There are 200 known species of Plasmodium, of which at least 11 species infect humans, while others infect other animals including reptiles, birds, rodents, and monkeys. The Plasmodium parasite has a two host life cycle: a vector – typically a mosquito, but sandflies are also a possibility – and a vertebrate host.
The parasite causes human malaria, when it is passed from one human to another by the bite of an infected Anopheles mosquito. In 1898, Italian physician Giovanni Battista Grassiproved that human malaria could only be transmitted by the Anopheles genus. In order to cause malaria, the Plasmodium parasite must go through complex and multistage life cycle, infecting both humans and mosquitoes as it matures and develops.
The cycle begins when a female mosquito bites a human in search of a blood meal to produce eggs—in fact only the female has the physiology necessary for sucking blood. The parasite is transferred through the mosquito saliva to the human host as the mosquito is taking her blood meal. After infecting its human host, the parasites, in sporozoites form, travel through the bloodstream to the liver and invade liver cells. Over 5-16 days (time-frame is dependent on the parasite species) the sporozoites grow, divide, and produce tens of thousands of merozoites, per liver cell.
The parasites as merozoites exit the liver and re-enter the blood stream where they invade red blood cells to feed on hemoglobin, an iron-bearing molecule that allows the cells to ferry oxygen to all parts of the body. The merozoites multiply inside the red blood cells, which eventually break open allowing the parasite to infect additional cells. Merozoites continue their cycle of invading red blood cells, asexual replication, and then releasing newly formed merozoites repeatedly for over 1-3 days, resulting in thousands of parasite infected cells in the blood stream. These blood stage parasites cause the illness and symptoms associated with malaria that can last for months if not treated.
Some of the merozoite-infected blood cells leave the cycle of asexual replication and instead develop into sexual forms of the parasite, male and female gametocytes, that circulate in the human blood stream. When a mosquito bites an infected host, it ingests the gametocyte.
When the gametocytes enter a female Anopheles mosquito during a blood meal, they begin another, different cycle of growth and multiplication in the mosquito knows as the sporogonic cycle. Inside the misquoto’s gut, the infected human blood cell bursts, releasing the gametocytes that mature into sex cells called gametes. Male and female gametes then fuse forming zygotes. The zygotes develop into active elongated ookinetes, which burrow into the mosquito mid-gut wall to form oocysts. The oocysts grow and divide producing thousands of sporozoites; after 8-15 days, the oocyst ruptures releasing the sporozoites inside the mosquito. The sporozoites travel within the mosquito body eventually invading the salivary glands. The human plasmodium cycle begins again when the female mosquito takes a blood meal, injecting the sporozoites from its salivary glands into the human bloodstream.
At IV Lab, our team of entomologists, epidemiologists, physicists, other scientists and engineers are working on innovative ways to help reduce and eradicate malaria. Click the links to learn more about our efforts in diagnostics, epidemiological modeling, mosquito control, and vaccine cold chain.