How Is Herpes (Oral or Genital) Spread?
HSV-1 is usually passed from person to person by kissing. HSV-1 can also spread from the
mouth to the genitals during oral sex (fellatio, cunnilingus, analingus). If this happens, it
becomes a case of genital herpes.
HSV-2 is most often passed by vaginal sex and anal sex. But just as HSV-1 can infect the
genitals and cause genital herpes, HSV-2 can pass from one person's genitals to another
person's mouth, resulting in oral herpes.
HSV-2 cannot survive long on a non-living surface, so there is no real risk of getting it from a
toilet seat or hot tub, for example.
How Can Genital Herpes Be Prevented?
Using a latex barrier (a condom or dental dam) during sex may protect you or your partner
from herpes, but only if it covers the area where the virus is shedding. You should avoid
having sex if you or your partner has visible sores on the genitals, and you shouldn't receive
oral sex from someone who has a sore on his or her mouth.
It's important to know that HSV can be contagious even when no symptoms are visible.
Use of Antivirals to Prevent the Transmission of Genital
Although the use of chronic, daily antiviral therapy has been shown for nearly 2 decades
to reduce the frequency of clinical reactivation of genital herpes infections, only more
recently has it been shown that daily antiviral therapy also reduces the frequency of
subclinical reactivations and the amount of HSV-2 that is shed, subclinically, on genital
mucosal surfaces, the principal source of transmitted infections. [17,18] These effects
provided the rationale for a large multicenter study that demonstrated the effectiveness
of once-daily valacyclovir therapy in reducing the risk of sexual transmission of genital
This randomized, placebo-controlled trial involved the study of nearly 1500
immunocompetent, heterosexual, monogamous couples who were serologically
discordant for HSV-2 infection. HSV-2-seropositive partners were randomized in a 1:1
ratio to receive valacyclovir 500 mg once daily or matching placebo.  Condoms were
provided free of charge to all participants in the trial throughout the study, and all
couples received counseling about the effective use of condoms. HSV-2-seronegative,
susceptible partners were evaluated monthly for 8 months for clinical and laboratory
evidence of HSV-2 infection. New infections were diagnosed on the basis of isolation of
HSV-2 from culture or HSV-2 seroconversion. Of 1498 couples at 96 centers worldwide,
1159 completed the study. During the study period, a total of 41 HSV-2 infections
occurred among susceptible partners: 20 were clinically symptomatic and 21 were
diagnosed on the basis of HSV-2 seroconversion only ( Table 3 ).
Of the 20 symptomatic infections, 16 occurred among the 741 partners of placebo
recipients (2.2%) and 4 occurred among the 743 partners of valacyclovir recipients
(0.5%) (relative risk, 0.25; 95% CI, 0.08-0.74; P = .01) (Figure 2). The time to
development of symptomatic first episodes of genital herpes was significantly longer
among the partners of valacyclovir recipients than among the partners of placebo
recipients. In all 41 cases of HSV-2 acquisition that were evaluated, HSV-2 had been
acquired by 27 of the susceptible partners of placebo recipients (3.6%) compared with 14
of the susceptible partners of valacyclovir recipients (1.9%) (hazard ratio [HR], 0.52; 95%
CI, 0.27-0.99; P = .04) (Figure 2).
Consistent with the findings of other studies of HSV-2 transmission, more female
partners than male partners of placebo-treated patients acquired HSV-2 infection (7.4%
vs 1.8%). No evidence of a significant difference in treatment effect of valacyclovir was
seen between susceptible female or male partners. There were several significant factors
that influenced the effectiveness of the medication, however. Valacyclovir-treated persons
who had genital herpes for less than 2 years were nearly 3 times more likely to transmit
than those who had genital herpes for more than 2 years. Similarly, those who were in a
monogamous relationship of less than 2.5 years' duration were also 3 times more likely to
transmit infection. Interestingly, past HSV-1 infection was not a factor in protecting
against the acquisition of HSV-2.
Condom use data were collected during the course of the trial. Couples were classified,
on a monthly basis, as those who never used condoms, sometimes used condoms (1% to
90% of sexual contacts), and nearly always used condoms (> 90% of sexual contacts). In
the study population as a whole, frequent condom use was found to reduce the
acquisition rate of genital herpes infections. Of interest, the effect of valacyclovir was
similar among all frequencies of condom use. While the numbers were small, there was
no evidence of transmission among couples who used condoms very frequently (> 90%)
and also received valacyclovir (Figure 3); the study was not powered, however, to confirm
that utilization of both modalities was 100% effective.
Condoms for Prevention of HSV-2
The effectiveness of using condoms for preventing transmission of HSV-2 infection has
been difficult to demonstrate. There have been no prospective studies specifically
designed to evaluate the efficacy of condom use in this regard. Retrospective analyses of
data from a prospective cohort study of incident genital herpes have been useful in
defining the fact that condoms are effective in reducing the transmission of HSV-2 from
men to women and, more recently, from women to men. The effect is incomplete at best,
however, with protection rates of only 40% to 50% being observed.[21,22] The most useful
available data on the effectiveness of condom use for preventing genital herpes are
shown in Table 4 and Table 5 .
It should be noted that in this analysis -- the first to document the effectiveness of
condoms with specific regard to preventing HSV-2 infection -- when data were examined
by sex, condoms appeared to be highly protective for women (adjusted HR, 0.085; 95%
CI, 0.011-0.67) but not for men (HR, 2.02; 95% CI, 0.32-12.5). In a second analysis of the
same study population, the authors reported that a higher frequency of condom use (ie, >
65% of sex acts) afforded equal and significant protection to heterosexual women,
heterosexual men, and men who have sex with men ( Table 5).
The reasons for the less-than-perfect efficacy of condom use are of interest.
Subclinical shedding studies have shown that perirectal shedding and
asymptomatic vulvar shedding from microscopic lesions are common in both
men and women.[23,24] Thus, one could hypothesize that skin to skin contact
that occurs prior to putting on the condom may be a factor in the continued
transmission of genital herpes. Differences in the degree of protection
provided by condoms in women and heterosexual men may also be explained
in this way, as viral shedding studies have indicated that penile skin is the
most common site of HSV-2 shedding in men.
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