Entamoeba histolytica

 Subphylum Sarcodina -> Superclass Rhizopoda -> class Lobosea -> family Entamoebidae -> genus
Entamoeba
 A pseudopod
 E. histolytica, E. dispar and E. moshkovskii are morphologically undistinguishable
 E. histolytica was distinguished from the two by:
o Isoenzyme analysis Polymerase Chain Reaction
o Restriction Fragment Length Polymorphism (RFLP)
o Typing with monoclonal antibodies
 Most invasive Entamoeba parasite
 Case manifestations:
o Asymptomatic
 Most E. histolytica cases in endemic communities
o Amebic colitis
 Abdominal pain
 Diarrhea w/ or w/o blood and mucus in the stool
 Fever (rare)
 Children may develop fulminant colitis with all clinical manifestations
 Most serious complication
 Perforation
 Secondary bacterial peritonitis
o Amebic Liver Abscess (ALA)
 Most common extra-intestinal form of amebiasis
 Right upper quadrant (RUQ) pain
 Hepatomegaly in acute cases (50% of cases)
 Incubation period of 8 to 10 days
 Most serious complications
 Rupture into pericardium
 Rupture into pleura
 Super infection
o Ameboma
 <1% of intestinal infections
 Mass-like lesion with abdominal pain and a history of amebic dysentery
 Can be mistaken for carcinoma
 Two stages:
o Infective cyst
 Quadrinucleated cyst is the diagnostic stage and is resistant to gastric acidity and dessication
o Vegetative (invasive) trophozoite
 Mode of transmission is through:
o ingestion of fecally-contaminated material
o venereal transmission through fecal-oral contact
 o Direct colonic inoculation
 Excystation occurs in the small or large vowel and undergoes nuclear then cytoplasmic division to
form eight trophozoites
 E. histolytica trophozoite:
o 12-60um diameter (20um avg) o Hyaline pseudopodia
o Progressive and directional movement o Ingested RBC in the cytoplasm
 E. histolytica cyst:
o Spherical o 1-4 nuclei
o 10-20um o Rod-shaped (cigar-shaped)
o Highly refractile hyaline cyst wall chromatoidal bars
 Trophozoites multiply by binary fission
 Trophozoite encyst to produce uninucleate cyst which will undergo two nuclear division to form
quadrinucleated cysts
 E. histolytica at one time may have contained mitochondria
 Differences in biochemical pathways from higher eukaryotes and E. histolytica:
o Lack of glutathione metabolism
o Use of pyrophosphate instead of ATP at several steps in glycolysis
o Inability to synthesize purine nucleotides de novo
 Mechanisms for virulence:
o production of enzymes or other cytotoxic substances
o Contact-dependent cell killing
o Cytophagocytosis
 Amebic killing of target cultivated mammalian cells:
o Receptor-mediated adherence of ameba to target cells
o Amebic cytolysis of target cells
o Amebic phagocytosis of viable target cells
 Trophozoites adhere to the colonic mucosa through Galactose-inhabitable adherence lectin (Gal
lectin)
 Amebae kill mucosal cells by activation of their caspase-3
 PCR has confirmed that there is a higher prevalence of E.dispar than E. histolytica
 Activated T-cells kill E. histolytica by:
o Directly lysing trophozoites
o Producing cytokines
o Providing helper effect for B-cell antibody production
 Cytokine studies revealed that Interferon (IFN) and Interleukin (IL-2) may have a role in activating
macrophages for amebicidal activity
 Principal Antibody dependent cell-mediated cytotoxicity (ADCC) did not work against amebae
 Bacillary dysentery vs Amebic dysentery
o Fever and significantly elevated leukocyte count are less common in amebic colitis
 Differential diagnosis of ALA include pyogenic liver abscess, tuberculosis of the liver and hepatic
carcinoma
 Differential diagnosis of genital amebiasis include carcinoma, tuberculosis, chancroid and
lymphogranuloma venereum
 Standard method of parasitologic iagnosis is microscopic detection in stool samples (examine w/in
30 minutes; minimum of three stool specimen collected on different days)
 Trophozoite motility can be observed using DFS with saline solution
 Using saline and methylene blue, Entamoeba species will stain blue
 Using saline and iodine will help us differentiate E. histolytica from non-pathogenic amebae
 Charcot-Leyden crystals can be seen in stools with amebiasis
 FECT and MIFC are more sensitive than DFS for detection of cysts
 Robinson’s and Inoki medium is more sensitive than stool microscopy, but is not routinely available
 Differentiation of E. histolytica and E. dispar can be done by
o PCR (gold standard)
o Enzyme –linked immunosorbent assay (ELISA) (gold standard)
o Isoenzyme analysis
 In ALA, trophozoites are missed because they are located in the periphery of the abscess
 Serological tests for amebic disease
o Indirect hemagglutination (IHAT) (can detect antibodies as long as 10 years ago) (gold standard)
o Counter immunoelectrophoresis (CIE)
o Agar gel diffusion (AGD)
o Indirect fluorescent antibody test (IFAT) (gold standard)
 o ELISA
 Noninvasive and sensitive methods in the early detection of ALA
o Ultrasound
o MRI
o CT scan
 Objectives of the treatment of amebiasis
o Cure invasive diseases at both intestinal and extraintestinal sites
o Eliminate the passage of cyst from the intestinal lumen
 Drugs for treatment of invasive amebiasis
o Metronidazole
o 5-nitroimidazole derivatives
 Secnidazole
 Tinidazole
o Diloxanide furoate (for asymptomatic cyst passers)
 Prevalence of amebiasis is approx. 1 to 5% worldwide
 It is the 3rd most important parasitic disease (next to malaria and schistosomiasis)
 E. dispar is prevalent in immigrants, travelers from endemic countries, homosexual males, HIV
patients and institutionalized people
 Prevention and control
o Proper sanitation
o Safe water supply
o Good personal hygiene
o Proper food preparation
o Vaccines

COMMENSAL AMEBAE
 Significance of the presence of commensal amebae in stool
o Be mistaken for the pathogenic E. histolytica
o Indication of fecal contamination of food or water
 Must be differentiated from pathogenic E. histolytica to avoid unnecessary treatments
Entamoeba Endolimax Iodamoeba
 Spherical nucleus  Vesicular nucleus  Large, chromatin-rich
 Nuclear membrane lined w/  Large, irregularly shaped karyosome surrounded by a
chromatin granules karyosome anchored to the layer of achromatic globules
 Small karyosome near the nucleus by achromatic fibrils  Anchored to the nuclear
center of the nucleus membrane by achromatic
 Trophozoites usually have fibrils
only one nucleus

 All species have the following stages

o Trophozoite
  Reproduce by binary fission
o Precyst o Metacystic trophozoite
o Cyst
 Entamoeba gingivalis has NO CYST STAGE and DOES NOT INHABIT THE INTESTINES
 Cyst walls can protect the cyst from the acidic stomach
 Excystation occurs in an alkaline environment
 Metacystic trophozoites colonize the large intestines
 Encystation occurs as amebae pass the lower colon (need a more dehydrated environment)
 Diagnosis through stool examination
 Species differentiation
o FECT
o Iodine stain
 Trophozoites are best demonstrated by DFS
 In recovering cysts, FECT and zinc sulfate flotation is useful
 No treatment is necessary for commensal amebae
 E. coli was the most prevalent in a 30,000-filipino study, while E. nana was the most prevalent in the
tests done among food workers/handlers
 Proper disposal of human waste and good hygiene for prevention and control

Entamoeba dispar/E. moshkovskii

 The difference of E. histolytica from E. dispar lies in the DNA and Ribosomal DNA
 E. moshkovskii is unique because it is osmotolerant and it can grow at room temperature and can
survive at temperatures ranging from 0 to 40°C

Entamoeba hartmanni
 Morphologically similar to E. histolytica apart from its smaller size
 Trophozoites measure from 3 to 12um in diameter
 Mature cysts measure from 4 to 10um
 E. hartmanni does not ingest RBC

Entamoeba coli
 Cosmopolitan in distribution
 More common than other human amebae
 E. coli trophozoites:
o 15 to 50um in diameter o Broader and blunter pseudopodia used
o More vacuolated or granular more for feeding
endoplasm with bacteria and debris o Sluggish, unidirected movements
o Narrower, less differentiated ectoplasm o Thicker, irregular peripheral chromatin
o Large, eccentric karyosome
 E. coli cyst:
o 10 to 35um in diameter
o Up to eight nuclei
o Granular cytoplasm
o Splinter-like chromatoidal bodies
 Iodine staining reveals dark-staining, perinuclear masses, which are actually Glycogen

Entamoeba polecki/E. chattoni

 Found in the intestines of pigs and monkeys
 Motility of trophozoite is sluggish
 Cyst are uninucleated and chromatodial bars are frequently angular or pointed
 Entamoeba chattoni (found in apes and monkeys) is morphologically identical to E. polecki
 Identification of E. polecki was done via isoenzyme analysis

Entamoeba gingivalis
 Found in the mouth
 E. gingivalis trophozoite:
o 10 to 20um
o Moves quickly
o Numerous blunt pseudopodia
o Food vacuoles that contain cellular debris and bacteria are numerous
 Abundant in cases of oral disease
 NO CYST STAGE
 Transmission is most probably direct
 Swab between the gums and teeth is examined for trophozoites

Endolimax nana
 Occurs with the same frequency as E. coli
 E. nana trophozoites
o 5 to 12 um
o Sluggish movement
o Blunt pseudopodia
o Large, irregular karyosome
o Food vacuoles in the cytoplasm contain bacteria
 Cysts are about the same size as trophozoites, and are quadrinucleated when mature

Iodamoeba butschlii
 I. butschlii trophozoite
o 9 to 14 um in diameter
o Large, vesicular nucleus
o Large, central karyosome
 o Surrounded by achromatic granules
o No peripheral chromatin granules on the nuclear membrane
 I. butschlii cyst
o 9 to 10um in diameter (6 to 16um)
o Uninucleated
o Large glycogen body
o Stains dark brown with iodine

FREE-LIVING PATHOGENIC AMEBAE

Acanthamoeba spp.
 Ubiquitous, free-living ameba
 Etiologic agent of Acanthamoeba keratitis (AK) and Granulomatous Amebic Encephalitis (GAE)
 Characterized by and active trophozoite stage with “thorn-like” appendages (acanthapodia)
 Highly resilient cyst stage which transforms when environmental conditions are not favorable
 It is an aquatic organism
 Motile trophozoites feed on
o Gram-negative bacteria
o Blue-green algae
o Yeasts
 Can also adapt to feed on corneal epithelial cells and neurologic tissue through phagocytosis and
secretion of lytic enzymes
 Acanthamoeba trophozoites:
o Single large nucleus o Acanthapodia (locomotion) that are
o Centrally-located, densely staining evident on phase-contrast microscopy
nucleolus o Replicate by mitosis
o Large endosome o INFECTIVE STAGE
o Finely granulated cytoplasm o Entry through the eye, nasal passages
o Large contractile vacuole to the Lower respiratory tract or broken
skin
 Only has two stages: cyst and trophozoite
 Possible reservoir hosts for medically important bacteria
o Legionella spp.
o Mycobacteria
o Gram-negative bacteria (E. coli)
 Its ubiquitous nature makes exposure unavoidable
 Acanthamoeba keratitis
o Acanthamoeba was first described as an opportunistic ocular surface pathogen causing keratitis
o Symptoms
 Severe ocular pain
 Blurring of vision
 Corneal ulceration with progressive corneal infiltration (not always)
 o Primary amebic infection or secondary bacterial infection may lead to hypopyon formation
o Progression of infection
 Slceritis
 Iritis
 Loss of vision
o Differentials that need to be ruled out include fungal and herpetic keratitis
o Diagnosis
 Epithelial biopsy or corneal scrapings
 Specific-specific identification can be made from culture and molecular analysis through PCR
 Species causing AK
 A. castellani  A. polyphaga
 A. culbertsoni  A. rhysoides
 A. hutchetti
o Treatment (corticosteroids should be avoided)
 S
 urgical excision of the infected  Neomycin
cornea  Paromomycin
 Clotrimazole w/ pentamidine  Polymyxin B
 Isethionate  Ketoconazole
 Neosporin  Miconzazole
 Polyhexamethylene biguanide  Itraconazole
 Propamidine  Advanced AK usually requires
 Dibromopropamidine isethionate debridement
o Contact lens hygiene is essential
o Physicians should maintain a high index of suspicion in the presence of compatible signs
and symptoms of infection that do not respond to conventional antimicrobial therapy
 Granulomatous Amebic Encephalitis
o Acanthamoeba was documented by Stamm as the causative agent of GAE
o Usually occurs in immunocompromised hosts
o AIDS epidemic in 1980s drastically increased the number of persons infected with GAE
o Signs and symptoms (generally related to destruction of brain tissue and Associated meningeal
irritation)
 Systemic manifestations
 Fever
 Malaise
 Anorexia
 Neurologic symptoms
 Increased sleeping time  Epilepsy
 Severe headache  Coma
 Mental status changes
 Neurologic findings depending on the location of lesions
  Hemiparesis  Cranial nerve deficits
 Blurring of vision  Ataxia
 Diplopia
 Increased intracranial pressure
o From a primary site of infection in the skin or lungs, the likely route of invasion is hematogenous
o Incubation period from initial oculation is approximately 10 days
o Post mortem examination
 Cerebral hemisphere that are edematous and soft
 Areas of hemorrhage and focal abscess
o Clinical manifestations
 Decreased sensorium
 Altered mental status
 Neurologic deficits
 Eventually results in coma and death
o Diagnosis
 Usually made post-mortem
 Unfamiliarity of physicians contribute to frequently missed diagnosis
 Patient with AIDS are at the highest risk
 Cryptococcus meningitis and toxoplasmosis are much more common than GAE

Naegleria spp.
 Two vegetative forms: ameba (trophozoite form), and a flagellate (swimming form)
 A dormant cyst forms when conditions are not favorable
 Thermophilic – they thrive best in warm aquatic environments
Naegleria fowleri
 Two forms of trophozoites: ameboid (only one found in humans)and ameboflagellate
 N. fowleri ameboid trophozoite (INFECTIVE STAGE)
o When rounded are usually 10 to 15um in diameter (may get over 40um in culture)
o Granular cytoplasm
o Many vacuoles
o Large single nucleus
o Large, dense karyosome
o Lacks peripheral chromatin
 Only species to consistently cause disease
 Three stages: cysts, trophozoites (replicate by promitosis) and flagellated forms
 Can turn into temporary nonfeeding flagellated forms
 Trophozoites infect by penetrating the nasal mucosa and migrating to the brain via the olfactory
nerves
 Trophozoites are found in CSF and tissue
 Flagellate forms are occasionally found in CSF
 Cysts are not seen in brain tissue
 Causative agent of Primary Amebic Meningoencephalitis (PAM)
PAM
 Rare, but fatal
 Usually occurs in healthy adults with a history of swimming
 In contrast to Acanthamoeba, which is largely an opportunistic organism, N. fowleri is considered a
true pathogen
 Symptoms of PAM are indistinguishable from bacterial meningitis
 PAM presents as
o Fever
o Nausea
o Headache
o Nuchal rigidity
o Mental status changes
o Rapid progression to coma and death
 Characteristic CSF findings
o Elevated WBC with neutrophilic predominance, high protein, and low glucose
 Postmortem examination of infected brain
o Hemorrhagic necrosis
o Congestion and edema of neural tissue
o Leptomeninges are inflamed and congested
 Diagnosis
o Introduced into bacteria-seeded agar culture medium to exhibit active trophozoites
o PCR and immunostaining
o ELISA is less useful
 Treatment
o Amphotericin B with clotrimazole
o Azithromycin
o Voriconazole
 Local Naegleria – N. philippinensis (isolates from a thermally polluted stream)
 Prevention and control
o Avoid accidental inhalation of water
o N. fowleri is easily killed by chlorination of water at 1ppm or higher

CILIATES AND FLAGELLATES

Balantidium coli
 Initially identified as Paramecium coli
 Causative agent of balantidiasis, balantidiosis or balantidial dysentery
 LARGEEST PROTOZOAN
 Only ciliate known to cause human disease
 Its normal host is pigs
 B. coli trophozoite:
o 30 to 150um long and 25 to 120um wide
o Cilia arranged in a longitudinal pattern extending from the oral to the caudal region
o Cytostome at the tapered anterior end
o Cytopyge which excretes waste
o Bean-shaped macronucleus
o Round micronucleus
o Two contractile vacuoles that act as osmoregulatory organelles
o Inhabits lumen, mucosa and submucosa of the large intestines, primarily the cecal region
o Capable of creating an ulcer with a rounded base
o Secretes hyaluronidase, a lytic enzyme
 B. coli cysts:
o Spherical to slightly ovoid
o 40 to 60um in diameter
o covered with thick cell walls (double-walled)
o encystation does not result in an increased number of nuclei
o infective stage
 Incubation period is normally from 4 to 5 days
 Intrinsic host factors contribute to the susceptibility and severity of B. coli infection
 Presence of Salmonella has been shown to aggravate balantidiasis
 Balantidiasis has three forms of clinical manifestations:
o Fulminant balantidiasis involves diarrhea with bloody and mucoid stools
o Acute cases may have 6 to 15 diarrhea episodes per day accompanied by abdominal pain,
nausea and vomiting. Often accompanied by immunocompromised and malnourish states
o In Chronic form, diarrhea may alternate with constipation, accompanied by abdominal pain or
cramping, anemia and cachexia
 B. coli can spread to extraintestinal sites
 Complications of balantidiasis
o Intestinal perforation
o Acute appendicitits
 Cases of mortality related to balantidiasis
o Intestinal hemorrhage and shock
o Intestinal perforation
o Sepsis
 Diagnosis
o Direct examination
o Sedimentation
o Flotation
o Presence of trophozoites in biopsy specimens through lesions obtained through sigmoidoscopy
 Treatment
o Tetracycline o Doxycycline
o Metronidazole o nitazoxanide
o Iodoquinol
 Pig feces as fertilizer should be avoided
 Cysts are easily inactivated by heat and by 1% sodium hypochlorite

Giardia duodenalis
 Worldwide distribution
 Discovered by Antonie van Leeuwenhoek
 First described as Cercomonas intestinalis
 Causes giardiasis. Significant, but not life-threatening
 Lives in the duodenum, jejunum, upper ileum
 Simple Asexual life cycle
 Has trophozoites and quadrinucleated infective cyst stages
 Classified as either A or B genotype
 G. lamblia Trophozoite:
o 9 to 12um long by 5 to 15um wide
o Pyriform or teardrop shaped, pointed posteriotly
o Pair of ovoid nuclei
o Bilaterally symmetrical with a medial line called axostyle
o Tumbling motion, falling leaflike
o Four pairs of flagella
o Divide by longitudinal binary fission
o Antigenic variation results in the entire surface of the parasite being covered with variant-
specific surface proteins (VSPs)
o May be found in the jejunum
 G. lamblia cysts:
o Ovoid
o 8 to 12um long by 7 to 10um wide
o Young cysts have two nuclei; mature cysts have four
o Flagella retracted into axonemes
o Median or parabasal body
o Deeply-stained curved fibrils surrounded by a tough hyaline cyst wall
o Excyst in the duodenum
 Infection through ingestion of contaminated food or water
 It has an adhesive sucking disc on its ventral side
 Able to avoid peristalsis by trapping itself within the villi or within the intestinal mucus
 1-4 weeks incubation
 Half of the patients with giardiasis may be asymptomatic
 Signs and symptoms of giardiasis
o Abdominal pain described as cramping
o Diarrhea (most common symptom, followed by malaise and flatulence)
o Excessive flatus with an odor of “rotten eggs” due to hydrogen sulfide
o Other features
 Abdominal bloating
 Nausea
 Anorexia
o Chronic infection is characterized by steatorrhea
o Weight loss
o Profound malaise
o Low-grade fever
 Diagnosis
o DFS for trophozoites
o Concentration techniques for cysts in stools
o Antigen detection tests
o Immunochromatographic assays detect the presence of Giardia antigen in stool
o Cyst Wall Protein 1 (CWP1) is the antigen used for the test
o Direct fluorescent antibody assays is considered as the gold standard in standard diagnosis
 Treatment
o Metronidazole
o Tinidazole
o Furazolidone
o Albendazole (equally effective as metronidazole at the above doses)
o Nitazoxanide (in drug-resistant cases)
 86% of the isolated genotypes belong to assemblage B
 Direct oral-anal sexual contact among men with men increases the chance of giardiasis
 Relative resistance to chlorine facilitates the transmission of Giardia
 For prevention and control, normal water chlorination will not affect cysts, but usual water
treatment modalities should be adequate

Trichomonas vaginalis
 Causes a sexually-transmitted disease called trichomoniasis
 Most prevalent nonviral STI (trichomoniasis)
 ONLY IN THE TROPHOZOITE STAGE
o Pyriform shape
o 7 to 23um
o Four free anterior flagella that appears to rise from a simple stalke (kinetosome)
o Fifth flagellum embedded in the undulating membrane
o Median axostyle
o Single nucleus
 o Multiply by binary fission
 Found in the urogenital tract
 Mode of transmission is by sexual intercourse
 Requires vaginal, urethral and prostatic tissues to survive
 Causes desquamation of the vaginal epithelium followed by leukocytic inflammation of the tissue
layer
 Results in liquid vaginal secretion, greenish or yellow in color
 Vaginal secretions may cause intense itchiness and burning sensations
 Symptoms of trichomoniasis
o Vaginal discharge
o Vulvitis
o Dysuria
o Hemorrhages of the cervix (strawberry cervix)
o In males (almost always asymptomatic), recurring urethritis may happen. Prostatitis is the most
common complication
 Diagnosis
o Saline preparation of vaginal fluid
o Gold standard is culture
o Unstained wet drop may be fixed and stained by
 Giemsa
 Papanicolau
 Romanowsky
 Acridine orange stains
o Can be cultured using
 Diamond’s modified medium
 Feinberg and Whittington culture medium
o PCR assays are available, but not widely used locally. PCR assays appears to detect more cases in
men, tho
 Treatment is Metronidazole or Tinidazole 2g
 Local isolates of T. vaginalis show low genetic polymorphism
 Prevention by limiting the number of sexual partners, use of protective sexual devices and having
good sex education
NON-PATHOGENIC FLAGELLATES
Trichomonas hominis
 Occurs ONLY AS TROPHOZOITE
o Pyriform shape
o 7 to 13um
o Five anterior flagella
o Posterior flagellum projecting from an undulating membrane
o Cytostome and nucleus at the anterior end
o Axostyle extends from anterior to posterior along the mid-axis
 Transmission through fecal contamination of food and drinks
 Habitat is the cecal area of the large intestine
 Non-invasive
 Prevalence in the ph is less than 1%

Trichomonas tenax
 Pyriform flagellate
 ONLY IN THE TROPHOZOITE STAGE
o 5 to 12 um
o Smaller and more slender than T. vaginalis
o Four free equal flagella and a fifth one on the margin of an undulating membrane
o Single nucleus
o Cytostome
o Multiplies by binary fission
 Harmless commensal living in the human mouth
 Quite resistant to changes in temperature
 Exposure through direct contact (like gingivalis)
 Diagnosis through swabbing (like gingivalis)
 Drug of choice is Metronidazole

Chilomastix mesnili
 Inhabits the cecal region of the large intestine
 Well-defined trophic and cyst stages
 C. mesnili trophozoite:
o Asymmetrically pear-shaped
o Spiral groove extending through the middle half of the body
o 6 to 10um
o Boring and spiral forward movement
o Three anterior free flagella and a more delicate one within the prominent cytostome
 C. mesnili cyst
o Pear or lemon-shaped
o Broadly rounded and somewhat bluntly conical at the other end (nipple-shaped)
o Has knob-like protuberance
o H&E films demonstrate the single large vestibular nucleus and the cytostome
o Good preparations reveal a fibril
 Transmission occurs through ingestion of cysts
 Prevalence is less than 1%
 No treatment indicated

OTHER INTESTINAL PROTOZOANS

Balantidium coli
 Previously classified as yeast under genus Schizosaccharomyces
 LEM shows that it lacks a cell wall
 It is capable of pseudopodal extension and retraction
 Does not grow on fungal culture, but responds to antiprotozoal drugs
 Reproduction is asexual. Either through binary fission or sporulation under strict anaerobic
conditions
 Life cycle is unclear
 Life cycle begins with the ingestion of cyst
 Morphological forms
o Vacuolated
 Most predominant form
 5 to 10um in diameter
 Large central vacuole (reproductive organelle)
 Cytoplasm and four nuclei to the periphery
o Ameba-like
 2.5 to 8um
 Active extension and retraction of pseudopodia
 Chromatin shows peripheral clumping
 Intermediate stage between the vacuolar form and the precystic form
 This stage allows the parasite to ingest bacteria
o Granular
 Multinucleated
 Mainly observed from old cultures
 10 to 60um
o Multiple fission
 Produce many vacuolated forms
o Cyst
 3 to 10um in diameter
 One or two nuclei
 Prominent and thick osmophilic, electron dense wall
 Oval or circular dense body surrounded by a loose outer membranous layer (seen in phase-
contrast microscopy)
o Avacuolar form
 Infection is called blastocystosis
o Abdominal cramps o Nausea
o Irritable bowel syndrome o Vomiting
o Bloating o Low grade fever
o Flatulence o Malaise
o Mild to moderate diarrhea without
fecal leukocytes or blood
 Diagnosis
o Clinical presentation alone may prove difficult
o DFS
o Concentration techniques
o Hematoxylin and Trichrome staining to differentiate the various stages of Blastocystis
o Can be cultured using Boeck and Dbrohlav;s or the Nelson and Jones media
 Treatment
o Difficult to eradicate
o Metronidazole
o Trimethroprim-sulfamethoxazole (TMP-SMX)
o Nitazoxanide
 Symptomatic cases are more often found in children
 Pig-tailed macaques, chickens, dogs, ostriches, lizards and cockroaches may harbor Blastocystis
 Cysts of B. hominis are resistant to chlorine

Dientamoeba fragilis
 Identified in all regions of the worlds
 Iron-hematoxylin stains have been carefully examined
 Originally described as an amoeba, but is actually a flagellate
 ONLY THE TROPHOZOITE STAGE IS KNOWN
o 7 to 12um
o One or two rosette-shaped nuclei
o No peripheral chromatin
o Karyosome consists of four to six discrete granules
o Resembles Trichomonas
 Lives in the mucosal crypts of the appendix, cecum and the upper colon
 Exact life cycle is unknown
 Transmission is probably fecal-oral or via transmission of helminth eggs particularly that of
Enterobius vermicularis
 Stools from macaques and gorillas are found to carry this
 Does not invade tissues, but its presence in the intestine produces irritation of the mucosa with
secretion of excess mucus and hypermotility of the bowel
 Usually asymptomatic
 Onset of infection is usually accompanied by
o Loss of appetite o Flatulence
o Abdominal pain o Anal pruritus
o Intermittent diarrhea with excess o Chronic infection may cause an Irritable
mucus bowel syndrome (IBS)
o Abdominal tenderness
o Bloating sensation
 Diagnosis
 o Observation of binucleate trophozoites in multiple fixed and stained fresh stool samples
o May be misdiagnosed as other amebae
o PVA or Schauddin’s fixative has been found to be helpful
 Treatment
o Antimicrobial therapy
o Iodoquinol
o Metronidazole
 As high prevalence rates in developed countries