C4. Malaria Life Cycle and Diagnosis

Question 1

What is a morphological diagnosis ?

Answer 1

Diagnosis of parasites in blood films using light microscopy.

Used to identify shapes and features of microorganisms

Question 2

What type of blood films do morphological diagnosis use ?

Answer 2

Mainly thin blood films

Question 3

Do morphological diagnosis require trained personnel ?

Answer 3

Yes

Question 4

How does rapid diagnosis tests work (RDTs) ?

Answer 4

Detection of antigen in blood samples

Question 5

Are microscopes required for RDTs ?

Answer 5

No

Question 6

Is a trained personal required for RDTs ?

Answer 6

No, less training than microscopes

Question 7

What are the limitations of RDTs ?

Answer 7

False negative: May not detect light infection (false negatives).

False positive: Antigens may be present after infection (false positive)..

Question 8

What does serodiagnosis detect ?

Answer 8

Detection of ani-material antibodies (antibodies our own immune system produces)

Question 9

Is a trained personnel required for serodiagnosis ?

Answer 9

Yes, and also requires equipment

Question 10

What does polymerase chain reactions detect (PCR) ?

Answer 10

Detection of parasite DNA ( sensitive and specific, but expensive for point of care site)

Question 11

What are the limitations to PCR ?

Answer 11

• Requires specialised equipment, lab and trained personnel

- Parasite DNA can persistent in blood after cure for up to a month

Question 12

In thin blood film of morphological diagnosis are RBCs lysed ?

Answer 12

No they’re not lysed as they are spread over a large surface

Question 13

What is the benefit of having RBCs that are not lysed ?

Answer 13

Allows determination of size/shape and other characteristic features in infected cells

Question 14

What is a limitation go thin blood films in morphological diagnosis ?

Answer 14

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

Question 15

What is a thick blood film ?

Answer 15

More blood spread on a smaller surface

Question 16

How much high is the sensitivity of thick blood film compared to thin blood films

Answer 16

20 fold since there are more cells on the slides

Question 17

What are the limitations to thick blood films ?

Answer 17

RBC are lysed therefore their shape and size cannot be observed

Question 18

Compare thin and thick blood films.

Answer 18

Thin: provides sensitivity
Thick: provides specificity

Question 19

At what region should examination of thin slides be examined ?

Answer 19

Middle region where mono layer of RBCs are. This gives good density, staining and morphology

Question 20

What stages are detected on a blood film of P.falciparum ?

Answer 20

Trophozoites: ring stage

Rare to see gametoocytes

Question 21

Why is it rare to see gametocytes on blood film of P.falciparum ?

Answer 21

Due to removal/separation of later developmental stages by the blood vessel (attachment of endothelium) which is not seen in other plasmodium species

Question 22

Besides the ring stage (trophozoites) are other stages detectable ?

Answer 22

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.

Question 23

What is the consequences of delayed preparation of blood films ?

Answer 23

Can result in changes in parasite morphology and their staining characteristics. This can lead to misidentification of the species and are to be avoided

Question 24

Describe the appearance of ring form trophozoites of P.falciparum

Answer 24

• 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

Question 25

When do trophozoites (ring-form) develop ? P.falciparum

Answer 25

Early development stage (0-14 hours after RBC infection

Question 26

Describe the appearance of the trophozoites between 24-36 hrs (P.falciparum)

Answer 26

Ring shape and looks thicker

Some traces of yelllow pigment

Question 27

At what time do shizonts develop ?

Answer 27

36/48hrs (late development)

Question 28

Describe the appearance of shizonts

Answer 28

Dark pigment

Contains 8-24 small merozoites

Rarely seen in the peripheral blood (hence rare to see on blood films)

Question 29

Describe the appearance of gametocytes (P.falciparum)

Answer 29

Crescent or sausage shaped

Contains RBC and surrounded by its membrane (but distorted)

Both male and female gametocytes are produced

Undergo exflagellation

Question 30

Describe the appearance of trophazoites (ring-form) in p.vivax

Answer 30

• large chromatine for and amoeboid in shape
• RBC are enlarged and distorted
• Wrapped around non-infected RBCs
• can contain scruffier dots
• Band-form

Question 31

How many merozoits do mature shizonts contain ?

Answer 31

12-24 can count under the microphone

Question 32

Describe the appearance of schizonts

Answer 32

• 12-24 merozoites
• infected seem larger
• pigment is usually organised in one or two clumps

Question 33

Describe the appearance of trophozoites in p.malaria

Answer 33

Single large chromatin dots (rarley two dots observed)

Tick cytoplasm ring

No RBC enlargement

Infected RBC are normal size or smaller

Question 34

Describe the appearance of p.malariae schizonts

Answer 34

Large visible yellow-brown chromatin in centre

Merozoites organised in rosette pattern around the centre usually around 8-10 (daisy head)

Question 35

Describe the appearance of p.ovale trophozoites

Answer 35

Large chromatine dot, usually single

James dots

Frequently oval shaped

Infected RBC not usually enlarged

Question 36

Describe the appearance of schizonts in p.ovale

Answer 36

4-16 merozoites

Elongation to an oval shape and fimbration are common