Introduction 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 . It is debatable whether viruses are truly living organisms. They entirely rely upon other cells for their replication.
Specific viruses attack specific types of cells.
Respiratory Syncytial Virus infects only the cells of the respiratory tract, for example. There is a special class of virus that attacks bacteria. These are the bacteriophage . Viruses have a nucleic acid core, either DNA or RNA but not both. Retroviruses are unusual in that the virion carries an RNA copy of the genome but upon infection of a host cell a cDNA copy of the virus genome is made using the enzyme reverse transcriptase .