion people globally under age 50 who have HSV-1 infection, and 491 million people aged 15 to 49 years with HSV-2 infection. In an effort to better understand the epidemiology of the virus, investigators systematically reviewed HSV-1 related publications, conducted meta-analyses, assessed pooled prevalence rates in populations, and estimated pooled proportions of HSV-1 viral detection in clinically diagnosed genital ulcer disease and in genital herpes. They gathered information from 142 usable previous publications.

Based on these findings, the team extracted 179 overall population prevalence measures, 4 overall proportions of HSV-1 in genital ulcer disease, and 64 overall proportions of HSV-1 in genital herpes. The analysis found that 67.4% of the population in Europe tested positive for HSV-1, which is far lower than the historical level of universal infection in childhood in other parts of the world, according to a press release. Approximately 32.5% of children and 74.4% of adults were infected in Europe, according to the results.

The researchers found that prevalence in the population increased steadily with age, with the lowest rates among those aged 20 years or younger and the highest rates among those aged 50 years and older. Population prevalence across Europe was declining by 1% per year, although the contribution of HSV-1 to genital herpes was rising by 1% per year.

According to the authors, the reasons for falling prevalence of HSV-1 could include a general decrease in both family size and school crowding, as well as improved hygiene and living conditions. They did note several potential limitations of the study, including the lack of data for 25 of 53 European countries. Despite this, the authors said these limitations did not appear to have posed a barrier to the interpretation of the study results.

“HSV-1 transition in Europe is leading to more heterogeneous and variable transmission by age and geography, and an increasing role for HSV-1 in genital herpes and as a sexually transmitted disease,” the authors concluded. “The findings highlight the importance of disease surveillance and monitoring of HSV-1 seroprevalence and genital herpes etiology and strengthen the case for an HSV-1 vaccine to limit transmission.”

REFERENCE
Oral herpes rates are falling in children [news release]. EurekAlert; July 16, 2020. https://www.eurekalert.org/pub_releases/2020-07/b-ohr071420.php. Accessed October 28, 2020.