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66 CHAPTER 3

for antibodies against these amoebae by blood testing.
TABLE 3-6 Differentiation of Bacterial Versus
These antibodies will most likely appear by the seventh
Amebic Dysentery
day of infestation, and an exam called a colonoscopy
may be required to obtain tissue samples to differentiate
BACILLARY AMEBIC
DYSENTERY DYSENTERY amebic infection from bacterial and other types of intes-
tinal inflammation. In extreme cases a liver abscess may
Acute onset Gradual onset
form and produce pain that imitates other diseases and
Poor general condition General condition normal an ultrasound procedure or CT scan may be required to
High fever Little fever in adults diagnose the involvement of the liver.
Severe tenesmus (pain Moderate tenesmus
and feelings of needing ASYMPTOMATIC CARRIERS
to empty bowel)
Entamoeba dispar is distributed worldwide. Because
Dehydration frequent Little dehydration (adult)
extremely high numbers of the people in endemic regions
Feces: no forms of Feces: trophozoites of the world may be cyst carriers (e.g., 10 percent), there
bacteria are identified as present is little rationale for treating them when they are found
trophozoites
by chance in isolated regions with a high infectivity rate.
Can be cultured on Unable to culture or In many cases, perhaps 90 to 95 percent of these people
nutritive media grow on media may be chronically infected with this possibly nonpatho-
genic species of amoebae called E. dispar. For service
workers, such as food handlers and medical personnel,
however, treatment may be indicated with a variety of
surgical biopsies are essential for the diagnosis of these
medications to ensure a reduction in the infective rate of
conditions. these workers. In regions of high potential for becoming
A standardized approach to empirically differen-
endemic, it may indeed be sensible to treat the patient
tiating between dysentery caused by bacteria or amebic even though the organism is considered nonpathogenic
organisms organisms is shown in Table 3-6.
except in rare cases. This would serve to prevent trans-
mission to the remainder of the uninfected population,
INTESTINAL AMEBIASIS creating endemic areas and also to prevent possible devel-
AND TREATMENT opment of later cases of invasive amebiasis by E. dispar.

Infection or colonization of the gastrointestinal system NONINTESTINAL AMOEBA
begins in the colon but is capable of spreading to other
organs and systems, such as the liver, where lesions are A number of organisms inhabit the mouth but are not
formed. Amebiasis often results from the ingestion of con- found in the intestines. A number of free-living amoebae
taminated food and beverages in which mostly cysts of may occasionally be encountered by humans, usually
the various organisms are found. The cysts enter the in- with little consequences.
testines where they release motile trophozoites, and these
forms invade the membranes of the colon or spread to the ENTAMOEBA GINGIVALIS
liver though the large vascular system, including the por-
tal vein. Trophozoites divide quickly to form more cysts, In addition to T. tenax, Entamoeba gingivalis is also a
which may be excreted in the feces and serve to contami- causative agent for gum diseases. E. gingivalis is found
nate water and food that will be ingested by others. in the mouth where there is soft tartar between the teeth
Again, a number of tools are available to diag- and in tonsillar fossae and crevices. Sometimes the
nose amoebiasis and to prevent damage to the infected organism can be recovered from sputum, and specimens
patient. The presence of amoebae may be determined from this source must be differentiated from E. histolytica.
by microscopic evaluation of stools, where both cysts Entabomeba gingivalis may be called either E. gingivalis
and trophozoites may be found, or by serological testing or E. buccalis. This is a nonpathogenic species of