 A pathogen is a microorganism that can cause disease. In this video, we are going to discover what they are exactly, how they can spread and cause infection, and how their spread can be reduced or prevented. Pathogens may be viruses, bacteria, protists or fungi. They are just microorganisms that can cause disease. Bacteria are microscopic. Even the biggest are only 10 micrometers long, which is minuscule. Once bacteria find their way into the body, they release toxins that make us feel ill. Examples of bacteria infections are cholera, typhoid, food poisoning, and gonorrhea. Although bacteria are very small, viruses are much, much smaller again. They are among the smallest organisms we know of. Bacterias not only enter your body, but they enter into cells and reproduce inside cells. They reproduce hundreds of thousands of times, and eventually cause the host cell to explode. The virus then passes out through the airwaves, bloodstream, or other route and can spread through populations. Examples of viral infections are the flu, influenza, measles, mumps, the common cold, and AIDS. Out of the thousands of species of fungi, a few can cause human diseases. They can cause minor skin conditions all the way up to life-threatening diseases. Some common fungal skin conditions are athletes' foot and ringworm, they are contagious and can pass from person to person through direct contact, or less commonly through contact with common surfaces. There are some opportunistic fungal diseases that can take advantage when the immune system is lowered for other reasons, such as cancer or AIDS. Protests are singles of organisms. Some protests can contaminate food and cause amoebic dysentery, which is an intestine infection and results in severe diarrhea. Protest pathogens can also be parasitic. They live in or on other organisms and cause harm. Malaria is an example of a protest pathogen that lives in the blood and is transmitted by mosquitoes. Watch the second part of this video to see how pathogens are spread and how their transmission can be prevented.