Definition of basic terms: Communicable disease: An illness due to specific infectious agent or its toxic products which develops through transmission of that agent or its toxic products from a reservoir to a susceptible host either directly or indirectly. Contagious disease - capable of spreading from one person to another Incubation period: The interval between exposure and first clinical manifestation. The time between exposure and first case is the minimum incubation period, The time between exposure and the last case, maximum incubation period. Communicable period The time interval during which an agent may be transferred directly andindirectly from a host to another (not necessarily of same species). Reservoir: Any human beings, animals, plants, arthropods, soil or inanimate matter in which an infectious agent normally lives and multiplies and from which it passes to a new host. For example, soil may harbor agents that causes tetanus, anthrax. Some diseases with human reservoirs are: Most bacterial and viral respiratory diseases HIV/AIDS/Sexually Transmitted Infections (STIs), measles,typhoid etc
