Diseases and Infections: We Are Constantly Battling Viruses and Bacteria

A disease is a result of an infection caused by germs, also called microorganisms or pathogens, in the body. An infection, or infectious disease, results when germs enter the body and affect one or more organs. Bacteria and viruses are the most common germs and cause most infectious diseases.

Germs are present everywhere: in the air, in our homes and offices, and in our mouths and digestive tracts. Many germs either do not cause disease or are killed by the body's immune system upon entering the body. Infectious diseases range from the common cold — a relatively mild infection — to fatal diseases such as HIV infection. Bacteria cause infections such as strep throat, tuberculosis, and meningitis. Antibiotics can help the body fight a bacterial infection, but medications are not very effective against viruses. The body's immune system is our primary weapon against viruses.

Disease Transmission

Infectious diseases can be transmitted from one person to another through four different routes.

Direct Contact

A disease is transmitted by direct contact when a person touches body fluids that contain germ from an infected person. Body fluids include blood, vomit, secretions, and saliva. The risk of disease from direct contact depends on these factors:

• The type of body fluid contacted.
• The concentrations of virus in the body fluid.
• The amount of body fluid with which contact is made.
• The body opening exposed to infectious material.
• The length of the exposure.

Indirect Contact

Some diseases are transmitted by indirect contact with germs on an object that has been in contact with an infected person's body fluids. Many germs can live a short time outside the human body on almost any object. For example, blood, fecal matter, or vomit on a piece of equipment can infect someone who later handles the equipment if the germ enters the person's body. Objects such as intravenous needles are particularly dangerous because they can penetrate the skin of another person.

Airborne Transmission

An airborne disease is transmitted when someone breathes out germs and you breathe them in. Usually the germs are present in tiny droplets that an infected person coughs or sneezes out from up to 3 feet from your face. Some germs, such as tuberculosis bacteria, may live a relatively long time in the air, requiring the infected person to be isolated until treatment is completed.

Vector Transmission

Some diseases can be transmitted if an animal, insect, or even a human bites or strings a person and transmits a pathogen into the person's body. The animal, insect, or person is called a vector and has to be carrying the germs already. Malaria, rabies, and Lyme disease are transmitted by vectors.