Summary Ch4: Malaria

CH4: MALARIA
GENERAL INFORMATION

Plasmodium is a protozoan parasite which is transmitted by the bite of an infected female Anopheles mosquito

PLASMODIUM LIFE CYCLE

- In the human:
o Infected mosquito that has the parasite in the salivary glands: sporozoites
 Do not replicate, are waiting in salivary glands to be transmitted when the female
mosquito takes a blood meal
 Blood meal is needed to take up proteins to be able to lay eggs
o Female mosquito deposits parasites in the human host
o Malaria parasites have the ability to cross several types of cells without attaching to the first
one they see
 When mosquito bites: parasites cross the skin until they find a blood vessel
 Migration to liver (1h)
o In the liver: cross cell types until they find a hepatocyte where they fix
o They start to multiply until they form 10 000 – 30 000 merozoites (9 days)
o When hepatocytes are full of merozoites: burst
o Merozoites released in blood circulation: invasion of red blood cells = erythrocytic cycle =
occurrence of malaria symptoms
 Cycles of invasion and rupture: depending on parasite species they take
shorter/longer
 In P. falciparum: 48 h
 Between 20-30 new parasites are formed in each RBC in each cycle: depends on
parasite species + environmental factors
 When RBC ruptures: all merozoites released in blood circulation
 Each merozoite can infect 1 cell  exponential growth of parasite density
o Some parasites (1-3%): come out of the erythrocytic cycle and form gametocytes
 Stay in circulation and wait for a mosquito to bite
 Gametocytes end in stomach of the mosquito
- In mosquito:
o Fusion of gametocytes into ookinete
o Multiplication forms thousands of sporozoites
o Travel towards salivary gland: sporozoites in salivary gland
 After 2 weeks: sporozoites are ready to be transmitted

 Malaria life cycle is an extremely complex lifecycle

MALARIA ENDEMIC REGIONS

Located in the Malaria belt: regions located around the tropics. 93% of these are found in Africa, but also some
occur in Latin-America/Asia. These are the regions where the presence of the mosquito is more consistent and
where there is a more efficient transmission.




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, HIGH RISK GROUPS

- Children < 5 years with no previous exposure to malaria
- Pregnant women + foetus
- Immune-supressed patients: especially HIV
- Travellers without previous exposure

HUMAN MALARIA PARASITES

- Plasmodium falciparum:
o Majority of deaths are caused by P. falciparum
o most prevalent species in Africa
o most studies / tools that are developed are targeting P. falciparum
- Plasmodium vivax:
o Most prevalent species in Latin-America and Asia
o In past few weeks, increased recognition that P. vivax can cause severe disease and death
o still major problem to eliminate P. vivax (+ P. ovale) is the formation of liver hypnozoites
(dormant)

GLOBAL MALARIA BURDEN THROUGH HISTORY

- we have already gone to 2 major global eradication programs
o first campaign to eliminate malaria: started after WWII
 successful campaign:
 eradicated malaria from North-America and Europe
 reduced significantly the number of cases and death in Asia
 BUT not successful in Africa
 used 2 tools: insecticide DDT + chloroquine
o around ‘70s together with increase of chloroquine resistance: huge increase in death in Africa
until the end of the 20th century
o at beginning 20th century: new global eradication campaign
 involved different initiatives: starting from different governments and foundations
 successful: in 15 years, 50% decrease in number of deaths by malaria
 major tools: still used
 vector control: indoor residual spraying + ITN’s
 artemisinin derivative drugs
- since 2015: after an unprecedented period of success in global malaria control, progress has stalled
around the world
o in Africa: number of cases and deaths increase
o means that we may not be able to eradicate malaria with the tools that we have/are using
now
 need to develop better tools + monitor major challenges to elimination (e.g. development
of drug resistance)




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