Cause: 4 species of the protozoan, Plasmodium
Transmission: The Anopheles mosquitoes are the hosts that transmit the disease to humans during the blood-sucking process.
Symptoms: The different stages in the life cycle of the protozoan cause the different symptoms of the disease:
- When the pathogen first enters the blood, it travels to the LIVER CELLS, where it hides from the immune system. There, it multiplies rapidly, producing dozens of cells called merozoites
- The merozoites then travel back into the blood, where they infect RED BLOOD CELLS, again, multiplying asexually producing many cells.
- The merozoites burst out of the red blood cells every 48-72 hours, and as they release toxins in this process, this causes the symptoms.
- The toxins cause recurring attacks of shivering, fever, headaches, nausea, sweating and lethargy. The destruction of many red blood cells causes anaemia.
- Host Response: At each stage of the parasite's life cycle, it produces a different set of antigens (they stimulate the immune response).
The host produces antibodies to fight the pathogens, but the antigens continually change, so the immune response is not effective. The merozoites in the liver escape detection
Treatment: Natural resistance can develop, but only very slowly. Treatment of sufferers includes using anti-malarial drugs such as quinine (effective against parasites in red blood cells), and primaquine phosphate (works in both blood and liver cells). Some strains of plasmodium are resistant however.
Prevention: Protective clothing, insect repellent, mosquito nets.
Control: Aims to keep incidence of disease to a minimum in population. Drugs to destroy vector, and parasite. Destroying vector's habitat. Vaccines against plasmodium. Genetic engineering of mosquitoes to resist parasite.