Medical
parasitology
traditionally has included the analysis of three main
groups of animals: parasitic protozoa, parasitic helminths
(worms), and those arthropods that precisely initiate disease
or act as vectors of numerous 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 help nor damage their host (for example,
Entamoeba coli). Though parasitology had its origins in
the zoologic sciences, it is nowadays an
interdisciplinary field, deeply influenced by
microbiology, immunology, biochemistry, and other life
sciences.
Infections of
humans caused by parasites number in the billions and
extend from relatively innocuous to lethal. The diseases
caused by these parasites constitute chief human health
problems throughout the world. (For example,
approximately 30 percent of the world's population is
infected with the nematode Ascaris
lumbricoides.)
The incidence of
many parasitic diseases (e.g., schistosomiasis, malaria)
have increased instead than decreased in latest years.
Other parasitic illnesses have enlarged in importance as
a outcome of the AIDS epidemic (e.g., cryptosporidiosis,
Pneumocystis carinii pneumonia, and strongyloidiasis).
The migration of parasite-infected people, including
refugees, from areas with high prevalence rates of
parasitic infection also has added to the health problems
of certain countries.
A misconception
about parasitic
infections is that they happen only in
tropical areas. 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 arrival with a parasite
infection.
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