Pathogenic Effects of Malaria

The symptoms of malaria are caused mainly by the blood stage, when merozoites multiply in red blood cells.Fever cycles. Infected red blood cells tend to burst at the same time. Each burst releases merozoites, parasite waste and toxins into the blood, which stimulate white blood cells to release cytokines. These cause attacks of shivering and chills, then high fever (up to about 40 °C) and heavy sweating. With P. vivax and P. ovale attacks recur about every 48 hours, and every 72 hours with P. malariae.Anaemia. Red blood cells are destroyed when merozoites burst out, and the spleen removes many infected cells. Fewer red blood cells means less haemoglobin to carry oxygen, causing tiredness, weakness and breathlessness. Anaemia is especially dangerous for young children and pregnant women. The spleen and liver often become enlarged.Blocked blood vessels. In P. falciparum malaria, infected red blood cells develop sticky knobs on their surface and attach to the walls of capillaries. This blocks blood flow and deprives tissues of oxygen. Blockage in the brain causes cerebral malaria, with seizures, coma and often death. The kidneys and lungs can also be damaged.Other effects include low blood glucose and a build-up of lactic acid in the blood.Malaria kills around 600 000 people each year, most of them children under five in Africa. People who survive repeated infections gradually build partial immunity.