Organism that grows, feeds, and is sheltered on or in a different organism and that does not contribute to the survival of its host. Ultimate micro-parasite smaller than bacteria; neither cells not organisms; can only reproduce within their host. Macroparasites composed of many cells; does not multiply in host, instead cycles through transmission stages eggs and larvae which pass into the external environment. Movement of a parasite from host to host. Incubation period the interval of time required for development of a disease. Seemingly inactive period between exposure to an infection and subsequent illness. Capacity of a parasite to cause disease. Animal infections that can be transmitted to humans. Direct occurs through direct contact, e. g. from person to person. Indirect through a common route / vector, e. g. contaminated air / water, mosquito. Ingestion through the mouth, e. g. e. coli in water. Endemic usual occurrence of a given disease within a given geographical area.