Malaria

A. Malaria : Malaria is a vector-borne infectious disease caused by the protist genus Plasmodium. Four species infect humans — P. vivax, P. ovale, P. malariae and P. falciparum — giving four corresponding types of malaria; only P. falciparum typically causes serious, potentially fatal illness, while infection with the other three is rarely fatal.

Signs and symptoms: Symptoms usually begin 7 to 15 days after the bite of an infective mosquito. Early symptoms — fever, headache and chills — can be hard to recognise as malaria at first. The classical symptom is a cyclic pattern of high fever followed by sweating and sudden shivering, an episode that lasts four to six hours and recurs every two or three days as the parasite's blood cycle repeats. Other features include vomiting, convulsions, joint pain (arthralgia), anaemia (from the rupturing of infected RBCs), haemoglobinuria, an enlarged liver (hepatomegaly), retinal damage, and — in severe P. falciparum infection — cerebral malaria (infection of the brain).

Mode of transmission: Plasmodium passes from person to person via the bite of the female Anopheles mosquito. When an infected mosquito bites, it injects sporozoites into the person's blood; these travel to the liver, where they reproduce asexually by fission (schizogony), and the resulting merozoites then invade red blood cells, where further schizogony continues the cycle of RBC rupture that causes the fever episodes. Within the erythrocytes, some merozoites instead develop into male and female gametocytes (gamogony). If a mosquito takes up these gametocytes during a blood meal, fertilisation occurs in the mosquito's gut, forming a diploid zygote that becomes an oocyst; through meiosis (sporogony), the oocyst produces large numbers of haploid sporozoites, which migrate to the mosquito's salivary glands, ready to infect the next human host bitten.

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