The female Anopheles mosquito spreads malaria to humans.
Malaria infects 600 million new patients per year, and kills up to 3 million of them. Four species of unicellular parasites belonging to the genus Plasmodium cause this disease. Female Anopheles mosquitoes are its primary vectors; scientists have identified more than 45 Anopheles species in India alone. These mosquitoes locate human hosts through smell and visual clues, and are more likely to infect males than females. Sporogony is the parasites' earliest developmental stage, which takes place in the mosquito host. Schizogony is a later stage that occurs once the parasite has infected human cells.
Sporogony
The Anopheles mosquito ingests malarial parasites when it feeds on an infected human. In the mosquito's stomach, the parasites move to the gut wall, where they reproduce asexually through the process of sporogony, and produce an oocyst, or spore. These oocysts eventually burst, releasing sporozoites that travel through the mosquito's body to its salivary glands, and finally to its central salivary duct.
Sporozoites
When a carrier mosquito drinks human blood, the malarial sporozoites travel through its saliva to the host's blood stream, and quickly make their way to the liver's functional cells. The parasites can also infect red blood cells, causing fever, anemia and -- in some cases -- death.
Schizogony
Schizogony is a form of asexual reproduction in which the multiple fission of sporozoites produces merozoites that can reproduce sexually or asexually. This process often begins as soon as the parasites enter their vertebrate host. For example, Plasmodium falciparum and P. malariae begin reproducing immediately. However, P. ovale and P. vivax may delay reproduction, by forming hypnozoites that remain dormant in the liver cells. P. vivax hypnozoites can have a dormancy of up to 10 months, whereas P. falciparum and P. malariae do not create hypnozoites at all.
Merozoites
Pre-erythrocytic schizogony occurs in the host's liver cells before the parasite invades red blood cells (erythrocytes). During this phase, each sporozoite produces multiple merozoites, which consist of a single nucleus encased in a narrow cytoplasmic ring. Each P. ovale sporozoite produces 15,000 merozoites. P. vivax produces 10,000, P. falciparum produces 40,000 and P. malariae produces 2,000. Merozoites typically invade red blood cells within two minutes of life.
Tags: blood cells, Anopheles mosquito, falciparum malariae, infected human, liver cells, produces merozoites, sporozoite produces