BOSTON - A form of the herpes virus that causes an AIDS-related skin cancer appears to spread through kissing.
Herpes virus 8 was discovered six years ago and causes a skin cancer called Kaposi's sarcoma. In the United States, the cancer occurs almost exclusively in people with AIDS.
Some had suspected that the virus was transmitted through sexual intercourse, but the new research from the University of Washington, reported in Thursday's New England Journal of Medicine, contradicts that idea.
Dr. John Pauk and others tested 39 gay men who were infected with the virus but did not have Kaposi's sarcoma. They found the virus in 30 percent of their saliva samples and mouth swabs, compared with 1 percent of anal and genital samples. When present, the virus levels were also much higher in saliva than in semen.
''The important thing is it suggests that oral-oral contact plays some role in transmission, although more study is needed to confirm that,'' said Pauk.
The study also found that homosexual men who engaged in ''deep kissing'' - kissing that involves a lot of contact with saliva - appeared to be at substantially higher risk of catching the virus.
Kaposi's sarcoma causes purple skin blotches and can also attack the internal organs. Like many other diseases that kill people with AIDS, it usually affects those with weakened immune systems. The virus alone rarely causes sickness among people with normal disease defenses.
The research ''definitely has public health implications for people infected with HIV,'' said Dr. Ronald O. Valdiserri of the U.S. Centers for Disease Control and Prevention. However, he said there was not enough data to recommend that people with HIV avoid deep kissing.
Thirty percent to 50 percent of HIV-infected people who catch herpes virus 8 will eventually get Kaposi's sarcoma. Kaposi's sarcoma has been present for centuries in Southern Europe, the Middle East and Africa. But it was rare in the United States until the start of the AIDS epidemic in the early 1980s.
Experts say the virus is still largely confined to homosexuals in the United States, and that is why kissing has not yet spread herpes virus 8 among heterosexuals.
Dr. Anna Wald, another University of Washington researcher, noted that herpes virus 8 is closely related to the common Epstein Barr virus, which causes mononucleosis, long known as the kissing disease.
''Teen-agers tend to get this when they start kissing,'' she said. ''The reason they get Epstein Bar virus and not herpes virus 8 is that most people have Epstein Bar virus, but relatively few have herpes virus 8.''
Dr. Patrick S. Moore of Columbia University, who discovered the virus, said exposure to saliva may explain the high rate of infection in parts of Africa, where more than 70 percent of people may carry herpes virus 8.
Other forms of the herpes virus cause chicken pox, shingles, cold sores and genital herpes.
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The New England Journal of Medicine: http://www.nejm.org/content/index.asp