C4. Malaria Life Cycle and Diagnosis Flashcards
What is a morphological diagnosis ?
Diagnosis of parasites in blood films using light microscopy.
Used to identify shapes and features of microorganisms
What type of blood films do morphological diagnosis use ?
Mainly thin blood films
Do morphological diagnosis require trained personnel ?
Yes
How does rapid diagnosis tests work (RDTs) ?
Detection of antigen in blood samples
Are microscopes required for RDTs ?
No
Is a trained personal required for RDTs ?
No, less training than microscopes
What are the limitations of RDTs ?
False negative: May not detect light infection (false negatives).
False positive: Antigens may be present after infection (false positive)..
What does serodiagnosis detect ?
Detection of ani-material antibodies (antibodies our own immune system produces)
Is a trained personnel required for serodiagnosis ?
Yes, and also requires equipment
What does polymerase chain reactions detect (PCR) ?
Detection of parasite DNA ( sensitive and specific, but expensive for point of care site)
What are the limitations to PCR ?
- Requires specialised equipment, lab and trained personnel
- Parasite DNA can persistent in blood after cure for up to a month
In thin blood film of morphological diagnosis are RBCs lysed ?
No they’re not lysed as they are spread over a large surface
What is the benefit of having RBCs that are not lysed ?
Allows determination of size/shape and other characteristic features in infected cells
What is a limitation go thin blood films in morphological diagnosis ?
Reduced sensitivity (especially to detect light infection.
Due to small amount of blood spread thinly therefore wont be able to see all the cells
This leads to reduced sensitivity due to the inability to scream meany cells
What is a thick blood film ?
More blood spread on a smaller surface
How much high is the sensitivity of thick blood film compared to thin blood films
20 fold since there are more cells on the slides
What are the limitations to thick blood films ?
RBC are lysed therefore their shape and size cannot be observed
Compare thin and thick blood films.
Thin: provides sensitivity
Thick: provides specificity
At what region should examination of thin slides be examined ?
Middle region where mono layer of RBCs are. This gives good density, staining and morphology
What stages are detected on a blood film of P.falciparum ?
Trophozoites: ring stage
Rare to see gametoocytes
Why is it rare to see gametocytes on blood film of P.falciparum ?
Due to removal/separation of later developmental stages by the blood vessel (attachment of endothelium) which is not seen in other plasmodium species
Besides the ring stage (trophozoites) are other stages detectable ?
Yes, if blood film is left too sit for several hours before processing as cells are still alive and parasites are still able to grow.
What is the consequences of delayed preparation of blood films ?
Can result in changes in parasite morphology and their staining characteristics. This can lead to misidentification of the species and are to be avoided
Describe the appearance of ring form trophozoites of P.falciparum
- Ring-form are often thin and delicate 1/5 diameter of the RBC
- Ring may posses one or two chromatin dots and may be found on the periphery of the RBC
- Usually no enlargement of RBC
When do trophozoites (ring-form) develop ? P.falciparum
Early development stage (0-14 hours after RBC infection
Describe the appearance of the trophozoites between 24-36 hrs (P.falciparum)
Ring shape and looks thicker
Some traces of yelllow pigment
At what time do shizonts develop ?
36/48hrs (late development)
Describe the appearance of shizonts
Dark pigment
Contains 8-24 small merozoites
Rarely seen in the peripheral blood (hence rare to see on blood films)
Describe the appearance of gametocytes (P.falciparum)
Crescent or sausage shaped
Contains RBC and surrounded by its membrane (but distorted)
Both male and female gametocytes are produced
Undergo exflagellation
Describe the appearance of trophazoites (ring-form) in p.vivax
- large chromatine for and amoeboid in shape
- RBC are enlarged and distorted
- Wrapped around non-infected RBCs
- can contain scruffier dots
- Band-form
How many merozoits do mature shizonts contain ?
12-24 can count under the microphone
Describe the appearance of schizonts
- 12-24 merozoites
- infected seem larger
- pigment is usually organised in one or two clumps
Describe the appearance of trophozoites in p.malaria
Single large chromatin dots (rarley two dots observed)
Tick cytoplasm ring
No RBC enlargement
Infected RBC are normal size or smaller
Describe the appearance of p.malariae schizonts
Large visible yellow-brown chromatin in centre
Merozoites organised in rosette pattern around the centre usually around 8-10 (daisy head)
Describe the appearance of p.ovale trophozoites
Large chromatine dot, usually single
James dots
Frequently oval shaped
Infected RBC not usually enlarged
Describe the appearance of schizonts in p.ovale
4-16 merozoites
Elongation to an oval shape and fimbration are common
