About Malaria

Malaria today is the second-most important human disease after AIDS, killing over 600,000 people annually, the majority of whom are infants in sub-Saharan Africa. More than 200 million people are infected every year in 108 countries, and half of the human population is at risk (WHO malaria report, 2010). In 2010, an estimated 3.3 billion people were at risk of malaria, although of all geographical regions, populations living in sub-Saharan Africa are the most exposed to malaria: 81% of cases and 91% of deaths are estimated to have occurred within Africa, with children under five years of age and pregnant women being most severely affected. Global warming is expected to promote the spread of malaria, and other mosquito-borne illnesses, from tropical regions to higher latitudes. In humans, malaria is caused by 5 different species of Plasmodium (P. falciparum, P. vivax, P. ovale, P. malariae and P. knowlesi), the most deadly of them being Plasmodium falciparum that predominates in Africa. P. vivax is less dangerous but more widespread, and the other three species are found less frequently. Malaria is transmitted to humans by the bite of infected anopheline female mosquitoes. Among the 20-30 malaria mosquito species, Anopheles gambiae is a major vector of P. falciparum in Africa. Extract from the World Malaria Report 2011

Plasmodium life cycle

Cycle in mosquitoes

Gametocytes, the sexual stages of the malaria parasite, are ingested by a mosquito during blood feeding and give rise to gametes that emerge and fertilize in the mosquito midgut. Resulting zygotes develop into ookinetes that cross and lodge beneath the midgut wall as oocysts. Growth and division of each oocyst produces thousands of active haploid forms termed sporozoites, which break out after 8–15 days, depending on the species, and invade the salivary glands. The sporozoites are injected when the mosquito bites and are carried to the liver where they invade hepatocytes.

Cycle in humans

The parasites grow and divide within each infected hepatocyte to produce tens of thousands of haploid forms over 5–16 days, depending on the species. Liver-stage parasites exit the hepatocytes as merozoites and enter the bloodstream. Parasite multiplication then ensues in the erythrocytes from repetitive rounds of invasion, growth and division, in 1-day (Plasmodium knowlesi), 2-day (Plasmodium falciparum, P. vivax and P. ovale) or 3-day (Plasmodium malariae) periods. This multiplication can result in 1012 or more parasitized erythrocytes in the bloodstream, leading to the illness and complications of malaria. In the course of this bloodstream parasitization, which can last for months if not treated, some erythrocytic stages leave the rounds of asexual multiplication and switch to develop over a period of about 2 weeks into mature male and female gametocytes. The parasite life cycle is completed when these gametocytes are taken up by another mosquito, perpetuating transmission.

Su, Xinzhuan, Karen Hayton, et Thomas E. Wellems. « Genetic Linkage and Association Analyses for Trait Mapping in Plasmodium Falciparum ». Nature Reviews Genetics 8, no 7 (janvier 7, 2007): 497‑506. doi:10.1038/nrg2126.

 

Map Gallery

 

  • World : Countries and territories affected by malaria, 2010 Date : 24 May 2012 Source : World Health Organization