Introduction to Parasitology Diagnostics Flashcards
What is a fecal floatation?
light eggs/oocysts float in high specific gravity, debris sinks to the bottom
What are the different types of fecal floats?
- qualitative (present or absent; small animal)
- quantitative (fecal egg counts; large animal; informed decisions)
- passive (gravity based; done in clinic & in the field; Ex: Mini-FLOTAC, fecalyzer, McMaster)
- centrifugal (higher sensitivity, labs (ex: Wisconsin))
What can you see on a fecal float?
helminth eggs, especially nematodes; some protozoal oocysts
What are some features useful for differentiating between nematode eggs?
- shape, size, can contain just egg or have larva inside, shell, presence of morula, some asymmetric, presence of polar plugs, presence of operculum (pad that opens for waste excretion)
- these eggs are usually seen @ 10x but if you have to go to 40x, you are probably dealing w/ a protozoan
What are some useful features for differentiating cestode eggs?
- often shed segments w/in eggs, some eggs are heavier so they dont float v well, can sometimes see hooks inside the eggs, shell stands out - thick, sometimes almost geometric in shape, sometimes just 1 egg inside or multiple
What are the false negative limitations of a fecal float?
Sensitivity issues
1. intermittent shedding
2. prepatent period
3. environment (some parasites stay dormant until right conditions to produce eggs)
4. single sex nematode infections
5. aged feces (hatched eggs)
6. may not detect segments, larvae
7. technical errors (wrong solution, small sample, diarrhea, non homogenized)
What are the false positive limitations of a fecal float?
Specificity Issues
1. pseudoparasites
2. coprophagia (spurious) & Ca ate Bo feces & then had a Bo parasite pass through GI tract
3. parasites in prey spp
4. INDISTINGUISHABLE EGGS (~70 possible spp w/ strongyle-type eggs, ~12 possible spp w/ Taeniid-type eggs)
How to get the most out of a fecal float?
- request multiple samples from the right animals (sometimes youngest of a flock are more prone to shedding or the parasites themselves)
- request fresh samples & ensure cold chain for transport to lab
- check animals annually
- get a detailed DIETARY & TRAVEL HISTORY & share w/ people doing the testing
- if using a diagnostic lab, train your personnel how to optimally store & ship samples, together with the INFORMATION you have on patient
- order the RIGHT TEST(S)
- if using in clinic testing, get a centrifuge, train your personnel, & do quality checks!
- understand the limits of field testing
What is a fecal sedimentation used for?
- larvae (ex: Baermann larval sedimentation)
- fluke eggs
How does Baermann larval sedimentation work?
- live larvae in fresh feces are submerged in a “tea bag” in water & will wriggle out & sink
- primarily used for lungworms (Ca & livestock)
What is fecal egg sedimentation used for?
- for eggs too dense to float
- primarily trematode eggs in large animals
What is a common feature of trematode eggs?
often operculate
What is the perianal tape method for?
- pinworms (nematodes) in large animals
- cyclophilid cestodes in small animals
- eggs adhered to the perianal region
What is total worm count used for?
- worm burden in GI tract
- Ru GI nematodes (GIN)
- echinococcus spp (cestodes) - canids
- GI tract lavage
What is skin scraping or parasite collection for?
- ticks, lice, fly maggots
- mites (deep/ superficial scraping)
