Lab 5 Malaria Investigations Flashcards
What are the different malaria species?
- Plasmodium falciparum (most common & deadly)
- Plasmodium vivax (most common)
- Plasmodium malariae
- Plasmodium ovale
- Plasmodium knowlesi
4 parts of diagnosing malaria
- FBC
Shows eosinophilia, thrombocytopenia - RDT
To determine presence + species of parasite. - Examine thick blood film
Useful for low grade parasitaemia. - Examine thin blood film
- Used to report % parasitaemia.
Acceptance criteria for malaria blood sample
Sample history needed
Needs to be <2hrs old.
Thick blood film function + stain
Stained with fields stain and used to establish if malaria is present or not.
Thin blood film function + stain
Stained with Giemsa at pH 7.2
Used to conduct % parasitaemia count.
Plasmodium falciparum identifiable features
Only species where more than one parasite in a RBC can occur.
1. RBC is not enlarged and contains maurers clefts (uneven distribution of dots)
2. Parasite is neat and does not fill cell.
3. 18-20 merozoites per RBC.
4. Crescent-shaped gametocytes.
5. Smaller ring forms - multiple in one rbc - may look like headphones.
Plasmodium vivax identifiable features
- RBC is enlarged (likes to infect retics)
- RBC contains Schuffners dots (even distribution of dots).
- Parasite is untidy and fills cells.
- 18-20 merozoites per rbc.
- Large rings with heavy chromatin dots.
- Gametocyte fills entire cell.
Plasmodium Ovale identifiable features
RBC -> enlarged and James dots (even distribution of dots).
Parasite -> neat and does not fill cell.
8-10 merozoites.
Plasmodium Malariae identifiable features
RBCs-> not enlarged (liked old RBCs) and no dots.
Parasite -> untidy and fills cells.
8-10 merozoites.
P.knowlesi identifiable features.
RBC -> not enlarged and light stippling.
Parasite -> neat and fills cell
18-20 merozoites.
Counting % parasitaemia
Need to count at least 115 RBCs x9 = 1000 in total.
Formula:
#RBCs with parasite inside big square /
(#RBCs with no parasite in small square x9)
x100 = %parasitaemia.
Preparing a thick blood film
1.Drop of blood on microscope slide and spread in a circular motion to an area of approx. 1cm3. - should just be able to read small print through film.
2. Let air dry and do NOT fix in methanol.
3. Stain in Field’s stain
4. Examine.
Preparing a thin blood film
- Allow to airdry
- Fix in methanol for 1min and rinse in tap water.
- Stain in Giemsa stain (pH7.2) for 45-60mins.
What is RDT?
Rapid Diagnostic Test
What are the two RDTs for malaria?
BinaxNOW Malaria
Onsite Malaria Pf
BinaxNOW Malaria RDT 2 positive lines indicates
P. falciparum or mixed population
BinaxNOW Malaria RDT 1 positive T1 line (HRPII) indicates
P.falciparum
BinaxNOW Malaria RDT positive T2 (LDH) indicates
any of the 4 plasmodium species except p.knowlesi.
Calculating sensitivity of RDT test
refers to the ability of the test to determine the patient cases correctly.
Sensitivity = TP / (TP+FN)
Calculating specificity of RDT test
refers to the ability of the test to determine the healthy cases correctly.
Specificity = TN / (TN+ FP)
Why is it important to validate sensitivity and specificity of RDT?
- Ensure accurate diagnosis.
High sensitivity ensures the test correctly detects malaria when it is present (avoid false negatives)
High specificity ensures the test does not falsely diagnose malaria in uninfected individuals (avoid false positives).
Important because=
False negatives can lead to untreated malaria.
False positive can lead to unnecessary antimalarial treatment increasing drug resistance risks. - Ensure detection of low parasitaemia + mixed infections
