Infectious diseases can be caused by worms, protozoa, fungi, bacteria,
viruses and even proteins (prions). Organisms, viruses and prions can be classified by
their infectivity, or their ability to enter, survive and multiply in a host. There are seven
classes of viruses, based on their DNA or RNA. By number, 90% of the cells in the
human body are bacteria. Even though our lives depend on symbiotic bacteria, it is
important that they stay in their proper places in our human bodies, or ecosystems. By
the mid-1980s strains of S. aureus emerged which were resistant to common
antibiotics. Multicellular parasites include four species of Schistosoma, a flatworm that
causes schistosomiasis, which is second in importance only to malaria, with hundreds
of millions infected worldwide. In addition to schistosomiasis, helminths can cause
ascariasis, dracunculiasis, elephantiasis, hookworm, lymphatic filiaruasis, onchocersiasis,
and trichuriasis.
Keywords: Bacteria, Fungi, Infectious diseases, Mycobacterium , S. aureus,
Tuberculosis, Viruses.
