Pathogens

• Bacteria and viruses are the main disease causing pathogens in humans. Even though they both cause disease, they vary in many ways
• Bacteria are prokaryotic cells meaning that they have no membrane bound organelles and, as such, do not have a nucleus – their genetic information is stored in the form of a circular strand of DNA whereas viruses consist of just nucleic acid enclosed in a protein coat and their genetic material can take the form of DNA or RNA
• Bacteria do not require a host to survive whereas viruses are entirely dependent on their hosts and cannot survive without them
• Viruses are significantly smaller than bacteria
• Bacteria have a cell membrane, cell wall and cytoplasm as well as other organelles such as ribosomes, plasmids, flagellum and pili whereas viruses possess no such structures.
• An example of a bacterial disease is tuberculosis also known as TB
• TB is caused by a bacterium called Mycobacterium tuberculosis which infects phagocytes in the lungs. The first infection is symptomless as the infected phagocytes are sealed in tubercles as a result of inflammatory response in the lungs
• However, the bacteria lie dormant inside the tubercles as they are not destroyed by the immune system as tubercles are covered with a thick waxy coat
• When the immune system becomes weakened, the bacteria become active again and slowly destroy the lung tissue thus leading to breathing problems, coughing, weight loss as well as fever. TB can potentially lead to death
• Meningitis can be caused by bacterial infection of the meninges (a set of protective membranes around the brain)