Plasmodium is a parasitic microbe that is associated with malaria. This eukaryotic bacterium invades and modifies the host cell's structure. There are over 200 known species of plasmodium causing disease in animals and people. Plasmodium begins its life inside of a mosquito. The mosquito bites a human and the parasite travels to the liver where if grows, changes, and reproduces. Life stages of this malarial organism are sporozoite, merozoite, and gametocyte.
The life of plasmodium begins when female Anopheles mosquitoes bite humans with malaria. The mosquito ingests plasmodium gametocytes. Plasmodium gametocytes are round or banana-shaped cellular structures with a grainy surface texture. Inside the mosquito the gametocyte become plasmodium gametes and fertilize each other. These produce zygotes divide into many small elongated sporozoites that travel to the mosquito salivary gland.
When Anopheles mosquitoes carrying plasmodium sporozoites bite a human, the sporozoites rapidly infest the liver. In the liver cells plasmodium matures into schizont cells, containing many merozoites. By this time the schizont cell is much larger than red blood cells. Within a short time, the infected liver cells bud off plasmodium merosomes. These structures, containing hundreds of thousands of merozoites, travel into small capillary blood vessels where they dissolve releasing the merozoites.
In the blood stream the merozoites attack blood cells. They develop first into a ring-shaped form, and then into larger structures called trophozoites. Trophozoites have a characteristic signet ring shape and are generally larger than an average blood cell. At this time the parasitic plasmodium cells feed on hemoglobin and produce more merozoites that will invade more red blood cells. Now, some of the plasmodium trophozoites develop further into gametocytes, which will infect mosquitoes to start the life cycle of plasmodium over again.
Plasmodium parasites in the merozoite stage are covered with specialized proteins and have special organelle structures on the narrow apical end of the cell. These structures are called micronemes and rhoptries, and they discharge their contents upon contact with a blood cell. This aids the plasmodium in invading the red blood cell. Another organelle structure discharges its contents only after the blood cell has been invaded. Called dense granules, the contents of these structures aid the plasmodium parasite in modifying the invaded host cell.