People with genital herpes simplex virus type 1 (HSV-1), which commonly causes cold sores, often shed the virus in the first months after infection, increasing the risk of transmitting the virus to sexual partners during this time.

But the rate of shedding declines during the first year, researchers at the University of Washington (UW) School of Medicine in Seattle found.

“The findings suggest that infection with genital HSV-1 is significantly different from genital HSV-2 in that it is much less severe in terms of recurrences and shedding. With HSV-2, we continue to see high levels of shedding many years after the first episode of infection,” said Dr. Christine Johnston, associate professor of allergy and infectious diseases. Johnston was lead author of the paper, which was published in October. 22 YAMA.

In the past, HSV-1 was associated mainly with blisters and sores on the lips, often called cold sores, or fever blisters and herpes simplex virus type 2 (HSV-2), a closely related virus, is mainly responsible for genital herpes. But that has changed over the past few decades, and today HSV-1 is the leading cause of new genital herpes infections in many parts of the world.

Over the past few decades, fewer people have been infected with HSV-1 as children, making them more susceptible to infection when they become sexually active.

Most genital herpes infections are asymptomatic. But when symptoms do occur, they can include often painful genital blisters and sores, fever, chills, fatigue, muscle aches and other flu-like symptoms. Infections can also cause emotional distresshow patients might experience it social stigma associated with the infection and worry about transmitting the virus to their sexual partners and, if they are about to give birth, to their newborn.

In the new study, Johnston and colleagues sought to better understand the course of genital HSV-1 infections and how immune system answers. Although HSV-1 is known to cause genital symptoms less often than HSV-2, this was the first study to comprehensively examine oral and genital HSV-1 shedding using a highly sensitive polymerase chain reaction test ( PCR).

They enrolled 82 men and women diagnosed with a first episode of genital HSV-1 infection. Fifty-four (66%) were female and 28 (34%) were male. Their ages ranged from 16 to 64 years, with a mean age of 26. Antibody studies showed that about half of the participants had been infected with HSV-1 before.

To detect shedding, participants had oral and genital swabs taken daily for 30 days, two months, and 11 months after their first episode of genital HSV-1. Swabs were tested for HSV-1. Blood samples were also collected at several points during the study to analyze the participants’ immune response to the infection. Participants were taking antiviral medication to treat their initial episode, but agreed not to take treatment to suppress the virus during the sample collection periods.

The number of days participants shed the virus varied. Some participants did not shed virus at all, but shedding was relatively common after two months, with participants shedding HSV-1 on 12% of days. However, after 11 months, the indicator dropped to 7% of days. In most cases, the participants had no symptoms even though they were shedding the virus.

Participants who shed at least 10% of days during the 11-month period had another 30 days of swabbing two years after their initial genital infection. In this group, shedding rate dropped even more, to 1.3% of days. Although the sample size was small, the rates are significantly lower than HSV-2, in which shedding occurs on approximately 34% of days in the first year and remains at 17% of days at 10 years. In parallel with shedding, relapses were rare, with an average of one relapse during the first year of infection.

“I think patients can feel some confidence that with a genital HSV-1 infection, you’re likely to have less shedding and a lower risk of transmission than with an HSV-2 infection,” Johnston said.

Analysis of the selected viruses and the participants’ immune response to infection did not explain why shedding rates differed among participants. But shedding was more common among those for whom it was a new infection.

Patients who lack antibodies to HSV-1 and -2 when first diagnosed with genital herpes should be advised to expect more frequent shedding, Johnston said, and may be candidates for suppressive antiviral therapy during the first year of infection.

And while neonatal herpes is rare, it can be devastating, she added. The finding that shedding is common in the first months after infection highlights the importance of identifying pregnant people at high risk of HSV-1 infection so that preventive measures can be taken to avoid infection.

The YAMA the article is accompanied by an editorial, “Fall Schemes genital herpes simple viral infections,” by Richard J. Wheatley and Edward W. Hook, University of Alabama at Birmingham Hersinck School of Medicine. They discuss the potential clinical and research implications of the findings.

The YAMA article entitled “Virus isolation 1 year after first episode of HSV-1 infection”.