Herpes type 1 shedding highest in first months

But shedding drops rapidly within the first year of infection, new research suggests.

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People with herpes type 1 shed the virus the most in the first few months after they are first infected, new research suggests.

However, shedding rapidly declines over that first year, the prospective cohort study in JAMA found.

“I think patients can feel some reassurance that with genital HSV-1 infection, you are likely to have less shedding and have a lower risk of transmitting the virus than you would with HSV-2 infection,” lead author Dr Christine Johnston, associate professor of allergy and infectious disease, said in a statement.

US researchers had 82 participants with a new infection of HSV-1 swab their mouths and genitals every day for 30 days, then again at two and 11 months after infection. This was the first study to test HSV-1 shedding using PCR tests, the authors said.

At two months, shedding was detected on 12% of days. By 11 months, participants were shedding on 7% of days.

“Most genital shedding was asymptomatic; genital and oral lesions and oral shedding were rare,” the authors wrote.          

In contrast, HSV-2 shedding lasted for several years, and rates could persist at 16% of days for as long as 10 years after infection, they said.

Nevertheless, some participants with HSV-1 shed the virus on as many as 10% of days even at 11 months. The researchers asked these participants to take a swab for another 30 days again, two years after the infection, and they found that shedding was then only occurring on 1.3% of days.

“Antibody responses to HSV-1 developed quickly over time, with most people considered HSV-1 seropositive or indeterminate by 12 weeks after first-episode genital HSV-1,” the authors wrote.

“A small rate of nonseroconversion at one year was found. This is in contrast with HSV-2, in which 100% seroconversion by six months has been previously reported.^”

Sexual health researcher Professor Basil Donovan, head of the Sexual Health Program at the Kirby Institute, said antiviral treatment was important for pregnant women, especially if they contract the virus in late pregnancy.

“That’s a very strong indication to put people on suppressive antiviral therapy, because for the next few months they’re going to be pumping the virus out and the baby will be at risk.”

HSV-1 had now become the leading cause of first genital herpes infections, and serological surveys suggest three in four Australians carried the virus, Professor Donovan told TMR.

“We’re all swimming in a soup of herpes virus. And that starts from the day we’re born,” he said.

Professor Donovan said first episodes of herpes should always be treated.

“If it’s a true primary, we don’t know how bad it’s going to be. For a first episode, there’s a 10% chance it will go on to meningitis.

“Once you’re infected, your immune system kicks in and that minimises the number of recurrences and minimises the quantity of virus that you shed, but that takes several months.”

For subsequent infections, antiviral treatment was generally only needed if a patient had symptoms, he said.

Professor Donovan noted that in the JAMA study, the median number of sexual partners among participants in the preceding four weeks was one.

“As the patient will most likely be having sex with the partner that was the source of the virus, antivirals serve no purpose without symptoms.”

Professor Donovan said antiviral treatment reduced how much virus was shed in both herpes type 1 and 2, but did not give 100% protection against shedding. 

And the shedding detected in the study was probably a low estimate, Professor Donovan said, pointing to HSV-2 studies showing that when patients swabbed several times per day, “the yield went up massively”.

“The virus is very intermittent. It has little bursts where it erupts for reasons we don’t understand.

“The clinical message that comes out of this study is to be honest with people that they probably got it from their current partner, because most of the current partners will have the virus either orally or genitally.

“It’s not a reason to give people lectures about being sexually safe, because the virus is so widespread in our community, you can’t avoid it.”

Professor Donovan said HSV-2 was more recurrent than HSV-1, and recurred on average four times a year.

“Type 1, because it’s in the genital area and outside its territory, doesn’t seem to be capable of causing symptoms as much, and most transmission is from people without symptoms.”

JAMA 2022, online 22 October