Parasitology Flashcards
What diagnostic test is recommended for nematode larvae?
baermann test as it is the most sensitive
what is the purpose of testing for parasites in small animals?
- identify cause of clinical signs (most commonly)
- monitoring asymptomatic animals – preventative medicine programs or treating small animals
what 3 tests/samples can be used for morphological detection of macroscopic parasites?
- necropsy
- stool, vomit (helminths)
- arthropods themselves (ex. lice)
What 3 tests/samples can be used for morphological detection of MICROSCOPIC parasites?
- feces
- blood and other fluids
- skin debris or scrapings
What 2 types of tests are used for immunologic detection of parasites in small animals? (very generally, not specific names)
- antigen tests
- antibody tests
What 2 test are used for molecular detection of parasites in small animals?
- PCR
- sequencing
What are the advantages and disadvantages of morphologic tests for parasite detection?
(morphologic tests are standard for most parasites and are generally the first tests done)
advantages:
-inexpensive materials
-allows dg for multiple parasites
disadvantages:
- requires trained technicians
- requires larger samples
Why must we use fresh samples for fecal exams?
old samples may have maggots, soil nematodes, or hatched nematode parasite eggs
what is the minimum size appropriate for fecal samples?
3 grams
Why should you NOT ship fecal flotation slides?
parasites will be destroyed by the flotation solution
Direct saline smears using very fresh feces are only used for __________.
trophozoites such as giardia and tritrichomonas because they move.
NOT for protozoan cysts
The standard procedure for fecal analysis is _________________.
fecal flotation test
when doing a routine fecal float, you should always do what with the sample?
centrifuge and mix sample thoroughly before taking sample for your test because parasites are not uniformly distributed in the feces.
With regard to fecal float solutions, higher density solutions float _________, whereas lower densities float __________ less efficiently.
higher density solutions float more debris, whereas lower density solutions float some eggs less efficiently.
___________ is the ability to identify true positives (a measure of false negatives)
sensitivity
__________ is the ability to identify true negatives (a measure of false positives)
specificity
what is the sensitivity and specificity of direct fecal smears?
sensitivity = low
specificity = moderate
if we have a low sensitivity, then we cannot decrease the # of false negatives which is our goal usually.
how can you improve sensitivity and specificity?
combine with other tests.
T/F: the sensitivity of a fecal float is higher than direct smear
true
sample volume is more
patency of infection
parasites that you are trying to detect are usually easier detected
What is the specific gravity of zinc sulfate fecal flotation solution?
1.18 - 1.20
What is the specific gravity for sheathers sugar fecal float solution?
1.25-1.28
What is the specific gravity of sodium nitrate (fecasol) solution?
1.2
Which parasites have “heavier” eggs?
taenia sp
physaloptera sp.
which parasite is the “lightest”?
giardia cysts
which fecal solution is required to detect giardia?
zinc sulfate
what 2 fecal solutions are best to detect the MOST parasites?
- sheathers sugar solution
- zinc sulfate
T/F: centrifugal flotation tests are better than passive
true
How can you improve the sensitivity of fecal exams?
- use larger samples
- repeat the test (esp if girdia, trichuris, lungworms)
- combine with other tests (zinc sulfate float and antigen for giardia if diarrhea)
_________ are things that look like parasites but are not.
pseudoparasites
________ are things that are parasites of other animals and show up in your sample because of coprophagy or predation.
spurious parasites
If you suspect you have seen pseudoparasites or spurious parasites, what should you do?
repeat sample in 3-4 days and ensure there is no foreign material ingested during that time period.
Specificity is MOST affected by…
reader error
common errors: pseudoparasites (pollen grains, fungal spores, plant and animal hairs, air bubbles, yeasts) and spurious parasites (coprophagy, predation)
Many things may LOOK like parasites, but the easiest way to rule it out is looking at ________.
size
helminths = > 40 um
protozoa = < 60 um
What are some NEW technologies that improve parasite diagnosis?
- fecal Dx antigen test (IDEXX) (hooks, rounds, whips, diplydium)
- KeyScreen GI Parasite PCR (Antech) (20 parasites – hooks, rounds, whips, protozoa, giardia, coccidia, tapes, A. caninum benzimidazole resistance and zoonotic potential of giardia)
- Vetscan Imagyst System (Zoetis) (cytologic and fecal diagnostics using scanner with AI technology)
What are the reasons we do annual fecal exams in healthy dogs?
- detects parasites that are not treated by monthly products
- owner compliance is not good
- positive tests emphasizes importance of environmental management
- emerging drug resistance
Which of the following is FALSE about sedimentation tests?
A. used for parasite stages that have high density and wont float readily
B. feces mixed with zinc sulfate solution, then allowed to settle for a few minutes, then the fluid poured off leaving sediment, then repeat several times.
C. rarely performed in small animal
D. limited concentration of feces
B. feces mixed with zinc sulfate solution, then allowed to settle for a few minutes, then the fluid poured off leaving sediment, then repeat several times.
the feces are mixed with WATER, not zinc sulfate solution.
Which of the following is FALSE about Baermann test?
A. used for infections where larvae are the diagnostic stage
B. requires fresh sample
C. allow test to sit for 10 minutes at room temp prior to examining results
D. one negative test is not definitive, repeating is necessary
C. allow test to sit for 10 minutes at room temp prior to examining results
you must allow the test to sit for 8-24 hrs at room temp for the larvae to migrate into the water
What can you use to kill larvae that you see in Baermann test?
Lugol’s iodine**
Heat
if you use formalin, they will curl up and make identification more difficult.
_________ is the muscle at the end of the esophagus that pumps to move food through the intestine.
Bulb
this is a nematode characteristic
____________ is a cell mass that gives rise to reproductive organs.
genital primordium
a characteristic of nematodes
If you perform a Baermann test in a fecal sample from a dog and you see a kinked tail, its probably a spurious parasite due to coprophagy. What parasites are seen in the following scenarios:
A. dog that eats cat feces
B. dog that eats SR or camelid feces
C. dog that eats deer feces
A. dog that eats cat feces – aelurostrongylus
B. dog that eats SR or camelid feces – meullerius
C. dog that eats deer feces – parelaphostrongylus
____________ recovers eggs of parasites passed in urine.
urine sedimentation
helminths – pearsonema, dioctophyme
Blood smears stained with Wright’s or Giemsa stain can help detect what parasites?
hemoprotozoa (babesia, theileria, cytauzoon, trypanosoma, HW microfilariae)
its most effective in acute infections because organisms are much less common in chronic infections.
What test should be performed in any animal where heartworm infection may be present?
Knott test
done in dogs over 7m old with no/unknown preventative hx, antigen positive + following tx, antigen negative but suspect hw, and/or following tx.
T/F: skin scrapings have limited sensitivity for sacroptes infestations
true
What should you preserve samples in?
70-90% ethanol in order to preserve DNA
Ascarids in feces or vomitus in small animals are usually __________.
toxocara
___________ usually segments on animal or in animal resting place sometimes whole or segmented.
tapeworms
A positive antibody test (ELISA, IFA, etc.) indicates what?
exposure and immune response
Which of the following statements is FALSE about antibody tests for parasite detection?
A. can provide info when parasite burden is low
B. can detect intracellular parasites
C. detects host response, NOT actual parasite
D. detects acute infections best
D. detects acute infections best
may not detect acute infections because time require for detectable antibody dev, might need paired titers.
What are common uses of antibodys tests in small animal for parasite detection?
- dirofilaria in cats
- babesia (+ other piroplasms)
- protozoa – toxoplasma, neospora, trypanosoma, leishmania
T/F: Toxplasma antibody positive cats are unlikely to be shedding oocysts.
true because the period of oocyst production usually occurs before antibodies are detectable.
Which of the following statements is FALSE about antigen tests used for parasite detection?
A. detects presence of parasite
B. examples are ELISA and IFA
C. commonly used as point of care tests
D. are used as screening tests
E. can be used when fecal sample volume small
D. are used as screening tests
they are indicated for animals with clinical signs (ex. giardia antigen test used only in patients with diarrhea; if you do these tests as screening tools in normal animals, you may end up with asymptomatic infections that you cannot clear.
what is considered the “gold standard” for giardia testing?
IFA antigen test.
in cases of diarrhea, do both antigen test and fecal float.
What parasites can PCR detect in small animals?
- protozoa (crypto, giardia, tritrichomonas)
- babesia
- cytauxzoon
- toxoplasma
- tritrichomonas blagburni
- neospora and others
- echinococcus
- canine lung worm (crenosoma, angiostrongylus)
Why is PCR not always the BEST or most sensitive test to use for parasite diagnosis?
like the other morphological and antigen tests, PCR requires a threshold level of parasites for detection.
If levels are very low, PCR may not be able to detect.
T/F: PCR is useful for determine the species of the parasite detected.
true
what is the purpose of testing for parasites in large animals?
- Test asymptomatic animals – preventative medicine programs, assess drug efficacy, selective tx, genetic selection, monitoring pasture contamination
- identify cause of clinical signs (not often though)
T/F: immunologic and molecular tests for parasite detection are not as widely used in large animals
true
Why are parasite numbers more of interest in large animals as opposed to small animals?
In large animals, you cannot eliminate common parasites. So, we are more interested in the numerical parasite burden to guide treatment and preventative programs.
in small animals, we pretty much treat any parasite regardless of burden #s.
why cant we use egg count to make clinical diagnosis in an animal? (4 reasons)
- the # of eggs/oocysts not necessarily correlated with parasite burden or pathogenicity
- pathogenic stage may not be adult
- species contributing most to count may not be very pathogenic
- there is not much info on what parasite numbers should be
T/F: clinically normal animals can have high coccidia oocyst counts, and patients with diarrhea may precede high oocyst shedding
true
what influences fecal egg counts?
- immunity of animal
- season (hypobiosis)
- fecal consistency (lower #s in diarrhea)
- luck – eggs are not evenly distributed in samples.
_______ are an estimate of the concentration of parasites in feces.
fecal egg/oocyst counts
__________ is the lowest egg count that can be detected with your test.
Limit of detection (LOD)
What LOD should you use if you EXPECT low epg?
LOW LOD
decreasing the LOD increases overall test sensitivity and increase negative predictive value.
_________ is the ability to measure as close to the true count as possible.
accuracy
which improve when you homogenize the sample to distribute the eggs/oocysts.
_____________ is the repeatability and how similar the repeated counts from the same sample are.
How can you improve this parameter?
precision
which improves as the volume of feces examined increases.
Which of the following statements is FALSE about Modified McMaster tests?
A. # parasite eggs/oocysts is mulitplied by factor to give epg
B. quick and inexpensive
C. usually uses LOD 100 epg
D. mixing well and using large samples will improve accuracy and precision of this test
E. only a portion of feces/flotation solution mixture is examined
C. usually uses LOD 100 epg
25 or 50 epg.
Which quantitative test is used in camelids mostly, uses the ENTIRE feces/flotation solution mixture, and does NOT require a multiplication factor because ALL of the eggs in the sample are counted?
Modified Wisconsin
Parasight, a new test technology available for horses, provides counts for which 2 parasites?
- strongylid
- ascarids
If you are trying to detect BIG differences in egg counts, what should your LOD be?
high
For camelids and cryptosporidium detection, which solution should you use?
sheathers sugar solution
T/F: in large animals, you should use the cheapest, most convenient solution for parasite detection
true
for lungworms, which tests should you use in horses vs ruminants vs pigs?
horses and ruminants – baermann test
pigs – fecal float
for fasciola hepatica, what test should you use to detect?
sedimentation test
what are immunologic tests used to detect in large animals?
- protozoan infections
- antibody detection for hemoprotozoa
- EPM diagnosis
- neospora in cattle
- toxoplasma in SR
what is the most common use of PCR in large animals?
to detect tritrichomonas foetus
what are anthelmintic treatment options for ancylostoma caninum?
- Benzamidazoles (fenbendazole, febantel)
- Nicotinic agonist (pyrantel)
- Macrocyclic lactones (milbemycin oxime, moxidectin)
Once you treat a dog for hookworms, when should you perform a follow-up fecal flotation test and why at this particular time period?
12 days later
because before 10 days, females stop making eggs, so if you see eggs before 10 days, then you know for a fact your treatment didnt work, however if you do NOT see eggs before 10 days, you cannot say for sure.
Don’t wait until 2 weeks because larval leak could be occurring and could make you think that your initial treatment isn’t working.
is anthelmintic resistance a problem in dogs?
yes.
MDR in A. caninum
why were greyhounds the breed they found majority of A. caninum resistance in?
- intense deworming for dog races
- unrestricted access to sand or dirty runs
- constant fecal contamination
- in ideal environments for nematode transmission
how can you evaluate if there is anthelmintic resistance? (3 ways)
- FECRT
- in-vitro drug bioassays
- molecular testing
T/F: checking FEC too soon post-treatment can yield false-negative results for resistance.
true
when should you do post-treatment FEC’s for the following drugs:
A. pyrantel
B. fenbendazole/febantel
C. moxidectin
A. pyrantel – 10-14d
B. fenbendazole/ febantel – 14d
C. moxidectin – 14d
< 75% FEC reduction is indicative of …
resistance (larval leak highly unlikely)
75-89% FEC reduction is suggestive of …
resistance (larval leak unlikely)
90-95% FEC reduction is suggestive of…
reduce efficacy, suspicion for resistance, but the results should be viewed as inconclusive (egg shedding can be due to resistance OR larval leak)
> 95% FEC reduction is suggestive of …
effective treatment (larval leak is likely the cause of persistant egg shedding)
What drug combos have shown to be an effective treatment of A. caninum?
- Emodepside + praziquantel (Profender)
- Febantel/pyrantel/praziquantel + moxidectin
- fenbendazole + pyrantel + moxidectin
Diagnosis of resistance should only be established if what 4 things are true?
- pt treated with proper dosage
- drug within exp date
- fecal sample stored correctly prior to fecal test
- standardized FECRT performed
