Medical Microbiology is the study of the causes and management of infectious diseases. These can be caused by viruses, bacteria, microfungi and protozoa. Medical Microbiology may overlap with parasitology, generally considered to be the study of diseases caused by multicellular parasites. This branch of microbiology is amongst the most widely studied and followed branches due to its great importance to medicine. Along with providing a deep knowledge and understanding of the nature of pathogens this line of study has also been applied in several immunological innovations in the field of medical science. Through the development of vaccines against invading organisms, deadly and debilitating diseases such as small pox, polio, and tuberculosis have been either eradicated or are more treatable because of the efforts of scientists and researchers in the field of medical microbiology. Bacteria, fungi, protozoans, and viruses can all cause disease in humans. Humans have been colonized by microorganisms from the beginning of time, and microorganisms are constantly evolving and changing to thwart human attempts at controlling them.