A portal of exit is the site from where micro-organisms leave the host to enter another host and cause disease/infection. For example, a micro-organism may leave the reservoir through the nose or mouth when someone sneezes or coughs, or in faeces.
A portal of entry is the site through which micro-organisms enter the susceptible host and cause disease/infection. Infectious agents enter the body through various portals, including the mucous membranes, the skin, the respiratory and the gastrointestinal tracts.