Oral exposure boosting infection

An animal model has been used by researchers at the University of Texas Southwestern Medical Center at Dallas to trace how the virus that causes AIDS in humans may enter and spread throughout the body following oral exposure.

By inoculating monkeys with SIV, the simian version of HIV, scientists traced which tissues in the mouth and digestive tract were infected during the first week. They also traced which organs and lymph nodes initially were infected while uncovering likely routes of the virus.

"This is the first study to assess which tissues had SIV nucleic acid at the earliest times following an oral infection," notes Donald Sodora, assistant professor of internal medicine and microbiology.

Oral transmission of HIV is problematic, especially in developing countries where bottle feeding infants is not practical. Up to one-third of newborns may become infected with the virus that causes AIDS as a result of breast-feeding from an infected mother. There is no evidence that saliva transmits the virus from one person to another. However, oral exposure through breast milk or semen (during sexual contact) may result in a higher number of infections than originally thought.

In the study, monkeys were infected with SIV administered onto the cheek pouch of the rhesus macaque, likely coming into contact with the oral mucosa and tonsils before being swallowed. Examining the monkeys after exposure, researchers uncovered the sites of transmission and a rapid spread of the virus to surrounding lymphoid tissues. Likely sites of infection included soft tissue in the mouth, esophagus, and tonsils.

Further examination of the digestive tract showed that SIV was not present in tissues below the esophagus until four days post-infection, indicating that stomach acids probably prevent the virus from entering through the intestines. "It is clear from our study that the oral and esophageal mucosa and the tonsils are likely to be the most important sites of viral entry," reports Sodora.

Because SIV spreads so rapidly, it may help to explain why antiviral therapies effectively can protect against HIV infection of humans only if they are given within hours of exposure.

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