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Genital Herpes Virus Can Spread Despite Lack of Symptoms


People without genital sores or other symptoms can still shed and transmit herpes simplex virus type 2 (HSV-2) during sex, according to a recent U.S. study.

Herpes simplex virus type 2 is the usual cause of genital herpes, while type 1 typically causes cold sores; both types, however, can infect either area.

HSV causes painful blisters on the skin and mucous membranes and sometimes also flu-like symptoms. Between outbreaks it lies dormant in nerve cells, but can be reactivated by triggered factors such as concurrent infections, hormonal fluctuations, or exposure to sunlight.

As described in the April 13, 2011, Journal of the American Medical Association, Anna Wald from the University of Washington and colleagues evaluated the virological and clinical course of genital virus shedding among people with symptomatic and asymptomatic HSV-2 infection.

HSV-2 is among the most common sexually transmitted infections worldwide, with global estimates of 536 million total people infected and 23.6 million new cases each year, Wald explained at a JAMA media briefing at the National Press Club in Washington, DC.

At any given time many people with HSV-2 will not have lesions or other symptoms, and some individuals rarely or never experience symptoms. A growing number of people are aware they have genital herpes thanks to the availability of commercial HSV-2 antibody tests, but screening is not widespread. In the U.S. an estimated 16% of adults are HSV-2 seropositive, but only 10% to 25% of them have recognized genital herpes. Furthermore, the natural history of HSV-2 infection in asymptomatic seropositive individuals is not fully understood.

The present study included 498 immunocompetent HSV-2 seropositive people enrolled in prospective studies of genital HSV shedding -- an indicator of active viral replication -- at the University of Washington Virology Research Clinic in Seattle and the Westover Heights Clinic in Portland between March 1992 and April 2008. Each participant collected swabs of genital secretions daily for at least 30 days. The researchers then used quantitative real-time polymerase chain reaction (PCR) assays to measure HSV-2 in samples.


  • HSV-2 was detected on 4753 of 23,683 total days, or 20% of the time, among 410 people with symptomatic genital herpes.
  • HSV-2 was detected on 519 of 5070 total days, or about 10% of the time, among 88 individuals with consistently asymptomatic infection.
  • Genital HSV-2 was detected at least once in 342 of 410 people (83%) with symptomatic infection and in 60 of 88 people (68%) with asymptomatic infection during an average 57 days of follow-up.
  • Subclinical shedding in the absence of symptoms was significantly more common among people with symptomatic HSV-2 infection compared with asymptomatic infection (2708 of 20,735 days or 13% vs 434 of 4929 days or 9%).
  • However the amount of HSV-2 detected during subclinical shedding episodes was similar in the symptomatic and asymptomatic groups (median 4.3 vs 4.2 log copies, respectively).
  • People with symptomatic infection had more frequent genital HSV-2 shedding episodes than people with asymptomatic infection (median 17.9 vs 12.5 episodes per year).
  • Days with evident lesions accounted for 2045 of 4753 days with genital virus shedding (43%) among people with symptomatic genital HSV-2 infection compared with 85 of 519 days (16%) among people with asymptomatic infection.

Based on these findings, the study authors concluded, "Persons with asymptomatic HSV-2 infection shed virus in the genital tract less frequently than persons with symptomatic infection, but much of the difference is attributable to less frequent genital lesions because lesions are accompanied by frequent viral shedding."

Though less common, HSV-2 shedding did occur among asymptomatic people without evident genital lesions, indicating that such individuals may transmit the virus between outbreaks of symptoms.

"Our findings suggest that 'best practices' management of HSV-2-infected persons who learn that they are infected from serologic testing should include anticipatory guidance with regard to genital symptoms, as well as counseling about the potential for transmission," Wald recommended at the press conference. "The issue of infectivity is both a patient management and a public health concern."

Measures including condom use and daily valacyclovir (Valtrex) treatment can help decrease HSV-2 transmission to sex partners, but risk reduction is not complete and many people do not take advantage of such measures because they do not realize they are infected. It is a common misconception that HSV-2 can only be transmitted when lesions are present, indicating the need for better public health education in this area.

Investigator affiliations; Departments of Medicine, Laboratory Medicine, and Epidemiology, University of Washington, Seattle, WA; Vaccine and Infectious Disease Institute and Program in Biostatistics, Fred Hutchinson Cancer Research Center, Seattle, WA; Westover Heights Clinic, Portland, OR.


E Tronstein, C Johnston, ML Huang, et al. Genital shedding of herpes simplex virus among symptomatic and asymptomatic persons with HSV-2 infection. Journal of the American Medical Association 305(14):1441-1449 (abstract). April 13, 2011.

Other Source
JAMA. Persons With Herpes Simplex Virus Type 2, But Without Symptoms, Still Shed Virus. Media advisory for April 12, 2011.