Module 1 Flashcards
Parasite
organism that lives upon or within another organism at whose expense it obtains something it needs for life
In the US, what are the parasites that are prevalent to children?
pinworms and round worms
What is the greatest source of infection?
Man
Harmful effects of parasites
- mechanical injury
- eating or digesting and absorbing host tissue
- poisoning
- robbing the host of nutrition
Ectoparasite
lives on surface of host
Endoparasite
lives inside a host
obligatory parasite
has to spend part of its life as a parasite
facultative host
not normally parasitic but can become so
definitive host
host in which the parasite reaches maturity and reproduces; most important host
intermediate host
some development of parasite occurs but doesn’t reach maturity
vector
insect that carries parasitic infection from one host to another; can be host
Main human host defensive mechanisms
- immunoglobulins in the mucous of intestines and respiratory tract, tears, saliva, and sweat
- phagocytosis
- reticuloendothelial system
- inflammation
- granuloma formation
- accommodation
Accommodation to parasites in humans
- parasite becomes immunologically inert
- parasite masks itself with host antigens
- parasite changes surface antigens
Stool types
- liquid: most likely to contain trophozoites
- soft: may contains pre-cysts
- formed: contains cysts, ova, and larvae
Times of collection for stool samples
10 day period, one every other day
Substances that interfere with the detection of intestinal parasites
- antibiotics
- bismuth
- kaolin
- antimalarials
- milk of magnesia
- mineral and castor oil
- barium enema
Other types of parasitic specimens
- sigmoid material
- duodenal contents
- urogenital material
- sputum
- aspirates
- biopsy material
- blood
Purge specimen
Fleet’s enema
Why should there not be any urine or water in the stool specimen?
Water can contain free living organisms and urine destroys motility
Specimens required for routine exam
- 2 normally passed
- 1 after Fleet’s enema
Ameobiasis protocol
- 3 normal
- 3 after enema
Preservation of specimens
-PVA: cysts, trophs, and/or ova; useful for liquid specimens
PVA
- 3:1 ratio of PVA to stool
- allows specimens to slide for staining
- permanent stained slides for months or years in sealed containers
Advantages of PVA
- both preservative and fixative so suitable for permanent staining procedures
- excellent preservative for protozoan cysts and trophozoites
Disadvantages of PVA
- Giardia and Trichamonas don’t concentrate well
- isospora is not usually seen
Advantages of formalin
- cysts are preserved for a long time
- specimens can be preserved to long periods of time without greatly compromising organism morphology
Disadvantages of formalin
- only for wet mounts: no permanent slides
- have to add formalin within an hour of passage
Schaudinn’s Fluid
used for fixing fresh smears for permanent smears; found in PVA
MIF
good stain for most kinds and stages of parasites; not for permanent stains
Sodium Acetate Formalin
used only with iron hematoxylin stain; used for both concentrates and permanent smears
Macroscopic appearance of specimens
- consistency
- blood: with mucous, suggests amoebic infection
- age of specimen
Direct wet mounts
detects trophozoites, cysts, ova, and larvae
Saline mount
used for the examination of all intestinal parasites
Material for saline wet prep
0.85% NaCl
Purpose for saline reagent
protozoan cysts are more refractile in saline and are easier to detect
Stages of parasites detected by saline wet prep
cysts, trophozoites, helminth eggs, and larvae
Material for iodine wet prep
D’Antoni’s iodine or Lugol’s iodine at 1:5
Purpose for iodine reagent
improves the detection and identification of protozoan cysts
Stages of parasites detected by iodine wet prep
protozoan cysts, larvae, and helminth eggs
Concentration methods
- routine procedure for the complete examination of parasites
- allows for detection of small numbers of parasites that may be missed in the direct smear
Two main concentration methods
flotation and sedimentation
Advantages of flotation
gives clean prep
Disadvantages of flotation
- helminth eggs don’t float due to high density
- must examine within 30 minutes
Advantages of sedimentation
-greater concentration of diagnostic parasites
Disadvantages of sedimentation
contains more debris than flotation method
Permanent stains
- mandatory for a thorough examination of all diarrheal specimens
- definitive diagnosis for protozoa
- greatly enhances the detection of the protozoa
- permanent record of organism detection and identification
Types of permanent stains
- trichrom stain
- iron hematoxylin
- modified acid fast
Trichrome stain
- good results from fresh or PVA sample
- rapid method
- good detail for protozoan cysts, trophozoites, human cells, yeast cells, and artifacts
Trichrome stain: green
cytoplasm of cysts and trophozoites; yeasts and molds; background material; cytoplasm of white cells
Trichrome stain: purple
Entamoeba coli; nuclear chromatin, chromatoid bodies, ingested red cells, and bacteria
Trichrome stain: red
nuclear chromatin, chromatoid bodies, ingested red cells, and bacteria; eggs and larvae; white cell nuclei
Trichrome stain: nonstaining cysts
incomplete fixation
Trichrome stain: over-destaining
dip the slide only once in the acid-alcohol solution, drain on paper towel, and rinse in 95% alcohol
Trichrome stain: cloudy smears
second 95% alcohol, xylene, and carbol-xylene must be kept moisture free
Iron Hematoxylin stain
- most exacting method to identify protozoan cysts and trophozoites
- timing and adequate destaining are critical
- not for unseasoned technologists
Modified acid fast stain
- for Crytosporidum and oocysts
- don’t have to heat
Occular micrometer
distance on stage micrometer/number of units on occular micrometer=distance between each occular unit in minutes
