In order for transmission among individuals to occur, the pathogenic microorganisms must leave the body through a portal of exit. Transmission can occur in the form of respiratory secretions expelled from the respiratory tract, or microorganisms can exit in the feces or urine, or they may be removed when blood is ingested by mosquitoes, ticks, or other arthropods. Skin contact, including contact made during sexual intercourse, is another mechanism for transport to the next individual.
