Amebiasis was first described as a disease by a Russian physician, F.
Losch, in 1875 (Anderson, 3). The history of amebiasis has centered on
the relationship of amebas found in the intestinal tract of mammals
and the role they play in causing disease (4). During the first half
of this century, the study of amebiasis has evolved from a disease
thought to be purely tropical and one that didn't necessarily require
concern to one that is "practically cosmopolitan in its distribution"
worldwide and easily treatable (Anderson, 6-8).
Amebiasis indicates presence of Endamoeba histolytica, a protozoan in
the class Rhizopoda, and it implies that certain invasion of the
intestinal tract, especially the colon and liver, has occurred (MDE,
1). Endamoeba histolytica is a pathogen that is capable of invading
and destroying the host's tissue without the aid of pathogenic
bacteria (Anderson, 8). It is a typically single-celled parasite whose
body consists of cytoplasm, nucleus or nuclei, ingested materials, and
vacuoles (Craig, 13).
Endamoeba histolytica has four stages in its life cycle: the
trophozoite or motile stage, the precystic stage, the cystic stage,
and the metacystic stage (Anderson, 39). The trophic ameba is
especially adapted for life in the tissues of its host. The ameba
passes out of the body of the human host in the feces into the
external environment in its precystic form (39). The cystic form of
the Endamoeba histolytica is the resistant form of the pathogen, and
it exists free in nature (40). The metacystic stage is basically the
reproductive stage, where each nuclei divides into two daughter
nuclei. These small amebas develop into the trophozoite form within a
few hours (40). It is this rapid multiplication of the ameba in the
host which causes various forms of amebiasis in man.
The appearance of amebiasis is world-wide, although it is more
frequently observed in tropical climates (Anderson, 12). The disease
appears in endemic form in Central and South America, the Indies,
Southeast Asia, Africa, Siberia, and the Mediterranean countries (12).
In the United States, incidence of the disease generally ranges from
five to ten percent (Anderson, 12). It has varied during the last few
decades, however, from about .05 percent in a Philadelphia hospital to
about 55.5 percent in a New Orleans orphanage (12).
The protozoan is transmitted from human to human, requiring no
intermediate hosts (Anderson, 12). There are several ways infection is
transmitted. Water is a suitable agent for the transfer of pathogen,
since they are able to remain viable in it for three to five days
(305). When the water supply in any community becomes contaminated
with sewage, lacking proper disposal and treatment, the risk of being
infected with amebiasis increases greatly. High...