Principles of parasite identification

What is parasitological diagnosis?

based on morphological characteristics of the parasite

can be specific in some cases

What is immunological diagnosis?

based on presence of antibodies or antigen

antibody is less specific; long lasting so do not indicate active infection by rather exposure

antigen tends to be more specific and indicates active infection

What is molecular diagnosis?

based on PCR

very specific

What are the principles of diagnosis?

ideally test should be sensitive

should be specific

should be reliable

clinical history can be very important

How are gastro-intestinal worms diagnosed?

by detection of eggs in stool

How do you concentrate the eggs?

in a salt concentration so the eggs float to the top

Can you tell the difference between species with strongyle eggs?

no- they all look the same

What does the quantitative method do?

allow counting of eggs per gram of feces

Why would you culture nematode larvae from fecal samples?

if eggs of two species are identical

ie canine hookworms

Which stage of dog lungworm can be detected in feces?

L1

What does a toxocara canis/cati egg look like?

rough pitted egg shell

What does a toxascaris leonina egg look like?

smooth egg shell

What do you use for antigen detection? What do you use for DNA detection?

antigen detection- ELISA test

DNA detection- PCR

Which species is detecting helminth parasites in the blood useful for?

microfilariae of dirofilaria species

Why is antigen detection in blood useful?

indicates current infection

best example is dog heartworm dirofilaria immitis

Why is antigen test alone not useful for heartworm infected cats?

antigen test only detects sexually mature female worms

cats often have few worms and often sexually immature

Why is it not the best to test for L1 in feces?

they are shed intermittently so you might have to collect samples over several days

What are the feco-oral transmission/GI of host parasites?

toxoplasma gondii

giardia spp

cryptosporidium parvum

What are the vetcor-borne protozoa?

babesia

leishmania

How do you diagnose toxoplasmosis (ovine)?

bright red placenta cotyledons

Ab in fetal fluids/precolostral lamb serum

ewe: antibody tests with paired samples or IgM detection

immunohistochemical/PCR detection of parasite in aborted tissue

How do you diagnose T. gondii (humans)?

pregnant mother: serology

congenital infection: prenatal- PCR of amniotic fluid/ultrasound

immuno-compromised (AIDS): PCR on blood, cerebrospinal fluid, brain scans

How can toxoplasmosis in cats be detected?

transient detection of oocysts in feces

can be detected serologically

hematology/biochemistry- alpha-1 glycoprotein

PCR/cytology of CSF or other samples

Why is cryptosporidium oocytes difficult to detect in unstained fecal samples?

small size

What type of stain improves detection of cryptosporidium?

ziehl-nieslen

What are alternative methods of diagnosis for cryptosporidium?

immunofluorescent antibody test

antigens in the feces can be detected by enzyme immunoassays

cryptosporidium PCR based assays

Where would you find the infective stage of vector-borne protozoa?

in the blood

What protozoan infections are blood smears used for?

trypanosomes, leishmania, theileria, babesia

What are more specific and more sensitive methods of diagnosis for blood-borne protozoa?

immunofluorescence

elisa

pcr

What are positives of PCR-based diagnosis?

very specific

very sensitive

can differentiate mixed infections

What are negatives of PCR-based diagnosis?

not that rapid/lab based

easy to contaminate, so need controls for false positives

for quantification need sophisticated thermal cycler

What are factors to consider for PCR assay?

source of material

selection of DNA target region for optimal amplification

ideally should by species-specific by show no/little variation within a species