Human Saliva Blocks Spread of AIDS Virus, Study Says
Human saliva contains a factor that prevents the AIDS virus from infecting cells, a finding that may explain why the disease is not transmitted orally, scientists at the National Institute of Dental Research reported Thursday.
Until now, there has been “a lot of very convincing, though indirect, evidence that AIDS is not spread by oral fluids,” said Dr. Philip Fox, who led the research team. Nevertheless, many people, especially dental professionals, have been concerned about the risk.
“What’s nice about this is that it provides some scientific backup for the already substantial epidemiological evidence that AIDS is not transmitted by the oral route--this may be the reason why,” Fox said in an interview. “The discovery . . . is reassuring.”
One Infection Reported
Thus far, only one dental health professional--a dentist who had experienced multiple needle-stick injuries--has become infected with the AIDS virus as a result of occupational exposure, according to the national Centers for Disease Control in Atlanta.
The AIDS virus is most commonly transmitted through blood or semen during unprotected anal or vaginal sexual intercourse or through the sharing of contaminated hypodermic needles by intravenous drug abusers.
Although the AIDS virus has been found in saliva, Fox said, “it has been found very infrequently” and in very low amounts. “If you put all of that together, you really should feel that saliva is, in fact, protective--and not dangerous,” he said.
The research, which appears in the May issue of the Journal of the American Dental Assn., was able to determine the presence of such a protective factor in salivary secretions but was not able to identify what it was or how it works.
Further research in these areas, Fox said, “could conceivably be useful in developing therapies for controlling AIDS.”
Part of Body’s Defenses
He added: “Many therapies that are being developed against AIDS are also toxic. But this is a natural product, produced by the body itself, which is not going to be a substance that is toxic. I see this as a form of the body’s natural defenses.”
Fox said he was not surprised by the discovery. “Saliva is somewhat unique,” he said. “The body has a number of defenses to protect an outside cavity from the outside environment. We know that saliva has a host of anti-bacterial and anti-fungal activities, so to find some antiviral activity is in keeping with this role.”
He said it is unclear whether saliva would be protective during oral sex, which typically involves semen, a body fluid known to carry and transmit the virus. He said he felt certain only that saliva itself could not serve as the source of transmission.
“I would not feel confident taking the results of this study and extrapolating them to say: ‘Don’t worry about oral sex,’ ” Fox said. “If you have cuts in your mouth and the virus in the semen could get access to the blood in that way, the saliva could be ineffective.”
He and his colleagues collected saliva samples from three healthy men aged 35, 40 and 42 who were not members of any group at risk for AIDS. In this country, AIDS has primarily afflicted homosexual and bisexual men, intravenous drug abusers and their sexual partners.
Whole Saliva Studied
They collected whole saliva, which contains secretions from the major and minor salivary glands, and samples from the three major glands: the submandibular, the sublingual and the parotid glands.
The researchers combined the saliva samples with the AIDS virus and then added lymphocytes, immune system cells that are the major targets of the virus.
They discovered that the virus was unable to infect the lymphocytes in the presence of whole saliva. They also found that secretions from the submandibular and sublingual glands--collected together because they share a common duct into the mouth--also protected against infection.
Secretions from the third major gland, the parotid, provided little or no protection, though samples from one of the subjects did inhibit infection, the scientists said.
Gland Secretions Held Vital
Because whole saliva also contains bacteria and blood leaked through cuts in the mouth and the gums, as well as other products, the scientists said that the experiment using only salivary secretions confirmed that the protective factor came from the gland secretions themselves, not from some other sources in saliva.
The study was not the first to suggest a protective role for saliva in AIDS. Two years ago, another researcher reported that whole saliva from a chimpanzee and a human inactivated the virus.
“What’s important is that we looked at the individual gland secretions,” Fox said.
Fox said that he and his colleagues would next try to identify the substance and determine how it works. “We are also looking at how widespread this activity is--is it found in women? In children and in people with AIDS? That’s not known at this point,” he said.
