Plasmodium

Question 1

How many countries is malaria endemic in?

Answer 1

Endemic in 83 countries (WHO, 2023)

Question 2

What is the death rate of malaria?

Answer 2

95% in sub-Saharan Africa death rate

Question 3

What percentage of deaths by malaria are children under 5?

Answer 3

80%

Question 4

What has allowed malaria to spread further?

Answer 4

Climate change:
- Increased rain means more pools of water where mosquitos breed
- Hotter temperatures allow mosquitos to thrive in areas that were previously too cold

Question 5

What conditions do mosquitos thrive in?

Answer 5

Warm and humid conditions

Question 6

What is the scientific name for mosquitos that spread malaria?

Answer 6

Anopheles gambiae

Question 7

How many species of malaria-causing plasmodium are there, and what are the main two?

Answer 7

There are 5 species, however the two responsible for the most cases and deaths are P. falciparum and P. vivax

Question 8

What is the difference in geographic distribution between P. falciparum and P. vivax?

Answer 8

P. falciparum = predominantly in subsaharan Africa
P. vivax = more widespread, Asia, Latin America and some parts of Africa

Question 9

What are the 3 main stages of plasmodium life cycle?

Answer 9

• Mosquito stage (sporogony)
• Liver stage (Exo-erythrocytic)
• Blood stage (Erythrocytic)

Question 10

Summarise the sporogenic stage in mosquitos

Answer 10

• Mosquito bites infected human
• Takes up male and female parasite gametocytes
• Inside mosquito gut, gametocytes fuse to make a zygote
• Zygote becomes motile ookinete, which penetrates the gut wall
• Ookinete forms oocyst under gut lining, where thousands of sporozoites are produced
• Oocyst bursts, releasing sporozoites that migrate to mosquito salivary glands

Question 11

Summarise the exoerythrocytic stage in the human liver

Answer 11

• Infected mosquito bites human, injecting sporozoites into bloodstream
• Sporozoites travel to liver, infecting liver cells
• Inside liver cells, sporozoites mature into schizonts
• Schizonts divide to produce thousands of merozoites
• Schizont ruptures, releasing thousands of merozoites into bloodstream

Question 12

Summarise the erythrocytic stage in human blood

Answer 12

• Merozoites invade red blood cells
• Merozoites develop into trophozoites (ring stage), which feed on haemoglobin
• Trophozoites mature into schizonts, which divide to produce more merozoutes
• Schizont ruptures, releasing new merozoies that can infect more red blood cells
• Some merozoutes develop into male and female gametocytes, which can be taken up by a mosquito again (continuing the cycle)

Question 13

What are some pathological symptoms of malaria?

Answer 13

• Cerebral malaria (brain endothelium infected -> seizures and coma)
• Severe anemia (from RBCs rupturing and phagocytosis of uninfected cells by immune system)

Question 14

What are some different diagnostic techniques for malarial infections?

Answer 14

• Microscopy of blood sample
• Rapid diagnostic tests
• Serological tests (e.g. ELISA)

Question 15

How do rapid diagnostic tests work?

Answer 15

• Drop of blood placed on test strip
• If specific parasite antigens are present, dye-labelled antibodies bind to parasite antigen
• A visible line appears

Question 16

What are the advantages of RDTs?

Answer 16

• Results in 15-30 mins
• Simple procedure (no training needed)
• Great for remote areas with no lab

Question 17

What are the disadvantages of RDTs?

Answer 17

• May miss low levels of parasites
• Most do not discriminate between species of plasmodium
• Can be expensive

Question 18

What are the advantages of using microscopy is malarial diagnosis?

Answer 18

• Cost-effective
• Can different species based on morphology- allows for correct choice of antimalarial drug
• Can determine parasitaemia (parasite count)

Question 19

What are the disadvantages of using microscopy is malarial diagnosis?

Answer 19

• Requires trained microscopist, microscope and electricity

Question 20

How does microscopy work in malarial diagnosis?

Answer 20

• Drop of blood is spread on slide to create thick and thin smears
• Smears are stained with Giemsa stain
• Slide is examined

Question 21

What is the purpose of the thick and thin smears?

Answer 21

• Thick smear = concentrates blood to initially detect parasite
• Thin smear = used to identify Plasmodium species based on morphology, and qualify parasitaemia

Question 22

What is the difference in symptoms between mild and severe malaria?

Answer 22

Mild:
- Fever, headache, muscle pain etc (generic)
Severe:
- Severe anemia, jaundice, kidney failure, respiratory distress etc

Question 23

What are involved in parasite control?

Answer 23

Drugs and vaccines

Question 24

How are antimarial drugs used to control malaria?

Answer 24

• Can be prophylactically (before infection) to prevent development of malarial parasites in the blood (most common for travellers to high risk areas)
• Or as treatment, to prevent passing on from one infected to a susceptible host

Question 25

What are some issues with antimalarial drugs?

Answer 25

- Many parasites, including Plasmodium falciparum, have developed widespread resistance to antimalarials like Fansidar and chloroquine - Ensuring access and adherence to medication can be difficult in some areas

Question 26

What is a common current treatment of malaria?

Answer 26

Artemisine-combination therapy (ACT), although there is resistance emerging in SE Asia

Question 27

What vaccine is available for malaria?

Answer 27

There is commercially available vaccine, and there never has been, however there are 16 candidates currently in clinical trials

Question 28

What are the most promising malaria vaccines currently?

Answer 28

RTS,S and R21. Both have undergone largely successful pilot introductions, and have been approved by the WHO R21 is the more recent, and has shown around a 70% vaccine efficacy, and is only $4 per dose to make

Question 29

What are 3 examples of vector control for malaria?

Answer 29

- Insecticide-treated nets - Indoor residual spraying - Larval source management (elimination of mosquito larvae by treating of breeding sites)