Malaria and the Challenges of Vaccine Development

Malaria kills more than one million people every year, especially children and pregnant women. The life cycle of malaria begins during the bite of an infected mosquito when sporozoites are injected into the blood stream. They are cleared from the circulation within a very short period with many of them entering the liver where they develop into the liver stage merozoites. Thousands of these merozoites rupture infected hepatocytes and invade the red blood cells to begin the blood stage of the disease. The various toxins and cytokines produced during the blood stage of the disease are responsible for its symptoms and pathology. Some of the blood stage merozoites may develop to form gametocytes or the sexual stages. When these gametocytes are ingested by the mosquito during a blood meal, they develop within the mosquito to the sporozoite stage, which then migrate to the salivary gland from where they are transmitted to another host. Attempts at eradicating the disease with insecticides and chemotherapeutic drugs failed because of the emergence of drug-resistant parasites and Anopheles mosquitoes that are resistant to insecticides.