Many diseases are caused by viruses or bacteria, which may be considered introduced species under certain circumstances (although viruses are not truly living organisms and need another organism as a host). describe the following exotic diseases and explain their origins.
smallpox
chestnut blight

If you're asking what the diseases do, smallpox makes all kinds of very irritating bumps on your body slowly. They tend to get very very irritating to your skin once they get around your eye and chest. The more you scratch yourself the more powerful the virus gets because it takes advantage of that.