Okay, so I am doing a case study for school on disease and what causes it. we have to include an example of a disease caused by a. a bacterium, b. a virus, c. a fungi, and d. a protist. my chosen diseases are Cholera (caused by bacteria), Influenza (caused by viruses), Malaria (caused by protists), and another that has to be caused by a fungi. I understand that the majority of the symptoms of a disease are caused by the immune system, but I am having trouble finding what the micro-organisms actually do to the body to necessitate a reaction from the immune system. What do they do to the body that actually kills you? Do they act as inhibitors? Do they kill cells? etc.

Direct answers would be great, but links to websites that explain it would be better.

Thanks,
LSRW

There is several things

Bacterial can release toxins – like cholera for example. In cholera the bacteria releases a toxin that causes cells in the gut to have a membrane ion pore locked open causing a large amount of ions to flow out of those cells into the gut. This in turn causes water flow into the gut through osmosis. So loss of fluids and electrolytes cauess severe dyhydration which can lead to loss of blood volume, causing decrease in blood pressure, causing less oxygen and nutrient supply to cells causing death. Alot of bacteria have some sort of toxin that most commonly interferes with some form of protein, either an enzyme or membrane protein that leads via a chain of steps to alter homeostasis of one essetial processes for life. (eg temperature, blood volume, blood pressure, oxygen levels ect)

Viruses have a different role in that they infect cells and cause damage to those cells. because viruses cannot replicate themselves, they infect cells (usually of a specific type) and disrupt their function and produce more viruses until the cell bursts and dies. Or in the case of influenza, the viruses bud off the cell taking with them some of the cell membrane which causes damage and when large numbers do this, leading to bursting and death. These cells dying cause problems.

In addition to killing your body cells and immune cells and releasing toxins with harmful effects, they also invoke an immune response. This is the body trying to eliminate them, and in itself can sometimes cause more harm then good. The area becomes inflamed to allowing more white blood cells (neutrophils) into the area which then release harmful degrading substances like proteases and respiratory bursts (unstable oxygen species) to kill the bacteria, unfortunately this can also damage surrounding tissue and cells which causes some of the damage.