A disease that afflicts members of red (iron-based)-blooded species with transitory pneumonia-like symptoms, but which is invariably lethal to green (copper-based)-blooded beings, such as Vulcans. Choriocytosis encases green blood cells so that they cannot carry oxygen to the body's tissues, slowly asphyxiating its victims at the molecular level. Because of this oxygen deprivation, choriocytosis manifests itself in copper-blooded organisms with symptoms that include extreme fatigue and greatly decreased concentration. The only known cure is strobolin, a naturally occurring drug that can be found only on a few planets in the galaxy, including the Beta Canopus system. Although the crew of the U.S.S. Enterprise survived an outbreak of choriocytosis shortly before stardate 6334.1 (2270), the starship's half-Vulcan first officer, Commander Spock, nearly died from the disease a few days later.