Malaria is caused by species of the protozoan genus Plasmodium which infect red blood corpuscles as well as other human tissues. There are estimated to be 300–500 million clinical cases of malaria each year, about 60% in tropical Africa (WHO & UNICEF, 2005), with almost all the remainder in tropical and subtropical Asia, Latin America and the Southwest Pacific. At the present time there is no malaria transmission in developed countries in the temperate zone, but a few thousand cases are “imported” each year in travelers who have been in tropical countries.

The only Plasmodium species which causes appreciable numbers of human deaths is P. falciparum which is the cause, or a contributory cause, of death of 1–2 million people per year (about 10 000 times the number of deaths per year from mosquito-borne West Nile fever in the recent much publicized outbreak in the USA). More than 80% of malaria deaths are among rural, lowland African infants and children, for whom malaria is one of the major causes of death. If children in the highly endemic parts of Africa survive the malaria attacks which they suffer early in life, they develop a degree of immunity which protects them from the very severe anemia, blockage of cerebral blood vessels and respiratory distress which are the main causes of malaria deaths (Berkeley et al., 1999).