Protozoa- these are microscopic creatures which may be fifty times larger than bacteria, but still cannot be seen without a microscope. Important disease caused by these organisms are malaria and amebic dysentery.
They are unicellular (single-cell), complex, animal-like microorganisms. They are characterized by an irregular or fluctuant shape without a cell wall, and many are motile. Protozoa can be divided into four categories: amebas, ciliates, flagellates, and sporozoa.
Protozoa normally live in soil and bodies of water. When introduced into the human body, infection can result. Transmission can occur through sexual contact, contaminated food or water, or by an insect or other arthropod, which carries the protozoa. Some protozoa are parasites and some are capable of living independently of the host. Those that are parasites compete for and deprive host cells of nutrition, causing tissue destruction. Amebic dysentery and giardiasis are caused by protozoan parasites. Malaria is caused by a sporozoa called Plasmodium malariae.