Plasmodium species live in mosquitos and humans.
Plasmodium is a type of parasite that causes the dangerous disease known as malaria. Due to the fact that the parasite is transmitted through mosquito bites, the parasite matures through several stages both in the human host and the mosquito itself. Only female mosquitos bite humans and transmit the disease. Examples of Plasmodium species include P. falciparum, P. vivax and P. ovale.
Liver Stage
After the mosquito bites the human host, it transfers the parasites from its salivary glands into the human bloodstream in immature forms known as sporozoites. These sporozoites travel through the bloodstream to the liver and make their way into liver cells. There, they grow into schizonts, which are asexually reproducing forms of Plasmodium. (Asexual reproduction means that the parasites simply divide into identical daughter cells without sharing genetic information from another individual parasite.) Before the parasites burst out of the liver schizonts, they turn into forms called merozoites. Sometimes the sporozoites do not immediately turn into schizonts and remain without maturing as hypnozoites for months or years, which is why P. vivax and P.ovale can cause relapsing malaria for some time after the initial infection.
Blood Stage
When the merozoites break out of the liver, they make their way into the red blood cells of the host. There, the parasites turn into schizonts, asexually reproduce, and new merozoites bud off into the bloodstream, where they infect fresh cells. The fever symptoms of malaria are due to the red blood cells rupturing during this cycle. The affected red blood cells can also stick to small veins in the organs, such as the brain, which can cause cerebral malaria.
Sexual Stage
Instead of asexually reproducing in the red blood cells, the parasites can also turn into female or male forms, known as micro- and macro-gametocytes, which act in the same way as sperm and eggs in humans. However, these gametocytes need to escape the human host first and enter a mosquito gut, before they can join together to form a new parasite.
Sporogony
After the mosquito drinks from the infected human host and ingests the gametocytes, the micro-gametocyte fertilizes the macro-gametocyte. The fertilized form is a zygote. The zygote becomes mobile and is called a ookinete. This ookinete burrows into the insect gut wall. There, it turns into a oocyst. Inside the oocyst, the parasites asexually reproduce. Then the oocyst releases the immature parasites as sporozoites. These sporozoites travel to the mosquito salivary gland; when the insect bites another human host, the life cycle of Plasmodium starts over.
Tags: human host, blood cells, turn into, into schizonts, After mosquito, asexually reproduce