BETHESDA, Maryland (AP) — The U.S. and Liberian governments are starting the first formal patient testing of an experimental Ebola virus treatment that's been used on an emergency basis.

The drug, ZMapp, contains three genetically engineered proteins designed to home on a target on the surface of the deadly virus to stop the disease's progression. ZMapp, developed by San Diego-based Mapp Pharmaceuticals Inc., is "grown" in tobacco plants engineered to make large quantities of the virus-blocking proteins.

Adults and children in both countries, infected with Ebola or with suspected infection, will be included in the study.

The National Institute of Allergy and Infectious Diseases says half the participants will receive three ZMapp injections. The other half will get standard supportive treatment, including intravenous fluids and therapy to maintain blood pressure and sufficient oxygen intake.