THE CILIATEs
Semester two
2018
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THE CILIATEs
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THE CILIATE
• Balantidium coli is the only member known to parasitize humans
• Distributed worldwide, although incidence of human infection is very
low
• Epidemics have been noted in mental hospitals in the United States
• Transmission usually through ingestion of contaminated food and
water by fecal-oral route
• Ingestion of water contaminated by pig feces which is a known
reservoir host
• As well as person to person especially through infected food
handlers
• Because the incidence of B. coli is low in both the population as a
whole and in persons who have regular contact with pigs, it has been
suggested that humans have a relatively high resistance to this
organism
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Trophozoite
Balantidium coli
• Considered as the largest protozoan known to human
• Two size ranges are consistently seen
• The smaller organism average 42 to 60 um long by 30 to 40
um wide, while
• The larger range from 90 to 120 um by 60 to 80 um.
• Ovoid to sac-shaped but tapers off at the anterior end
• B. coli trophozoite is often referred to as resembling a sac in
its shape
• As a reflection of the shape, the organism was named
balantidium, meaning “little bag”
• A funnel-shaped cytosome opens near the anterior end
• The body surface is covered with cilia, which are especially
long and stout near cytosome
• Exhibits rotary, boring motility like a thrown football
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Balantidium coli
Trophozoite
• Unstained organisms are readily recognized by their size,
ciliary covering and motility
• Trophozoite contains two nuclei
• The macronucleus which may be spherical, elongate, ellipsoid,
curved or kidney – shaped is situated near the middle of the
organism
• The micronucleus involved in genetics and cell division is
spherical and located quite close to the macronucleus.
• The micronucleus is often not readily visible even in stained
preparation whereas the macronucleus may often appear as
a hyaline mass especially in unstained preparation
• Food vacuoles, contractile vacuoles as well as ingested
microbes (bacteria) may be seen in the cytoplasm
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Balantidium coli Trophozoite
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Balantidium coli Trophozoite
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Cysts
Balantidium coli
• Spherical to oval
• Size ranges from 43 to 66 um long with an average size
of 50-57 um long
• Contains a double, thick, refratile cyst wall
• In newly encysted cysts the cilia are present between
the two cysts layers and the organism is slowly rotating
• The cilia disappear in mature cysts
• Although the cysts contains both the micronucleus and
macronucleus, the micronucleus may not be observed
in wet or permanent preparations
• Stained cysts typically reveal only the macronucleus,
other structures are not usually transparent
• One or two contractile vacuoles may be visible,
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particularly in young unstained cysts
Balantidium coli
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Systematic diagram of a
Balantidium coli cyst
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Balantidium coli cyst
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Balantidium coli
Life cycle
• Very similar to that of Entamoeba histolytica
• Infection initiated upon ingestion of infective cyst in
contaminated food and water
• Excystation occurs in the small intestine
• Unlike that of Entamoeba histolytica, excystation
results in the emergence of two trophozoites
following binary fission
• Resulting trophozoites take up residence and feed in
the cecal region, ileum, as well as in the lumen,
mucosa and submucosa of the large intestine
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Balantidium coli
Life cycle
• The B. coli trophozoites are delicate and do
not survive in the outside environment
• Encystation occurs in the lumen
• Resulting cysts mature and become the
infective form for transmission into a new host
• Cysts may survive for weeks in the outside
environment
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Life cycle of Balantidium coli
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Balantidium coli
Symptoms and Pathogenesis
 Asymptomatic / carrier state
• Some patients are simply carriers of B. coli and
remain asymptomatic
 Balantidiasis
• Balantidium coli produces the enzyme hyaluronidase
which facilitates its tissue invasion.
• Symptoms ranges from mild colitis and diarrhea to
full-blown clinical balantidiasis which may often
resemble amebic dysentery
• Abscesses and ulcers may form in the mucosa and
submucosa of the large intestine followed by
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secondary bacterial infection
Balantidium coli
• After bacterial invasion, a striking inflammatory
reaction is noted around Balantidium coli
trophozoite present in tissue
• Acute infections are characterized by up to 15 liquid
stools per day containing pus, mucus and blood
• Chronic infection characterized by tender colon,
anemia, and occasional diarrhea alternating with
constipation
• Rarely, there may be extraintestinal spread to the
liver, lungs, pleura, mesenteric nodes and urogenital
tract
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Balantidium coli
Laboratory Diagnosis
• Examination of stool for the presence of
trophozoites and cysts. (Multiple samples may
be required to correctly determine the
presence or absence of parasite)
• Sigmoidoscopy material may also be examined
for Balantidium coli
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Balantidium coli
Treatment
• Oxytetracycline (terramycin) or iodoquinol are
drugs of choice
• Metronidazole may also be used
Prevention and control
• Personal hygiene and proper sanitary
conditions
• Proper precautions should be excercised when
handling and dealing with pigs and their feces
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