Herpesviruses are everywhere!

A population-based study of primary human herpesvirus 6 infection is reported in the current issue of the The New England Journal of Medicine (NEJM).

The Human herpesvirus 6 (HHV-6) is now established as the cause of the sixth clinically distinct eruptive disease of childhood. Measles virus, rashes in group A streptococci, and rubella virus are the causes of the first three diseases; parvovirus B19 is the cause of the fifth disease.

Herpesviruses have a lot in common; the most interesting factor shared by all is their ability to establish a persistent state following primary infection.

This means that once a person has become infected with a herpesvirus, he or she is always susceptible to re-current infections; re-infection sees the emergence of the transmissible virus. The site of viral latency varies .Despite the absence of visible symptoms the infection might commonly appear in oral secretions (for HSV-1, EBV, CMV, HHV-6, and HHV-7), genital secretions (HSV-2, CMV, and HHV-6), urine

(CMV), white cells (CMV, HHV-6, and HHV-7), and breast milk (CMV and HHV-7). Host immunity affects both the possibility of re-infection and the severity of the illness. In general, the greater the immune impairment, the greater the possibility of recurring infections.

Given the high incidence of herpesvirus infections and their latent capacity, the occurrence of these viruses is clear. In the U.S., infections contracted in infancy, are present in at least 50 percent of young adults.

In the current issue of the Journal, Zerr et al. (pages 768–776) note that approximately three quarters of children have been infected with HHV-6 by two years of age. Data from other studies suggest that infection with HHV-7 has a similar pattern. Clearly, herpesvirus infections are very common, and at any given time, a substantial proportion of the population is spreading one or more of these infectious agents, maintaining the chain of transmission and the high occurrence of infection.

Even though the majority of infections caused by herpesviruses are symptomless or mild the degree of infections attributable to herpes viruses remains substantial. Furthermore, death due to herpesviruses is a major issue for the ever-increasing immune impaired population.

HHV-6 was initially isolated in 1986 from the antibodies of immune impaired adults; within two years it was described as the cause of most cases of roseola (sixth disease),an infection dating back to 1910, is characterized in children by high fever for up to five days, followed by the onset of a pink rash, on the neck and trunk. The sudden appearance of the rash gave the disease the name " exanthema subitum" (“subitum” meaning “sudden” in Latin).

HHV-6, as a major cause of illness in young children, was consequently recorded in children brought to emergency departments with fever.

10 to 50 percent of fever illnesses leading to an emergency room visit have been attributed to HHV-6 infection, the peak age of infection being six to nine months. Our understanding of the full spectrum of illness that is attributable to this virus is hampered by the lack of a conclusive, population-based study of HHV-6 beyond the hospital setting. A study by Zerr et al. using an intensive study program addresses this shortcoming.

Previous studies have indicated that saliva is the main source of the infectious virus. These studies also demonstrate that persons who test positive for forms of Herpesvirus,shed reactivated viruses frequently throughout their lives. Taken together, these studies show us an unavoidable medically proven fact: Herpesviruses are everywhere!

See http://content.nejm.org/ and http://content.nejm.org/cgi/content/short/352/8/768