In a transmission experiment, the transmission of an infectious agent in a group of animals is studied. Common elements are: * The animals are housed such that they are in (direct or indirect) contact with each other. The contact possibilities may be manipulated by the investigators. Indirect contact may include, for example, contact via a fecal-oral route. * An initial situation is created in which one or more animals are known to be infected with a particular agent, and all the other animals are known to be free from that particular agent and can thus potentially become contact-infected. * After a certain period of observation, the experiment is ended and the final number of contact-infected animals is determined. * Often, the number of contact-infected animals is monitored throughout the experiment, e.g. through daily swabs.