2 - DIAGNOSTIC PARASITOLOGY Flashcards
specimens used in the clinical lab
- stool
- urine
- blood
- lymphatic fluids
- sputum
- csf
- biopsy
Most common method of diagnosis in parasites (protozoans and metazoans)
Best collected in clean, wide-mouthed containers made of waxed cardboard or plastic with tight-fitting lid to ensure retention of moisture and prevent spillage
examination of fecal specimens
recommended time of examination for liquid and soft stools
within half hour
recommended time of examination for fully-formed stool
within 3-4 hours
liquid and soft stools contain what type of parasites
protozoan trophozoites
fully-formed stools may contain what type of parasite?
protozoan cysts
? may be found in both liquid and fully-formed stools
helminth eggs
parasite stages detected in examination of fecal specimens
- cyst
- trophozoites
- oocysts
- eggs
- larvae
- adult worm
examination of 3 specimens must be collected ?
every other day
substances that interfere with stool examinations
- urine contamination
- castor or mineral oil
- barium, bismuth, kaolin, milk of magnesia, antacids]
- antibiotics/antimalarials
- enemas
amount of formed stool collected
2-5 grams
amount of watery stool collected
5-6 tablespoons
examination techniques for fecal specimens
- wet mount technique
- concentration techniques
- permanently stained smears
- culture
- immunoassay (antigen detection) - Giardia spp, Cryptosporidium spp, Entamoeba histolytica
Stool preservatives
- formalin
- Schaudinn’s solution
- polyvinyl alcohol
- sodium acetate formalin
- modified PVA
- two-vial system
recommended ratio of fixative to stool
3:1 (3 parts fixative, 1 part stool)
all purpose fixative
formalin
concentrations of formalin
5% — for cysts and protozoans
10% — for metazoans
advantages of formalin
- easy to prepare
- preserves specimens for several years
- long shelf life
disasvantages of formalin
not suitable for permanent stains
- fixative for permanent staining
- contains mercuric chloride
- can cause disposal problems
Schaudinn’s solution
- acts as an adhesive for the stool specimen when preparing slide for staining
- combined with Schaudinn’s fixative
Polyvinyl Alcohol
- useful for fixation of parasite
- cannot be used in permanent staining because it will lead to unsatisfactory result
merthiolate-iodine-formalin
- used for permanent stains, direct mounts, and concentration procedures
- does not contain mercury
- quality is not good
Sodium Acetate-Formalin
in modified PVA, mercuric chloride is replaced by ?
copper sulfate and zinc sulfate
components of MIF
- merthiolate — staining component; AKA thimerosal
- iodine — staining component
- formalin — preservative
- one portion of specimen is fixed in three parts of 5%-10% buffered formalin
- one portion in three parts of polyvinyl alcohol fixative
Two-vial technique
macroscopic examination
- color (brown, LB, DB)
- consistency (formed, soft, loose, watery)
- presence of mucus, blood, larval, adult worms, proglottids
Type 1
- separate hard lumps
- very constipated
Type 2
- lumpy and sausage like
- slightly constipated
Type 3
- a sausage shape with cracks in the surface
- normal
Type 4
- like a smooth, soft sausage or snake
- normal
Type 5
- soft blobs with clear-cut edges
- lacking fiber
Type 6
- mushy consistency with ragged edges
- inflammation
Type 7
- liquid consistency with no solid pieces
- inflammation and diarrhea
macroscopic findings
- macroscopic parasites
- blood-tinged mucus
- bloody mucus
- bright red blood
- occult blood
macroscopic parasites
pinworms, tapeworm proglottids, helminths
blood-tinged mucus
trophic amoebae
bloody mucus
amoebic ulcerations in the large intestine
bright red blood
bleeding hemorrhoids
occult blood
other gastrointestinal disorders, intestinal bleeding
microscopic examination
- DFS
- concentration techniques
- permanent stain
- wheatley’s trichrome stain
- iron hematoxylin stain
- modified acid fast stain
- microsporidia stain
- most easily performed parasitological test
- most useful when fresh specimens, liquid stools, or duodenal aspirates are examined for motile trophozoites/helminth larvae
Direct Wet Mount / Direct Fecal Smear
DFS process
small amount of stool is mixed with a drop of 0.85% saline and Lugol’s iodine and covered with a coverslip
alternative for DFS
- modified D’Antoni’s iodine solution and Gram’s iodine
saline smear findings
huge amount of eggs, trophozoites, and cysts
iodine smear findings
eggs, cysts
(no trophozoites since iodine kills them)
additional mounting medium for DFS
buffered methylene blue
more sensitive in detecting cysts, larvae, and eggs, to prevent false positives
concentration techniques
concentration techniques
- sedimentation
- flotation
the heavier parasites settle at the bottom as a result of gravity or centrifugation
sedimentation
lighter parasite cysts and eggs rise to the surface of a solution of high specific gravity
flotation
sedimentation procedures
- Formalin Ether Concentration Technique (FECT)
- Acid Ether Concentration Techniques (AECT)
- Mini Parasep SF Kit
- reagents: 10% formalin, ether
- recommended for protozoans, helminth larvae, and eggs
formalin ether concentration technique
- reagent: 40 % hydrochloric acid, ether
- recommended for helminth (Trichuris, Capillaria, and trematode) eggs only
Acid Ether Concentration Techniques (AECT)
- reagents: 10% formalin, Triton C
- minimalist preparation
Mini Parasep SF Kit
flotation techniques
- zinc sulfate (ZnSO4) flotation
- brine flotation
- sheather’s sugar flotation
- reagent: 33% ZnSO4
- specific gravity: 1.18-1.20
- most common flotation technique
Zinc Sulfate Flotation
reagent: saturated table salt (NaCl)
disadvantage: not applicable for operculated eggs
brine flotation
reagent: boiled sugar with phenol
most recommended method for coccidian oocyst
sheather’s sugar flotation
- provides a permanent record of a patient’s specimen
- allows review by consultants should difficulties arise in identification
permanent stains
widespread acceptance because of its simplicity, reliability, and cost-effectiveness
Wheatley’s Trichrome Stain
appropriate specimens for WTS
fixed in Schaudinn’s fixative or PVA fixative
? -preserved specimens may be stained with trichrome, but results are less satisfactory
SAF- or MIF-
- previously more difficult to perform than the trichrome stain
- may stain clearer and sharper than trichrome
Iron Hematoxylin Stain
modified iron hematoxylin stain that may prove useful by incorporating ?
carbol fuchsin
Modified iron hematoxylin stain that may prove useful by incorporating carbol fuchsin, allowing concurrent staining of acid-fast organisms such as
Cryptosporidium, Cyclospora, and Cystoisospora
- Detects oocysts of Cryptosporidium, Cyclospora, and Cystoisospora
modified acid-fast stain
acid fast-staining techniques
- modified Kinyoun method
- modified acid-fast dimethyl sulfoxide
- auramine-O
stain for microsporidia (specifics)
- Enterocytozoon bieneusi
- Encephalitozoon intestinalis
Modified trichrome stain uses an increased (10-fold) concentration of ? with increased staining time
chromotrope 2R
additional techniques for examination of enteric parasites
- Cellulose Tape Technique for Pinworms
- Kato Thick Smear
- Egg Counting Techniques
- Egg Hatching Method
- Nematode Culture and Recovery Techniques
Test for Enterobius vermicularis
Cellulose Tape Technique for Pinworms
In Cellulose Tape Technique, specimens should be collected:
- late night
- first thing in the morning before bathing or defecation
- Qualitative test for detecting helminth eggs
- Simple technique for mass stool examinations
- Good for detecting eggs with thick egg shells
Kato Thick Smear
how much stool is needed for Kato Thick Smear?
50-60mg
materials for Kato Thick Smear
cellophane, glycerine, malachite green solution
kato thick smear material that acts as a coverslip
cellophane
kato thick smear material that acts as a cleaning reagent
glycerine
kato thick smear material that provides color and minimizes brightness
malachite green solution
Egg Counting Techniques
- Kato Katz
- Stoll Egg Count
Uses measured amount of stool (quantitative)
Kato Katz
additional equipment for Kato Katz
- wire mesh
- template
wire mesh is for?
filtering stool sample
template is for?
standardizing measurements
- Reagent: 0.1N NaOH
- Dilution of the sample in sodium hydroxide
- To count 24-hour stool sample
Stoll Egg Count
- Analysis of schistosomiasis
- Detects the presence of eggs in light infections and determines their viability
Egg Hatching Method
Materials for Egg Hatching Method
Urine/stool + water + Erlenmeyer Flask
Hatched ? are positively phototropic and move towards/near the light
miracidia
Stool is incubated in a humid environment to encourage egg hatching
Nematode Culture and Recovery Techniques (Coproculture)
Nematode Culture and Recovery Techniques (Coproculture)
- Harada Mori Filter Paper Strip Culture
- Charcoal Culture
- Baermann Funnel Technique
- Larvae migrate from the feces into a paper strip, where they may be readily detected
- Detects Hookworms and Strongyloides spp
Harada-Mori Filter Paper Strip Culture
- Larvae migrate into a dampened gauze pad, which is then placed in water, allowing the larvae to settle out
- Charcoal simulates soil to encourage eggs to hatch
Charcoal Culture
- Sensitive and reliable method for recovery of Strongyloides and other nematode larvae from stool
- Fecal sample is placed on several layers of gauze on top of a wire screen that is suspended in a funeral
- Bottom of the funnel is clamped off, and water is added to the level of gauze
- Larvae actively migrate through the gauze and settle to the bottom of the funnel
Baermann Funnel Technique
Objects that Might Resemble Enteric Parasites
White blood cells/macrophages/squamous and columnar epithelial cells
Yeast and starch granules
Pollen and fungal conidia
Plant fibers
Pieces of vegetables or vegetable skins
White blood cells/macrophages/squamous and columnar epithelial cells
Amoeba
Yeast and starch granules
Protozoan Cyst
Pollen and fungal conidia
Helminth eggs
Plant fibers
Nematode larvae
Pieces of vegetables or vegetable skins
Adult worms or proglottids
- Hexagonal bipyramidal crystal
- Localized in the granules and cytoplasm of eosinophil and basophil
- Presence indicated parasitic infection
- Encountered during observation of KOH preparation of sputum
Charcot-Leyden crystals
Examination of Blood
Thick and Thin Blood Smear
Buffy Coat Smear
Blood Concentration Technique
- For species identification
- Spread over the slide in a thin layer, yielding intact, non-overlapping cellular elements
Thin Smear
- Used for diagnosis
- Concentrated in a small area that is many cell layers deep
Thick Smear
Concentration Techniques
Buffy Coat Smears
Membrane Filtration
Knott’s Concentration
Diagnosis of Leishmania, Trypanosomes, Microfilariae
These do not reside in RBC
Buffy Coat Smears
Lysed blood + 5-um Membrane filter
Membrane Filtration
Blood + 2% Formalin = Centrifuge
Sediment: check for Microfilariae
Knott’s Concentration
Blood for examination may be obtained by ?
fingerstick, earlobe puncture, venipuncture
? anticoagulant is preferred
EDTA
Best blood stain
Giemsa
- Host cell and parasite chromatin stains vividly but the hemoglobin in erythrocytes is only a pale red
- Only stain that allows visualization of the erythrocyte stippling that occurs with infection by certain malarial parasites
Giemsa stain
Alternative stain
Wright stain
Stains parasite less well than Giemsa
Stains erythrocytes, producing a busier background
Wright
Fresh Giemsa stain must be made each day of use by diluting stock solution into
phosphate-buffered water
Buffered water must be maintained at
pH 6.8-7.2
Urine
Trichomonas vaginalis
Schistosoma haematobium
CSF
Trypanosoma spp.
Naegleria fowleri
Angiostrongylus cantonensis
Taenia solium (cysticercus larvae)
Duodenal material
Entero test (Enteric capsule test)
Giardia lamblia
Strongyloides stercoralis
Sigmoidoscopy material
Entamoeba histolytica
Vaginal and urethral discharges, prostatic secretions
Trichomonas vaginalis
Sputum
Paragonimus westermani, Pneumocystis jirovecii
Skin biopsy
Onchocerca spp., Mansonella spp.
Muscle biopsy
Trichinella spp.
Rectal biopsy
Schistosomes eggs
Lymph Node biopsy
Adult filarial worms
Tissue Culture biopsy
Leishmania spp., Trypanosoma spp.
Skin Hypersensitivity Tests
Bachman Skin Test
Casoni Skin Test
Dr. Montenegro Intradermal Test
Bachman Skin Test
Trichinella spiralis
Casoni Skin Test
E. granulosus
Dr. Montenegro Intradermal Test
Leishmania spp
- Tests that can detect current infection
- Can be performed without microscopy skills
- Rapid, allows batch processing
- Disadvantage: False-positives, cross-reactions
Immunoassays (Antigen Detection)
Histidine-rich Protein II (HRP-II)
Plasmodium falciparum
Parasite Lactate Dehydrogenase (pLDH)
Plasmodium spp
Trichomonas vaginalis antigen
Trichomonas vaginalis