Final answer:
Transfer of pathogens necessitates an exit from the host, a method of transmission, and entry into a new host. Common portals of exit and entry include the skin and various body tracts, while breaches in these barriers can also serve as entry points.
Step-by-step explanation:
Transfer requires a route for the infectious agent to exit the host through a portal of exit, a mode of travel to the susceptible host (a mode of transmission) and a portal of entry to enter the susceptible host. Pathogens must find a way out of the infected individual, traverse to another host, and then enter that new host. The common portals of exit are the skin and the respiratory, urogenital, and gastrointestinal tracts. These portals are where pathogens can leave the host through means such as coughing, sneezing, or through excretions like feces or urine. Pathogens have specialized means of transfer, such as being carried by insect vectors or through sexual contact, enabling them to reach new hosts.
Pathogens such as viruses, bacteria, parasites, or fungi have adapted to exploit specific portals of exit and entry. The skin and mucous membranes serve as major gateways for entry and exit points. Breaches in these barriers, like wounds or insect bites, offer an alternative entry route, known as the parenteral route. Understanding these transmission pathways is crucial in controlling the spread of infectious diseases.