By Steven Reinberg
THURSDAY, Oct. 17 (HealthDay News) -- Today's teens may be at higher risk than ever of contracting genital herpes because they don't have enough immune system antibodies to shield them against the sexually transmitted virus, a new study suggests.
This increase in risk may be the result of fewer teens being exposed in childhood to the herpes simplex virus type 1 (HSV-1), a common cause of cold sores, researchers reported Oct. 17 in the online edition of the Journal of Infectious Diseases.
"HSV-1 now is the predominant herpes strain causing genital infection," explained Dr. David Kimberlin, chair of infectious diseases at the University of Alabama at Birmingham School of Medicine, and the author of a journal editorial.
According to Kimberlin, the new findings suggest that almost one in 10 adolescents who a decade ago would have already acquired HSV-1 and built up some immunity may now encounter HSV-1 when they first become sexually active. That could leave them more susceptible to genital herpes than young people were in the past.
"This [also] has potentially significant consequences on neonatal herpes transmission," which occurs when a baby contracts the herpes virus from a genitally infected mother, Kimberlin said. "We must continue to monitor these changes and watch for shifts in neonatal herpes infection that possibly could result."
Of the eight types of herpes, the two that are most important in terms of disease transmission are HSV-1 and herpes simplex virus type 2 (HSV-2), both of which cause lifelong infections with no known cure. These viruses can have dormant periods after an initial outbreak. HSV-1 is usually contracted in childhood, by skin-to-skin contact with an infected adult, whereas HSV-2 is most often sexually transmitted.
However, recent research indicates that HSV-1 is becoming a major cause of genital herpes in industrialized countries. One study found nearly 60 percent of genital herpes infections were caused by HSV-1, the researchers noted.
"I tell patients herpes is like your credit history -- whatever you did you can never get rid of," said one expert not connected to the study, Dr. Marcelo Laufer, a pediatric infectious disease specialist at Miami Children's Hospital.
"Every year the proportion of patients who get infected with HSV-1 through oral sex is increasing," he said. "Adolescents who reach that age without being exposed to HSV-1 might, through oral sex, be more susceptible to the infection."
The virus is usually passed through saliva, but in more recent years better hygiene may have kept the virus from spreading to young children, Laufer theorized. That means that fewer children are now exposed and are producing antibodies against HSV.
HSV-1 and HSV-2 can also cause significant problems for newborn infants, who don't yet have mature immune systems capable of fighting the viruses. As many as 30 percent of infected babies die from this infection if they have the most severe form of the disease, Kimberlin noted.
In the new study, a team of researchers led by Heather Bradley of the U.S. Centers for Disease Control and Prevention used data from federal government surveys to track the prevalence of herpes among 14- to 49-year-olds in the United States.
Overall, they found that 54 percent of Americans in this age range were infected with HSV-1.
Among 14- to 19-year-olds, however, the prevalence of protective HSV-1 antibodies fell by nearly 23 percent from 1999 to 2010, the research team found.
Among those aged 20 to 29, HSV-1 prevalence dropped more than 9 percent. HSV-1 prevalence remained stable among those in their 30s and 40s.
These data suggest that more teens lack HSV-1 antibodies at their first sexual encounter now than in decades past, and so are more susceptible to genital herpes.
"In combination with increased oral sex behaviors among young people, this means that adolescents may be more likely than those in previous time periods to genitally acquire HSV-1," the researchers concluded.