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Parasitology > Diagnostic Techniques > Flashcards

Diagnostic Techniques Flashcards

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1
Q

Why test for parasites?

A
  • Tailor therapy/ prophylaxis for individuals.
  • Detect developing resistance
  • Reduce unnecessary use of medications in low risk population’s.
  • Detect emergence of new parasites especially with warming climate.
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2
Q

Who needs parasitology testing?

A
  • Clinically ill ( Diarrhea, vomiting, bloody stool, anemia, eosinophilic enteritis, coughing, once bacteria/ virus r/o)
  • High risk animals ( young, high exposure, susceptible such as immunocompromised, pregnant, old, young, nursing)
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3
Q

What is the definition of the word Prevalence?

A

Proportion of animals (%) infected with a parasite

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4
Q

What is the definition of Intensity of infection?

A

Number of parasite/parasitic stage in an individual animal
• Usually expressed in eggs/oocyst/larva per gram of feces • When expressed as mean/median of a herd/population only positive
animals are considered

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5
Q

What is the definition of sensitivity?

A

The ability of the test to correctly detect individuals infected with a parasite

(true positives)

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6
Q

What is the definition of specificity?

A

The ability of the test to correctly detect individuals without a parasite (true
negatives?

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7
Q

What is the definition of a pseudoparasite?

A

an object or organism that resembles or is mistaken for a parasite

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8
Q

What kind of tests can be run on fecal samples?

A
  • Fecal smear
  • Fecal flotation
  • Fecal sedimentation
  • Baermann method
  • McMaster method/ FLOTAC
  • Coproculture (Fecal culture)
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9
Q

What are the most important things to remember when doing a fecal examination?

A

• Important to have fresh samples, preferably directly collected from the animal
• At least 10 g of feces should be collected
• Feces collected from yard, pen or litter box may be old and egg may embryonate, oocyst
may sporulate
• Refrigerate (4 degree C) to prevent development
• Freezing is inefficient – freeze thaw destroys eggs/larvae

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10
Q

What is a direct fecal smear and what are the pros and cons?

A
  • Qualitative fecal exam
  • Simple quick and easy
  • Good for moving protozoal trophozoites (giardia), mobile amoeba
  • Can be fixed with a special stain (e.g for Cryptosporidium)
  • Negative result inconclusive, positive result equally valid!
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11
Q

What is a fecal flotation and what is the most important thing to remember when preforming the test?

A
  • Based on differential specific gravity of parasite eggs/cysts, fecal debris and flotation solution.
  • Flotation solution must have higher specific gravity than parasite eggs or oocysts.
  • Specific gravity of most parasite eggs are 1.1 – 1.2 g/ml
  • Flotation solutions should be > 1.2
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12
Q

What parasite would a fecal float be best used for?

A
  • Best for most nematodes and cestode eggs, some protozoal (oo)cysts
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13
Q

What happens if you use a solution for fecal float that is too low in specific gravity? To high?

A
  • Some fluke eggs won’t float especially if solutions of lower specific gravity are
    used
  • Higher specific gravity solution – distorts protozoal trophozoite, cysts and
    some helminths eggs, larvae – Proper choice of flotation solution
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14
Q

What is the ideal specific gravity of a fecal float solution?

A

> 1.2

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15
Q

What are the steps to complete a passive/ standing fecal float?

A
  1. ) Feces + flotation solution in beaker / cup.
  2. ) Strain and transfer into test tube/ fecalizer
  3. ) Add coverslip and let it stand for some time
  4. ) Examine coverslip under microscope
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16
Q

What are the steps to complete a centrifugal fecal flotation?

A
  1. ) Feces + flotation solution in a beaker/ cup
  2. ) Strain and transfer to test tube
  3. ) Add coverslip and centrifuge ~ 1500 rpm for 5 minutes
  4. ) Examine coverslip under microscope
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17
Q

What are the pros and cons of using a passive/ standing fecal flotation?

A

Pro:

  • Simple and Fast
  • Commercial kits available

Cons:

  • Lower sensitivity
  • Qualitative or semiqualitative.
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18
Q

What are the pros and cons of using centrifugal fecal flotation?

A

Pro:

  • Recovers more eggs/ ova
  • Higher sensitivity
  • Can be quantitative

Con:

  • More labor intensive
  • More expensive
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19
Q

What is most important to remember when deciding between a passive/ standing fecal floatation or a centrifugal fecal flotation?

A

Centrifugation increases the sensitivity of your tests. Centrifugation recovers 3-5 times as many eggs over other passive floatation techniques

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20
Q

What is the McMaster Method?

A
  • Commonly used quantitate technique for helminth eggs in
    livestock
  • It uses a counting chamber that enables a known volume of fecal
    suspension to be examined microscopically
  • Based on the principle of passive flotation (no centrifugation
    required)
  • Quantitative
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21
Q

What is the steps to preforming the McMaster method?

A
  1. ) The fecal slurry is made with a known amount of feces and a known amount of flotation solution
  2. ) The slurry is sieved through a strainer
  3. ) Filtrate is used to fill the counting slide chamber
  4. ) Calculation (according to the protocol)
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22
Q

What is the Wisconsin double centrifugation?

A

Sensitive test that has 2 centrifugation steps, it is quantitative.

Most sensitive flotation technique in low
infection intensities (1 epg or less)
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23
Q

What are the two centrifugation steps in the wisconsin double centrifugation?

Study These Flashcards
A

Two centrifugation steps

  • 1st – Fecal slurry made up of feces and water
  • 2nd – Sediment of 1st step homogenized with flotation solution
24
Q

Why is the wisconsin double centrifugation test challenging in clinics?

Study These Flashcards
A
  • Requires larger space (centrifuges)
  • More time
  • Expensive
25
What is fecal sedimentation and when would it be used?
- For eggs with higher specific gravity (e.g trematodes and acanthocephalan eggs) that do not float easily or eggs that are easily distorted by flotation solution - More sensitive than direct smear
26
What are the steps to the traditional sedimentation method?
Mix 10 g of feces with 100 ml of water 1. ) Mix and strain, collect filtrate in a beaker 2. ) Allow to sediment for 5 minutes 3. ) Allow to sediment for 5 minutes 4. ) Siphon off supernatant 5. ) Examine the sediment
27
What is the Baermann method? What would be a parasite this would be an ideal test for?
- For parasites that shed larvae in the feces (e.g. Dictyocaulus, lungworms) - Feces suspended in water overnight -\> Migration of live larvae out of the fecesinto water - Should only be used in fresh feces (live larvae)
28
What is a coproculture (fecal culture)? What is it used for?
- Eggs of strongyles/trichostrongyles are virtually impossible to diagnose morphologically so eggs are grown in a culture medium (vermiculite) at room temperature for several days to the third stage larvae (L3) - L3s are morphologically distinguishable - Usually done in pooled samples
29
What are the steps to a coproculture?
1. ) 20-30 grams of feces + tap water vermiculate 2. ) Incubate at room temperature, maintain moisture 3. ) After 7-14 days Larvae recovered (Baermann technique) 4. ) Microscopy
30
What are the limitations of fecal based diagnosis?
1. ) Chances of false negatives 2. ) Chances of false positives
31
Why may there be false negatives on fecal tests?
- Sporadic shedding - Prepatent period – Parasites not yet mature to shed eggs/larvae - Single-sex nematode infections - Senescent infections - Old feces (hatched eggs)
32
What is a false negative test?
Negative test result but the host has parasites
33
What is a false positive test?
Positive test result but no parasitism
34
Why may there be a false positive on fecal tests?
- Coprophagia/Predation – Spurious parasites - Pseudoparasites - Many parasite species shed identical eggs – Diagnostic challenge
35
What is a direct blood smear? What kind are there?
S implest blood parasite detection procedure is by direct microscopic examination of whole blood. - Thick smear - Thin smear
36
What is a thick bloodsmear and what is a parasite it is good to use for?
o Examining a drop of blood on a slide o Mainly for motile microfilariae of D. immitis o Quick and easy method but less reliabl
37
What is a thin bloodsmear and what is a parasite it is good to use for?
o A drop of blood spread on the slide o Not suitable for microfilaria larvae o Suitable for Trypanosomes, Babesia, Thelaria, Anaplasma
38
What is the steps for thin blood smears?
1. ) Make slide ( Make blood smear, you know how to do this) 2. ) Fix in methanol for 2 minutes 3. ) Stains ( Giemsa, fields stain)
39
What is the Modified Knotts test used for?
Rapid detection and identification of microfilariae (larvae) of filarial nematodes in blood - Concentrates microfilaria from 1 ml of blood à more sensitive
40
What can be used to diagnose ectoparasites?
- Skin scrapping KOH digestion • Collection and examination
41
What is superficial skin scraping? What wouls you use it for? Where should you scrape?
- On animal with pruritic or scaly skin ( Scabis, Cheyletiella, Otodectes etc.) - The best areas to scrape are typically crusty ear margins and crusty areas on the elbows or hocks.
42
What is deep skin scrapping? What is a parasite this is used for, and what is the process to take a deep skin scrape?
For mites that reside deep in the hair follicle (E.g. Demodex ) - Squeeze the skin - Scrape unitl there is light capillary bleeding – multiple sites
43
What is KOH digestion? What/ when is it used for?
If the scrapping contains much debris § If lice/mites are suspected and not found by inspection
44
What are the steps to KOH digestion?
1. ) 1 volume of skin scrappings + 10 volumes of KOH in large beaker 2. ) Heat until hair disolves 3. ) Centrifuge and transfer the sediment to a petridish and observe under microscope at 10x ( you can see mite eggs, mites, and lice with this)
45
What is tissue digestion used for? What are the general instrictions? What is an example of a parasite you can use this for?
- For parasites that have their larval or adult stages in host tissues and organs - Tissue is digested in digest solution (mostly acid pepsin) at a certain temp for certain time -\> centrifugation -\> digest examined (e. g – Trichinella spp., some arthropods)
46
What is the peri-anal tape method? What are its pros and its cons?
- Preferred method to detect eggs of pinworms in large animals - Eggs often attach to perianal region and may not been present in the feces - In dogs/cats- used to detect segments and eggs of cyclophyllid cestodes (e.g Taenia spp.) - Risky technique in regions where Echinococcus spp. is endemic.
47
What are immunologic tests against parasites? What is an example of one?
``` Detecting antibodies (against the parasites) and antigens (of the parasites) • ELISA – testing serum antibodies against parasites, parasite antigens ```
48
What are the strengths of Immunologic testing for parasites?
* Can identify presence of parasites when eggs are not recovered by flotation (e.g prepatent infection, intermittent egg shedding) * Relatively simple, fast (commercial kits)
49
What are the limitations of immunological testing of parasites?
* Measures immune response to exposure – not necessarily active infection * Cross-reactivity * Not universally available
50
What are coproantigen tests? What is an example?
Coproantigen tests: Parasite antigens in feces Increasingly common for in-house detections (e.g cyst wall antigen for Giardia in dog/cat feces) Example: Blood antigen test – E.g. 4dx snap test (IDEXX) Coproantigen ELISA exists for Ascaris, hookworms, giardia.
51
What immunological tests are available for protozoal infections?
Antibody tests – Protozoal infections - Complement fixation test - Immunodiffusion - Haemagglutination test - Florescent antibody test
52
What are PCR tests for parasites?
- Extraction of parasitic DNA from eggs/larvae in feces (Copro PCR); blood or tissue stages, or adult stage - Amplification of a specific genetic marker/gene or genes - Analyzing the DNA sequence to ID the species
53
What is the Advantages of PCR parasite testing?
- Higher Sensitivity ( copro pcr than egg based method) - Accurate - Sequences for species level ID, genotyping, phylogenetics
54
What are limitations of using PCR testing for parasite identification?
- Not possible in clinics - Expensive, Highly technical
55

Parasitology (10 decks)

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