The
Apicomplexa are among the most important phyla in this kingdom with
respect to human health. This phylum includes Plasmodium
, the cause of Malaria. Until recently over 250 million
people world wide, mainly in the tropics, were infected with this or one
of four species of Plasmodium.
The Apicomplexa receive their name because the apex of the cells of certain life stages of these parasites have intricate structures that enable these parasites to penetrate the tissues of their hosts.
The image to the left shows an Apicomplexan known as a Gregarine. These organisms are important parasites of invertebrates.
All Apicomplexa are specialized parasites found in most animal species. They have complex life cycles often involving multiple species as hosts. For instance, the Malaria parasites have various species of Anopheles mosquitoes as hosts for part of the life cycle. At least part of the life cycle is spent as an intracellular parasite.
1. Uptake of male and female gametes by the mosquito from a human blood meal
2. Fusion of gametes to form a zygote which penetrates the mosquito's stomach lining.
3. Meiosis and production of haploid sporozoites which travel to the insect's salivary gland.
4. Injection of Sporozoites into a new human host, migration to the liver to form cryptozoites
5. Penetration of red blood cells by cryptozoites and asexual reproduction in red blood cells
6. Sexual reproduction in red blood cells and production of new gametes to complete the cycle.
Another important Apicomplexan group are the Toxoplasma. At least 1/3 of the human population is believed to be harboring these parasites. Until fairly recently it was thought that the only route for infection was through the placenta, but we now know that these parasites can be transmitted from cats to people when people clean their cat's litter boxes. The symptoms may vary from mild to severe and vary in type depending on which tissues are involved. Pregnant women should avoid cleaning cat feces due to the risk for the fetus.
6/14/99 pgd
pgd revised 2/17/01