Diagnostics Flashcards
Fecal Flotation
-Basically the light eggs/oocysts will float in high specific gravity AND the debris will go down
ways to diagnose- fecal flotation
- Qualitative- used in small animal; present/absent
- Quantitive - used for large animals; fecal egg counts.
>informed decision: sometimes more is not necessarily worse than one parasite of a higher pathogenicity
Two ways that fecal flotation is conducted
- Passive- gravity based; clinics and fieldwork (mini-FLOTAC, Fecalyzer, McMaster)
- Centrifugal- high sensitivity labs (ex. Wisconsin)
What does fecal flotation show?
-Helminth eggs (especially nematodes)
-Some protozoal oocysts
What features help to differentiate nematode eggs?
-shape
-symmetry
-presence of plugs
-shells
-size
-presence of morula
What are features that can help differentiate cestode eggs?
**not shed all the time- lucky to see them!
- they are heavy and don’t float well
Features:
-hooks in egg
-shell/capsule
-geometric shape
-presence of single or multiple in eggs
Limitations of fecal flotation
Can result in false negatives (sensitivity) or false positives (specificity)
What causes false negative in fecal flotation?
- intermittent shedding
-prepatent period
-environment
-single sex nematode infections
-aged feces (hatched eggs)
-may not detect segments, larvae
-technical errors (wrong solution, small sample, diarrhea, non homogenized)
What causes false positives in fecal flotation?
-pseudoparasites
-coprophagia (spurious)- dog ate cow feces and is now displaying parasite (but probably just when right through)
-parasites in prey species
-indistinguishable eggs**
Tips for doing a fecal flotation
-get multiple samples
-fresh samples (kept cold)
-annual check
-detailed dietary and travel history to help narrow down what you could expect
-train personnel how to store and ship
-order right tests
-understand limitations of field testing
Fecal sedimentation
-used for eggs too dense to float or detecting larvae (ex. Baermann larval sedimentation)
-often used for trematode eggs in large animals
Baermann larval sedimentation
- live larvae in fresh feces submerged in water wriggle out and sink
How do you determine the presence of trematode eggs?
-often operculate (lets miracidia out)
-sizes
-shape
Tests to recover and determine morphology of parasites
1.Perianal tape method
2.Total worm count
3. Skin scraping/parasite collection
4. Tissue digestion
5. Coproculture
When would you use perianal tape method?
- Pinworms (nematodes) in large animals
-Cyclophilid cestodes in small animals - Eggs adhered to the perianal region
When would you use worm count?
- Worm burden in GI tract
-Ruminant GIN
-Echinococcys sp (cestodes) in canids
-GI tract lavage
When would you use skin scraping/parasite collection?
-ticks, lice, fly maggots
-mites (deep/superficial scraping)
When would you use tissue digestion?
-Larvae and adult helminths that reside in host tissues/organs
-digest solution
eg.Trichinella spp
When would you use coproculture?
-Nematodes have many identical eggs. Let the eggs culture to develop into L3 where you can then determine species/morphology
Fecal smear
-used to determine protozoan infections (trophozoites and cysts)
-simple, quick
-low sensitivity (because shedding is not occurring all the time)
PCR
-use DNA sample and combine with primers (for specific type of parasite). Put in thermal cycler (Denaturing, Annealing, Extension)
-Specific primers will confirm on gel the presence/absence of different parasites
What samples can you do PCR in?
-feces
-blood
-urine
-isolated eggs/larvae
If DNA present or absent, does this mean that parasite is actually there or not there?
No
Antigen tests
-SNAP tests- commercially available, no equipment
- looking for specific parasite-associated compounds
-use blood or fecal samples
-antigen binds to positive spot and pathogen specific coloured particle binds to determine positive
Antibody tests
-host immune response to a parasite through production of specific antibodies
>positive test just means exposure!
-uses blood, saliva, CSF to detect protozoans
-regulatory or large-scale screening
Histology and immunohistochemistry
-detect tissue helminths and protozoa
-use histological sections collected at necropsy to look for antibodies
Importance of effective diagnostics
-screening or surveillance
-treatment/control strategies
-adoption of preventative measures
-access risk of infections of other animals in herd/household or humans
