World of Parasites Flashcards
Common name for platyhelminths
Flatworms
Common name for cestodes
Tapeworms
Common name for trematodes
Flukes
Common name for nematodes
Roundworms
Common name for arthropoda
Insects, spiders, mites, and ticks
These are single celled parasites that contain many phyla
Protozoa
What are flatworms, tapeworms, flukes, and roundworms known as?
Helminths
Impact of parasites in the U.S. and the world w/ regards to such issues as health, economics, etc.
- Parasite infections outnumber humans
- Tropics/temperate zones (3rd world) → life-threatening, hindrance to economic development
- U.S. → increased #s due to: increased mobility, compromised patients, refugees, free trade, climate change
Factors that influence the prevalence of parasites in society
- Geographic
- Social customs
- Host factors
How does geography influence the prevalence of parasites?
- Climate
- Modifications to environment
- Vector population
How do social customs influence the prevalence of parasites?
- Fecal disposal
- Diet/food prep
- Agricultural methods
- Housing (rats, mosquitos)
- Sexual practices (AIDS, etc.)
How do host factors influence the prevalence of parasites?
- Nutritional state
- Immune status → detrimetnal, possible immunological benefits
- Genetics
- Age
Life cycle for protozoa
- Trophozoites
- Cysts
Life cycle for helminths
- Egg
- Larva
- Adult stages
What protozoan stage would you find in formed stool?
Cysts (and eggs); trophs wall themselves up to form cysts as protection
What protozoan stage would you find in liquid stool?
Trophs (and eggs); these are more motile and fragile, commonly found higher up in the GI tract
What protozoan stage can be found in semiformed/soft stool?
Cysts, trophs, and eggs
What is the ratio of preservative to stool?
3 parts preservative: 1 part stool
This preservative serves as a fixative (mercuric chloride), is a resin for adhesion to the slide, and is used for PERMANENT smears.
PVA-polyvinyl alcohol
This preservative is used for concentrations or wet mounts, NOT smears.
10% buffered formalin
Two methods of concentration are based on specific gravity
Flotation and sedimentation
Preservative used in the flotation concentration technique
Modified Zinc Sulfate
Specific gravity in concentration techniques
1.18-1.2
Disadvantages of using the flotation technique
Dense eggs sink and operculated eggs rupture
Advantages of doing flotation techniques
Allows detection of most eggs, larvae, and cysts; also eliminates debris (will settle to the bottom)
Advantages of doing sedimentation concentration techniques
Allows detection of most eggs, larvae, and cysts by gravity or centrifugation
Disadvantages of using sedimentation concentration techniques
Smaller eggs may not sediment; more fecal debris than flotation methods
Advantages of doing permanent stains
Able to view internal structures (trophs or cysts)
Most common/best permanent stain for viewing internal structures
Trichrome
Specimen types collected for parasite identification
- Gastrointestinal (most common)
- Vaginal
- Sputum
- Aspirates (lung, liver, LNs, bone, etc.)
- Biopsy (lung, cornea, skin, LN, GI, etc.)
- Blood (thick, thin preparations)
How many specimens are collected for fecal parasite identification?
Three fecal specimens on alternate days (6 for amoebiasis)
Describe the transportation of fecal specimens collected for parasite identification
Clean, dry container
Gross examination of fecal specimens
- Blood (red, black)
- Barium (white-clay) → Not acceptable!
- Mucus
- Adult worms
Specimen processing of liquid fecal samples
- Examine or preserve w/in 30 minutes, after collection
- Wet mounts, concentrations, permanent-stained smears
Specimen processing of semi-formed/soft fecal samples
- Examine or preserve w/in 1 hour after collection
- Wet mount, concentrations, permanent-stained smears
Specimen processing of formed fecal samples
- Usually not sent for parasite studies
- Examine w/in 24 hours (or preserve them)
- Concentrations, permanent-stained smears
Why aren’t wet mounts observed w/ formed fecal samples?
No trophs will be found
Describe the timing of fecal specimens collected for parasite identification
- Before radiologic studies w/ barium (or 1-2 weeks post-barium)
- Avoid medications (mineral oil, bismuth, antidiarrheal medications, some antibiotics, e.g., tetracycline)
- Avoid contamination w/ water, urine
Three identification techniques performed in an “O and P” examination
- Wet mount
- Concentrations
- Permanent stains
Wet mounts
From direct specimen (not formed stool)
- Drop of physiologic saline
- Drop of iodine (one slide w/ and one w/o)
Screen w/ 10x objective (NEVER USE OIL)
Concentration techniques
Separates parasites from fecal debris
Always performed from fresh or formalin-preserved stool (NEVER PVA)
Trichrome stain
- Procedure
- Fresh specimen is fixed or can use PVA preserved specimen (thin smear)
- Requires experience
- Stains takes hours (usually overnight)
Trichrome stain
- Interpretation
- Scan at low power (10x or 40x), then examin at 100x oil immersion (at least 300 fields)
- Background debris = green
- Protozoa = blue-green cytoplasm, red-purple nuclei, inclusions
- Helminth eggs (may be distorted)
- Larvae = dark red-purple
What types of fecal specimens are used w/ a modified acid-fast stain?
- Fresh stool or formalin fixed specimens
- Not PVA-preserved specimens!
How quickly should blood smears be prepared?
< 1 hour
Two types of blood smears that are prepared
Thick and thin
Which type of blood smear is best for identification?
Thin smears
Which type of blood smear has the best sensitivity?
Thick smears
