"Level 4 is the highest degree of laboratory containment for isolation and experimentation on microbiological organisms. Level-4 organisms produce lethal illnesses in humans and, for the most part, have no treatment and no prevention. Among the most infamous are Ebola and Lassa." —from Level 4 Virus Hunters of the CDC
  Husband-and-wife team Dr. Joseph B. McCormick and Dr. Susan Fisher-Hoch journey through equatorial Africa, Brazil's ghettos and rainforests, and settlements in northern Pakistan in search of those already infected by these killers. Filled with scientific knowledge, Level 4 explains how and why these viruses are so deadly and how we can prevent further devastating epidemics from breaking out.