Chapter 26, Problem 1RQ

Summary Introduction

To review:

The classification of pathogens based on the portal of their entry.

Introduction:

A pathogen can enter inside the body of the host through appropriate portals. It is the site through which the microorganism enters the susceptible host and causes infection. The entry route of a pathogen is generally same as its exit portal from a reservoir host. The pathogens can be categorized based on the portal of entry.

Explanation of Solution

The various classes of pathogens based on the portal of entry are listed below:

1. Respiratory pathogens: The most common diseases of humans include the infection of the lung and upper respiratory tract. The portal of entry of these pathogens is the respiratory tract. Most of the lung pathogens have well-developed mechanisms to avoid various lung defenses. These pathogens include viruses, bacteria, and fungi. The influenza virus that causes common flu is transmitted directly through nasal secretion or airborne route in which the inhalation of aerosol produced by an infected person leads to infection. The examples of respiratory pathogen include Bordetella pertussis, Blastomycesdermatitidis,and severe acute respiratory virus (SARS).

2. Gastrointestinal pathogens: These pathogens cause gastroenteritis which is an inflammation of the gastrointestinal tract involving both the stomach and the intestines. An example of gastrointestinal pathogen is Vibrio cholerae that causes cholera. It is an infectious disease that causes severe diarrhea and the bacteria is usually transmitted through contaminated food and water. The most common gastrointestinal pathogens that cause diarrhea are rotavirus, Salmonella enterica serovar Typhimurium, and Campylobacter. These enter the body with food and hence, are termed as foodborne pathogens.

3. Entry via breaks in the surface of the skin: The skin is the largest organ in the body and acts as a barrier to pathogens. However, breaks and wounds in the skin can lead to many infectious diseases like tetanus. It is caused by the bacterium Clostridium tetani which has spores to enter the body through a wound or cut on skin.

5. Sexually transmitted pathogens: They enter the body of the host through mucous membrane present in the genital organs. They require direct contact between the membranes of infected reservoir and susceptible host. The requirement of direct contact is due to the susceptibility of pathogen to the dry environment outside the membrane. The different sexually transmitted pathogens are Neisseria gonnorhoeae, human papillomavirus, herpesvirus, and Treponema pallidum.