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Malaria affects approximately 300 million people each year, mostly in the tropical and subtropical areas of Africa, Asia, and Latin America where the parasites that cause the virus can thrive. There are four types of malaria, each one caused by a different species of parasite from the Plasmodium genus. These malaria parasites, P. falciparum, P. vivax, P. ovale, and P. malariae, are all spread by mosquitoes.
P. falciparum is the deadliest of all the malaria parasites. Mostly found in Africa, infections caused by this parasite kill approximately 1 million people each year. The most prevalent form of malaria is caused by P. vivax, found throughout Asia, Central America, and Africa. This form can be difficult to diagnose because of its tendency to remain dormant in the liver, sometimes for years after a person is infected.
Similar to the P. vivax is P. ovale, a species of parasite found throughout Africa and the islands of the Pacific. P. malariae is found worldwide, and is difficult to get rid of. Patients can relapse due to dormant parasites that result in a chronic infection.
All four of the different types of malaria parasites incubate and multiply in the stomach of mosquitoes. Passed on to humans through biting, parasites only infect female anopheles mosquitoes. Males feed only on the juices of plants, and are not exposed to the parasites. There are approximately 60 different species of anopheles mosquitoes capable of serving as a host for the malaria parasites.
Mosquitoes are infected with the parasites when they feed on an individual that has been infected. After the parasites lay their eggs in the midgut of the mosquito, the eggs then erupt and produce spores eight to 10 days later. These spores are transferred to the saliva of the mosquito, and are in turn injected into the next individuals the mosquito bites.
Once inside a human host, the malaria parasites enter the cells of the liver. Parasites P. ovale and P. vivax can remain dormant in the liver for days, months, or even years before invading the blood cells of the infected individual. Once parasites enter the bloodstream and attacks the red blood cells, the person will develop signs and symptoms of malaria.
There is also another species of malaria parasite that is found in areas of Southeast Asia. P. knowlesi typically infects long-tailed and pig-tailed macaques in the area, traveling between the monkeys in the same way as other parasites commonly infect humans. Although this parasite can infect humans with sometimes fatal results, it is fairly rare.