Blood parasite passed to humans through malaria infected mosquito bites (specifically the female Anopheles mosquito). There are four different types of malaria strains: Plasmodium falciparum, p. vivax, p. ovale and p. malariae. The last three remain in the host indefinately; only falciparum can be completely irradicated from the body, though harmless gametocytes will remain in the bloodstream for at least a month after treatment.

The parasite infects the red blood cells, where it reproduces and eventually causes the blood cell to burst. This creates the symptoms of a malaria infection: first fever and chills, accompanied by headache and occasionally a cough (much like flu symptoms). The reproductive cycle is about 1 1/2 days, during this time the infected host will feel fine. After several cycles, the blood count will drop significanly, causing severe fatigue and a feeling of being out of breath as the body attempts to compensate for the lack of oxygen through the respiratory system. If treatment does not come in a few days, death will result. It is a MOST fatal disease, affecting 500 million people (that's no typo) and killing more than 2.5 million people a year.

The falciparum strain is the most deadly; untreated it can lead to central nervous system failure. Vivax can lead to the rupture of the spleen. All can cause severe anemia, resulting in coma and death.

Malaria occurs in tropical and subtropical climates, mostly Africa, South America, the Middle East, India and all of Southeast Asia. Treatment is nearly always the same: 7-10 days of either one or a combination of chloroquine, sulfadoxine-pyrimethamine, quinine, tetracycline, doxycycline, mefloquine, and primaquine. Some particularly nasty strains like falciparum, especially in areas of Southeast Asia, have developed resistences to traditional medication like doxycycline and larium. In most cases Quinine is still the most effective treatment.

Additional note: As I've now been infected with two strains (falciparum and vivax) I want to update this node to say that while p. vivax, p. ovale and malariae can stay resident in the liver and affect a person throughout their life, with use of primaquine it is possible to clear the body of all traces of the disease.