Menacing Microbiology Science Club Meeting 3 – parasite diagnostic lab
Your task:
You are working in a tropical disease diagnostic laboratory and have been asked to analyse a
blood sample. Blood has been taken from a patient, smeared on a glass microscope slide and
allowed to dry. The patient has recently returned from Uganda in Africa, where she was
carrying out some voluntary work in remote areas, and went to see her GP complaining of
headaches, fevers and generally feeling unwell. Since she visited areas where several
parasitic infections were common, her GP sent her to the tropical diseases unit hospital so
that blood smears could be made to allow any parasitic infection she might have to be
diagnosed.
You should familiarise yourself with control stained slides of Plasmodium (causative agent of
malaria), Leishmania (Leishmaniasis), Trypanosoma brucei (sleeping sickness), which live in the
blood. We also have stained slides ofToxoplasma (toxoplasmosis), which lives in the muscles
and brain for you to have a look at. You should stain the patient’s blood smear with Giemsa
and examine it under the microscope to determine whether the blood is infected with
Plasmodium, Leishmania or T. brucei.
Step 1: staining parasites with Giemsa
Protocol
1. Put on gloves, lab coat and safety goggles
2. Place blood smear slide on staining rack over sink
3. Flood slide with methanol for 30 s
4. Pour off methanol down the sink
5. Flood the slide with Giemsa stain
6. Leave for 15 mins, checking back every so often to make sure the slide does not dry
out (add more stain if necessary). While your slide is staining, take a look at the prestained slides of Plasmodium, Leishmania, T. brucei & Toxoplasma so that you know
what they look like down the microscope.
7. Pour off the Giemsa down the sink and gently wash slide in tap water
8. Leave slide to air dry vertically
9. Examine under the microscope
10. Record your results and answer the questions below.
Step 2: diagnosing the infection
Background
Giemsa stain is named after Gustav Giemsa (1867-1948), a chemist and bacteriologist who
developed the stain to detect malaria parasites. It is also used to stain other parasites
such as trypanosomes and Leishmania. Red blood cells stain pink with Giemsa, while white
blood cells and parasites stain purple.
Results
Using the microscopes and the laminated sheets, fill in this table for the control pre-stained
parasites. You may like to draw the parasites you see.
Parasite
What cell type does it
live inside or does it
live extracellularly?
What shape is it?
How big is the
parasite compared to
the red or white blood
cells?
Plasmodium
Leishmania
T. brucei
Toxoplasma
Now make a labelled sketch of your patient’s blood smear. Can you see any parasites? Based
on your analysis of the parasites above, what do you think your patient might be infected
with?
Sketch:
Now compare your observations of the parasites with those of the bacteria you analysed last
time. Which organisms are bigger – parasites or bacteria?