Medical parasitology traditionally has included the study of three major groups of animals: parasitic protozoa, parasitic helminths (worms), and those arthropods that directly cause disease or act as vectors of various pathogens. A parasite is a pathogen that simultaneously injures and derives sustenance from its host. Some organisms called parasites are actually commensals, in that they neither benefit nor harm their host. Although parasitology had its origins in the zoologic sciences, it is today an interdisciplinary field, greatly influenced by microbiology, immunology, biochemistry, and other life sciences.
Infections of humans caused by parasites number in the billions and range from relatively innocuous to fatal. The diseases caused by these parasites constitute major human health problems throughout the world. For instance, mosquito-borne diseases and diseases caused by soil-transmitted helminths possess great burden to human well-being. The incidence of many parasitic diseases have increased rather than decreased in recent years. Other parasitic illnesses have increased in importance as a result of the HIV-AIDS epidemic, or concurrent with other comorbid. The migration of parasite-infected people, including refugees and international travels, from areas with high prevalence rates of parasitic infection also has added to the health problems of certain countries. Although most parasitic infections are more prevalent in the tropics, many people in temperate and subtropical areas also become infected, and visitors to tropical countries may return with a parasite infection.
The unicellular parasites (protozoa) and multicellular parasites (helminths, arthropods) are antigenically and biochemically complex, as are their life histories and the pathogenesis of the diseases they cause. During their life, parasitic organisms typically go through several developmental stages that involve changes not only in structure but also in biochemical and antigenic composition. Some helminth larval stages have little resemblance to the adult stages. Some parasitic protozoa also change greatly during their life history in different hosts. Some of these infections can convert from a well-tolerated or asymptomatic condition to life-threatening disease. Many parasitic infections are transmitted from animals to humans (zoonotic infections), and the human disease may or may not resemble the disease caused in the lower animal host.
Because early recognition of history, physical and laboratory findings are highly important in diagnosis of parasitic diseases, it is vital for medical students, medical professionals and patients to understand about the nature of parasitic diseases. The general contents of the web page deal with the description of specific human parasites and the diseases they cause, including the classification of parasites and the mechanisms of parasitic disease. Emphasis is placed throughout on the basic biology of the pathogens and their host-parasite relationships. Practical information on clinical manifestations, diagnosis, and control has been included as well.
References:
Castro GA, Olson LJ. Introduction to Parasitology. In: Baron S, editor. Medical Microbiology. 4th ed. Galveston, TX: University of Texas Medical Branch at Galveston; 1996.
Cox FEG. Introduction. In: Cox FEG, editor. Modern Parasitology: A textbook of parasitology. 2nd ed. Oxford: Blackwell Science Ltd.; 1993.
