Microbiology - Parasitology

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Cause of amebic dysentery, pathogenesis, & most common extra-intestinal disease

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E. histolytica

fecal-oral humans, flies, cockroaches
Invasive through mucosa

>90% asymptomatic

LIVER ABSCESSES

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Name & identifying characteristics

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Entamoeba histolytica
Cyst form
Chromatin at edge of nucleus, beaded

Trophs:
- Unidirectional motility (vs E coli, multiple)
- INGESTION OF RBCs
-Cyst can have up to 4 nuclei (>4 rules out!)

Generally:
- E hist is smaller (T 12-40um, C10-20) vs E coli (T15-50, C10-35)
- Intranuclear karyosomes more central in E hist
- Rim of nuclear chromatin is beadlike in E hist, vs blotchy

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Entamoeba coli
Cyst

Usually non-pathogen but can cause diarrhea

>4nuc rules out E histolytica

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Entamoeba coli
Trophozoite

Very similar to E histolytica; chromatin more blotchy & clumpy; cytoplasm less smooth; larger

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Entamoeba coli
Trophozoite

MAY HAVE VACUOLES

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Entamoeba coli
Cyst form

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Iodamoeba butschlii
Non-pathogenic

T:6-25um
C: 5-15

ID:
- ball-in-socket nucleus (~E nana)
- Cyst contains large iodine staining glycogen vacuole (E coli & E hist can also have vacuoles in early stage, but usu >1nuc)

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Endolimax nana
Troph

Smallest:
T 5-8um; C 5-24um
Can be difficult to distinguish from Iodamoeba

No peripheral chromatin; Has ball-in-socket nucleus; up to 4 nuclei per cyst

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Giardia lamblie
Flagellate
Cyst form

Cysts: 8-12um
- oval
- 4 nuclei (mature form)
- Eccentric karyosome
- no peripheral chromatin on nuc membrane
- clear space beneath cyst wall = HALO EFFECT
- ill-defined longitudinal fibrils

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Giardia
Trophozoite form; 9-21um
Symmetrical
2 nuclei
"falling leaf" motility on wet prep

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Cryptosporidium

- protozoan
- GI illness; usu kids & HIV pts
- cysts remain in GI tract x 5wks
- small infectious load (2-10 cysts)
- resistant to chlorine

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Organism?

Species infectious to humans?

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Cryptosporidium

C. parvum
C. hominis

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Isospora belli

Mature form (2 sporocysts)

25-30um
Rare cause of diarrhea; increased in AIDS
Fecal-oral transmission

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Isospora belli, immature form (1 sporocyst)

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Cyclospora cayetanensis

- 2x size of cryptosporidium; ill-defined internal structure
- Not detected with normal fecal stains; must use acid-fast, saffranin, or auto-fluorescence
- Causes traveler's diarrhea
- Sporulation takes several weeks so person-person transmission does not occur

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Microsporidium species

-Very small! 1-3um
- 700 species
-Infect insects, fish, crustaceans, some human
-Dx: H&E, silver, PAS of intestincal epithelium; EM is gold standard; fecal smear will show tiny spores, characteristically with transverse septum

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What special stain is used to ID microsporidium?

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WEBER STAIN; stains them salmon-colored

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Sarcocystis

-Ingestion poorly cooked pork/beef or ingestion of cysts from animal stool
-Can develop in skeletal muscle or in GI (fecal smears with 10-20um oval oocysts)

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Blastocystis hominis

-Questionable pathogen
- irregularly sized spherical cells 5-15um
- Homogeneous staining central body occupies >70% of the cell
- Nuclear material scattered around central body OR in 2 elongated masses

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Chilomastix mesnili

-Flagellate
-Warm climates; fecal-oral
-Non-pathogen
T: Pear shaped; **single large nuc immediately beneath outer membrane; 3 anterior flagella; pointed end

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Chilomastix mesnili

C: pear shaped; distinctive hyaline knob off to one side; single nuc; **CURVED cytosome "shepherd's crook" which is diagnostic

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Dientamoeba fragilis

-Flagellate
-D, abd pain, wt loss
-No known cyst form
-T: asymmetrical; 2 nuclei; prominent karyosomes

-**Higher incidence in kids with pinworm
-Thx with tetracycine, metro

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Trichomonas hominis

-Flagellate
-not pathogenic; don't stain well; no cyst form
-Teardrop shape with single anterior nucleus (though not against the membrane like chilomastix)
-Undulating membrane extends entire cell, vs T vag extends half
-Stiff rotary motility
-DDx: T vaginalis in females, contaminant

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Only member of the ciliates to infect humans?

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Balantidium coli

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Balantidium coli

-Fecal-oral; found in swine
-Asymptomatic, self-limited infxn
-Ciliates
- Easy to recognize in stool: LARGE (100um)
-T: Short cilia cover outer membrane; large kidney shaped nuc with small micro-nuc adjacent; rotary motility
-C: Spherical to elliptical, 50-65um; single macro nuc with a hof containing a micronuc; small vacuoles

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Ascaris lumbricoides

very large; 15-35 cm

fecal-oral: eggs- larvae in GI- circulation- lungs- trachea- swallow- become adults in GI- lay eggs in feces

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ova of ascaris

maybe fertilized (cleaved) or unfertilized. oval, thick shell. big (50-90um)

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Diagnostic ova of trichuris thrichiura (whipworm)

-Distinct barrel shape
-Refractile hyaline plugs at both ends

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Trichuris trichiura
(Whipworm)

Adults 3-5cm
Male with typical coiled tail

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Ova of enterobius vermicularis
(Pinworm)

Ova have thin transparent shell, are oval and asymmetrical with one flatter side resembling an underinflated football

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Adult female enterobius vermicularis

Characteristic pointed "pin" tail; other side has open para-oral alae

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Old World hookworm

New World hookworm

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Ancylostoma duodenale

Necator americanus

Same life cycle; same ova appearance
Circulation --> lungs --> swallow --> attach to small intestine Cause anemia

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Hookworm ova

OVAL
Thin smooth transparent shell
** clear space beneath shell from yolk sac retraction

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How to diagnose strongyloides? And how to tell apart from other hookworms?

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Observing motile rhabditiform larvae rather than ova in stool specimens, because they hatch in the intestine

SS larvae have short buccal cavity (vs long in other hookworms) and a prominent genital primordium 1/3 from the tail

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Strongyloides stercoralis

Rhabditiform larvae (stage before filariform larvae)
arrow pointing to large genital primordium (diagnostic)

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Strongyloides stercoralis

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Hookworm, rhabditiform larvae

LONG buccal cavity

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Strongyloides

SHORT buccal cavity

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Capillaria philippinensis

Fish-bird life cycle
Always pathogenic; High IgE

Ova very similar to Trichuris trichiura except have BROAD FLAT protuberances and a STRIATED SHELL

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Taenia saginata

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Taenia saginata tapeworm

Closeup of proglottid outlining uterine branching segments. T saginata has >14, while solium <13

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Taenia saginata tapeworm scolex

Does not have hooklets

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Brain lesion

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Cysticercosis

Cysts have two walls: outer fibrous reactive tissue and inner thin membrane from worm

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Cause of cysticercosis?

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Taenia solium

CNS involvement in 70-90%
Other tapeworms as a rare cause

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neurocysticercosis

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Taenia eggs

Cannot ID further

Thick-walled spherical eggs; distinctive radial striations.

Many enclose 3 pairs of hooklets

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Diphyllobothrium latum

Fish tapeworm

Tiny scolex and broad narrow proglottids

Longest tapeworm that infects humans!

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D latum proglottid

Characteristic width-over-length dimensions
Nondescript central branching uterus & ovaries (ROSETTE)

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D latum egg

Large
Oval with thin smooth shell
Nub at one end (arrow)
**Non-shouldered operculum at other end, inconspicuous, vs the shouldered operculum of paragonimus westermani

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Hymenolepis nana egg

Double membrane
3 pairs of hooklets inside
40-60 um
Polar thickenings on either side of inner hexacanth membrane

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Hymenolepis diminuta egg

Larger than H nana (60-80um)
ABSENCE of polar thickenings
6 hooklets

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Dipylidium caninum proglottid

Genital pore on either side is unique (other tapeworms have one lateral genital pore)