Parasitology 3 - Parasitic Protozoans (Michael)

Question 1

Describe the Plasmodium spp. lifecycle

Answer 1

• Human infection begins with a bite from an infected female Anopheles mosquito which injects saliva infected with sporozoites into the bloodstream.
• Sporozoites travel to the liver where they enter cells and divide to produce schizonts.
• The schizonts give birth to many merozoites which are released into the bloodstream.
• The merozoites are directed towards red blood cells which they invade and evolve into trophozoites.
• The trophozoites give birth to a new generation of merozoites so that after the RBCs rupture they are released into the bloodstream in order to invade other RBCs.

Question 2

Outline the symptoms and current global status of malaria

Answer 2

• Approximately 300 million people infected worldwide.
• Each year approximately 1/2 million people die from malaria.
• Young children, pregnant women, and non-immune travellers from malaria-free areas are particularly vulnerable when infected.
• Infected pregnant women are at risk of spontaneous abortion, premature delivery, stillbirth, and severe maternal anaemia.
• Most affected regions are South American and African countries.
• Symptoms include:
  Headache
  Fever
  Chills and sweating
  Muscular pain and fatigue
  Nausea and vomiting

Question 3

Describe the main diagnostic techniques for protozoan parasite infections

Answer 3

Preparing blood smears for parasite diagnosis:

• Thin film: Bring a clean spreader slide, held at a 45 degree angle, toward the drop of blood on the specimen slide. Wait until the blood spreads along the entire width of the spreader slide. While holding the spreader slide at the same angle, push it forward rapidly and smoothly.
• Thick film: Using the corner of a clean slide, spread the drop of blood in a circle (diameter 1-2 cm). Do not make the smear too thick or it will fall of the slide.
• Wait until the films are completely dry before staining.
• Fix the thin film with methanol and let it dry completely before staining.
• The thick film should not be fixed.
• Malaria is diagnosed microscopically using Giemsa stain which stains the DNA of the parasite.

Question 4

Identify Plasmodium, Leishmania, Trypanosoma, Entamoeba, and Giardia spp. From light micrographs

Answer 4

See practical handbook

Question 5

Name the viruses and vectors responsible for cutaneous and visceral leishmaniasis, Chagas’ disease, and trypanosomiasis

Answer 5

Cutaneous leishmaniasis

• Parasite = Leishmania tropica or L. mexicana
• Vector = sandfly

Visceral leishmaniasis

• Parasite = Leishmania donovani
• Vector = sandfly

Chagas’ disease

• Parasite = Trypanosoma cruzi
• Vector = triatomine bug

Trypanosomiasis

• Parasite = Trypanosoma brucei
• Vector = tsetse fly

Question 6

Name the parasite responsible for amebic dysentery

Answer 6

Entamoeba histolytica

Question 7

Name the parasite that is responsible for giardiasis

Answer 7

Giardia intestinalis