Mode of Entry Into a Susceptible Host

The following are the main routes of entry for pathogens into the human body :

• The respiratory tract which involves the nose, mouth, throat and lungs. All  air-borne infections enter through this rout.
• The gastrointestinal tract is the route by which all pathogens that find their way into food and water or into the the mouth of the host enter the human body. This is the most common route for the pathogens to enter a host.
• The genitourinary tract which involves the male and the female sex organs. Pathogens of diseases like AIDS and syphilis enter a host.
• The skin provides entry to infectious agents of diseases like leprosy and scabies which spread by direct contact, or rabies is a vector-borne disease. 
• The mucous membrane of the eyes, mouth and nose. Pathogens of infections like the common cold, diphtheria, whooping cough and eruptive fevers find this route to enter the host.