04-15 Parasitology Lab

Question 1

Answer 1

Schistosoma mansoni [Pronounce: Schist-o-Soma] egg: Look for the large lateral spine.

Question 2

Answer 2

Enterobius vermicularis [Pronounce: enn- tuh-ROW-bee-us]: In fresh scotch-tape preparation you find eggs that contain a larval worm.

Concentrate on the characteristics of the eggshell, thick and flattened on one side.

Question 3

Answer 3

This is a Giardia lamblia cyst [Pronounce: JAR-dee-uh]

• Giardia are small pear-shaped organisms with a pair of nuclei (the eyes of the smiling face) on the wider end.
• It may be possible under 100X to observe the flagellae, of which there are four pairs.

Question 4

Who dis?

Answer 4

Strongyloides stercoralis: Remember that the diagnostic stage is a larval worm (not an egg). Beware of the worm-like fecal artefacts. Look for a pointy tail and a gut.

Question 5

Answer 5

This is a Giardia lamblia trophozoite [Pronounce: JAR-dee-uh]

• Giardia are small pear-shaped organisms with a pair of nuclei (the eyes of the smiling face) on the wider end.
• It may be possible under 100X to observe the flagellae, of which there are four pairs.

Question 6

Answer 6

Plasmodium falciparum

• You should see ring stage parasites but very few or no later stages of infection.
  
  • Infected cells with these later stages are “sticky” and thus often not found in the peripheral blood.
• Banana-shaped gametocytes (unique to P. falciparum).
  
  • Gametocytes are rarely seen early in infection.

Question 7

Answer 7

Plasmodium vivax: You should see some rings, but mostly later stages of infection (post-cytoplasm-synthesis or post- nuclear replication).

• Later stages of infection have reddish Schüffner’s dots on the RBC membrane. These are most apparent at the periph of the RBC when they do not overlie the intracellular parasites.
• Note the infected RBC’s are generally larger than the average RBC’s in the smear because they prefer reticulocytes.

Question 8

Answer 8

Plasmodium malariae

• The infected cells will be small (prefer old RBC).
• A few of the parasites will be in band forms.
• Many later stages will have brown malarial pigment.

Question 9

Simple Minded Flow Sheet for Reading Malaria Thin Films

Answer 9

1. Can you see intra-erythrocytic organisms with red or purple nuclei and blue cytoplasm? If the answer is NO, the thin film is negative. (All of the slides in this laboratory are positive. But in the real world, the patient may have a low parasitemia that you could see only by examining a thick film or may not have malaria.) Since the answer is YES for all slides in this laboratory, go on to questions 2 and 3.
2. Are nearly all parasites in the ring stage? If the answer is YES, suspect Plasmodium falciparum. To confirm suspicion, ask the additional questions below, under Plasmodium falciparum. (In the real world, you should also consider babesiosis. The patient’s history may help.)
3. Are malaria parasites that have completed cytoplasm synthesis or nuclear replication common? If the answer is YES, suspect Plasmodium vivax, or Plasmodium malariae [or Plasmodium ovale in the real world]. To decide between vivax and malariae, answer the additional questions below, looking first for Schüffner’s dots as described under Plasmodium vivax, above.

ADDITIONAL QUESTIONS

Plasmodium vivax: Are Schüffner’s dots seen in some infected cells? Are most infected cells relatively large (reticulocytes)?

Plasmodium malariae: Are most infected cells relatively small (old RBC)? Is (brown) malarial pigment prominent? Are band forms found?

Plasmodium falciparum: Do some RBC have multiple rings? Are banana-shaped gametocytes found?