malaria

= ague; = marsh fever; = periodic fever; = paludism; n.

an infectious disease due to the presence of parasitic protozoa of the genus Plasmodium (P. falciparum, P. malariae, P. ovale, or P. vivax) within the red blood cells. The disease is transmitted by the Anopheles mosquito and is confined mainly to tropical and subtropical areas.

Parasites in the blood of an infected person are taken into the stomach of the mosquito as it feeds. Here they multiply and then invade the salivary glands. When the mosquito bites an individual, parasites are injected into the bloodstream and migrate to the liver and other organs, where they multiply. After an incubation period varying from 12 days (P. falciparum) to 10 months (some varieties of P. vivax), parasites return to the bloodstream and invade the red blood cells. Rapid multiplication of the parasites results in destruction of the red cells and the release of more parasites capable of infecting other red cells. This causes a short bout of shivering, fever, and sweating, and the loss of healthy red cells results in anaemia. When the next batch of parasites is released symptoms reappear. The interval between fever attacks varies in different types of malaria: in quartan malaria (or fever), caused by P. malariae, it is three days; in tertian malaria (P. ovale or P. vivax) it is two days (these two types are known as benign malarias). In malignant (or falciparum) malaria (caused by P. falciparum) – the most severe kind – the interval between attacks varies from a few hours to two days (see also blackwater fever). Preventive and curative treatment includes such drugs as chloroquine, proguanil, mefloquine, and pyrimethamine.