Tuesday, December 07, 2004

Researchers Trace how AIDS Virus Spreads After Oral Exposure

Researchers from the UT Southwestern Medical Center (Dallas) just released the results of a study aiming to understand how SIV (the simian/monkey equivalent of HIV) oral transmission proceed by tracing the presence of viral genomes in various tissues. "By innoculating monkeys with SIV they traced which tissues in the mouth and digestive tract were infected during the first week. Furthermore, they traced which organs and lymph nodes were first infected and uncovered likely routes of infection. The findings are published in the Dec. 3 issue of the journal AIDS." Previously, our understanding of oral infection by SIV/HIV was deficient compared to the usual sexual relation/blood transfusion/Infected Seringe routes. The results define in time and space the spread/speed of oral infection.

Digest of the press release :

"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 breastfeeding from an infected mother. There is no evidence that saliva transmits the virus from one person to another. However, oral exposure to the virus 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. Studying 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 the stomach acids probably prevented the virus from entering through the stomach or 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," Dr. Sodora said. "These tissues should be a major focus of any additional studies of HIV or SIV oral transmission."

At one day following oral exposure, the first lymph nodes infected were closest to the head and neck. Four days after infection, the virus could be detected in nearly all tissues.

"The ability of virally infected cells to spread so quickly from the site of infection to numerous lymph nodes throughout the body was surprising," Dr. Sodora said.

Because SIV spreads so rapidly throughout the bodies of infected monkeys, it may help to explain why antiviral therapies can effectively protect a monkey or HIV infection of humans only if they are given within hours of exposure to the virus.



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