Diagnostic Techniques

Question 1

What is a perfect gold standard of diagnosis?

Answer 1

test is 100% specific and sensitive

Question 2

Is the perfect gold standard of diagnosis often achieved?

Answer 2

no

Question 3

What is a gold standard?

Answer 3

best available test: sensitivity & specificity are well defined but less than gold standard

Question 4

What steps are involved in a direct wet smear?

Answer 4

1. ~2mg feces w/ saline are put on a slide 2. observe under microscope

Question 5

Why is a direct wet smear not the preferred method of fecal sampling?

Answer 5

false negatives bc # of eggs in feces is too low

Question 6

Describe the formalin-ethyl acetate sedimentation concentration method.

Answer 6

1. mix 4g of feces with formalin 2. strain through gauze 3. mix with saline 4. centrifuge & discard supernatant 5. add more fomalin & ethyl acetate 6. centrifuge & discard supernatant 7. sediment - bottom layer with parasite eggs 8. put small amounts on slide and look under microscope

Question 7

How are urine samples tested for parasites?

Answer 7

sample is collected in clean container -> centrifuge -> examine sediment

Question 8

How would a blood test be done?

Answer 8

sample -> smear -> look under microscope

Question 9

In which class is Toxocara canis classified?

Answer 9

Chromadorea

Question 10

What is the normal DH of Toxocara canis?

Answer 10

dog

Question 11

How do dogs become infected by Toxocara canis?

Answer 11

1. ingest eggs 2. if pregnant dog becomes infected then larva crosses fetus 3. if lactating dog becomes infected -> transmammary 4. ingest prey with larvae

Question 12

How does a human become an accidental host in Toxocara canis?

Answer 12

ingests eggs

Question 13

What are visceral larva migrans and ocular larve migrans?

Answer 13

visceral larva migrans - larva that migrate through tissues & do not complete development (developmental arrest) just extended random wandering through body vs. ocular larva migrans - inflammation, scarring, blindness

Question 14

What are the symptoms of Toxocara canis infection?

Answer 14

fever, cough, abdominal pain, vision problems

Question 15

How can an infect be diagnosed and treated?

Answer 15

diagnosed by ELISA & treated by mebendazole and albendazole

Question 16

What is an ELISA?

Answer 16

enzyme linked immunosorbant assay

Question 17

Draw and describe the steps involved in this method.

Answer 17

1. serum from patient 2. wash 3. add antibody and enzyme 4. wash 5. add enzyme substrate 6. color change = enzymatic rxn = infection

Question 18

Why are the wash steps necessary?

Answer 18

to remove any unbound enzyme

Question 19

What does it mean if there is a color change in the well?

Answer 19

infection is present

Question 20

For what types of parasite infections is this diagnostic technique useful?

Answer 20

infection where antibody is produced against parasite antigen