Newsday - June 7, 1996
Laurie Garrett - Staff Writer

In a report today in the journal Science, researchers wrote that oral administration of the monkey form of the HIV, known as SIV, caused lethal infection in six of seven macaque monkeys studied.

"What we are addressing here is not casual [oral] contact. Casual contact is not a danger," said Dr. Ruth Ruprecht of the Dana Farber Institute in Boston. "It took 800 times more virus for the oral transmission route compared to intravenous [injected] transmission route."

Nonetheless, Ruprecht said the researchers concluded that "oral sex should not be considered safe sex." As for other oral contacts, such as deep kissing or mouth-to-mouth resuscitation, Ruprecht said "that will require more research."

The new study does not address biological differences between monkey and human mouths, or the fact that the virus was introduced to the monkeys differently than it would be introduced in nature, the researchers said.

But there have been documented cases of person-to-person transmission of HIV via oral sex, federal officials said, and it's been unclear whether they were blood-to-blood. Additionally, scientists say the SIV / macaque system has been a fairly reliable model of human AIDS for well over a decade of research.

Ruprecht and her collaborators isolated a mixture of SIV viruses from monkey cells, and then carefully placed droplets of the concoctions on the tongues of seven adult macaques. All the animals were first examined for minute gum or mouth sores that might allow the virus to enter their bloodstream.

Six of the seven monkeys became infected and developed AIDS.

The dose required to produce infection was 800 times greater than that needed to cause disease by direct injection of SIV into a monkey's bloodstream, Ruprecht said. But it was also 6,000 times less than that required to cause direct vaginal or rectal transmission of SIV in monkeys.

Experts scrambled this week to offer some insight into why transmission occurred in the six monkeys and what implications these findings may hold for human beings.

Dr. Helen Gayle, director of AIDS and HIV efforts at the Centers for Disease Control and Prevention in Atlanta, said it was too early to draw conclusions.

In the Ruprecht experiment, the macaques were exposed to viruses that were outside of cells. But in nature, HIV and SIV spread while hiding inside of large cells - cells that at least one study has suggested are less likely to get through mucosal tissue than are free viruses.

Ruprecht said there was no way to administer specific doses of SIV or HIV without using cell-free viruses. Future research by the team will attempt to repeat the experiment with cell-bound SIV, said Dr. Louis Martin, of the university's primate center.

It also is unclear whether macaque saliva contains factors, such as are found in the human mouth, that neutralize AIDS viruses.

Last year, researchers reported that a chemical dubbed SLIPI (secretory leukocyte protease inhibitor) almost completely blocked HIV in test-tube studies. No one has looked for SLIPI-like factors in macaques. If there are no such chemicals, the monkey results may have less bearing upon the human situation.

But there have been cases of human-to-human oral transmission of HIV, verified by the CDC. In 1989, a Massachusetts man contracted AIDS as a result of oral sex with an infected female prostitute.

But Gayle said she doesn't foresee a change in safe sex recommendations in light of the new research.

"As we have always said, people should take precautions when engaging in any sexual activity that involves the exchange of fluids," Gayle said.
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