Module 10 Flashcards
(17 cards)
What is parasitism?
Symbiotic relationship where host is damaged
What types of hosts are there?
Definitive- has reproductive stages
Intermediate- has larval or smaller stages
What are the different types of parasites?
Protozoa- unicellular
Metazoa- multicellular
What is the most common specimen for parasites? What other specimens are suitable?
Stool
Fluid aspirates
Urine
Sputum
CSF
Genital swabs
Corneal scrapings
When should parasite specimens not be collected?
After barium X-rays
After ingestion of mineral oil, bismuth, some antidirarrheals and antimicrobials
What specimens are used for detecting live protozoans?
Fresh, nonpreserved
Liquid within 30min
Semiformed within 1hr
What collection systems are used? What are they used for?
Two vial system using PVA- stained preps
One vial system using SAF- poor quality stained preps
What are the components of PVA?
Vial 1- 5-10% formalin preserves cysts and ova (not trophs)
Vial 2- PVA preserves trophs and cysts
What are the components of SAF?
Sodium acetate formalin
- Sodium acetate
- Acetic acid
- Formaldehyde
- Water
Preserves trophs, cysts and ova
What are the stages of parasites?
Protozoa- cysts (resting) and trophozoites (reproductive)
Metazoa- ova and worms
Tape worms have proglottids containing eggs
What are direct wet preps for parasites used for?
Detects live trophs by their characteristic movement
How can cysts be detected in a wet prep?
Add a drop of Lugol’s or D’Antoni iodine
What stains are used for parasites? What are the results?
Trichrome
- Cytoplasm is blue/green
- Nuclear material, RBCs, chromatin bars are purple/red
- Eggs/larvae are red
- Debris and slide background are green
Iron hematoxylin
- Cytoplasm is blue/grey
- Nuclear material is dark blue/black
- Slide background is light blue/grey
How is Cryptosporidium demonstrated?
Acid fast component causes it to stain pink
What is the purpose of the concentration procedure?
Concentrates helminth ova and protozoan cysts
Preserves parasitic structures
What is the concentration procedure?
Stool mixed with 10mL saline, use formalin if not preserved (30min)
Centrifuge and decant supernatant until light tan or clear
Decant and resuspend in 10mL formalin
3mL ethyl acetate and shake
Centrifuge- four definitive layers
Ova and cysts will be in sediment
How is the size of parasites determined microscopically?
Multiply the number of micrometer divisions by the conversion factor
