The Four Routes of Infection

How Pathogens Enter the Body

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Whether you've had a cold or an oozing cut, everyone gets infections of some sort or another. But how do infection-causing pathogens enter the body? Understanding the four main ways that infections start can help you protect yourself.

The Respiratory Tract

Another name for the common cold is an upper respiratory infection. It occurs when one of 200 different cold-causing viruses is breathed in and enters the respiratory tract into the lungs.

Rhinoviruses are the most common of the viruses that cause colds. Coughs, influenza, and other airborne infections are also contracted in this fashion.

Breaks in the Skin

One of the many functions of the skin is to act as a barrier against infection. However, if you have a bug bite, scratch or puncture wounds by needles, the germs that your skin is meant to keep out can enter your bloodstream. In addition, cuts, scrapes or sores in mucous membrane that lines the mouth or nose, provide a route for infection to enter.

Common infections that start through breaks in the skin include:

  • Cellulitis: When bacteria (usually streptococcal bacteria) enter your body through a bruise, burn, wound or surgical incision, you may get a potentially dangerous infection called cellulitis. Skin will become red, inflamed and painful, and you may experience fever, fatigue or chills. Antibiotics can treat the infection before it spreads into your bloodstream.
  • Impetigo: Usually caused by staph or strep bacteria, impetigo is a very contagious bacterial skin infection. It is the most common type of skin infection in children and does not affect adults nearly as often.

The Digestive Tract

Food, drink or other infected products infection with bacteria or a virus can be swallowed and infect the stomach or bowels.

Most people have experienced an upset stomach at one point in their life, which sometimes reveals itself in the form of diarrhea and/or vomiting. A common example of this is bacterial gastroenteritis, otherwise known as food poisoning. You can get food poisoning if you eat meat or poultry that came in contact with bacteria during processing; if your produce has touched water, during growing or shipping, that contained animal or human waste; or from improper food handling.

The Urinary and Reproductive Systems

Pathogens can also enter the body through the urinary system, as is the case of a urinary tract infection, or the reproductive system, as is the case with sexually transmitted diseases.The infectious agent may remain localized or may enter the blood stream. For example, sexually transmitted diseases most commonly infect the genitals, which HIV, the AIDS virus, is carried in bodily fluids and can be transmitted in saliva, seminal fluid or blood.

Sources:

Johns Hopkins Medicine. (n.d.). Upper Respiratory Infection (URI or Common Cold). Retrieved February 28, 2016.

U.S. National Library of Medicine. (2014, February 10). Bacterial gastroenteritis: MedlinePlus Medical Encyclopedia. Retrieved February 28, 2016.

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