HIV spreads much more rapidly through the body after initial infection than previously believed, apparently causing immediate immune reactions that effectively fuel its replication. Researchers vaginally exposed 44 rhesus monkeys to SIV, HIV’s simian cousin, and analyzed the animals during the first 10 days postinfection.

The investigators found that in most of the animals that were analyzed one day after infection, viral RNA was present in at least one tissue outside their reproductive tract and SIV had apparently already prompted an inflammatory immune response in tissues infected with the virus. There was a connection between increasing amounts of viral RNA and greater amounts of a protein that suppresses a general immune response to viruses.

“This tells us that the virus goes beyond the mucosal surface very, very quickly,” says Anthony S. Fauci, MD, director of the National Institute of Allergy and Infectious Diseases (NIAID), referring to the surface of the reproductive tract in the case of this study.