What can you tell me about a viral infection called herpes simplex 6? Is there any connection to genital herpes? I was seeing someone who was diagnosed with genital herpes. Four weeks later, his 18-year-old son lapsed into a coma with what has been diagnosed as herpes simplex 6. He had a positive stain on tests they did. The son has permanent brain damage from the severe encephalitis caused by this virus. It is suspected he's been carrying this "stealth" herpes 6 for about six years. I need to know if I have to be concerned due to sexual contact with the father. I have been tested for genital herpes and it is negative so far.

A.G.

Human herpesvirus (HHV) 6 is one of eight viruses in the herpes family. These include herpes simplex 1 and 2, which cause oral and genital herpes; the varicella-zoster virus, which causes chickenpox and shingles; Epstein-Barr virus, which causes mononucleosis (mono); cytomegalovirus (CMV), which can cause a variety of syndromes in healthy individuals and in people with impaired immunity; HHV-8, which has been linked to Kaposi sarcoma, a skin malignancy common in patients infected with HIV (the virus that causes AIDS); and HHV-6 (which I will discuss in detail) and a very similar virus, HHV-7.

Almost 95 percent of adults have been infected with HHV-6. About three-fourths of people are infected by age two. Most of these infections are either asymptomatic (without symptoms) or cause only mild, nonspecific illness.

One of the most recognized syndromes associated with HHV-6 is roseola, also known as exanthem subitum. In this infection, the infant or young child has a few days of high fever, irritability and other symptoms, such as diarrhea and cough. When the fever finally comes down, a rash develops over much of the body, especially in the groin and the neck. Most infants recover uneventfully; however, encephalitis, a severe infection of the brain, is a rare complication of roseola. HHV-6 is also frequently the cause of a syndrome in infants and young children that is even more common than roseola, high fever (without a rash), often resulting in seizures (convulsions).

HHV-6 can also cause encephalitis, leading to coma and brain damage, even in the absence of any other more typical findings of infection, including fever. Studies show that this virus frequently can be found in the spinal fluid of patients with roseola, febrile seizures or encephalitis, including individuals who have no signs or symptoms of brain infection. Often, HHV-6 can be detected in the spinal fluid years after the initial infection, which has caused speculation that a number of neurologic disorders may be due to HHV-6, including many cases of encephalitis and multiple sclerosis.

However, it is very difficult to definitively prove the relationship of HHV-6 to encephalitis in an individual patient, because many people have detectable levels of HHV-6 in their spinal fluid for years without developing encephalitis. While I cannot, of course, discount the possibility that your boyfriend's son had HHV-6 encephalitis, I am not entirely convinced that he did. Of note, herpes simplex virus 1 is a far more common cause of serious encephalitis, and it frequently leaves a patient with severe neurologic problems, even with treatment.

Regardless, you are at virtually no risk of developing encephalitis from contact with your boyfriend. You are very likely immune to HHV-6 already. Even if you were not already immune and you did, by chance, acquire the infection from your boyfriend (HHV-6 is spread through the saliva and respiratory secretions), you would most likely have a mild or even asymptomatic infection. Encephalitis is a very rare complication of HHV-6 infection.