Symptoms of malaria include fever, shivering, arthralgia (joint pain), vomiting, and convulsions. There may be the feeling of tingling in the skin, particularly with malaria caused by P. falciparum. Complications of malaria include coma and death if untreated - young children are especially vulnerable.
The parasite is relatively protected from attack by the body's immune system because it stays inside liver and blood cells. However, circulating infected blood cells are killed in the spleen. To avoid this fate, the parasite produces certain surface proteins which infected blood cells express on their cell surface, causing the blood cells to stick to the walls of blood vessels. These surface proteins are highly variable and cannot serve as a reliable target for the immune system. The stickiness of the red blood cells are particularly pronounced in P. falciparum malaria and this is the main factor giving rise to hemorrhagic complications of malaria.
Some merozoites turn into male and female gametocytes. If a mosquito bites the infected person and picks up gametocytes with the blood, fertilization occurs in the mosquito's gut, new sporozoites develop and travel to the mosquito's salivary gland, completing the cycle.
Pregnant women are especially attractive to the mosquitos, and malaria in pregnant women is an important cause of still births and infant mortality.
Certain strains of Plasmodium have recently developed resistance to chloroquine which has been the first line of treatment in many countries, thus complicating the treatment. In west Africa, where the local strains of malaria are particularly virulent, Lariam is now the recommended prophylactic, despite causing psychological problems in some vulnerable people. It seems inevitable that resistance to this will also occur.
In addition to the antimalarial drugs, the use of mosquito repellents such as DEET, and mosquito nets and screens can reduce the chance of malaria, as well as the discomfort of insect bites.
Extracts from the plant Artemisia (specifically Artemisia annua), containing the compound artemisinin, a substance unrelated to the quinine derivatives, offer some future promise.
Efforts to eradicate malaria by attacking mosquitos have been successful in some areas. Malaria was once common in the United States and southern Europe, but the draining of wetland breeding grounds and better sanitation eliminated it from affluent regions.
Malaria was eliminated from the northern parts of the USA in the early twentieth century, and the use of the pesticideDDT during the 1950s eliminated it from the south.
Since most of the deaths today occur in poor rural areas of Africa without health care, the distribution to children of mosquito nets impregnated with insect repellants has been suggested as the most cost-effective prevention method. These nets can often be obtained for less than US$10 or 10 euros when purchased in bulk from the United Nations or other organizations.
Some advocates believe that DDT spraying is even cheaper and more effective than nets, and charge that environmentalists have created perverse restrictions on DDT use that have multiplied African malaria deaths into the millions in countries where the disease had been all but eradicated.
Carriers of the sickle cell anaemia gene are protected against malaria because of their particular hemoglobin mutation; this explains why sickle cell anemia is particularly common among people of African origin. There is a theory that another hemoglobin mutation, which causes the genetic disease thalassemia, may also give its carriers an enhanced immunity to malaria.
Another disease that gives protection against malaria is G6PD (glucose-6-phosphate dehydrogenase deficiency). It protects against malaria caused by Plasmodium falciparum as the presence of this enzyme is critical to survival of these parasites within red blood cells.
It is thought that humans have been afflicted by malaria for about 8,000 years, and several human genes responsible for blood cell proteins and the immune system have been shaped by the struggle against the parasite.