Viral shedding declines during the first year

People with a genital infection of the herpes simplex virus type 1 (HSV-1), which usually causes cold sores, frequently shed the virus in the first months after infection, raising the risk that they might spread the virus to sexual partners during this time.

But the rate of shedding declines during the first year, researchers from the University of Washington School of Medicine in Seattle have found.

“The findings suggest that the infection with genital HSV-1 is quite different than genital HSV-2, as it is substantially less severe both in terms of recurrences and shedding. With HSV-2, we continue to we see high rates of shedding many years after first-episode infection,” said Dr. Christine Johnston, associate professor of allergy and infectious disease. Johnston was the lead author on paper, which was published Oct. 22 by JAMA.

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

In the new study, Johnston and colleagues, including senior author Dr. Anna Wald, professor and head of the Division of Allergy and Infectious Diseases, sought to better understand the course of genital infections with HSV-1 and how the immune system responds.

Although it is known HSV-1 appears to cause less frequent genital symptoms than HSV-2, this was the first study to comprehensively examine oral and genital HSV-1 shedding using the highly sensitive polymerase chain reaction (PCR) test.

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

The number of days participants shed virus varied. Some participants shed no virus at all, but shedding was relatively common at two months, with the participants shedding HSV-1 on 12% of days. At 11 months, however, the rate had fallen to 7% of days. In most instances, participants did not have symptoms even though they were shedding virus.

“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,” said Johnston.