Wiki Sumber Informasi iSIKHNAS

Firstly an animal must be susceptible to a disease to become infected. A susceptible animal must be exposed to an infectious agent in order for infection to occur. Exposure means that the infectious agent has entered the body of the animal in some way. Not every exposure will result in infection. Sometimes after exposure the infectious agent will die or be killed by the animal's immune system before it can cause infection. If the infectious agent begins to grow and replicate within the body then at this point the animal moves from exposure to infection. In the very early stages of infection the animal will usually show no signs of disease. This is called the incubation period.