pathogenesis of malaria

Question 1

what are the different malarial species

Answer 1

p. falciparum
p. vivax
p. ovale
p. malarie
p. knowlesi

Question 2

what are the problems with rapid diagnostic tests?

Answer 2

1. They are less sensitive by 10 – 100x than microscopy
2. Detect parasite antigen rather than live parasite
   may therefore be positive in patients who have been recently treated (up to 2 weeks) or come from a malaria endemic area and have a low level of asymptomatic parasitaemia
3. Not possible to determine the % parasitaemia or stage of parasite

Question 3

what is the severity classification for malaria?

Answer 3

uncomplicated and severe

UNCOMPLICATED
Parasitaemia <2% AND no schizonts AND no clinical complications

SEVERE
Parasitaemia >2%  
or
Parasitaemia <2% plus…
either schizonts reported on blood film 
or complications

Question 4

how bad is severe malaria?

Answer 4

MULTI SYSTEM DISEASE
Rapid progression to DEATH
Mortality of 10-40% in first 24 hr

Malaria is a
MEDICAL EMERGENCY.
\

Question 5

how can malaria falciparum escape the immune response?

Answer 5

• the antigen expressed on red blood cell surface is PfEMP-1- falciparum erythrocyte membrane protein
• a single cell only expresses one of these at a time
• this is encoded by the 60 var gene
• parasites regularly exchange the expressed var gene
• as antibodies develop for one PfEMP1 there is a switch of expression to alternative

Question 6

what scoring system is used for children with cerebral malaria?

Answer 6

blantyre coma score

Question 7

why is iv quinine no longer used to treat severe malaria?

Answer 7

hypoglycaemia
arrhythmias
potentially lethal hypotension in rapid infusion

AND
significant mortality still: cerebral malaria has a treated mortality rate of 15–20%

Question 8

what is the current treatment for severe malaria?

Answer 8

artesunate

safer to use than quinine and reduces parasite burden more quickly

Question 9

what is the difference in the mechanism of action of artusenate vs quinine against malaria?

Answer 9

Artesunate kills circulating ring-stage parasites as well as schizonts

whereas quinine only kills mature schizonts

Question 10

which antimalarial should you add to your management if dealing with viva and ovale?

Answer 10

primaquine

Question 11

key drivers of antimalarial drug resistance

Answer 11

1. Unusual genetic structure of malaria parasites in regions known for antimalarial drug resistance
2. mono therapy is being used instead of combination therapy
3. poor adherence to medication
4. Counterfeit or substandard treatments: cause 25% of all malaria deaths

Question 12

what do the paroxysms in malaria relate to?

Answer 12

• period of infected erythrocyte rupture and merizoite invasion

Question 13

how do the different malaria species vary?

Answer 13

• in geographical distribution
• lifecycle
• clinical features
• demographics
• resevoir

Question 14

what type of paroxysm is present in p. falciparum?

Answer 14

malignant tertian

-intense fever stage occurring every 3rd day

Question 15

paroxysm present in p.vivax?

Answer 15

benign tertian

- fever every 3rd day

Question 16

paroxysm in p.ovale?

Answer 16

• tertian

- every 3rd day

Question 17

paroxysm in p.malarie?

Answer 17

quartan

- every 4th day

Question 18

which malaria has fever occurring in quotidian fashion- every day?

Answer 18

p.knowlesi

Question 19

describe the malaria lifecycle

Answer 19

• mosquitos are the vector for malaria parasite
• injected into human blood when they take their blood meal
• can invade liver cells and be inactive- hypnozoites
• can become activated in liver to schizonts and release merizoites
• merizoites invade RBCs and form rings
• they then become trophozoites
• trophozoites become schizonts which can replicate
• schizonts can burst out of RBCs and infect other RBCs

Question 20

how does entomological inoculation rate relax to severity of malaria in different individuals?

Answer 20

1. stable transmission areas- EIR >10/yr - 10 bites per person per yr= then diseases is severe in the very young
2. unstable transmission areas EIR <1-5/yr
   disease is severe in possibly all

Question 21

what is the vector for malaria?

Answer 21

female anopheles mosquito

Question 22

what things can be done o prevent malaria?

Answer 22

• insecticide treated nets
• indoor residual spraying
• improved diagnostics
• prevention in pregnancy

Question 23

what can microscopy of malaria diagnosis find?

Answer 23

• species
• parasitemia= density
• parasite stage- having schizonts in peripheral film is significant

Question 24

what are the non rapid testing diagnostic methods for malaria?

Answer 24

• giemsa stained blood film
• thick film
• thin film

Question 25

what can be seen on a thick film in malaria?

Answer 25

• its not fixative
• you can see rbcs lysing
• thick films have increased sensitivity

Question 26

what can be seen on a thin film?

Answer 26

• cells are fixed and intact
• used for quantification of parasites
• used for parasite specification

Question 27

how do RDT strips work?

Answer 27

• there is bound antibody
• there is free labelled antibody
• the free antibody captures malaria antigens if they are present and subsequently binds to the bound antibody
• when free antibody binds bound antibody it will appear as a line

Question 28

what can severe malaria cause?

Answer 28

• anaemia
• cerebral malaria
• hypoglycaemia
• blackwater fever
• renal impairment
• respiratory distress
• jaundice