Hello - this one causes "Rocky Mountain Spotted Fever" and acts at times like a virus and at other times like a bacteria. This is why sometimes anti-biotics work in removing it and sometimes they don't. It is spread by fleas and ticks and it can also affect plants! It is a strange one indeed! It is also strange in the fact that different types of rickettsia can be found in clumped in different geographic groups all over the world.