: Simian immunodeficiency virus
(SIV) is a non-human-primate equivalent to HIV that is studied to better understand HIV. Francois Villinger of Emory University and his colleagues used radioactive tracers to study the spread of SIV in macaque monkeys. They tagged SIV antibodies, which bind to the virus, with copper-64, an isotope that shows up in positron emission tomography
and computed tomography
scans. The images helped them map the spread of the virus through the monkeys' bodies. In chronically infected monkeys, the virus was heavily concentrated in the large intestines, lymph nodes, spleen, and nasal areas. In monkeys resistant to infection or receiving antiretroviral treatment, only residual levels of the virus were found in those areas. In newly infected monkeys, SIV was first seen in the upper body and respiratory organs and then cleared those areas as it settled into the organs in the lower body. The technique could be used to find areas of untreated HIV in humans and to help map the behavior of the virus.