Have you ever gone to the doctor for a sinus infection, the flu, or a bad cold? Depending on your illness, the doctor may have told you the infection was caused by a bacteria or a virus. Have you ever thought about the difference between the two? You may be used to hearing about bacterial or viral infections, but have you ever thought about how these microorganisms— organisms too small to be seen without a microscope—can actually make you sick?
There are plenty of microorganisms that you are in contact with every day that do not make you sick. Millions of bacteria live in your body and help you digest food, destroy harmful bacteria, and protect you by creating environments in which disease-causing organisms cannot survive. Other microorganisms infect you and cause you to become sick. You may get a fever, have swollen lymph glands, cough a lot, and have a runny nose or high fever.
Why do only some microorganisms make you ill?
How Microbes Are Transmitted
The first step in infection is the microbe entering the body. This can happen in a number of different ways and each is specific to the pathogen. Transmission is the process by which an infectious agent leaves its reservoir or host, travels by some mode, and enters and infects a susceptible host.
There are direct and indirect transmission methods. Direct transmission methods include contact with soil, plants, or people infected with a pathogen. Indirect transmission methods are methods by which a pathogen travels to a host. These methods include those that are:
airborne–an infectious agent is carried from a source to a host while suspended in air particles.
vector borne–an infectious agent is carried by a live carrier, such as a mosquito, flea, rat, or tick.
vehicle-borne–an agent is carried by an inanimate object, such as food, water, blood or items such as surgical instruments.
Knowing how an infectious agent is transmitted allows you to take actions to avoid infection. For example, if a pathogen is airborne, avoid being in an environment of someone who is coughing without covering his mouth. If the infectious agent is vector-borne, avoid the carriers, such as mosquitos or fleas by using an insect repellant.
Once inside the body, pathogens (disease-causing organisms) attack specific cells or travel to specific tissues, depending on the pathogen.