Parasitology: Laboratory Diagnosis

Question 1

How should a faecal sample be collected?

Answer 1

A feacal sample should be collected and handled properly in a clean, wide-mouthed, waterproof container with a tight fitting lid to ensure and maintain adequate moisture

Question 2

What must a faecal specimen not be contaminated with and why?

Answer 2

• Water
• Soil
• Urine

Question 3

What medication should the patient of the faecal sample not be on and why?

Answer 3

• Barium
• Bismuth
• Medication containing mineral oils
• Antibiotics anti-malarial drugs

Question 4

What corrective measures are in place if the patient is on medication that compromise parasite detection and why?

Answer 4

• Delay specimen collection by 5-10 days

- Delay specimen collection by 2 weeks

Question 5

What should be done with an unpreserved faecal sample?

Answer 5

-Sent to lab 2hrs after passage

Question 6

Discuss the morphology of a stool sample.

Answer 6

• Liquid Stool

- Soft and Loose Stool

Question 7

What are the macroscopic techniques used to examine stool in the diagnostic lab?

Answer 7

• Evaluate Colour
• Evaluate Consistency
• Evaluate Composition
• Check for presence of worms
• Check for presence of proglottids

Question 8

What are the microscopic techniques used to examine stool in the diagnostic lab?

Answer 8

• Permanent Stains
• Wet Mounting
• Concentration Techniques

Question 9

Discuss permanent staining.

Answer 9

• Permanent records
• Stains: Trichrome, Iron hematoxylin, Phosphotungstic Acid hematoxylin stain
• Cryptosporidium: Acid Fast Stain

Question 10

Discuss wet mounting.

Answer 10

• Saline and iodine
• Detects: motile trophozoites, larvae, helminth eggs, protozoan cysts, WBC’s and RBC’s
• Iodine kills trophozoites
• Cytoplasm: yellow or light brown
• Nucleus: Dark brown

Question 11

Discuss the use of concentration techniques when examining stool microscopically.

Answer 11

-Formalin ethyl acetate sedimentation and zinc sulphate floatation and stained with iodine to separate protozoan cysts and helminth eggs and to enhance detection of a small number of organisms

Question 12

What are the most commonly used methods for stool preservation?

Answer 12

• 10% formalin
• PVA
• MIF
• SAF
• Sored at 4°C

Question 13

Discuss parasitic infections of blood and tissue.

Answer 13

• More difficult to detect than intestinal and urogenital parasites
• Microscope exam is done directly
• Wet Prep: microfilariae and trypanosomes
• Thick and thin permanent stained films
• Sputum sample: helminth ova or larvae
• Skin/muscle biopsy: Nematode infection

Question 14

What does the diagnosis of blood and tissue parasites depend on when evaluating a blood film?

Answer 14

• Appropriate collection time of blood samples

- Mistake free microscopic evaluation of prepared and stained thick and thin blood films

Question 15

What is the lab preparation for detecting blood and tissue parasites?

Answer 15

• Prepare 2 blood films (thin & thick)
• Prepare a wet mount
• Stain the blood films: Thin (Cells w/ RBC’s), Thick (RBC’s lysed)

Question 16

What concentration procedures are used to detect light infections?

Answer 16

1. Microhematocrit centrifugation
2. Examination of buffy coat preps
3. Triple centrifugation techniques (trypanosomes)
4. Membrane filtration technique (microfilariae)

Question 17

The optimal collection time varies from organism to organism. What is the optimal collection time for the detection of Malaria?

Answer 17

Malaria

• Acutely life threatening
• Collection and Examination: Immediately
• Repeated at: 6, 12, 24 hours after 1st collection

Question 18

What must blood films be stained with?

Answer 18

• Giemsa Stain: Protozoa (malaria and trypanosomes)

- Hematoxylin-based Stain: Microfilariae