Week 1 Lecture 1 - Malaria Flashcards
Life Cycle Stages of Malaria in Humans
Shizont
Trophozoite
Gametocyte
Malaria - Clinical
Mild-asymptomatic
Acute self-limiting febrile, myalgia, nausea, vomiting, diarrhoea
Severe, life-threatening
Poor prognosis
- severe anaemia, respiratory distress, cerebral malaria, jaundice, renal failure, shock etc.
Haematological Changes due to Malaria
Anaemia
- sequestration of parasitised RBC within bone marrow
- maturation defects
- dyserythropoiesis (P. vivax)
- destruction of parasitised RBC at merogony
- enhanced splenic clearance of infected RBC
Thrombocytopenia
- common P. vivax, P. falciparum
- decreased platelet survival (2-4 days)
- enhanced splenic clearance, destruction/sequestration
Leukopenia
- mild in uncomplicated cases
Leukocytosis
- associated with severe P. falciparum malaria
Laboratory Diagnosis of Malaria
Thrombocytopenia (<120 x 10^9/L)
Leukopenia (<4.0 x 10^9/L)
Demonstration of parasites in blood film:
- thin film (x3 for screening)
- thick film (x2 for conformation)
Thick Film Preparation
Place a drop of blood onto microscope slide & spread the drop until it is about 1-2 cm2
Adjust thickness so that its just possible to see through it
Allow the films to dry
DO NOT fix thick films
Stain:
- prepare a 10% solution of Giemsa stain in phosphate buffer pH 7.2
- filter into a coplin jar
- stain slides for 20 min
- allow to air dry
Thin Film Preparation
Thin films are made in the standard manner:
- air dry
- fix
- stain with May-Grünwald & Giemsa (or equivalent
Romanowsky stain)
pH of the stain:
- slightly alkaline stain is recommended (pH 7.2)
- staining in an acid (pH < 6.8) may fail to show parasites
Thick Film vs Thin Film
Thick
- more likely to detect Plasmodium organisms
- organisms distorted so more difficult to determine species
Thin
- allows better assessment of morphology of parasites
- allows speciation
- low density infections may be difficult to detect organisms
Parasitaemia
No. parasites 100-10^6 per uL of blood
Combined circulating RBC & sequestered RBC
Parasitaemia determined as no. parasitised RBC per 1000 RBC
Can be used to follow course of disease/response to treatment
4 Most Common Species of Malaria
Plasmodium falciparum
Plasmodium vivax
Plasmodium ovale
Plasmodium malariae
In Australia: P. vivax > P. falciparum > P. ovale and P.malariae
Malaria Species Characteristics - RBC Enlargement
Plasmodium vivax - yes
Plasmodium falciparum - none
Plasmodium ovale - yes
Plasmodium malariae - none
Malaria Species Characteristics - Trophozoite
Plasmodium vivax
- size > 1/3 of RBC
- multiple parasites rare
- rough shape; single chromatin dot
Plasmodium falciparum
- size <1/3 of RBC
- multiple parasites common
- delicate shape; often double chromatin dot
Plasmodium ovale
- size >1/3 of RBC
- multiple parasites rare
- rough shape; single chromatin dot
Plasmodium malariae
- size >1/3 of RBC
- multiple parasite rare
- compact shape; inverted chromatin dot
Malaria Species Characteristics - Schizont
Plasmodium vivax
- frequency common
- random configuration
- no. of merozoites is 12-24
Plasmodium falciparum
- frequency very rare
- random configuration
- no. of merozoites is 8-24
Plasmodium ovale and Plasmodium malariae
- frequency common
- daisy-head configuration
- no. of merozoites is 8-12
Schuffner’s Dots
Visible in Romanowsky-stained blood smears as multiple brick-red dots
Presence of Schuffner’s Dots in Malaria species:
- Plasmodium vivax: yes, fine
- Plasmodium falciparum: no
- Plasmodium ovale: yes, large
- Plasmodium malariae: no
Plasmodium vivax
Most commonly seen Plasmodium species in Australia
Usually not life threatening
Invades reticulocytes
~48 hour cycle
Diagnostic points:
- infected red cells are typically enlarged
- ring forms usually large ~ 1/3 size of red cell
Usually responds well to treatment
Plasmodium falciparum
Invades reticulocytes & mature RBCs
~48 hour cycle
Typically greater parasitaemia than other Plasmodium species
Most pathogenic
- cerebral sequestration
- sequestration other organs
- life threatening => multiple organ failure, death
- children most vulnerable
Diagnostic points
- RBC typically not enlarged
- small, fine ring forms
- occasional gametocytes recognised
Treatment often difficult due to drug resistance
Plasmodium Ovale
RBC enlarged
~48 hour cycle
Typically not life-threatening
Diagnostic Points
- red cells enlarged
- comet forms common (top right)
- rings large and coarse
- Schuffner’s dots, when present, may be prominent
- mature schizonts similar to those of P. malariae but larger and more coarse
Plasmodium Malariae
RBC not enlarged
~72 hour cycle
Typically not life-threatening
Diagnostic Points
- ring forms may have a squarish appearance
- band forms are a characteristic of this species
- red cells are not enlarged
- chromatin dot may be on the inner surface of the ring
Plasmodium knowlesi
Definitive host: macaque monkeys => Zoonotic
Present throughout SE Asia
Causes severe disease in humans
Lifecycle of 24h
Infects young & mature RBC
