Practical 5: Malaria Investigations Flashcards
What five species of parasite cause malaria in humans
Plasmodium falciparum
Plasmodium vivax
Plasmodium malariae
Plasmodium ovale
Plasmodium knowlesi
What species of parasite cause malaria most commonly
Plasmodium falciparum
Plasmodium vivax
What parasite causes the most deadly form of malaria
Plasmodium falciparum
What is malaria
A mosquito-borne haemolytic febrile illness caused by Plasmodium parasites
What mosquito transmits malaria
Anopheles mosquitoes
When can you detect parasite specific antigens
They are detectable near the end of the incubation period during primary infection
When can you detect parasite antibodies
Near the end of the primary infection
What response is seen if you become reinfected with malaria
Reinfection leads to a secondary response with a high and rapid rise in antibody levels
What does a case of malaria often present with in the lab
Often the patient presents with a high fever
But there is usually no remarkable features on blood film bar sometimes a thrombocytopenia
What are the three parts to the diagnosis of a parasite
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
Write a note on the thick blood film
(3)
Stained with fields stain
Used to detect the presence of the parasite
Useful in low grade parasitaemias
Write a note on the thin blood film
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
Why might you have a negative antigen test in a malaria case
Malaria might still be incubating in the liver
What can you determine if there is more than one parasite per cell?
It is plasmodium falciparum
What are the five identifiable stages of malaria in a blood film
Ring forms
Early schizont
Schizont
Merozoites
Gametocyte
What stage is a ring form
An early trophozoite
What stage is a schizont
Late trophozoite
Why is malaria common in spelectomized patients
Malaria is not phagocytosed by macrophages as they are removed in the splenectomy
Why is the percentage parasitaemia important?
It has implications for prognosis and the pattern of treatment that will be employed
How is a percentage parasitaemia determined?
Count the number of infected cells as a percentage of the red blood cells (1000 cells)
What is an alternative way of determining % parasitaemia?
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
Why would you still have a positive antigen test even after being treated for malaria
Might have not cleared the infection completely i.e. might have dead parasites still left in your system
How do you make a thin film
(6)
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
How do you use your thin film to determine % parasitaemia
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
How do you make a thick slide
(8)
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
How do you know youve made your thick slide correctly
You should be just able to read small print through the thick film
How do you use the BinaxNOW Malaria RDT
(4)
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
What is a positive plasmodium falciparum BinaxNOW Malaria RDT?
top and middle line
What is a positive BinaxNOW Malaria RDT for species other than p.f.?
Top and bottom line
What is a mixed BinaxNOW Malaria RDT
All three lines
What is a negative BinaxNOW Malaria RDT
Just the top control line
How do you use the Onsite Malaria test
Add 5ul of blood to the S well
Add 2 drops of blood lysis buffer to B well
What is true positive
The number of cases correctly identified as Malaria
What is false positive
The number of cases incorrectly identified as Malaria
What is true negative?
The number of cases correctly identified as not having malaria
What is false negative
The number of cases incorrectly identified as not having Malaria
What is sensitivity
A tests ability to determine the patient cases correctly
What is the equation for sensitivity
True positive/ (true positive + false negative)
What is specificity?
A test’s ability to determine the healthy cases correctly
What is the equation for specificity?
True negative/ (true negative + false positive)
