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2.2 Haematology > Practical 5: Malaria Investigations > Flashcards

Practical 5: Malaria Investigations Flashcards

1
Q

What five species of parasite cause malaria in humans

A

Plasmodium falciparum

Plasmodium vivax

Plasmodium malariae

Plasmodium ovale

Plasmodium knowlesi

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2
Q

What species of parasite cause malaria most commonly

A

Plasmodium falciparum

Plasmodium vivax

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3
Q

What parasite causes the most deadly form of malaria

A

Plasmodium falciparum

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4
Q

What is malaria

A

A mosquito-borne haemolytic febrile illness caused by Plasmodium parasites

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5
Q

What mosquito transmits malaria

A

Anopheles mosquitoes

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6
Q

When can you detect parasite specific antigens

A

They are detectable near the end of the incubation period during primary infection

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7
Q

When can you detect parasite antibodies

A

Near the end of the primary infection

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8
Q

What response is seen if you become reinfected with malaria

A

Reinfection leads to a secondary response with a high and rapid rise in antibody levels

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9
Q

What does a case of malaria often present with in the lab

A

Often the patient presents with a high fever

But there is usually no remarkable features on blood film bar sometimes a thrombocytopenia

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10
Q

What are the three parts to the diagnosis of a parasite

A

Use of a rapid diagnostic test to determine the presence and species of the parasite

Examination of a thick blood film stained with fields stain

Examination of a thin blood film stained with Giemsa stain

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11
Q

Write a note on the thick blood film
(3)

A

Stained with fields stain

Used to detect the presence of the parasite

Useful in low grade parasitaemias

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12
Q

Write a note on the thin blood film

A

Stained with Giemsa stain at pH 7.2

Used to determine % parasitaemia count

Used to determine species of parasite

Used to note the different stages of development seen

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13
Q

Why might you have a negative antigen test in a malaria case

A

Malaria might still be incubating in the liver

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14
Q

What can you determine if there is more than one parasite per cell?

A

It is plasmodium falciparum

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15
Q

What are the five identifiable stages of malaria in a blood film

A

Ring forms

Early schizont

Schizont

Merozoites

Gametocyte

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16
Q

What stage is a ring form

A

An early trophozoite

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17
Q

What stage is a schizont

A

Late trophozoite

18
Q

Why is malaria common in spelectomized patients

A

Malaria is not phagocytosed by macrophages as they are removed in the splenectomy

19
Q

Why is the percentage parasitaemia important?

A

It has implications for prognosis and the pattern of treatment that will be employed

20
Q

How is a percentage parasitaemia determined?

A

Count the number of infected cells as a percentage of the red blood cells (1000 cells)

21
Q

What is an alternative way of determining % parasitaemia?

A

First count the number of parasites per 200 wbcs in a thick film

Calculate the total parasite count/uL from the total white blood cell count/ul

22
Q

Why would you still have a positive antigen test even after being treated for malaria

A

Might have not cleared the infection completely i.e. might have dead parasites still left in your system

23
Q

How do you make a thin film
(6)

A

Make a blood film

Fix in methanol for 1 min

Rinse in tap water

Place in Giemsa stain for 45 to 60 mins

Dip 3-4 times in Giemsa buffer

Dry

24
Q

How do you use your thin film to determine % parasitaemia

A

Use the Miller square to count:

  • the number of parasite cells inside the big square
  • the number of non-infected rbcs in the small square

(infected cells/ (non-infected x 9)) x 100

25
Q

How do you make a thick slide
(8)

A

Place a drop of blood on a slide and spread in a circular motion using a capillary tube

Air dry completely (horizontally)

Dip into Field’s stain A for 3 seconds

Dip into water for 3 seconds (agitate gently)

Dip into Field’s stain B for 3 seconds

Wash gently

Dry (vertically)

Investigate

26
Q

How do you know youve made your thick slide correctly

A

You should be just able to read small print through the thick film

27
Q

How do you use the BinaxNOW Malaria RDT
(4)

A

Apply 15ul of blood to the pruple pad

Apply 2 drops of reagent to white pad immediately after

Apply 4 drops of reagent to pad found at the top of the left-hand side of the test card after the blood runs up the full length of the test strip

When the blood sample reaches the base of the white absorbant pad at the top of the test strip, close the device and read the results

28
Q

What is a positive plasmodium falciparum BinaxNOW Malaria RDT?

A

top and middle line

29
Q

What is a positive BinaxNOW Malaria RDT for species other than p.f.?

A

Top and bottom line

30
Q

What is a mixed BinaxNOW Malaria RDT

A

All three lines

31
Q

What is a negative BinaxNOW Malaria RDT

A

Just the top control line

32
Q

How do you use the Onsite Malaria test

A

Add 5ul of blood to the S well

Add 2 drops of blood lysis buffer to B well

33
Q

What is true positive

A

The number of cases correctly identified as Malaria

34
Q

What is false positive

A

The number of cases incorrectly identified as Malaria

35
Q

What is true negative?

A

The number of cases correctly identified as not having malaria

36
Q

What is false negative

A

The number of cases incorrectly identified as not having Malaria

37
Q

What is sensitivity

A

A tests ability to determine the patient cases correctly

38
Q

What is the equation for sensitivity

A

True positive/ (true positive + false negative)

39
Q

What is specificity?

A

A test’s ability to determine the healthy cases correctly

40
Q

What is the equation for specificity?

A

True negative/ (true negative + false positive)

2.2 Haematology (38 decks)

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