[Elizabeth_Zeibig]_Clinical_Parasitology__A_Practi(z-lib.org)

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CHAPTER 7 Miscellaneous Protozoa
particularly in young unstained cysts. A doubleprotective
cyst wall surrounds the organism. A
row of cilia may be visible between the two cyst
wall layers in unstained young cysts. Mature
cysts tend to lose their cilia. Stained cysts typically
reveal only the macronucleus; the other
structures are not usually apparent.
Laboratory Diagnosis
Laboratory diagnosis of B. coli is accomplished
by examining stool specimens for the presence
of trophozoites and cysts. Stools from infected
patients experiencing diarrhea are more likely to
contain B. coli trophozoites. Although it does
not occur frequently, suspicious formed stools
may contain cysts. Sigmoidoscopy material may
also reveal B. coli organisms when collected from
patients suffering from sigmoidorectal infection.
As with any sample submitted for parasitic study,
thorough screening of the wet preparations and
the permanent stain is crucial to ensure an accurate
laboratory test report. In addition, the study
of multiple samples may be required to determine
the presence or absence of the parasite
correctly.
Life Cycle Notes
The B. coli life cycle is similar to that of Entamoeba
histolytica. Human infection with B.
coli is initiated on ingestion of infective cysts in
contaminated food or water. Unlike that of E.
histolytica, multiplication of the B. coli nuclei
does not occur in the cyst phase. Following
excystation in the small intestine, the resulting
trophozoites take up residence and feed primarily
in the cecal region and terminal portion of
the ileum, as well as in the lumen, mucosa, and
submucosa of the large intestine. The multiplication
of each trophozoite occurs by transverse
binary fission, from which two young trophozoites
emerge. The B. coli trophozoites are delicate
and do not survive in the outside environment.
Encystation occurs in the lumen. The resulting
cysts mature and ultimately become the infective
form for transmission into a new host. These
cysts may survive for weeks in the outside
environment.
Epidemiology
Although B. coli is distributed worldwide and
outbreaks have been known to occur, the typical
incidence of human infection is very low. The
documented frequency of infections in the general
population is considered rare. However, epidemics
caused by infections with B. coli have been
noted in psychiatric facilities in the United States.
B. coli infections are transmitted by ingesting
contaminated food and water by the oral-fecal
as well as person-to-person routes. Recently, it
has been presumed that water contaminated with
feces (the oral-fecal route) from a pig, which is a
known reservoir host, may be a significant source
of infection. There is now considerable evidence
to support the theory that the pig may not be
the primary infection source, because the documented
incidence of infection among humans
with high pig contact is relatively low. Infected
food handlers appear to be the culprit in personto-person
spread of the disease.
Clinical Symptoms
Asymptomatic Carrier State. Similar to that
seen in certain patients infected with E. histolytica,
some patients are just carriers of B. coli
and remain asymptomatic.
Balantidiasis. Symptomatic patients may
experience a variety of discomforts, ranging from
mild colitis and diarrhea to full-blown clinical
balantidiasis, which may often resemble amebic
dysentery. In this case, abscesses and ulcers may
form in the mucosa and submucosa of the large
intestine, followed by secondary bacterial infection.
Acute infections are characterized by up to
15 liquid stools daily containing pus, mucus, and
blood. Patients who suffer from chronic infections
may develop a tender colon, anemia,
cachexia, and occasional diarrhea, alternating
with constipation. B. coli has been known to
invade areas other than the intestine, such as
the liver, lungs, pleura, mesenteric nodes, and