The causes of appendicitis are thought to relate to some event that leads to the colonization of the appendix either by bugs or some micro organisms.
Appendicitis as you may know is the inflammation of the appendix usually by some form of micro organism, which is often cause by some kind of blockage that leads to a reduced blood supply to the appendix.
This can lead to a perforation of the appendix which can result in a large pus formation if the appendicitis is not quickly and correctly diagnosed.
Other causes of appendicitis include:

• Faecolith: Faecolith is when faeces get lodged in the lumen of the appendix and then proceed to become very hard.
  This then causes the blockage and additional faeces are unable to pass through the lumen which in turn leads to appendicitis.
  Eating a well balanced diet that is rich in fiber is thought to counteract this from happening.
  
• Swollen Lymph Glands: Even something as common as a cold or any other type of infection be it bacterial or viral can lead to appendicitis.
  Glands on the wall of your appendix can become swollen which can lead to them blocking the path to the lumen.
  This is why appendicitis is known to be more prevalent in winter.
  
• Mucus: For unknown reasons the appendix can secrete copious amounts of thick mucus into the lumen.
  This mucus can bind with cells from the walls of the appendix to create a thick substance which again can cause a blockage of the lumen, which in turn will lead to a reduced blood supply to the appendix leading to a case of appendicitis.
  
• Worms: Although it's not very common in the western world it is quite common in third world countries for people to become infested with worms which can actually block the lumen, again once this happens there is the reduced blood supply to the appendix and the possible onset of appendicitis.
  Shistosomiasis and Pinworm worms are most commonly associated with this.
  

• Tumor: While this is rare it has been known to lead to appendicitis especially in elderly people.
  The tumor may have originated in the appendix or it may have spread from another area.
  Characinoid tumors are more commonly associated with this type of appendicitis.
  

Sometimes the body can heal itself or even a course of antibiotics are all that is needed to remedy the situation but more often than not , surgery under a general anesthetic is performed with the appendix being taken out.