Malaria is caused by Plasmodium species — P. vivax, P. ovale, P. malariae and P. falciparum — each producing a distinctly named type of malaria with its own erythrocytic-cycle duration (48 hours for vivax/ovale, 72 hours for malariae, 36–48 hours for falciparum). It is transmitted only through the bite of an infected female Anopheles mosquito.
P. vivax is digenic: humans are the secondary host, the female Anopheles mosquito the primary host. The cycle has three phases — schizogony, gamogony and sporogony. A feeding mosquito injects sporozoites into the human bloodstream; these enter liver cells and undergo asexual schizogony (exo-erythrocytic schizogony), producing merozoites. Released merozoites invade RBCs and pass through early trophozoite and signet-ring stages into a schizont bearing yellow-brown Schuffner's granules; the schizont divides and the erythrocyte lyses, releasing fresh merozoites and haemozoin toxin — this erythrocytic cycle repeats roughly every 48–72 hours, producing the classic pattern of fever and chills (malarial paroxysms), driven partly by malarial toxins triggering macrophage release of TNF-α and interleukin. Some merozoites instead become macro- and micro-gametocytes; ingested by a mosquito, these fertilize in its gut to form a diploid zygote (ookinete), which develops on the gut wall into an oocyst and undergoes meiotic sporogony to yield sporozoites that migrate to the salivary glands, ready to restart the cycle at the next bite. Incubation is about 12 days; early symptoms are headache, nausea and muscular pain.
Prevention targets the mosquito vector: oil sprayed on stagnant water suffocates larvae/pupae, larvae-eating fish (Gambusia) can be stocked in ponds, Bacillus thuringiensis preparations kill larvae without harming other life, and nets/window screens prevent bites. WHO's 1950s Malaria Eradication Programme was undermined by Plasmodium drug resistance and mosquito DDT resistance. The only WHO-approved vaccine as of 2015, RTS,S (Mosquirix), needs four doses and has only 26–50% efficacy, so it is not recommended for infants aged 6–12 weeks.