Plasmodium Flashcards
How many countries is malaria endemic in?
Endemic in 83 countries (WHO, 2023)
What is the death rate of malaria?
95% in sub-Saharan Africa death rate
What percentage of deaths by malaria are children under 5?
80%
What has allowed malaria to spread further?
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
What conditions do mosquitos thrive in?
Warm and humid conditions
What is the scientific name for mosquitos that spread malaria?
Anopheles gambiae
How many species of malaria-causing plasmodium are there, and what are the main two?
There are 5 species, however the two responsible for the most cases and deaths are P. falciparum and P. vivax
What is the difference in geographic distribution between P. falciparum and P. vivax?
P. falciparum = predominantly in subsaharan Africa
P. vivax = more widespread, Asia, Latin America and some parts of Africa
What are the 3 main stages of plasmodium life cycle?
- Mosquito stage (sporogony)
- Liver stage (Exo-erythrocytic)
- Blood stage (Erythrocytic)
Summarise the sporogenic stage in mosquitos
- 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
Summarise the exoerythrocytic stage in the human liver
- 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
Summarise the erythrocytic stage in human blood
- 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)
What are some pathological symptoms of malaria?
- Cerebral malaria (brain endothelium infected -> seizures and coma)
- Severe anemia (from RBCs rupturing and phagocytosis of uninfected cells by immune system)
What are some different diagnostic techniques for malarial infections?
- Microscopy of blood sample
- Rapid diagnostic tests
- Serological tests (e.g. ELISA)
How do rapid diagnostic tests work?
- Drop of blood placed on test strip
- If specific parasite antigens are present, dye-labelled antibodies bind to parasite antigen
- A visible line appears
What are the advantages of RDTs?
- Results in 15-30 mins
- Simple procedure (no training needed)
- Great for remote areas with no lab
What are the disadvantages of RDTs?
- May miss low levels of parasites
- Most do not discriminate between species of plasmodium
- Can be expensive
What are the advantages of using microscopy is malarial diagnosis?
- Cost-effective
- Can different species based on morphology- allows for correct choice of antimalarial drug
- Can determine parasitaemia (parasite count)
What are the disadvantages of using microscopy is malarial diagnosis?
- Requires trained microscopist, microscope and electricity
How does microscopy work in malarial diagnosis?
- Drop of blood is spread on slide to create thick and thin smears
- Smears are stained with Giemsa stain
- Slide is examined
What is the purpose of the thick and thin smears?
- Thick smear = concentrates blood to initially detect parasite
- Thin smear = used to identify Plasmodium species based on morphology, and qualify parasitaemia
What is the difference in symptoms between mild and severe malaria?
Mild:
- Fever, headache, muscle pain etc (generic)
Severe:
- Severe anemia, jaundice, kidney failure, respiratory distress etc
What are involved in parasite control?
Drugs and vaccines
How are antimarial drugs used to control malaria?
- 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
What are some issues with antimalarial drugs?
- 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
What is a common current treatment of malaria?
Artemisine-combination therapy (ACT), although there is resistance emerging in SE Asia
What vaccine is available for malaria?
There is commercially available vaccine, and there never has been, however there are 16 candidates currently in clinical trials
What are the most promising malaria vaccines currently?
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
What are 3 examples of vector control for malaria?
- Insecticide-treated nets
- Indoor residual spraying
- Larval source management (elimination of mosquito larvae by treating of breeding sites)
