Q: How did I get this infection?

A: Most cases of HSV-2 infection are spread through sexual transmission. An infected person can have virus in his or her saliva, semen, or vaginal secretions. When a seronegative partner comes in sexual contact with these secretions, the virus can enter the body through mucosal surfaces (such as the vagina, anus, or mouth) or micro-abrasions on the skin (eg, the penile shaft, scrotum, thighs, or perineum).

Once the virus enters the new host, it replicates and often produces the primary outbreak. Following resolution of the initial outbreak of genital HSV-2 infection, the virus enters a latent stage in which it lies dormant in the dorsal (sensory) sacral nerve routes. In oral HSV-2 (or HSV-1) infection, the trigeminal ganglion serves as the reservoir for the latent virus.

Q: My boyfriend told me that he's clean and never had genital herpes. How do you know that I don't have herpes type 1 infection?

A: adolescents learn about HSV-1 and HSV-2 infections in their middle-school health classes. They often label HSV-2 as "the bad kind" of herpes--even though both types can lead to sores on the mouth or genitalia.

HSV-1 infections are often asymptomatic and usually occur in infancy or childhood. A person with a history of oral HSV-1 can shed the virus asymptomatically and spread the infection to a partner through kissing or oral sex. However, HSV-1 is not responsible for the great majority of cases of genital herpes. (Details about confirmatory diagnostic testing follow.)

Q: What makes you sure it's herpes? Is there anything else it could be?

A: As with most sexually transmitted diseases (STDs), the history and clinical examination results provide the bulk of diagnostic clues. Primary infection with HSV-2 occurs about a week after sexual exposure, although the incubation period can be as long as 7 weeks. The patient will often describe a 1- to 2-day prodromal phase characterized by flu-like symptoms (headache, fever, and malaise) and mild genital sensations of tingling, burning, or pruritus.

An outbreak of painful vesicles in the exposed area follows this phase. In girls, vesicles may develop on the thighs, vaginal opening, vaginal canal, and cervix. Boys usually find the vesicles on the penile shaft or glans. If the vesicular inflammation involves the urethra, the patient may present with dysuria. Both males and females can have vesicles and inflammation in the perineum, mouth, and anus--depending on the types of sexual activity in which they have engaged.

Carefully consider other diagnoses in the differential before you give an adolescent a diagnosis with a lifelong tenure. Most of the other possible entities can be effectively ruled out with a careful physical examination.

•The chancre seen in primary syphilis is often solitary and painless.

•In chancroid, the ulcers tend to be larger, irregularly shaped, and deeper than herpetic vesicles.

•Genital warts are generally painless, raised, and fleshy.

•The lesions in molluscum contagiosum are typically firm, dome-shaped, smooth, and umbilicated in the center.

•Behçet syndrome can manifest with genital lesions similar to the ones seen in HSV infection, but these are classically accompanied by oral ulcerations and uveitis.

The diagnosis needs to be confirmed once a presumptive clinical diagnosis has been made. The 3 principle diagnostic tools are HSV culture, HSV polymerase chain reaction (PCR) assay, and assays of HSV antibodies.

Culture sensitivity varies, depending on the age and stage of the HSV lesion tested. This method is not as sensitive as the PCR technique--the most sensitive means of isolating the virus. Unlike the PCR, however, cultures can distinguish between HSV type 1 and type 2 infections.

If your patient wants or needs to know which virus infection he has contracted (type 1 or 2), you can order serologic tests to determine the presence of HSV type-specific antibodies several weeks after a primary infection occurs.

Q: Is there any way for me to know if this outbreak was caused by my current partner or by my ex?

A: There is no test that can accurately "tell" which partner gave the patient HSV infection. That said, however, results of serologic tests for HSV do at least suggest whether the patient has a primary infection or a secondary outbreak. HSV antibodies are not detectable early in a primary infection. But they can be detected several weeks after a primary infection and remain present indefinitely. Therefore, if you test a patient who has had lesions for only a few days and his HSV serology demonstrates anti-HSV antibodies, then he probably had an initial infection at some point in the past. (Thus, the current outbreak indicates a recurrence). Conversely, the absence of these antibodies (with a positive type-specific culture) suggests that the patient has a primary HSV infection.

Q: My friend got herpes and had to stay in the hospital. Will that happen to me?

A: HSV-2 infection can vary in severity. While most cases present with self-resolving ulcers, the breakdown in the mucosal and skin surfaces can lead to complications. Secondary bacterial infections can lead to localized cellulitis of the anogenital region. Uncircumcised males with lesions over the urethral area can present with urinary retention or phimosis. Vaginal outbreaks can result in labial adhesions and urinary retention. Anorectal HSV infection outbreaks often present with pain, bleeding, discharge, tenesmus, and inability to defecate.

Serious secondary complications involve herpetic involvement of the brain and meninges. Most cases of herpes encephalitis are caused by HSV-1 infection. A significant minority of cases of HSV meningitis and transverse myelitis result from primary infection with HSV-2. Unlike HSV-1 encephalitis, however, complications of HSV-2 infection tend to be nonfatal and infrequently require hospitalization.