In an unprecedented study, an experimental drug protected all members of a group of monkeys three days after they were infected with the deadly Marburg virus. The study is the first to show that a drug treatment can stop the disease after it has already taken hold (Sci. Transl. Med. 2014, DOI:10.1126/scitranslmed.3009706). The Marburg virus is a close relative of the Ebola virus, and together they make up the group known as filoviruses. Thomas W. Geisbert and coworkers at the University of Texas Medical Branch in collaboration with researchers at Tekmira Pharmaceuticals exposed macaques to a particularly deadly Marburg strain, which kills up to 90% of its victims. Sixteen macaques were given siRNA encapsulated in lipid nanoparticles. The snippets of RNA were designed to bind to the virus’s mRNA, preventing the virus from replicating. All 16 macaques survived, whereas all untreated animals died. Previous studies have shown that the siRNA strategy can protect Ebola-infected monkeys treated soon after exposure. But this time the monkeys had detectable levels of Marburg in their blood and showed signs of illness. The results are promising for developing a treatment for infected human populations, the researchers note. Geisbert’s team will be performing further studies to find whether monkeys can be treated at even later stages of infection.