Animal health management is influenced by a number of factors. These include animal factors such as species, breed, age and stage of production, and behaviour, as well as, in the case of domesticated animals, the production systems in which they are kept and the way in which they are managed, as well as the purpose for which they are kept. The level of management depends to an extent on the importance and impact of the diseases that must be managed. Much of the effort that goes into animal health management is directed towards ensuring the safety of trade in animals, animal commodities and products. How animal health is managed is guided by certain basic principles that include preventing the transmission and spread of infectious diseases. The options for doing this are determined by the epidemiology of the diseases and the animal and production factors that contribute to their epidemiology.