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)
What is tissue digestion used for?
- larval & adult helminths
- using host tissues or organs
- solution that digests it
- ex: Trichinella spp (Nematodes)
What is coproculture for?
- nematodes w/ identical eggs
- eggs are cultured to develop into L3
How do you test for protozoan infections?
fecal smear
- simple, quick, low sensitivity (false negatives are common)
- for protozoal trophozoites (esp. if patient is symptomatic) & cysts
What is coproPCR?
- PCR done on fecal samples or blood, urine, isolated eggs/larvae for detection & identification of parasites
- PRESENCE or ABSENCE of DNA in a sample does not always mean PRESENCE or ABSENCE OF PARASITES
What are antigen tests?
- specific parasite-associated compounds
- done on blood or fecal floats
- SNAP tests - commercially available & no additional equipment needed
- tests have a pathogen-specific antibody conjugated to a coloured particle
What are antibody tests?
- host immune response to a parasite through production of specific antibodies (we are looking for this immune response)
- positive test means patient has been exposed to parasite
- done on blood, saliva, CSF -(protozoans)
- COMMONLY USED FOR REGULATORY (ex: bringing Eq across the border) OR LARGE-SCALE SCREENING
What is histology & immunochemistry used for?
- tissue helminths & protozoa
- histological sections collected @ necropsy/biopsy
- immunohistochemistry - detection of antibodies in histological sections
Why is effective diagnostics extremely relevant?
- screening or surveillance
- treatment/control strategies
- adoption of preventative measures
- access risk of infections of other animals in herd/household or humans
Things to remember:
- use parallel tests if results are inconclusive
- animals w/ annual heartworm treatment can be infected w/ other parasites
- anthelmintic resistance is increasingly concerning!
- PREVENTION IS ALWAYS BETTER THAN TREATMENT
