Parasitic Diseases

Traditional Parasites

Research has shown that parasites existed in ancient civilizations as evidenced by written records and the discovery of eggs of parasites in ancient Egyptian mummies. In 1875, Fedor A. Lo

¨sch demonstrated that the causative agent of dysentery was the protozoan Entamoeba histolytica. Protozoa are single-celled, heterotrophic eukaryotes, most of which are freeliving. The discovery of E. histolytica as a pathogen led to the identification of other species of pathogenic protozoa. The flagellated protozoa Trypanosoma rhodesiense that is transmitted to humans through the bite of infected tsetse flies causes sleeping sickness (African trypanosomiasis). The organisms reproduce rapidly, avoiding recognition by antibodies in the blood and possibly out number in gredblood cells. They travel through the bloodstream and eventually reach the spinal cord and brain, leading to coma and death. In a healthy human infected with T. rhodesiense, the disease may become a chronic condition, with the organism later becoming opportunistic if the immune system is weakened. The protozoa of the Leishmania species are transmitted to humans by infected sand flies and infect macrophages that attempt to engulf and digest the foreign pathogen. Eventually, the macrophages and immune defenses become overwhelmed causing leishmaniasis. This is a debilitating and fatal disease and epidemics have occurred in India, China, Africa, and Brazil.

Descriptions of malarial disease have dated back to ancient Chinese and Greek civilizations; however, the actual cause of malaria, protozoans of the genus Plasmodium, was not discovered until 1898, when it was found that humans could become infected through the bite of an infected mosquito. Once in the bloodstream, the Plasmodium travels to the liver where it infects and replicates within cells. The burden of organisms within a single cell will cause it to burst, releasing the Plasmodium, and allowing it to infect red blood cells, where it replicates rapidly, again causing the cell to rupture. The infection cycle into red blood cells may happen several times, resulting in a large quantity of Plasmodium and the symptoms of infection, such as intermittent fever.

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