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